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Keywords: Brain development; Neuroimaging; Prefrontal functioning; Magnetic resonance imaging * Corresponding author medications that cause hyponatremia cheap 600mg trileptal with amex. While these latter techniques may be used with pediatric patient populations when clinically warranted symptoms 6dpiui cheap trileptal online american express, the ethics of exposing children to radioactive isotopes for the advancement of science are less clear (Casey and Cohen medicine 95a order 150 mg trileptal amex, 1996; Morton medications hair loss buy generic trileptal 600 mg, 1996; Zametkin et al treatment viral pneumonia effective 150mg trileptal. Despite the signi cant gains in the elds of pediatric neuroirnaging and develop mental neurobiology medicine buy trileptal 300mg line, surprisingly little is known about the developing human brain. In part, this is due to low mortality rates across this age range in addition to the rare occurrence of autopsies on this population. Nonetheless, pioneering work in both developmental neurobiology and pediatric brain imaging has begun to paint a picture of how the developing human brain unfolds through out childhood. Most of the dynamic activity of brain development occurs in utero but changes continue for the rst two postnatal years. By this point, the brain has reached close to 80% of its adult weight (Kretschmann et al. This is also a period of rapid synapse formation that begins well before birth in primates (Rakic, 1972, 1974; Rakic et al. This process of synaptogenesis appears to occur concurrently across diverse regions of the non-human primate cerebral cortex (Rakic et al. However, in humans postmortem data indicates that synaptogenesis does not occur concurrently with synaptic density peaking earlier in the auditory cortex, at three months, and later in the middle frontal gyrus, at 15 months (Huttenlocher, 1997). In both human and non-human primate studies the early synaptic density peaks are followed by a plateau phase that decreases during childhood and into adulthood. These regions of prolonged development are perhaps most interesting when considering the developing child throughout adoles cence and into adulthood. The most informative studies to date are those based on carefully quanti ed volumetric measures and large sample sizes of 50 or more subjects. The most consistent ndings across these studies include: (1) a lack of any signi cant change in cerebral volume after ve years of age (Giedd et al. White matter volume appears to increase throughout childhood and well into adulthood (Caviness et al. For example, there appears to be an increase in white matter in dorsal prefrontal cortex, but not in more ventral prefrontal regions. Total temporal lobe volume appears relatively stable across the age range of 4 to 18 years, while hippocampal formation volume increases with age for females and amygdala volume increases with age for males (Giedd et al. This latter nding may be consistent with the distribution of sex hormone receptors for these structures, with the amygdala having a predominance of androgen receptors (Clark et al. Taken as a whole, these neuroimaging and post-mortern studies seem to suggest that some age-related changes are regional. Based on the nonhuman and human primate post-mortern studies and pediatric neuroimaging studies published to date, the prefrontal cortex appears to be one of the last brain regions to mature, particularly the dorsolateral prefrontal cortex. If so, is the prefrontal cortex region more susceptible to the aging process than other cortical regions There is neuropsychological evidence to suggest that prefrontal function is sensitive to changes with age (Daigneault et al. This impairment is paralleled by a disproportionate degeneration of the prefrontal cortex 244 B. This pattern of degeneration is different from that observed in individuals with Alzheimer disease (Stout et al. If this is indeed the case, then why might the last area to mature be the rst to go One possibility is that brain regions that are most plastic over prolonged periods of development are more sensitive or susceptible to environ mental factors. To date, little is known regarding the neural bases of cognition in normally developing children. In order to address the neural circuits underlying cognitive development, a means of assessing, in vivo, the developmental physiological course of the behavior is needed. This methodology capitalizes on the fact that hemoglobin becomes strongly paramagnetic in its deoxygenated state. This method eliminates the need for exogenous contrast agents, including radioactive isotopes. Given the prolonged physiological development and organization of the prefron tal cortex during childhood, tasks believed to involve this region are ideal for investigating development with this methodology. Cognitive processes that have been attributed to the prefrontal cortex include working memory, response inhibi tion and attention allocation (Goldman-Rakic, 1987; Diamond, 1988; Fuster, 1989). Memory, inhibition, and attention are often treated as three distinct psycho logical constructs. However, aspects of these cognitive processes may be part of a single construct or common underlying circuitry. For example, memory and inhibition are both involved in maintenance of information in that when relevant information is represented and maintained in memory, competing representations or memories are subsequently suppressed or inhibited. Likewise, selective attention and inhibition are part of a similar construct in that when we attend to a relevant event, other salient and competing, but nonetheless irrelevant events are suppressed or inhibited in favor of the relevant event. Similarly, selective attention and memory may represent a single construct in that the classic description of working memory (Baddeley, 1986) includes a component referred to as a central executive that allocates attentional resources to relevant events. Therefore, memory can be de ned in part as the selective allocation of attention to relevant events or representations. Perhaps the common component of overlap in the three previous examples of the psychological constructs of attention, memory, and inhibition, is the presumed presence of interfering or competing information. In the case of attention, the interference may be from simultaneous input or output. In the case of memory, interference may be due to competing memories/representations. If there is no interference, then inhibitory processes are seemingly not necessary and the con structs of attention and memory may be more easily distinguished. One distinguish ing component is within the temporal domain with attention predominantly involving present information and memory involving past information. When there is interference from competing sources then the de nitions of attention and memory are less discrete in that they can be de ned as the ability to represent relevant events in the presence of salient, competing, and compelling, yet otherwise irrelevant events. How do we ignore and select from competing sources