Page 436. CHAPTER 22 Reinventing Primate Neuroscience for the Twenty-First Century Todd M. Preuss... more Page 436. CHAPTER 22 Reinventing Primate Neuroscience for the Twenty-First Century Todd M. Preuss The manner in which an organism perceives and responds to features of its environment reflects the state of the neural systems that make up its brain. ...
Subdivisions of the prefrontal cortex (PFC) evolved at different times. Agranular parts of the PF... more Subdivisions of the prefrontal cortex (PFC) evolved at different times. Agranular parts of the PFC emerged in early mammals, and rodents, primates, and other modern mammals share them by inheritance. These are limbic areas and include the agranular orbital cortex and agranular medial frontal cortex (areas 24, 32, and 25). Rodent research provides valuable insights into the structure, functions, and development of these shared areas, but it contributes less to parts of the PFC that are specific to primates, namely, the granular, isocortical PFC that dominates the frontal lobe in humans. The first granular PFC areas evolved either in early primates or in the last common ancestor of primates and tree shrews. Additional granular PFC areas emerged in the primate stem lineage, as represented by modern strepsirrhines. Other granular PFC areas evolved in simians, the group that includes apes, humans, and monkeys. In general, PFC accreted new areas along a roughly posterior to anterior trajectory during primate evolution. A major expansion of the granular PFC occurred in humans in concert with other association areas, with modifications of corticocortical connectivity and gene expression, although current evidence does not support the addition of a large number of new, human-specific PFC areas.
Modern studies of granular frontal cortex (GFC) in large-brained, anthropoid primates, such as Ma... more Modern studies of granular frontal cortex (GFC) in large-brained, anthropoid primates, such as Macaca, indicate that this region is comprised of many areal subdivisions. These areas vary in their architectonic appearance and each has a distinctive, diverse set of corticocortical connections. The great extent of the GFC region in anthropoids, and its high degree of areal parcellation, suggest that some GFC areas may be specializations of anthropoids, not found in other mammals. To investigate this possibility, we studied the corticocortical connections of GFC in the relatively small-brained, strepsirhine primate Galago, with a series of eight tracer injections in the frontal cortex, and an additional eight injections of parietal and temporal cortex. Tracers used were wheat-germ agglutinin conjugated to horseradish peroxidase and tritiated amino acids. Our results indicate that Galago GFC has strong, reciprocal connections with the parietal area-7 complex and with higher-order temporal areas; there are additional connections with extrastriate visual cortex, parahippocampal, and cingulate areas, and frontal cortex. Thus GFC has an extremely diverse array of cortical connections in Galago, as in Macaca. However, we also found that the pattern of parietofrontal connections is simpler in Galago than in Macaca. Specifically, parietal areas project to fewer discrete zones within the GFC of Galago, consistent with the view that these animals have fewer GFC areas than Macaca. In addition, Galago GFC possesses connections that specifically resemble those of Macaca arcuate cortex, but lacks connectional patterns that are characteristic of principalis cortex. These results are in accord with our previous architectonic studies, which indicated that Galago does not possess homologues of principalis areas. We conclude that the arcuate areas are common elements of primate GFC organization, while the areas located within and adjacent to the principal sulcus are anthropoid specializations.
We have conducted a systematic comparison of the ipsilateral (uncrossed) and contralateral (cross... more We have conducted a systematic comparison of the ipsilateral (uncrossed) and contralateral (crossed) thalamic connections of prefrontal cortex in macaque monkeys, using cortical implants of horseradish peroxidase pellets and tetramethyl benzidine histochemistry to demonstrate anterograde and retrograde thalamic labeling. Contrary to the prevailing belief that thalamocortical projections are entirely uncrossed, our findings indicate that a modest crossed projection to prefrontal cortex arises from the mesial thalamus, principally the anteromedial and midline nuclei. Also, while confirming that corticothalamic projections are bilateral, we found that the pattern of crossed projections differs from that of uncrossed projections. Projections to mesial thalamic nuclei, specifically to the anteromedial nucleus, the midline nuclei, and the magnocellular part of the mediodorsal nucleus are bilateral, the contralateral projection being nearly as dense as the ipsilateral projection. Projections to the parvicellular part of the mediodorsal and ventral anterior nuclei are also bilateral, but the contralateral projection is much weaker than the ipsilateral projection. Prefrontal projections to the reticular nucleus, medial pulvinar, suprageniculate nucleus, and limitans nucleus appear to be exclusively ipsilateral.These results indicate that prefrontal cortex has prominent bilateral and reciprocal connections with the nuclei of the mesial thalamic region. As this region of the diencephalon has been implicated by anatomical and behavioral studies in memory functions, our findings suggest that prefrontal cortex, through its connections with this region, may be involved in the bilateral integration of mnemonic systems.
