Cerebral Cortex

The cerebral cortex, especially that part customarily designated "neocortex," is one of the hallmarks of mammalian evolution and reaches its greatest size, relatively speaking, and its widest structural diversity in the human brain. The evolution of this structure, as remarkable for the huge numbers of neurons that it contains as for the range of behaviors that it controls, has been of abiding interest to many generations of neuroscientists. Yet few theories of cortical evo­ lution have been proposed and none has stood the test of time. In particular, no theory has been successful in bridging the evolutionary gap that appears to exist between the pallium of non mammalian vertebrates and the neocortex of mam­ mals. Undoubtedly this stems in large part from the rapid divergence of non­ mammalian and mammalian forms and the lack of contemporary species whose telencephalic wall can be seen as having transitional characteristics. The mono­ treme cortex, for example, is unquestionably mammalian in organization and that of no living reptile comes close to resembling it. Yet anatomists such as Ramon y Cajal, on examining the finer details of cortical structure, were struck by the similarities in neuronal form, particularly of the pyramidal cells, and their predisposition to laminar alignment shared by representatives of all vertebrate classes.

I. Nonmammalian Vertebrates.- 1 The Telencephalon of Cartilaginous Fishes.- 2 The Telencephalon of Actinopterygian Fishes.- 3 The Telencephalon of Sarcopterygian Fishes.- 4 The Pallium of Anuran Amphibians.- 5 The Cerebral Cortex of Reptiles.- 6 Neurobiology of the Reptile-Bird Transition.- 7 Evolution of Neocorte.- 8 Fossil Evidence on the Evolution of the Neocorte.- 9 Modulatory Events in the Development and Evolution of Primate Neocorte.- III. Mammals.- 10 Why Does Cerebral Cortex Fissure and Fold? A Review of Determinants of Gyri and Sulc.- 1. Introduction.- 2. Definitions and Nomenclature.- 2.1. Gyral Nomenclature.- 2.2. Sulcal Nomenclature.- 2.3. Cross-Sectional Morphology of Gyri and Sulci.- 2.4. Standardization of Nomenclature.- 3. Ontogeny of Convoluted Cortex.- 3.1. Normal Macroscopic Developmental Events.- 3.2. Initial Formation of the Cortical Mantle: Migration.- 3.3. Gyrogenesis.- 3.4. Mechanical Forces Generated during Gyrogenesis.- 3.5. Role of Nonneural Structures in Cortical Development.- 3.6. Experimental Alterations of Developing Gyri and Sulci.- 3.7. Pathological Gyral and Sulcal Patterns.- 4. Neuroanatomical Features of Convoluted Cortex: Architecture and Connectivity.- 4.1. Architectural Differences between Crowns, Walls, and Fundi.- 4.2. Architectonic Areas and Their Relation to Gyral Crowns, Sulcal Walls, and Fundi.- 4.3. Thalamocortical and Corticothalamic Connections.- 4.4. Intergyral Connections.- 4.5. Interhemispheric Connections.- 4.6. Other Efferent Connections.- 4.7. Intragyral Connections.- 5. Electrophysiological Correlates of Gyri and Sulci.- 6. Comparative Studies of Gyri and Sulci.- 6.1. Phylogeny Evaluated by Paleoneurology.- 6.2. Evolution of Gyri and Sulci Inferred from Comparative Neurobiology.- 6.3. Taxon-Specific Gyral―Sulcal Patterns.- 6.4. Significance of Taxon-Specific, Individual, and Interhemispheric Differences.- 6.5. Questions of Evolution and Homology.- 7. Explanation of Gyrification and Fissuration.- 8. Methodological Issues.