of information (stimulus selection), or from competing response alternatives (response selection), or for that matter, ignore or inhibit a behavior or response altogether (response execution) This question suggests that inhibition can occur at different stages of attentional processing. So, both attention and memory appear to involve inhibitory processes when there is interference from competing sources. Developmentally, inhibitory processes of this nature are of interest because they appear to be involved in both cognitive and social learning throughout childhood and adolescence. Clinically, inhibitory processes are important because they appear to be disrupted in a number of developmental disorders that have as a core de cit a problem inhibiting inappropriate behaviors and thoughts. Attention De cit-Hyperactivity Disorder, Obsessive Compulsive Disorder, and Tourette syndrome). Interestingly, the prefrontal cortex and related circuitry have been implicated in these developmental disorders. How does prefrontal circuitry relate to the normal development of inhibitory processes Here, emphasis may well be placed on the role of the prefrontal cortex in supporting different types of information. A number of classic developmental studies have demonstrated that these memory and attention related processes develop throughout childhood and adolescence (Flavell et al. Further, the converging evidence of prolonged development and organization of prefrontal cortex throughout child hood and adolescence (Huttenlocher, 1979; Chugani et al. This decrease in synaptic density is gradual during late childhood and adolescence and coincides with the continued development of cognitive capacities. Accordingly, increasing cognitive capacity during childhood may coincide with a gradual loss rather than formation of new synapses and presumably a strengthening of remaining synaptic connections. These processes may represent the behavioral, and ultimately, the physiological suppression of competing, irrelevant behaviors. One can imagine that a response to a particular event in the environment will be speeded with repeated exposure and subsequent strengthening of the relation between that event and response. With concurrent myelination of connecting bers, one can begin to understand factors that may contribute to the change in speed of information processing that is observed throughout childhood and adolescence. What we know about the anatomy, physiology and connective circuitry of a particular region can provide insight into the behavior or construct of interest. One of the central themes of this paper is the importance of examining the functional develop ment of the prefrontal cortex and related circuitry in the context of cognitive development, particularly with regard to memory and attention. First, as stated earlier, there is considerable development and organization of the prefrontal cortex throughout childhood and adolescence. Second, cognitive processes such as memory and attention that have been attributed to the prefrontal cortex appear to develop during this period. Third, the prefrontal cortex and related circuitry have been implicated in a number of developmental disorders that involve disruption of attention and memory in the context of interference. The study included two task conditions: a memory condition and a comparison/ control condition. In other words, children responded to repeats of letters with a single intervening (interfering) letter. In the comparison condition, subjects monitored similar sequences of letters for any occurrence of a single, pre-speci ed letter. Both the memory and comparison conditions required subjects to monitor sequences of letters presented visually one at a time, encode each letter, evaluate its identity, and respond to a target by pressing a button. The conditions differed in that the memory task required the subject to keep in mind the two previous letters rather than just a single target letter, and to continuously update this mental record over time. These latter cognitive operations are central to the concept of working memory (Baddeley, 1986) and consistent with our view of prefrontal involvement in the representation of information over time against interference from competing sources. Images were registered to a reference image to correct for movement using a modi ed version of Woods et al. Movement did not correlate with the experimental manipulation, but rather appeared to increase as a function of time on task and was minimal. Areas of signi cant activation were identi ed, by performing pixel-wise t-tests, comparing the memory and comparison conditions. The results demonstrated reliable activity in the dorsolateral prefrontal cortex in children. The similar distribution of activity across frontal gyri for children and adults taken from the Casey et al. Taken together, these two initial studies suggest a similar distribution of prefrontal cortical activity in children and adults during performance of a working memory task. However, the percent change in signal observed for the children was on average two to three times that observed for the adults in the Cohen et al. Based on the behavioral data available, the children had more dif culty with the task. This demonstrates the importance of collecting behavioral responses in the scanner, but also raises concerns with regard to the interpretation of the ndings given the behavioral differences. They performed the same sort of memory task as described previously, but varied the memory load from 0 to 3 as can be seen in Fig. The subject monitored a sequential display of single letters and responded only when the current letter was the same as the letter n trials before it. Subjects practiced until they reached 90% accuracy on the highest memory load of n=3. This paradigm allows for the manipula tion of memory load (number of trials back the subject must remember) by age and/or ability. Each participating group examined brain activity in both adults and children during performance of a spatial working memory task designed as an analog of the verbal working memory task just described. In this task, subjects monitored a linear array of four boxes for the location of a dot. Participants maintained xation on a central crossbar, and received instructions for three different response conditions. In the motor condition, partici pants were required to indicate the current spatial location of the dot by pressing the corresponding key on a four-button box. In the memory condition, participants were asked to indicate the location at which the dot had appeared a given number of trials previously. For example, in a 2-back paradigm, subjects responded by indicating the location at which the dot had appeared two trials previously. Therefore, the motor and memory conditions are identical except in the memory demands and extent of interference from preceding trials. Further, the number of intervening stimuli to be remembered could be manipulated, so as to vary memory load. Participants were pre-tested outside of the scanner to assess which memory load was appropriate for each individual.