In macaque monkeys with injections of tritiated amino acids or horseradish peroxidase in the vent... more In macaque monkeys with injections of tritiated amino acids or horseradish peroxidase in the ventrolateral granular frontal cortex, we observed extensive anterograde and retrograde labeling of the premotor and somatosensory cortex in and around the lateral sulcus. Comparable labeling was not present with large and small control injections of the dorsal granular cortex. Cytoarchitectonic evaluation of the perisylvian cortex in the three cases examined in detail indicated that labeled areas included the ventral premotor cortex (area 6V); the precentral opercular and orbitofrontal opercular areas (PrCO and OFO); the second somatosensory area (S-II); the opercular cortex immediately anterior to S-II, possibly corresponding to area 2 of the S-I complex; and the central part of the insular cortex, including portions of the granular and dysgranular insular fields (Ig, Idg). Labeling was particularly dense and extensive in areas 6V, S-II, and OFO. Lighter labeling was also present in the rostral inferior parietal lobule (areas 7b and POa). The distribution of label within perisylvian areas was not uniform: certain parts were heavily labeled, while other parts were lightly labeled or unlabeled. Comparison of label distribution with published accounts of the somatotopy of these areas indicates that forelimb and orofacial representations were selectively labeled. Further, our results, taken together with other recent anatomical findings (e.g., Matelli et al.: Journal of Comparative Neurology 251:281-298, 1987; Barbas and Pandya: Journal of Comparative Neurology 256:211-228, 1987) suggest strongly that there is a network of interconnected forelimb and orofacial representations in macaque cortex, involving the ventral granular frontal cortex, area 6V, OFO, opercular area 2, S-II, the central insula, and area 7b. Each injection of frontal cortex which labeled the perisylvian somatic cortex involved the cortex of the ventral rim of the principal sulcus (PSvr). The cortex surrounding the PSvr does not stand out as a distinct area in Nissl-stained material. However, examination of myelin-stained sections prepared from uninjected hemispheres with the Gallyas technique revealed the existence of a distinct zone centered on the PSvr. This myeloarchitectonic area, which we term area 46vr, is more heavily myelinated than the ventral bank and fundus of the principal sulcus (area 46v) but is less heavily myelinated than the ventral (inferior) convexity (area 12). Involvement of area 46vr in our injections was probably responsible for the strong labeling observed in perisylvian somatic areas.(ABSTRACT TRUNCATED AT 400 WORDS)
Our understanding of human brain evolution has advanced enormously over the past decade, owing to... more Our understanding of human brain evolution has advanced enormously over the past decade, owing to contributions of scientists from many different branches of the life sciences. This chapter reviews some of the concepts and findings from evolutionary biology and neuroscience central to human brain evolutionary studies, surveys some major recent findings, and identifies issues for future research.
Page 436. CHAPTER 22 Reinventing Primate Neuroscience for the Twenty-First Century Todd M. Preuss... more Page 436. CHAPTER 22 Reinventing Primate Neuroscience for the Twenty-First Century Todd M. Preuss The manner in which an organism perceives and responds to features of its environment reflects the state of the neural systems that make up its brain. ...
Subdivisions of the prefrontal cortex (PFC) evolved at different times. Agranular parts of the PF... more Subdivisions of the prefrontal cortex (PFC) evolved at different times. Agranular parts of the PFC emerged in early mammals, and rodents, primates, and other modern mammals share them by inheritance. These are limbic areas and include the agranular orbital cortex and agranular medial frontal cortex (areas 24, 32, and 25). Rodent research provides valuable insights into the structure, functions, and development of these shared areas, but it contributes less to parts of the PFC that are specific to primates, namely, the granular, isocortical PFC that dominates the frontal lobe in humans. The first granular PFC areas evolved either in early primates or in the last common ancestor of primates and tree shrews. Additional granular PFC areas emerged in the primate stem lineage, as represented by modern strepsirrhines. Other granular PFC areas evolved in simians, the group that includes apes, humans, and monkeys. In general, PFC accreted new areas along a roughly posterior to anterior trajectory during primate evolution. A major expansion of the granular PFC occurred in humans in concert with other association areas, with modifications of corticocortical connectivity and gene expression, although current evidence does not support the addition of a large number of new, human-specific PFC areas.