- 9. Structural―Functional Significance of Gyrification.- 10. References.- 11 Comparative Aspects of Olfactory Corte.- 1. Introduction.- 2. Definition of Olfactory Cortex.- 3. Comparative Anatomy and Physiology.- 3.1. Mammals.- 3.2. Reptiles.- 3.3. Amphibians.- 3.4. Sharks.- 4. Comparison of Olfactory Cortex to Other Types of Cerebral Cortex.- 4.1. Comparison to Hippocampal Cortex.- 4.2. Comparison to Neocortex.- 5. Summary and Conclusions.- 6. References.- 12 Comparative Anatomy of the Hippocampus: With Special Reference to Differences in the Distributions of Neuroactive Peptides.- 1. Introduction.- 2. Cytoarchitectonics.- 3. Allometric Relationships.- 4. Comparative Differences in Afferent Topographies.- 4.1. Major Intrinsic Afferent Systems.- 4.2. Afferents from Entorhinal Cortex.- 4.3. Lack of Exclusive Afferent Lamination in the Hamster Dentate Gyrus.- 4.4. Summary.- 5. Comparative Differences in the Distribution of Neuroactive Peptides within Hippocampal Circuitry.- 5.1. Enkephalin.- 5.2. Cholecystokinin.- 5.3. Tachykinin.- 5.4. Consideration of Differences in Peptide Localization.- 6. Concluding Comments.- 7. Abbreviations.- 8. References.- 13 Comparative and Evolutionary Anatomy of the Visual Cortex of the Dolphin.- 1. Introduction.- 2. Cerebral Cortex: Evolutionary Aspects.- 2.1. General Phylogenetic Considerations.- 2.2. The “Initial” Brain Concept.- 3. Neocortex of Hedgehog as Model of “Initial” Brain Compared to Dolphin Neocortex.- 4. Studies of Neuronal Typology in Dolphin Neocortex.- 5. Image Analysis of Dolphin Visual Cortex.- 6. Ultrastructural Analysis of Dolphin Visual Cortex.- 7. Concluding Remarks.- 8. References.- 14 Organization of the Cerebral Cortex in Monotremes and Marsupials.- 1. Evolutionary Relations of Marsupial, Monotreme, and Eutherian Mammals: Historical Aspects.- 2. Brain Studies in Marsupial and Monotreme Species.- 3. Indices of Brain and Cerebral Cortical Development.- 3.1. Brain Size and the Encephalization Index.- 3.2. Regional Brain Development: Extent of the Neocortex in Monotremes and Marsupials.- 3.3. Cortical Folding as an Index of Brain Development.- 4. Sulcal and Laminar Patterns within the Cerebral Cortex of Marsupial and Monotreme Species.- 4.1. The Marsupial Cerebral Cortex.- 4.2. The Monotreme Cerebral Cortex.- 5. The Somatosensory Cortex.- 5.1. Electrophysiological Studies of Somatosensory Cortex: Historical Aspects.- 5.2. Organization of Somatosensory Cortex in Marsupials.- 5.3. Organization of Somatosensory Cortex in Monotremes.- 6. The Auditory Cortex.- 6.1. Organization of Auditory Cortex in Marsupials.- 6.2. Auditory Cortex in Monotremes.- 7. The Visual Cortex.- 7.1. Organization of Visual Cortex in Marsupials.- 7.2. Visual Cortex in Monotremes.- 8. Sensory Cortex in Marsupialia and Monotremata: Summary and Concluding Comments.- 8.1. Location and Organization of Cortical Sensory Areas.- 8.2. Multiple Representation in Cortex for Particular Sensory Modalities.- 8.3. Interhemispheric and Thalamic Connectivity.- 9. Localization of Motor Function within the Cerebral Cortex.- 9.1. Motor Areas in the Marsupial Cerebral Cortex.- 9.2. Lende’s Hypothesis: A Sensorimotor Amalgam in Marsupials and Monotremes.- 9.3. Motor Representation in Monotremes.- 9.4. Corticospinal Projections from Motor Cortex in Marsupials and Monotremes.- 9.5. Cortico-cortical Connections of the Marsupial Motor Cortex.