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Any experienced discomfort or bodily imbalance which results from the sudden word blindness absence of a drug or other substance to whose n. A colloquial term for alexia or inability to presence the body has become accustomed. A task employed in studies of cognition imbalance which results from the sudden in which a subject is given a set of letters and absence of a drug or other substance to whose asked to combine them into as many words as presence the body has become accustomed. Thus a subject are given a cue such as cl and asked to supply might have previously learned the word claw the missing letters to make an entire word. Neuropsychological syndrome character ized by severe diffculties in understanding word salad spoken language, with sparing written lan n. A collection of spoken words without any guage understanding and language produc apparent meaning or coherent order, often tion. Patients who have this disorder can uttered by forid schizophrenics or others hear, but they cannot discriminate the lan with markedly disturbed thought processes. When a clear and overt dissociation between oral and written word-stem completion task language understanding is observed, fre n. An experimental task in which subjects quently the term pure word deafness is used. Thus a subject as an auditory processing defect (verbal might have previously learned the word claw auditory agnosia). Some phoneme dis word superiority effect crimination defects are usually found in n. This is an interesting caused by cerebrovascular accidents or head fnding in research on reading in which it had injuries, with left or bitemporal cortico-sub been assumed that individual letter recogni cortical lesions. In cases primary reason for meeting is to complete a of unilateral pathology, signifcant recovery task or set of tasks. A form of learning disability in which the individual is not able to recognize whole working hypothesis words but must sound them out each time n. Working memory refers to the temporary are given a cue such as cl from a previously storage of information that is currently being 582 working self-concept Xanax used in a cognitive task. The concept emerged the variability of self-concept over time, the from studies of a related but simpler concept, susceptibility of the self-concept to outside short-term memory. The distinction may be infuence, and the partial use of the self-con clarifed by comparing two memory tasks. In a simple span test, which is often used to assess short-term memory, individuals are working through given a series of items. In psychotherapy, the process of remem memory span is the number of items that can bering, analyzing and coming to emotional be reliably recalled in the correct order. A general term for occupational, indus trial, and organizational psychology, as well (5 5) + 1 = 26 cat as ergonomics and human factors design. Any sensory, motor, or cognitive prob contrast, the simple span score is not corre lem that prevents a person from learning to lated with such tasks. It is thought that until 1915 which was developed in Wurzburg, working memory consists of a limited pool of Germany, by Oswald Kulpe and his associ resources, and that storage and processing ates, which rejected the idea that conscious functions compete for resources. The self as experienced by the individual in which may be conscious but have no imaginal a given moment of time, thus acknowledging aspect. A brand name for alprazolam, which is dose potential is low, as it requires more one of a family of addictive central nervous than a thousand normal doses to be fatal system depressant drugs which are used to to an average adult. This group includes treat anxiety, sleeping problems, and seizure chlordiazapoxide, alprazolam, bromaze disorders and relieve symptoms of alcohol pam, clonazepam, clorazepate, diazepam withdrawal. They are frequently prescribed (Valium), estazolam, furazepam,lorazapam, 583 xanthopsia yellow-sightedness midazolam, oxazepam, quazepam, temaze female chromosomes. A visual disorder in which everything that averages about 10 points lower than sib appears yellow. It can be temporarily induced lings; a moderate increase in the probability by staring at a blue screen for several moments of learning disabilities is also associated with and is sometimes a symptom of jaundice and the syndrome. A genetic disorder of males character X chromosome ized by the presence of an extra X, or female n. A female sex chromosome, one copy of sex, chromosome in all the cells of the body. A genetic disorder in which a male has two humans and other animals, it is often associ copies of the male sex chromosome instead of ated with territoriality, and those perceived one. Most males who have this syndrome are as intruders are met with hostility and some normal, and their chromosomal abnormality times physical aggression. It is most often used its shape, which roughly approximates the let in 2x2 chi-square tests when a frequency ter Y, as opposed to the female sex chromo of less than 5 occurs in a cell and is accom some, which roughly resembles the letter X. This correction reduces yellow-sightedness the likelihood of a false positive result but n. A small yellow spot in the retina of the eye given either no control over the situation or a in which cones are highly prevalent, which different test from the experimental subjects. An artifcial written language using geomet be perceived as the face of a young woman ric shapes on computer keyboards for words, wearing a hat or an old woman wearing a scarf. A theory of color vision in which it is sup yoga posed that there are three color receptors n. Any of several schools of stretching exer sensitive to different parts of the light spec cises which have been found conducive to trum corresponding to the colors blue, green, reduction in many medical problems and are and red. It was supposed that combinations either derived from or are a part of Hindu of these produced all the colors perceived spiritual traditions. The Hindu religion, and the combination of all three receptors which seeks union of the individual with the produced a perception of white. The effect tends to be tem average of 0 and a standard deviation of 1 often porary and dependent on the type of task. An environmental cue such as a sunrise deviation to produce a z