Modern studies of granular frontal cortex (GFC) in large-brained, anthropoid primates, such as Ma... more Modern studies of granular frontal cortex (GFC) in large-brained, anthropoid primates, such as Macaca, indicate that this region is comprised of many areal subdivisions. These areas vary in their architectonic appearance and each has a distinctive, diverse set of corticocortical connections. The great extent of the GFC region in anthropoids, and its high degree of areal parcellation, suggest that some GFC areas may be specializations of anthropoids, not found in other mammals. To investigate this possibility, we studied the corticocortical connections of GFC in the relatively small-brained, strepsirhine primate Galago, with a series of eight tracer injections in the frontal cortex, and an additional eight injections of parietal and temporal cortex. Tracers used were wheat-germ agglutinin conjugated to horseradish peroxidase and tritiated amino acids. Our results indicate that Galago GFC has strong, reciprocal connections with the parietal area-7 complex and with higher-order temporal areas; there are additional connections with extrastriate visual cortex, parahippocampal, and cingulate areas, and frontal cortex. Thus GFC has an extremely diverse array of cortical connections in Galago, as in Macaca. However, we also found that the pattern of parietofrontal connections is simpler in Galago than in Macaca. Specifically, parietal areas project to fewer discrete zones within the GFC of Galago, consistent with the view that these animals have fewer GFC areas than Macaca. In addition, Galago GFC possesses connections that specifically resemble those of Macaca arcuate cortex, but lacks connectional patterns that are characteristic of principalis cortex. These results are in accord with our previous architectonic studies, which indicated that Galago does not possess homologues of principalis areas. We conclude that the arcuate areas are common elements of primate GFC organization, while the areas located within and adjacent to the principal sulcus are anthropoid specializations.
We have conducted a systematic comparison of the ipsilateral (uncrossed) and contralateral (cross... more We have conducted a systematic comparison of the ipsilateral (uncrossed) and contralateral (crossed) thalamic connections of prefrontal cortex in macaque monkeys, using cortical implants of horseradish peroxidase pellets and tetramethyl benzidine histochemistry to demonstrate anterograde and retrograde thalamic labeling. Contrary to the prevailing belief that thalamocortical projections are entirely uncrossed, our findings indicate that a modest crossed projection to prefrontal cortex arises from the mesial thalamus, principally the anteromedial and midline nuclei. Also, while confirming that corticothalamic projections are bilateral, we found that the pattern of crossed projections differs from that of uncrossed projections. Projections to mesial thalamic nuclei, specifically to the anteromedial nucleus, the midline nuclei, and the magnocellular part of the mediodorsal nucleus are bilateral, the contralateral projection being nearly as dense as the ipsilateral projection. Projections to the parvicellular part of the mediodorsal and ventral anterior nuclei are also bilateral, but the contralateral projection is much weaker than the ipsilateral projection. Prefrontal projections to the reticular nucleus, medial pulvinar, suprageniculate nucleus, and limitans nucleus appear to be exclusively ipsilateral.These results indicate that prefrontal cortex has prominent bilateral and reciprocal connections with the nuclei of the mesial thalamic region. As this region of the diencephalon has been implicated by anatomical and behavioral studies in memory functions, our findings suggest that prefrontal cortex, through its connections with this region, may be involved in the bilateral integration of mnemonic systems.
