Advances in the Modularity of Vision Selections From a Symposium on Frontiers of Visual Science (1990) / Chapter Skim
Currently Skimming:
Areas and Modules in Visual Cortex
Areas and Modules in Visual Cortex
Pages 24-38
The Chapter Skim interface presents what we've algorithmically identified as the most significant single chunk of text within every page in the chapter.
Select key terms on the right to highlight them within pages of the chapter.
From page 24... ...
We have some idea of what we mean by nucleus, although the term has been used somewhat inconsistently for subdivisions of the brain. David Van Essen has already talked about the difficulty of experimentally defining an area; the same criteria do not apply to what constitutes an area as one moves from lower to higher areas in a processing hierarchy.
|
From page 25... ...
A brain section through somatosensory cortex in a rat, when reacted for cytochrome oxidase (CO) , reveals a map of the rat body surface, with the hindfoot, the trunk, the forefoot, and the head, including the mouth parts and the lower lip, all represented by CO dense regions.
|
From page 26... ...
oup! ~3 ~ 1 4 ~_ snclI4Rd r z _ O ' O O O Z Z O O VJ 0 ° l~r~SUV.3A JO SNOlilIW Z UJ _ J ~ Z ~ , ~ ~ 1.
|
From page 27... ...
I 1 em . FIGURE 2 An example of how brains vary in size relative to body weight.
|
From page 28... ...
(V-II) have been identified lay multiple cntena, they are quite different in histological appearance (modified Tom Kaas, 1987a)
|
From page 29... ...
AREAS AND MODULES IN VISUAL CORTEX 29 B , / trunk Climb M FIR ~ Forelimb 04 Nosed FBP&UL FIGURE 4 The cytochrome oxidase reaction pattern of primary somatosensory ortex in a rat showing the details of the body surface representation. Source: Li et al., (1990)
|
From page 30... ...
Ocular dominance columns obviously evolved independently a number of times, which raises several questions. Are ocular dominance columns functionally significant, in that some visual functions are improved by the monocular activation of
|
From page 31... ...
-- -I -- , Another example of a type of modular organization with implications for how modules form is the lamination patterns in the lateral geniculate nucleus. One of the remarkable features of the lateral geniculate nucleus is that the laminar pattern is so variable across different mammals and even different primates.
|
From page 32... ...
, and a number of hypotheses have been born and died along the way. Although some understanding of the nature of lamination in some species in coming is about, an adequate explanation for the great variety still is not available Looking at a relatively simple lateral geruculate nucleus of an owl monkey, one can see two poorly separated paIvocellular layers of medium-sized neurons, two obvious magnocellular layers of large neurons, and a large number of small cells in the interlaminar zone between the magno- and parvocellular layers (Figure 7~.
|
From page 33... ...
33 ~n z o I cn c o .
|
From page 34... ...
VISUAL CORTEX ORGANIZATION IN PRIMATES There are many uncertainties in our understanding of how visual cortex is organized in primates, and differences in proposals for how cortex is subdivided vary for New World and Old World monkeys and even from laboratory to laboratory for the same species. Undoubtedly there are major differences across the major primate groups, since such features as brain size relative to body weight vary considerably from prosimians to humans.
|
From page 35... ...
In area 17 of primates, the most widespread connections are between neurons in the cytochrome oxidase blobs. Widespread and discontinuously distributed intrinsic connections appear to exist in all visual areas of primates, suggesting that all areas are modularly organized.
|
From page 36... ...
histological appearance produced many conclusions we now know to be in error. Thus, we need to critically evaluate past and current proposals, with the realization that establishing valid subdivisions is difficult, and often will depend on evidence from a multitude of procedures.
|
From page 37... ...
Casagrande Ocular dominance columns and retinal projections in New World spider monkeys. (Ateles ater)
|
From page 38... ...
Wilson, J.H. Kaas, and S.V Webb 1976 X and Y cells in the dorsal lateral geniculate nucleus of the owl monkey (Aotus trivirgatus)
|
Key Terms
This material may be derived from roughly machine-read images, and so is provided only to facilitate research.
More
information on Chapter Skim is available.