The principles of classification and a classification of mammals. Bulletin of the AMNH ; v. 85

http://www.unicog.org/publications/DehaeneChangeux_ReviewConsciousness_Neuron2011.pdf

Experimental and Theoretical Approaches to Conscious Processing

We explore the extent to which neocortical circuits generalize, i.e., to what extent can neocortical neurons and the circuits they form be considered as canonical? We find that, as has long been suspected by cortical neuroanatomists, the same basic laminar and tangential organization of the excitatory neurons of the neocortex is evident wherever it has been sought. Similarly, the inhibitory neurons show characteristic morphology and patterns of connections throughout the neocortex. We offer a simple model of cortical processing that is consistent with the major features of cortical circuits: The superficial layer neurons within local patches of cortex, and within areas, cooperate to explore all possible interpretations of different cortical input and cooperatively select an interpretation consistent with their various cortical and subcortical inputs.

Neuronal circuits of the neocortex

Despite a hundred years' research, the neuropathology of schizophrenia remains obscure. However, neither can the null hypothesis be sustained--that it is a 'functional' psychosis, a disorder with no structural basis. A number of abnormalities have been identified and confirmed by meta-analysis, including ventricular enlargement and decreased cerebral (cortical and hippocampal) volume. These are characteristic of schizophrenia as a whole, rather than being restricted to a subtype, and are present in first-episode, unmedicated patients. There is considerable evidence for preferential involvement of the temporal lobe and moderate evidence for an alteration in normal cerebral asymmetries. There are several candidates for the histological and molecular correlates of the macroscopic features. The probable proximal explanation for decreased cortical volume is reduced neuropil and neuronal size, rather than a loss of neurons. These morphometric changes are in turn suggestive of alterations in synaptic, dendritic and axonal organization, a view supported by immunocytochemical and ultrastructural findings. Pathology in subcortical structures is not well established, apart from dorsal thalamic nuclei, which are smaller and contain fewer neurons. Other cytoarchitectural features of schizophrenia which are often discussed, notably entorhinal cortex heterotopias and hippocampal neuronal disarray, remain to be confirmed. The phenotype of the affected neuronal and synaptic populations is uncertain. A case can be made for impairment of hippocampal and corticocortical excitatory pathways, but in general the relationship between neurochemical findings (which centre upon dopamine, 5-hydroxytryptamine, glutamate and GABA systems) and the neuropathology of schizophrenia is unclear. Gliosis is not an intrinsic feature; its absence supports, but does not prove, the prevailing hypothesis that schizophrenia is a disorder of prenatal neurodevelopment. The cognitive impairment which frequently accompanies schizophrenia is not due to Alzheimer's disease or any other recognized neurodegenerative disorder. Its basis is unknown. Functional imaging data indicate that the pathophysiology of schizophrenia reflects aberrant activity in, and integration of, the components of distributed circuits involving the prefrontal cortex, hippocampus and certain subcortical structures. It is hypothesized that the neuropathological features represent the anatomical substrate of these functional abnormalities in neural connectivity. Investigation of this proposal is a goal of current neuropathological studies, which must also seek (i) to establish which of the recent histological findings are robust and cardinal, and (ii) to define the relationship of the pathological phenotype with the clinical syndrome, its neurochemistry and its pathogenesis.

/pdf/the-neuropathology-of-schizophrenia-a-critical-review-of-the-1zxk39qd1v.pdf

The neuropathology of schizophrenia. A critical review of the data and their interpretation.

Behavioural, cellular and molecular studies have revealed significant effects of enriched environments on rodents and other species, and provided new insights into mechanisms of experience-dependent plasticity, including adult neurogenesis and synaptic plasticity The demonstration that the onset and progression of Huntington's disease in transgenic mice is delayed by environmental enrichment has emphasized the importance of understanding both genetic and environmental factors in nervous system disorders, including those with Mendelian inheritance patterns A range of rodent models of other brain disorders, including Alzheimer's disease and Parkinson's disease, fragile X and Down syndrome, as well as various forms of brain injury, have now been compared under enriched and standard housing conditions Here, we review these findings on the environmental modulators of pathogenesis and gene-environment interactions in CNS disorders, and discuss their therapeutic implications

Enriched environments, experience-dependent plasticity and disorders of the nervous system.

Arguably the most complex cortical functions are seated in human cognition, the how and why of which have been debated for centuries by theologians, philosophers and scientists alike. In his best-selling book, An Astonishing Hypothesis: A Scientific Search for the Soul, Francis Crick refined the view that these qualities are determined solely by cortical cells and circuitry. Put simply, cognition is nothing more, or less, than a biological function. Accepting this to be the case, it should be possible to identify the mechanisms that subserve cognitive processing. Since the pioneering studies of Lorent de No and Hebb, and the more recent studies of Fuster, Miller and Goldman-Rakic, to mention but a few, much attention has been focused on the role of persistent neural activity in cognitive processes. Application of modern technologies and modelling techniques has led to new hypotheses about the mechanisms of persistent activity. Here I focus on how regional variations in the pyramidal cell phenotype may determine the complexity of cortical circuitry and, in turn, influence neural activity. Data obtained from thousands of individually injected pyramidal cells in sensory, motor, association and executive cortex reveal marked differences in the numbers of putative excitatory inputs received by these cells. Pyramidal cells in prefrontal cortex have, on average, up to 23 times more dendritic spines than those in the primary visual area. I propose that without these specializations in the structure of pyramidal cells, and the circuits they form, human cognitive processing would not have evolved to its present state. I also present data from both New World and Old World monkeys that show varying degrees of complexity in the pyramidal cell phenotype in their prefrontal cortices, suggesting that cortical circuitry and, thus, cognitive styles are evolving independently in different species.