In macaque monkeys with injections of tritiated amino acids or horseradish peroxidase in the vent... more In macaque monkeys with injections of tritiated amino acids or horseradish peroxidase in the ventrolateral granular frontal cortex, we observed extensive anterograde and retrograde labeling of the premotor and somatosensory cortex in and around the lateral sulcus. Comparable labeling was not present with large and small control injections of the dorsal granular cortex. Cytoarchitectonic evaluation of the perisylvian cortex in the three cases examined in detail indicated that labeled areas included the ventral premotor cortex (area 6V); the precentral opercular and orbitofrontal opercular areas (PrCO and OFO); the second somatosensory area (S-II); the opercular cortex immediately anterior to S-II, possibly corresponding to area 2 of the S-I complex; and the central part of the insular cortex, including portions of the granular and dysgranular insular fields (Ig, Idg). Labeling was particularly dense and extensive in areas 6V, S-II, and OFO. Lighter labeling was also present in the rostral inferior parietal lobule (areas 7b and POa). The distribution of label within perisylvian areas was not uniform: certain parts were heavily labeled, while other parts were lightly labeled or unlabeled. Comparison of label distribution with published accounts of the somatotopy of these areas indicates that forelimb and orofacial representations were selectively labeled. Further, our results, taken together with other recent anatomical findings (e.g., Matelli et al.: Journal of Comparative Neurology 251:281-298, 1987; Barbas and Pandya: Journal of Comparative Neurology 256:211-228, 1987) suggest strongly that there is a network of interconnected forelimb and orofacial representations in macaque cortex, involving the ventral granular frontal cortex, area 6V, OFO, opercular area 2, S-II, the central insula, and area 7b. Each injection of frontal cortex which labeled the perisylvian somatic cortex involved the cortex of the ventral rim of the principal sulcus (PSvr). The cortex surrounding the PSvr does not stand out as a distinct area in Nissl-stained material. However, examination of myelin-stained sections prepared from uninjected hemispheres with the Gallyas technique revealed the existence of a distinct zone centered on the PSvr. This myeloarchitectonic area, which we term area 46vr, is more heavily myelinated than the ventral bank and fundus of the principal sulcus (area 46v) but is less heavily myelinated than the ventral (inferior) convexity (area 12). Involvement of area 46vr in our injections was probably responsible for the strong labeling observed in perisylvian somatic areas.(ABSTRACT TRUNCATED AT 400 WORDS)
Our understanding of human brain evolution has advanced enormously over the past decade, owing to... more Our understanding of human brain evolution has advanced enormously over the past decade, owing to contributions of scientists from many different branches of the life sciences. This chapter reviews some of the concepts and findings from evolutionary biology and neuroscience central to human brain evolutionary studies, surveys some major recent findings, and identifies issues for future research.
Understanding how human brain organization differs from that of other species is essential for un... more Understanding how human brain organization differs from that of other species is essential for understanding the neural bases of human cognitive and behavioral specializations. Nevertheless, neuroscientists have largely ignored this subject. A review of the small body of available evidence indicates that the human brain heume enormously enlarged following the divergence of humans from African apes, with association cortex expanding disproportionately. There is,
however, no evidence that humans evolved new cortical areas; indeed, a reasonable Ulie can be made that classical language areas have homologs in nonhuman primates. Humans possess morphological characteristics (sylvian-fissure asymmetries) and features of cortical histology that monkeys lack, although apes are more similar to humans in these respects. We can improve our understanding of human brain specializations by directly comparing humans. apes, and oilier nonhuman primates using the wide array of available morphological and histological techniques that do not require invasive or terminal procedures.
""
"Primates are unique among mammals in possessing a region
of dorsolateral prefrontal cortex with... more "Primates are unique among mammals in possessing a region
of dorsolateral prefrontal cortex with a well-developed internal
gr.anular layer. This region is commonly implicated in higher
cognitive functions. Despite the histological distinctiveness of
primate dorsolateral prefrontal cortex, the work of Rose, Woolsey, and Akert produced a broad consensus among neuroscientists that homologues of primate granular frontal cortex exist in nonprimates and can be recognized by their dense innervation from the mediodorsal thalamic nucleus (MD). Additional characteristics have come to be identified with dorsolateral prefrontal cortex, including rich dopaminergic innervation and involvement in spatial delayed-reaction tasks. However, recent studies reveal that these characteristics are not distinctive of the dorsolateral prefrontal region in primates: MD and dopaminergic projections are widespread in the frontal lobe, and medial and orbital frontal areas may play a role in delay tasks. A reevaluation of idt frontal cortex suggests that the medial frontal cortex, usually considered to be homologous to the dorsolateral prefrontal cortex of primates, actually consists of cortex homologous to primate premotor and anterior cingulate cortex. The lateral MD-projection cortex of rats resembles portions of primate orbital cortex. If prefrontal cortex is construed broadly enough to include orbital and cingulate cortex, rats can be said to have prefrontal cortex. However, they evidently lack homologues of the dorsolateral prefrontal areas of primates. This assessment suggests that rats probably do not provide useful models of human dorsolateral frontal lobe function and dysfunction, although they might prove valuable for understanding other regions of frontal cortex."