score distribution. An illusion in which a line drawn between zeitgeist the outsides of two circles appears to be longer n. The spirit of the times; used to denote a than a line of the same length which crosses shared mentality or worldview common to a the two circles before joining them. The observation that problems which have Vietnam, which emphasizes direct experi been interrupted and not completed are ence through meditation (zazen) and the 585 Zener cards Zurich school using of ever yday life as a part of mindfulness common word, and so on. It is part of Mahayana Buddhism, that there is an equilibrium between unifor which suggests that compassion is inherent mity and diversity. A visual illusion in which several parallel lines appear to converge and diverge when Zener cards crossed with short lines uniformly at 45-de n. The brand name for sertraline hydro chloride, which acts as a selective serotonin zenith distance reuptake inhibitor and is currently the most n. The direction of a point or object in widely used antidepressant and antianxiety the visual feld relative to a point directly drug in the United States. A balance between births and deaths ries of Lev Vigotsky, the actual level of ability in a group of animals such that the popula of a child in any particular area and the level tion remains stable. A slogan used by birth at which he or she could achieve with the help control advocates to point out the negative of guidance from an adult or more knowl effects on the environment of human popu edgeable child. A measure of the linearity of a relation ship on which a regression analysis has been z score performed. A transformed score which has had the average of a set of scores subtracted from it Zipf curve and the result divided by the standard devia n. The observation that in natural lan guages there is a power relation between fre Zurich school quency of use and rank such that the most n. A glass tube open on both ends, one of empyreumatic, hircine, foul, and nauseous, which was inserted in the nostril while the which were hypothesized to serve as the basis other was connected to a tube flled with for all odors as the primary colors combine to a measured amount of a substance to be form all the hues humans can perceive. The amount of the substance to be smelled was controlled by the length of the zygote Zwaardemaker tube. A fertilized ovum with two half-sets of chro mosomes, one-half contributed by the mother Zwaardemaker smell system and one-half by the father, which normally n. A classifcation system for describing odors in divides into an embryo which grows into an which there are nine primary odors, ethereal, infant. Professor of Neurology and Chairman Department of Neurology University of Goettingen Goettingen, Germany Michael Frotscher, M. Professor of Anatomy and Chairman Department of Anatomy and Cell Biology University of Freiburg Freiburg, Germany With contributions by Wilhelm Kueker Founding author Peter Duus Translated by Ethan Taub, M. Insofarasthis Michael Frotscher; with contributions by book mentions any dosage or application, readers Wilhelm Kueker; translated by Ethan Taub; may rest assured that the authors, editors, and pub illustrated by Gerhard Spitzer. Topical check, if necessary in consultation with a physician diagnosis in neurology. Title: Topical or specialist, whether the dosage schedules men diagnosisinneurology. The authors and publishers request every user to report to the publishers any discrepancies or inaccuracies 1st Brazilian 1st Greek edition 1992 noticed. Cover design: Cyclus, Stuttgart this book, including all parts thereof, is legally Typesetting by primustype Hurler, Notzingen protected by copyright. As is well known, the intervening time has witnessed major developments, both in the clinical neurosciences and in basic research. In particular, modern imaging techniques such as magnetic resonance imaging and positron emission tomo graphy on the one hand, and the new molecular biological understanding of the development, plasticity, and pathology of the nervous system on the other, have brought about substantial progress in our knowledge in the field of neuroscience. We have replaced older case studies based mainly on history by new ones more closely reflecting current practice, provided multicolored il lustrations to ease and enhance comprehension, and added state-of-the-art neuroradiological images to demonstrate the correlation of structure and func tion in nervous system lesions. We have also newly color-coded the section headings to enable readers to distinguish at a glance between neuroanatomical (blue) and clinical (green) material, without having to disrupt the thematic continuity of the text. Kundmueller for their dil igence and for many constructive discussions, as well as Mrs. Neurons make contact with each other at junctions called synapses,atwhichinformationistransferred from one neuron to the next by means of chemical messenger substances called neurotransmitters. The organization of the nervous system is easier to understand after a brief consideration of its (ontogenetic) development. Information Flow in the Nervous System Information flow in the nervous system can be broken down schematically into three steps (Fig. Thus, when a pedestrian sees a green traffic light, afferent impulses are generated in the optic nerves and visual system that convey information about the specific color present. Efferent impulses to the legs then effect the motor response (crossing the street). At the synapses, information is transferred from one neuron to the next by means of chemical substances called neurotransmitters. Neurons transfer information in one direction only be cause they are bipolar: they receive information from other neurons at one end, and transmit information to other neurons at the other end. The receptive structures of a nerve cell, called dendrites, are branched processes attached to the cell body. Neurons vary considerably with regard to the number and branching pattern of their dendrites. The forward conducting structure is the axon, which in humans can be up to a meter in length. In con trast to the variable number of dendrites, each neuron possesses only a single axon. At its distal end, the axon splits into a number of terminal branches, each of which ends in a so-called terminal bouton that makes contact with the next neuron (Fig.