- 10. Frontal Cortex.- 11. Marsupials as Models for the Study of Cerebral Cortical Development.- 12. Functional Localization in the Cerebral Cortex and the Evolutionary Place of the Marsupials and Monotremes: Concluding Comments.- 13. References.- 15 Comparative Development of Somatic Sensory Corte.- 1. Introduction.- 1.1. Plan of Approach.- 1.2. Somatosensory Projections to Forebrain Pallium in Nonmammalian Vertebrates Compared with the Organization of the Forebrain Somatosensory System in Mammals.- 1.3. Survey of Data, in Phylogenetic Order.- 2. Monotremes.- 2.1. Duckbill Platypus.- 2.2. Spiny Anteater (Echidna).- 3. Marsupials.- 3.1. Opossums.- 3.2. Australian Marsupials.- 4. Edentates.- 4.1. Sensory Projections.- 4.2. Relation to Other Areas.- 4.3. Structure.- 4.4. Corticocortical Connections.- 4.5. Other Connections.- 4.6. Comparison Summary.- 5. Insectivores.- 5.1. Sensory Projections.- 5.2. Relation to Other Areas.- 5.3. Structure.- 5.4. Thalamic Connections.- 5.5. Comparison Summary.- 6. Chiroptera.- 6.1. Sensory Projections.- 6.2. Structure.- 6.3. Comparison Summary.- 7. Scandentia.- 7.1. Sensory Projections.- 7.2. Relation to Other Areas.- 7.3. Structure.- 7.4. Corticocortical Connections.- 7.5. Comparison Summary.- 8. Primates.- 8.1. Prosimians and Marmosets.- 8.2. Other Anthropoids (Monkeys, Apes, and Humans).- 9. Lagomorphs.- 9.1. Sensory Projections.- 9.2. Relation to Other Areas.- 9.3. Structure.- 9.4. Thalamic Connections.- 9.5. Corticocortical Connections.- 9.6. Other Connections.- 9.7. Comparison Summary.- 10. Rodents.- 10.1. Rats and Mice.- 10.2. Gray Squirrels.- 10.3. Other Rodents.- 11. Carnivores.- 11.1. Cats.- 11.2. Raccoons.- 11.3. Other Carnivores.- 12. Artiodactyls.- 12.1. Pigs.- 12.2. Llamas.- 12.3. Sheep and Goats.- 13. Perissodactyls.- 14. Hyracoids.- 15. Cetaceans.- 16. Discussion: Constancies, Variations, and Trends in the Organization of Somatic Sensory Cortex.- 16.1. Sensory Projections.- 16.2. Relation to Other Areas.- 16.3. Structure.- 16.4. Thalamic Connectivity.- 16.5. Corticocortical Connections.- 16.6. Other Connections.- 17. References.- 16 The Role of Somatic Sensory Cortex in Tactile Discrimination in Primates.- 1. Introduction.- 1.1. Localization of Tactile Areas in Cerebral Cortex in Primates...- 1.2. Clinical Studies of Tactile Deficits in Human Patients.- 2. Experimental Lesions and Tactile Testing in Nonhuman Primates.- 3. Comparative Studies of Somatic Sensory Cortex and Tactile Discrimination Capacity in Primates.- 3.1. Contribution of Multiple SI Hand Areas to Tactile Capacity.- 3.2. Organization of Somatic Sensory Areas (SI and SII) in Prosimian Primates.- 3.3. Behavioral Significance of SI―SII in Macaca and Galago.- 4. Single or Multiple SI Areas and Tactile Capacity in New World Anthropoids.- 4.1. SI Maps in Cebus and Saimiri.- 4.2. SI Map in Saguinus.- 4.3. Behavioral Significance of Different SI Maps for Tactile Discrimination Capacities in New World Primates.- 5. Developmental Studies of Somatic Sensory Cortex and Tactile Discrimination Capacity in Macaca and Galago.- 5.1. Tactile Discrimination Capacity in Infant Macaca.- 5.2. Tactile Capacity following SI or SII Lesions in Infant Macaca.- 5.3. Thalamocortical Projections in Infant and Adult Galago.- 5.4. Early Tactile Deprivation and Tactile Discrimination Capacity.- in Infant Macaca.- 6. Conclusions.- 7. References.