Most cognitive neuroscience research to date has focused on brain mechanisms. We can gain additio... more Most cognitive neuroscience research to date has focused on brain mechanisms. We can gain additional insights into the neural basis of cognition and action by considering how this finely tuned organ came to be, both from an evolutionary and a developmental perspective. This article focuses primarily on developmental and evolutionary changes in higher cognitive functions, in particular the ability to reason about the world and about others’ mental states. These functions are supported by neural circuits involving prefrontal cortex, a part of the brain that has expanded over evolution and that develops slowly over childhood and adolescence in humans.
Cortical neuroscience is founded on studies of a very few model organisms, mainly rats, cats, and... more Cortical neuroscience is founded on studies of a very few model organisms, mainly rats, cats, and macaque monkeys. The concentration of effort on such a few species would be defensible if cortical organization were basically uniform across mammals, as is commonly believed. Although there is little reason to doubt that some features of cortical organization are indeed widespread among mammals, phyletic variation in cortical organization is far more extensive than has generally been appreciated or acknowledged. Rats, for example, differ from other mammals in the genetics and chemistry of their cortical neurons, in connectivity and areal organization, and in the functions of specific cortical regions. Likewise, macaque monkeys, although widely used as models of the human visual system, lack a number of features found in human visual cortex. Given the variability of cortical organization, how should neuroscientists approach the study of nonhuman species, and what can we reasonably expect to learn from them? First, by examining a wider range of species than are currently employed, and by using modern techniques of phyletic analysis, neuroscientists can more rigorously identify those features of cortical organization that are, in fact, widely shared among mammals or among particular mammalian subgroups. Second, by taking account of variations, neuroscientists can abstract more reliable and general principles of structure-function relationships in the nervous system. Finally, freed from the doctrine of basic uniformity, neuroscientists can pursue the study of human cortical specializations, and so advance our understanding of what distinguishes humans as a biological species.
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Neuroscientists make inferences about the human brain by studying nonhuman species, an enterprise... more Neuroscientists make inferences about the human brain by studying nonhuman species, an enterprise that depends on assumptions about the nature of evolution. Traditionally, many neuroscientists have supposed that all mammals possess variants of the same brain which differ only in size and degree of elaboration. Under this model, the brains of nonhuman species can be treated as simplified versions or models of the human brain. However, there is evidence thai mammalian cerebral organization is much more variable than is commonly acknowledged. The diversity of mammalian brain organization implies that neuroscientists can make better inferences about human brain organization by comparing multiple species chosen based on their evolutionary relationships to humans, than by studying individual "model" or "representative" species. The existence of neural diversity also suggests that nonhuman species have evolved cognitive specializations that are absent in humans."
Understanding how humans differ from other animals, as well as how we are like them, requires com... more Understanding how humans differ from other animals, as well as how we are like them, requires comparative investigations. For the purpose of documenting the distinctive features of humans, the most informative research involves comparing humans to our closest relatives–the chimpanzees and other great apes. Psychology and anthropology have maintained a tradition of empirical comparative research on human specializations of cognition. The neurosciences, by contrast, have been dominated by the model-animal research paradigm, which presupposes the commonality of "basic" features of brain organization across species and discourages serious treatment of species differences. As a result, the neurosciences have made little progress in understanding human brain specializations. Recent developments in neuroimaging, genomics, and other non-invasive techniques make it possible to directly compare humans and nonhuman species at levels of organization that were previously inaccessible, offering the hope of gaining a better understanding of the species-specific features of the human brain. This hope will be dashed, however, if chimpanzees and other great ape species become unavailable for even non-invasive research.
Page 1. What's Human about the Human Brain By Todd M. Preuss From Cognitive Neuroscience (... more Page 1. What's Human about the Human Brain By Todd M. Preuss From Cognitive Neuroscience (Gazzaniga Editor) Page 2. Outline Homo sapiens: The undiscovered primate Identifying human brain specializations Continuity versus diversity in cerebral evolution ...
The temporal lobe is a morphological specialization of primates resulting from an expansion of hi... more The temporal lobe is a morphological specialization of primates resulting from an expansion of higher-order visual cortex that is a hallmark of the primate brain. Among primates, humans possess a temporal lobe that has significantly expanded. Several uniquely human cognitive abilities, including language comprehension, semantic memory, and aspects of conceptual processing, are represented in the temporal lobe. Understanding how the temporal lobe has been modified and reorganized in the human lineage is crucial to understanding how it supports human cognitive specializations. Identifying these structural modifications requires a direct comparison with other primates, with special attention to our closest relatives, the chimpanzees. Comparative examination of data from architectonics, tract tracing, and newer imaging methodologies suggests modifications to external morphology (gyri and sulci), preferential expansion of association areas, and elaboration of white matter fasciculi, distinguishing the human temporal lobe from those of Old World monkeys. Chimpanzees and humans share some of these features of cortical expansion, although more research is needed in order to elucidate whether humans possess simply a large hominoid temporal lobe or whether important reorganization has happened since our divergence from chimpanzees.