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This func the social order is generally disrupted tion is based on the limited capacity of when the operated animal is introduced or neural processing systems as well as the reintroduced in the colony medicine cost of trileptal. By and wherever goal-directed behavior needs de nition medicine 5113 v cheap trileptal american express, attention is selective; it is the to be integrated in time treatment gout purchase 300 mg trileptal fast delivery. All sen and re-emerge in the discussion medicine reminder alarm discount 600mg trileptal fast delivery, below treatment kidney disease buy trileptal overnight, sory and motor systems have rudiments of of the effects of prefrontal lesions on such what in the cognitive sphere we call atten functions as discrimination and working tion treatment zenker diverticulum buy 300 mg trileptal with visa. Wherever a discrete sector of senso memory; indeed, there is no successful dis rium or motility is engaged in the selective crimination without attention, and working processing of information, there lies the memory can be properly considered atten biological root of what in the realm of cog tion to an internal representation. Note, tion: it provides attention with its temporal however, that in both places the optimiza dimension. While integrating behavior in tion of excitatory processing in a given sec the time domain, as it happens in the per tor of the sensory or motor apparatus is formance of a neuropsychological task, the accompanied, collaterally, by the inhibition prefrontal cortex makes it possible for the of other sectors: inhibition of retinal cells animal to attend to recent events as well around the receptive elds at the center of as prospective events, to recent sensory the processing or inhibition of antagonis cues as well as upcoming motor acts. This pro level of consciousness and cognition, those spective or preparatory attention is what reciprocal excitatory-inhibitory processes we call preparatory set or, simply, set. One is to priate to consider, albeit brie y, the experi emphasize that attention is inseparable ments by Dias, Robbins and Roberts (1996a, from other cognitive functions such as sen 1996b, 1997). For this rea keys to discriminate between visual stimuli son, among others, it is futile to attempt the presented in pairs, such as those in Figure neuropsychological localization of atten 4. The pattern of black lines superimposed on a other purpose is to lay the groundwork geometrical gure. In a series of consecu for the evidence that the prefrontal cortex tive trials, the stimuli were presented in V. Subjects with lateral lesion were notoriously de cient in per forming those shifts. They failed to trans fer attention from lines to gures, and vice versa; presumably, they failed to inhibit the previous set. That failure to inhibit inap propriate attention was most conspicuously displayed by the orbital-lesion animals on a simple discrimination reversal task (see next section). Here we have, therefore, in a visual discrimination task, the two aspects of attention impaired by prefron tal lesions. The task is very similar to the binations of stimuli, especially if they are Wisconsin Card Sort Test (see Chapter 5), highly familiar. It can also learn without a test used to test humans with prefrontal dif culty new simple habits that are predi damage, in which the subject is required to cated on the perception of clear and unam classify cards by the shape or color of the biguous cues. The frontal animal is able to learn unrelated stimuli as well, especially if they and retain such a task, although the learn are new. The animal is unusually distract ing usually takes place at a slower pace ible and unusually reactive to novel stimuli than in a normal animal, especially if the (French and Harlow, 1955; Brush et al. These dif culties are most conspicu order (Harlow and Dagnon, 1943; Settlage ous if one of the stimuli demands a given et al. The older the behavioral disinhibition of the frontal ani habit and the more familiar the discrimi mal more evident than in the performance nanda, the greater is the dif culty that the of tasks that involve conditioned inhibition, frontal animal ordinarily shows in reversals. The frontal animal contin 1961; Brutkowski, 1964; Mishkin, 1964; ues to approach the previously baited loca Gerbner and Pasztor, 1965; Eichenbaum tion long after another location has become et al. The animal seems unable animal in such a situation shows a marked to bene t from errors and to adjust to the tendency to make errors of commission, change in the rules of the game (Settlage persistently responding to the stimulus that et al. This dif culty in inhibi and delay tasks (see next section) may be tory response control is at the root of most prompted not only by external sensory errors in discrimination tasks. Previous responses gain cate by selective ablations the areas of the the upper hand, so to speak, and obliter prefrontal cortex that are most involved ate the response that the speci c cue of any in sensory discriminations. In later chapters, we will see the is little evidence of topographic speci city importance of the anterior cingulate cortex with respect to sensory modality, either for error correction. It appears, rather, that the criti dif culties in learning and retaining certain cal factors underlying the localization of forms of discrimination behavior, especially discrimination de cits are supramodal those requiring successive differentiations and related to the formalities of the tasks and reversals, appear to be common to fron employed. It is of singular interest that a de cit By manipulating the physical characteristics in discrimination reversal has also been of the discriminanda and their association identi ed in the pigeon after lesions of the with reward, Dias et al. On account of its ana Monkeys with inferior convexity lesion tomical connections and neurochemical exhibit loss of inhibitory attention control, transmission properties, including an excep whereas monkeys with orbital lesion cannot tionally dense dopaminergic innervation, overcome response tendencies. Both lateral and orbitomedial cor that depend on inhibitory control are tices may be responsible for the inhibition most disrupted by medial prefrontal of sensory events that at any given time lie lesions (Brutkowski and Dabrowska, 1963; outside of the focus of attention. In rodents, similar three general categories of adaptive inhibi effects can be obtained by lesions of the sul tory control emanating from the prefrontal cal cortex (Eichenbaum et al. Delay Tasks: Working Memory We will encounter disinhibition again in humans with prefrontal lesions (Chapter 5). Since Jacobsen (1935, 1936) rst described the principal inference from the ndings it, the de cit induced, by frontal ablation, summarized in this animal section is that in delayed response has been the fulcrum the prefrontal cortex of the primate, espe of behavioral research into the cognitive cially its orbital region, or its homolog in aspects of prefrontal function, and the rhesus rodents