Biomedical subjects

D J Felleman

Publications and source records attributed to D J Felleman.

21 records · Page 2Linked to original sources

PubMed1983

The representation of the body surface in S-I of cats.

In both cats and monkeys, the traditional region of the first somatosensory area of cortex, S-I, has been described as containing four strip-like architectonic fields, areas 3a, 3b, 1, and 2. In monkeys, a number of recent studies have provided evidence that each of these architectonic fields constitutes a separate representation of the body. Because of the observations in monkeys, we decided to re-examine the S-I region of cats to determine whether the evidence supported the traditional concept of a single representation, or the existence of several representations related to the described architectonic fields. Microelectrode multiunit mapping techniques were used to determine the somatotopic organization of the S-I region of 10 cats. The results indicate that a single representation of the body surface occupies most or all of the traditional S-I region including cortex defined as area "3b," area "1," and much of area "2," but excluding area "3a." Neurons throughout this single representation were activated by cutaneous stimuli, indicating that all parts of S-I receive input from cutaneous receptors. Neurons in area 3a were activated by inputs from deep receptors, as reported by others. Neurons caudal to S-I were activated by cutaneous stimuli and appeared to constitute the additional body surface representations of S-II and possibly S-III. Thus, the significance of the architectonic fields "3b," "1," and "2" is quite different in cats than in monkeys. We propose that most or all of these three fields, as described in cats, constitute the homologue of area 3b in monkeys.

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PubMed1980

Representations of the body surface in postcentral parietal cortex of Macaca fascicularis.

The somatotopic organization of the postcentral parietal cortex of the Old World monkey, Macaca fascicularis, was determined with multi-unit microelectrode recordings. The results lead to the following conclusions: 1) There are at least two complete and systematic representations of the contralateral body surface in the cortex of the postcentral gyrus. One representation is contained within Area 3b, the other within Area 1. 2) While there are important differences in the organization of the two representations, they are basically mirror-images of each other. 3) Each representation maintains body-surface adjacency by cortical adjacency in some mediolateral regions. In other regions, two types of discontinuities can be described: first, in which adjacent body surfaces are represented in separate cortical loci; second, in which adjacent cortical regions represent disparate body-surface regions. The internal organization of each representation is better described as a composite of somatotopic regions (Merzenich et al., '78) than as a serial array of dermatomal bands, or as a "homunculus." 4) While architectonic Area 2 responds to stimulation of deep body tissue, at least parts of Area 2 also respond to cutaneous stimulation. The organiation of the cutaneous representation of the hand in Area 2 is basically a mirror-image of the hand representation in Area 1. 5) Area 3a is activated by deep body tissue stimulation, suggesting the possibility of a fourth body representation within the traditional "S-I" region of somatosensory cortex in macaques. In accord with a previous study in a New World monkey (Merzenich et al., '78), we suggest that the cutaneous representation in Area 3b be considered as SI proper, and that the cutaneous representation in Area 1 be termed the posterior cutaneous field. Furthermore, based on the orientation of the representations of the body surface, as well as other factors, we suggest that the representation in Area 3b is homologous to "SmI" (or "SI") in non-primates.

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PubMedDate not supplied

Distributed hierarchical processing in the primate cerebral cortex.

In recent years, many new cortical areas have been identified in the macaque monkey. The number of identified connections between areas has increased even more dramatically. We report here on (1) a summary of the layout of cortical areas associated with vision and with other modalities, (2) a computerized database for storing and representing large amounts of information on connectivity patterns, and (3) the application of these data to the analysis of hierarchical organization of the cerebral cortex. Our analysis concentrates on the visual system, which includes 25 neocortical areas that are predominantly or exclusively visual in function, plus an additional 7 areas that we regard as visual-association areas on the basis of their extensive visual inputs. A total of 305 connections among these 32 visual and visual-association areas have been reported. This represents 31% of the possible number of pathways if each area were connected with all others. The actual degree of connectivity is likely to be closer to 40%. The great majority of pathways involve reciprocal connections between areas. There are also extensive connections with cortical areas outside the visual system proper, including the somatosensory cortex, as well as neocortical, transitional, and archicortical regions in the temporal and frontal lobes. In the somatosensory/motor system, there are 62 identified pathways linking 13 cortical areas, suggesting an overall connectivity of about 40%. Based on the laminar patterns of connections between areas, we propose a hierarchy of visual areas and of somatosensory/motor areas that is more comprehensive than those suggested in other recent studies. The current version of the visual hierarchy includes 10 levels of cortical processing. Altogether, it contains 14 levels if one includes the retina and lateral geniculate nucleus at the bottom as well as the entorhinal cortex and hippocampus at the top. Within this hierarchy, there are multiple, intertwined processing streams, which, at a low level, are related to the compartmental organization of areas V1 and V2 and, at a high level, are related to the distinction between processing centers in the temporal and parietal lobes. However, there are some pathways and relationships (about 10% of the total) whose descriptions do not fit cleanly into this hierarchical scheme for one reason or another. In most instances, though, it is unclear whether these represent genuine exceptions to a strict hierarchy rather than inaccuracies or uncertainities in the reported assignment.

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