The evolution of the human brain can be inferred from the endocasts of the skulls of extinct ance... more The evolution of the human brain can be inferred from the endocasts of the skulls of extinct ancestors, which reveal the sizes and shapes of brains, and the results of comparative studies of brain organization in present-day mammals. Early mammals had small brains with little neocortex and few cortical areas. The brains of early primates were different in that the visual system was greatly expanded and reorganized, and posterior parietal cortex was a large part of the brain guiding motor behaviors via an expanded motor system. Early monkeys had larger brains specialized for diurnal vision, mediated in part by an expanded temporal cortex. Early hominins had brains the size of those of great apes that became three times larger with modern humans. This large size, together with specializations of the two hemispheres and an increase in number of cortical areas, provided brain systems for language, tool use, and human cognition.
Primates and Their Relatives in Phylogenetic Perspective, 1993
If behavior is the leading edge of evolution, and if the brain is the principal organ of behavior... more If behavior is the leading edge of evolution, and if the brain is the principal organ of behavior, one might expect the neurosciences to occupy a central place in evolutionary biology. Obviously, this is not the case—at present. Yet the founders of modern physical anthropology and primatology included several individuals who also made significant contributions to neuroanatomy, particularly Grafton Elliot Smith, Wilfred E. Le Gros Clark, and Raymond Dart. (Examples of these contributions include Elliot Smith, 1897, 1910, 1919; Le Gros Clark, 1932, 1941, 1956; Dart, 1934). Such a confluence of professional interests was no accident: these individuals regarded the understanding of brain evolution as crucial for understanding primate phylogeny. As Elliot Smith (1924, p. 21) put it, the facts of brain evolution are “the cement to unite into one comprehensive story the accumulations of knowledge concerning the essential facts of Man’s pedigree.” In the works of Elliot Smith and Le Gros Clark, it was the increasing complexity of the brain, a result of life in the trees, that enabled primates to become behaviorally flexible or adaptable, and so escape the narrowing adaptations that beset terrestrial mammals (see especially Elliot Smith, 1924; Le Gros Clark, 1959).
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however, no evidence that humans evolved new cortical areas; indeed, a reasonable Ulie can be made that classical language areas have homologs in nonhuman primates. Humans possess morphological characteristics (sylvian-fissure asymmetries) and features of cortical histology that monkeys lack, although apes are more similar to humans in these respects. We can improve our understanding of human brain specializations by directly comparing humans. apes, and oilier nonhuman primates using the wide array of available morphological and histological techniques that do not require invasive or terminal procedures.
""
of dorsolateral prefrontal cortex with a well-developed internal
gr.anular layer. This region is commonly implicated in higher
cognitive functions. Despite the histological distinctiveness of
primate dorsolateral prefrontal cortex, the work of Rose, Woolsey, and Akert produced a broad consensus among neuroscientists that homologues of primate granular frontal cortex exist in nonprimates and can be recognized by their dense innervation from the mediodorsal thalamic nucleus (MD). Additional characteristics have come to be identified with dorsolateral prefrontal cortex, including rich dopaminergic innervation and involvement in spatial delayed-reaction tasks. However, recent studies reveal that these characteristics are not distinctive of the dorsolateral prefrontal region in primates: MD and dopaminergic projections are widespread in the frontal lobe, and medial and orbital frontal areas may play a role in delay tasks. A reevaluation of idt frontal cortex suggests that the medial frontal cortex, usually considered to be homologous to the dorsolateral prefrontal cortex of primates, actually consists of cortex homologous to primate premotor and anterior cingulate cortex. The lateral MD-projection cortex of rats resembles portions of primate orbital cortex. If prefrontal cortex is construed broadly enough to include orbital and cingulate cortex, rats can be said to have prefrontal cortex. However, they evidently lack homologues of the dorsolateral prefrontal areas of primates. This assessment suggests that rats probably do not provide useful models of human dorsolateral frontal lobe function and dysfunction, although they might prove valuable for understanding other regions of frontal cortex."
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