and carnivores, is especially impor monkey has been the standard species for tant for the inhibitory control of discrimina this research. It will be remembered (Chapter 2) is undoubtedly one of the clearest and best that the orbitomedial sector of the prefron documented phenomena in physiological tal cortex has distinct connections with the psychology. That de cit is complex, however, medial thalamus, the hypothalamus, the in large part because the task is complex. Those From the de cit itself, no one single func structures and their connections constitute tion can be inferred for the prefrontal cor the orbital system postulated by Rosvold tex. It is through that system that the pre one of those functions most prominently: frontal cortex executes inhibitory control. Which of those functions fail for a whole is an important source of inhibitory the animal to fail at delayed response will control over behavior. The lateral prefron depend to some extent on the prefrontal tal cortex, probably through the caudate area affected. The screen is then lowered, blocking the view of the objects for a period of a few seconds or minutes. Otherwise, response buttons for performance of so-called indi the trial is terminated without reward. The position of rect-method delay tasks (mouth spigot is for delivery the bait is changed randomly between trials. The display of a discrete item of press the one that was lit at the start of the trial. An enforced delay of a few seconds or on the upper button; after a delay, both colors appear minutes, during which the objects are in the lower buttons, and the animal must press the out of reach and, in some test versions, one matching the sample color; both that color and out of sight the positions of the two colors in the lower buttons are changed randomly between trials. The simultaneous presentation of the diagrams, white triangles mark the site of the correct objects for choice response, which is rewarded with a squirt of fruit juice 4. If it chooses the baited object, the ani mal is allowed to retrieve the food as the Apparatus (Harlow, 1949) or a variant of it. The position of the bait is changed Some versions of the test are administered at random from one trial to the next. Thus in automated instruments, in which the site far described is the classic, so-called direct of the correct response is signaled at the method delayed-response test, usually start of a trial by a visual or auditory stimu administered in the Wisconsin General Test lus (indirect method, Figure 4. The degree of impair alternation, in which the trials are tempo ment varies considerably, depending on the rally interlocked with one another (Figure species and on a number of factors related 4. The animal is required to alter to the testing method and the cortical areas nate the site of response, usually between affected. Next, we attempt to weigh the role right and left, with an enforced delay of each of those factors. The correct site for each response is thus predicated on the previous Anatomical Factors response. Many have tried to delimit sub-areas Monkeys with frontal ablation fail a of the prefrontal cortex speci cally con third type of delay test: delayed matching cerned with particular aspects of delay-task to-sample (Spaet and Harlow, 1943; Glick performance. Animals with bilateral lesions of the pre Contrary to early reports (Jacobsen et al. The de cit has been demonstrated in primates of several species (Jacobsen and Nissen, 1937; Crawford et al. From Rosenkilde (1979), and insectivores (Passingham, 1978; Skeen slightly modi ed, with permission. No not seem directly involved in the mnemonic relationship has been found between hemi aspect of working memory (Rushworth spheric dominance and the magnitude of et al. According to respectively, the dorsolateral (proreal) this, the extent of the de cit depends on and the medial cortex (Brutkowski, 1964, the quantity of tissue removed as much 1965; Dabrowska, 1971, 1972; Konorski, as (or more than) the site of the removal. The homology of the dorsola this notion has received support from the teral cortices of the two species, however, results of other experiments. For example, is functionally better established than is some studies have indicated that complete the homology of other prefrontal sectors. Stamm and Weber-Levine, 1971; Gentile On the other hand, there is evidence that at and Stamm, 1972). It shows at responses (Brutkowski and Dabrowska, least some quantitative differences in the 1963; Brutkowski, 1964; Dabrowska, 1971, involvement of two broadly de ned pre 1972). In the monkey, functional dichotomy approximately cor the picture reveals a functional dissociation responds to the dichotomy of thalamic con between the dorsolateral cortex (includ nections pointed out in Chapter 2. All Goldman and Rosvold, 1970; Goldman too often and mistakenly, however, differ et al. Lesions of the arcuate cortex have cortex, such as the mediodorsal nucleus also been noted to disrupt a conditional of the thalamus (Schulman, 1964; Isseroff go/no-go task (Petrides, 1986) as well as et al. In the mon after lesions of the cingulate and medial pre key, selective lesions of the head of the cau frontal cortex in the monkey (Pribram et al. The nal interpretation and other behavioral ndings, and the ana of the effects of many published ablation tomical evidence, Rosvold postulated two studies must await further experimen functional systems of interconnected neu tal evidence. The testing tasks may differ vastly insight into the neural pathways used in a with respect to the factors under study, but delay task. With the aid of split-brain pro also with respect to imponderable factors cedures, Glickstein and collaborators (1963) that may complicate the interpretation of were able to show that at least some of the V. These to the prefrontal cortex by way of cortico have been interpreted as visual nonspatial cortical connections from the posterior de cits. Yamaguchi and cal sense, since the area ablated receives Myers (1973) showed that the animal with profuse inputs from visual areas of poste a commissurotomy can transfer the learn rior (inferotemporal) cortex (Chapter 2). The ing of delayed response and alternation inferotemporal-frontal disconnection leads from one hemisphere to the other, even to visuomotor de cits (Eacott and Gaffan, though it is unable to do so with discrimi 1992; Parker and Gaffan, 1998; Bussey et al. In related experiments, the reversible sumed, is that for delay tasks the animal lesion of inferotemporal cortex, by cooling, uses proprioceptive cues related to body impairs the performance of a visual delay orientation and movement that, unlike the task (Fuster et al. As we shall prefrontal cortex executes its crucial role in see later in this chapter, the cooling of the delay tasks. Temporal Sensory Factors factors, however, override sensory fac Attempts have been made to reduce tors. The delay of the delay task is all the delayed-response de cit to a defect of important for the de cit from prefrontal sensory function of a particular modal lesion to occur, regardless of the sensory ity.