Cortex, Cognition and the Cell: New Insights into the Pyramidal Neuron and Prefrontal Function

The present investigation was designed to determine the organization of somatosensory fields in the lateral sulcus of macaque monkeys using standard microelectrode recording techniques. Our results provide evidence for two complete representations of the body surface. We term these fields the second somatosensory area (SII) and the parietal ventral area (PV) because of their similarities in position, internal organization, and relationship to anterior parietal fields, as described for SII and PV in other mammals. Areas SII and PV are mirror-symmetrical representations of the body surface, sharing a common boundary at the representations of the digits of the hand and foot, lips, and mouth. These fields are located adjacent to the face representations of anterior parietal fields (areas 3b, 1, and 2), and are bounded ventrally and caudally by other regions of cortex in which neurons are responsive to somatic or multimodal stimulation. The finding of a double representation of the body surface in the region of cortex traditionally designated as SII may explain conflicting descriptions of SII organization in macaque monkeys. In addition, the present study raises some questions regarding the designation of serial processing pathways in Old World monkeys, by suggesting that fields may have been confused in studies demonstrating such pathways. We propose that SII and PV are components of a common plan of organization, and are present in many eutherian mammals.

/pdf/a-redefinition-of-somatosensory-areas-in-the-lateral-sulcus-2a17bev3kn.pdf

A redefinition of somatosensory areas in the lateral sulcus of macaque monkeys

Here we present evidence that the pyramidal cell phenotype varies markedly in the cortex of different anthropoid species. Regional and species differences in the size of, number of bifurcations in, and spine density of the basal dendritic arbors cannot be explained by brain size. Instead, pyramidal cell morphology appears to accord with the specialized cortical function these cells perform. Cells in the prefrontal cortex of humans are more branched and more spinous than those in the temporal and occipital lobes. Moreover, cells in the prefrontal cortex of humans are more branched and more spinous than those in the prefrontal cortex of macaque and marmoset monkeys. These results suggest that highly spinous, compartmentalized, pyramidal cells (and the circuits they form) are required to perform complex cortical functions such as comprehension, perception, and planning.

https://www.jneurosci.org/content/jneuro/21/17/RC163.full.pdf

The pyramidal cell in cognition: a comparative study in human and monkey.

The basal dendritic arbors of pyramidal cells in prefrontal areas 10, 11, and 12 of the macaque monkey were revealed by intracellular injection in fixed, flat-mounted, cortical slices. The size, number of branches, and spine density of the basal dendrites were quantified and compared with those of pyramidal cells in the occipital, parietal, and temporal lobes. These analyses revealed that cells in the frontal lobe were significantly more spinous than those in the other lobes, having as many as 16 times more spines than cells in the primary visual area (V1), four times more those in area 7a, and 45% more than those in area TE. As each dendritic spine receives at least one excitatory input, the large number of spines reported for layer III cells in prefrontal cortex suggests that they are capable of integrating a greater number of excitatory inputs than layer III pyramidal cells so far studied in the occipital, parietal, and temporal lobes. The ability to integrate a large number of excitatory inputs may be important for the sustained tonic activity characteristic of neurons in prefrontal cortex and their role in memory and cognition.

https://www.jneurosci.org/content/jneuro/20/18/RC95.full.pdf

Pyramidal Cells of the Frontal Lobe: All the More Spinous to Think With

The basal dendritic arbors of layer III pyramidal neurons are known to vary systematically among primate visual areas. Generally, those in areas associated with "higher" level cortical processing have larger and more spinous dendritic arbors, which may be an important factor for determining function within these areas. Moreover, the tangential area of their arbors are proportional to those of the periodic supragranular patches of intrinsic connections in many different areas. The morphological parameters of both dendritic and axon arbors may be important for the sampling strategies of cells in different cortical areas. However, in visual cortex, intrinsic patches are a feature of supragranular cortex, and are weaker or nonexistent in infragranular cortex. Thus, the systematic variation in the dendritic arbors of pyramidal cells in supragranular cortex may reflect intrinsic axon projections, rather than differences in columnar organization. The present study was aimed at establishing whether cells in the infragranular layers also vary in terms of dendritic morphology among different cortical areas, and whether these variations mirror the ones demonstrated in supragranular cortex. Layer V pyramidal neurons were injected with Lucifer yellow in flat-mounted cortical slices taken from cytoarchitectonic areas TEO and TE and the superior polysensory area (STP) of the macaque monkey. The results demonstrate that cells in STP were larger, had more bifurcations, and were more spinous than those in TE, which in turn were larger, had more bifurcations and were more spinous than those in TEO. These results parallel morphological variation seen in layer III pyramidal neurons, suggesting that increasing complexity of basal dendritic arbors of cells, with progression through higher areas of the temporal lobe, is a general organizational principle. It is proposed that the differences in microcircuitry may contribute to the determination of the functional signatures of neurons in different cortical areas. Furthermore, these results provide evidence that intrinsic circuitry differs across cortical areas, which may be important for theories of columnar processing.

https://espace.library.uq.edu.au/view/UQ:139962/UQ139962_OA.pdf

Pyramidal cells, patches, and cortical columns: a comparative study of infragranular neurons in TEO, TE, and the superior temporal polysensory area of the macaque monkey.

Guy N. Elston

Papers

Cortex, Cognition and the Cell: New Insights into the Pyramidal Neuron and Prefrontal Function

A redefinition of somatosensory areas in the lateral sulcus of macaque monkeys

The pyramidal cell in cognition: a comparative study in human and monkey.

Pyramidal Cells of the Frontal Lobe: All the More Spinous to Think With

Pyramidal cells, patches, and cortical columns: a comparative study of infragranular neurons in TEO, TE, and the superior temporal polysensory area of the macaque monkey.