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Striate cortex (no layers) (isolated rudimentary (several secondary medicine cabinet shelves discount trileptal 300mg with visa, fur layers) ther differentiated lay ers) Olfactory bulb Hippocampus Presubicular area (27) Olfactory peduncle Dentate gyrus Retrosubicular area (48) Olfactory tubercle Subiculum Entorhinal area (28 symptoms cervical cancer trusted 300mg trileptal, 34) Anterior perforated Indusium griseum Perirhinal area (35) substance Septum pellucidum Prepyriform area (51) Amygdala Preterminal area (25) Homogenetic cortex (All types derived from the basic six-layered variety) 1 treatment 1st line cheap 300mg trileptal free shipping. Histological cortical localisation in relation to morphology 211 many animals medicine pill identification buy trileptal no prescription, they consist of secondarily highly atrophied structures symptoms of colon cancer generic trileptal 600mg overnight delivery. To this group of primitive cortical structures belong the olfactory bulb symptoms thyroid problems generic trileptal 600mg otc, the anterior perforated substance and the amygdaloid nucleus. One can include in this category the hippocampus with the dentate gyrus, the subiculum, the indusium griseum (*162) and the preterminal area (*157). To this type of cortex belong the entorhinal, the perirhinal, the prepiriform, the presubicular, and the retrosubicular areas (and perhaps also the ectosplenial area). As can be seen from the foregoing, the ways in which the different cortical locations have differentiated are very diverse. The major types of differentiation are once again summarised in Table 7 4); at the same time a list is given of the main regions and areas of human homogenetic cortex. Cortex with surface grey matter, corresponding in the main to our homogenetic group, but of which he only distinguishes two types: a) the five-layered cortex (including the common variety and the claustral formation); b) the eight-layered cortex (corresponding to our calcarine cortex). Ariens Kappers, Die Phylogenese des Rhinencephalon, des Corpus Striatum und der Vorderhirnkommissuren. These variations frequently have such obvious and consistent characteristics that one can recognise the relevant animal group from the specific structural type. They are associated on the one hand with extrinsic shape, size and position, and on the other with the intrinsic structure of the particular areas and regions, and are thus partly of a quantitative and partly of a qualitative nature. Of the quanitative features, the most important are the volume, or more exactly the surface area, of the cortical zone under discussion. I should like to illustrate a particularly striking case in the accompanying Figures 147 and 148. It concerns the hippocampal region of man and hedgehog, represented by two coronal sections through the widest extent of this region. In the hedgehog the zone extends over far more than half, and almost two-thirds, of the section (50 to 66%), whereas in man the figure is about 1/20, only about 5%. The difference in surface area appears even more clearly in the surface view of this region (Figures 144 to 146). The qualitative divergence between homologous cortical zones is manifest ed in differences in histological structure, of which the important ones for our purposes concern the laminar cytoarchitectonics. In the preceding chapters we have also tried to give illustrative examples of this. From the outset one must distinguish between two forms of cortical evolution that are related in essence, but the results of which diverge profoundly. On the one hand, a cortical area of a particular animal group undergoes special development such that its intrinsic structure (its cyto and myeloarchi tectonics) differentiates further than in other groups, and in a similar way over the whole of its surface, laying down larger or more numerous cells of a given type or developing completely new cellular structures, or even introducing new sublayers by the aggregation of certain cell types (eg: the calcarine cortex or area 17 of the capuchin monkey). In doing this the surface area need not nec essarily increase; it can remain the same as in related species with an incomplete differentiation of the area in question, or it can even diminish relatively, in spite of the increase in structural complexity (eg: the human entorhinal area, area 28). The second form of qualitatively divergent development consists of the structural differentiation within a cortical area of distinct loci in different, but specific, ways. Thus regions that are homogeneously built in other species are split into several spatially separate special zones, or areas are divided into several subareas. The retrosplenial area, area 29, of the rabbit is a particularly striking example of the latter process (Figure 107), and another is the postcen tral region of primates. Among these major forms of divergent cortical development are included Histological cortical localisation in relation to morphology 213 Fig. Diagrams of coronal sections through the hemispheres of man and hedgehog at the level of the largest extent of the piriform lobe or hippocampal region, drawn in their natural size relations. They are the causes of the surprising multiplicity of forms of cortical organisation in the various mammalian species. We describe as special homologies, or homologies in the strict sense according to C. Various degrees of homology can be distinguished according to the appearance of a particular organ, depending upon whether its morphological state is essentially unaltered compared with other animals or if it has undergone modifications in individual animals through additions or deletions of parts. We have now to determine whether the different subdivisions of special homology defined by morphologists can be demonstrated in the mammalian cortex 7). Naturally, homologies will usually only be complete between closely related groups, as many new features have been added to individual parts and old ones lost in the course of ontogeny through progressive and regressive events: a cortical type seldom remains unaffected by fundamental changes throughout the whole mammalian class. Nevertheless there are enough examples where one can accept such complete homology over a broad front. Examples are cortical types in the hippocampal region (areas 27, 28 and 35), the hippocampal cortex itself together with the dentate gyrus, and also the giant pyramidal cortex of several orders, especially primates, prosimians, many carnivores and ungulates. It is also true of parts of the retrosplenial region in a large number of species, such as area 29 in prosimians, macrochiropterans, carnivores and ungulates on the one hand, and in many rodents on the other. In primates this whole region is completely homologous and represents a regressed organ, as opposed to other orders in which it is defectively homologous. Finally complete homology can be accepted for individual polymorphic types in several species, such as the calcarine cortex of many primates, prosimians, carnivores and macropods. Histological cortical localisation in relation to morphology 215 component parts, in relation to other zones that are otherwise completely homologous or structurally similar. We also find everywhere the two subtypes of incomplete homology that Gegenbaur distinguished: defective homology arising from loss of elements, and augmentative homology from the addition of new elements. We have already seen (Chapter I, page 36) that one can speak of defective homology in a narrower sense not only with reference to cortical areas them selves but to the lamination within an area, and that imitative homologies (Furbringer) also appear in the cerebral cortex in a specific sense. Together with generation (Generatio) and growth (Crescentia), differentiation (Divergentia) is the most important fundamental function responsible for the formation of individual organs, and on it all their secondary development and refinement depends 8). This process, which involves the emergence of dissimilar elements from similar fundamental bases as an adaptation to differing life styles, or, in physiological terms, to functional differences, has led to an enormous multiplicity of organisational patterns in the cerebral cortex of various animals and also often in one and the same brain, especially in higher species, as we have seen. The final laminated cortex develops by morphological differentiation from a homogeneous Anlage that is common to all mammals, the primitive unlaminated cortical plate (W. His), and within this cortex emerge numerous extensive regional structural modifications as a result of local heterogeneous differentiation. See also: ibid, Gesammelte populare Vortrage aus dem Gebiet der Entwicklungslehre, Part 1, p. However, I feel that, according to the usual zoological terminology, the concept is justified in its strictest sense. As one can see, all these definitions can be applied without difficulty to our cortical areas. What we have determined to be an ensemble of structural areas and regions in the preceding chapters, represents a complex of organic elements subordinate to a higher organism when considered morphogenetically. From the organic point of view, the mammalian cerebral cortex is thus to be considered as an organ complex or, in other words, an ensemble or aggregate of suborgans derived from a common Anlage and subjected to various degrees of progression and regression, sometimes coordinated and sometimes subordinate, that are specifically differentiated and more or less sharply demarcated from each other by their histological structure. In this sense the cerebral cortex would be a lower order organ system subordinate to the whole central nervous system. Organ formation relies on functional activity which itself depends on adaptation to changing conditions of life. An organ changes according to the conditions that influence it, like the whole organism. If such an influence operates in a particular way for a long time, the organ will change its function; it adapts to new circumstances because this represents an advantage for the organism in the struggle for survival. With the change in function goes a slow, but steady, change in the form of the organ. By an accumulation of very small alterations parts of the organ change permanently and differentiate morphologically. The newly structured elements with their new function develop certain characteristics and become more clearly differentiated from each other with time, and so finally spatially separate parts emerge as new organs. Thus, adaptation and the resultant differentiation determine functional localisation, that is a feature of increased overall performance. Certain functions originally subserved by the whole organ are now accomplished by particular parts and the performance of the organ is therefore divided into various partial functions that, all together, represent the total function. Refinement of an organ is necessarily related to this process of differentiation, that is expressed physiologically as functional adaptation and morphologically as anatomical complexity. The greater multiplicity and independence of different sections of the cortex means greater freedom of action, and with the larger number of relatively autonomous elements there is more latitude for differentiation. Histological cortical localisation in relation to morphology 217 refinement of the whole cortex, along with a multiplication of functions 11). In this sense, one might often consider certain regions of the more simply organised mammals described above as primitive organs from which the multiple cortical areas present in more highly developed species have emerged. In the final analysis, of course, one can also postulate such a primitive condition for the whole cortex somewhere in its ancestral past, that is to say a single relatively poorly differentiated primitive cortex, but this condition has long been surpassed in phylogeny and is no longer demonstrable. They manifest themselves to us as development towards a higher level, or progressive development, in some cases, and as regressive changes towards a lower level in others. Here also one must distinguish between qualitative and quantitative divergence as well as between progressive and regressive development of individual zones as above. Both processes, phylogenetic differentiation that leads to transmutations of species and thence to gradual development of various parts of the cortex in more highly organised groups, and ontogenetic differentiation that governs the emergence of different cortical organs in individual animals, are the expression of one and the same basic biological phenomenon of physiological functional specialisation based on adaptation and heredity 15). Hertwig, Uber die Stellung der vergleichenden Entwicklungslehre zur vergleichenden Anatomie etc. Accordingly, development and regression, anatomical complexity and simplicity, are not only not mutually exclusive, but they proceed together and are mutually dependent in all sites and at all times, according to the correlation principle. This correlation is visible grossly in the cortex both in the size and shape of its organs (areas and regions), and in their number and position. If a cortical area or a larger cortical zone increases in relative size in an animal, or if the number of the component subfields increases considerably, we frequently see a regression in neighbouring or even distant cortical zones, and this is again expressed partly by a decrease in volume and partly by a reduction of dif ferentiated component parts, that is of regions and areas. Sometimes changes brought about by such correlation lead merely to a spatial displacement, that is to say a relocation of an organ. In earlier chapters we have encountered abundant examples of all these developmental processes. The way in which rudimentary elements arise is obviously the same as that by which new elements are formed. In both cases adaptation and heredity work together and reveal natural selection as the underlying cause in the struggle for existence. Cortical organs of moderate developmental level within a mainly poorly organised cortex will differ little, if at all, in terms of morphological importance, from organs that have regressed from a higher cortical type. In certain circumstances it may be particularly difficult to avoid confusion between rudimentary cortical areas and developing or newly formed cortical organs. Anaplastic or newly developing structures may appear morphologically regressed or rudimentary, and thus of little physiological value. Histological cortical localisation in relation to morphology 219 demonstrated anaplastic and cataplastic processes. Where they are to be found and what particular morphological features might represent them cannot yet be stated. As we are here dealing with the end product of the development of physiological function, a major part of the work of determining these various types will fall upon comparative physiology. I should now like to briefly raise the question as to how much localisational data can contribute to our knowledge of mammalian phylogenetic relations. The principle and most important manifestations of family relations that we know are comparative anatomy and ontogeny. The difficulties in drawing definite conclusions about phylogeny from them are particularly great when dealing with such a highly complex and so profoundly secondarily modified organ as the cerebral cortex.

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