The visual areas in the splenial sulcus of the cat

1. The extreme periphery of the visual field is represented in the upper wall of the splenial sulcus where the sulcus is horizontal, and in its anterior wall more posteriorly where the sulcus runs downwards and laterally. About half the cells whose fields lie between 50 and 90 degrees from the area centralis have a sharply horizontal preferred orientation.2. Beyond the lateral edge of visual I there is a narrow band of visual cortex in which the receptive fields return towards the area centralis as one moves 1-1.5 mm laterally. Their receptive fields are usually about 20-30 degrees degrees across, but all orientations are found. The more central fields may be binocular and those at the area centralis may be as small as 1 degrees in diameter.3. This band has been called the splenial visual area. It does not seem to have properties corresponding to those of visual II nor of visual III.

Kitten visual cortex: short-term, stimulus-induced changes in connectivity

Single neurons in the kitten visual cortex can be induced to increase their responsiveness to a repeated stimulus applied while the neurons are under observation. These short-term changes are in the same direction as the permanent modifications produced in whole populations of neurons following environmental manipulations during the "critical period" of cortical development, but are less pronounced and probably transient.

Development of rabbit visual cortex: late appearance of a class of receptive fields

In young rabbits before the age at which the eyes open, only three of the seven receptive field types described in the adult visual cortex are detectable. The remaining four receptive field types-which share the property of having radially asymmetric fields-appear later, coincident with a decline in the percentage of cells that are visually responsive but not classifiable as to receptive field type.

Selective visual experience fails to modify receptive field properties of rabbit striate cortex neurons

During development, rabbits were exposed only to vertical or horizontal lines to determine if the receptive field characteristics of visual cortex cells would be altered as they are in the cat. Motion and directional selectivity were preserved, and orientation specificity remained unaffected by the restricted experience, which suggests that the rabbit may lack the neural plasticity seen in some other mammals.

A light and electron microscopic study of the visual cortex of the cat and monkey

A light and electron microscopic study has been made of areas 17, 18 and 19 of the cat and area 17 of the monkey(Macaca mulatta). An attempt has been made to clarify the somewhat confusing terminology applied to the laminar cytoarchitectonic pattern of the visual cortex. The cytoarchitectonic features of the subdivisions of the visual cortex of the cat and of area 17 of the monkey have been described. In both animals layer IV is characterized by the predominantly stellate nature of its cells. In the cat the stria of Gennari is situated in the upper part of layer IV and the extreme lower part of layer III, while in the monkey most of it is found outside layer IV, mainly in layer IIIc . There are other horizontally orientated axonal plexuses in layers I, III, V and VI. In Golgi material stellate cells can be classified as large and small 'smooth’, large and small 'spiny’ and small 'intermediate’. Stellate cells with large spines on long pedicles are particularly common in layer IV. A correlation has been made between the features of stellate and pyramidal cells in light and electron microscopic material, and the features of spine-bearing varicose dendrites derived from stellate cells described.

An experimental study of the termination of the lateral geniculo-cortical pathway in the cat and monkey

The thalamic projection to the visual cortex has been studied in the cat and monkey by experimental light and electron microscopic techniques. After large lesions of the lateral geniculate nucleus degeneration is confined to the ipsilateral hemisphere. In the cat it is found in areas 17, 18 and 19 and in the lateral suprasylvian area, terminal degeneration occurring predominantly in layer IV, with less in layers I, III and V ; fibre degeneration crossing layers VI and V towards layer IV is coarser in area 18 than elsewhere. Some fine horizontal degenerating fibres are seen in layer I. In the monkey terminal degeneration is restricted to area 17; again degenerating fibres ascend to layer IV where there is dense fragmentation, but in contrast to the cat there is also a second, less dense, but distinct, band in layer Illb. A little fine, horizontal fibre degeneration is present in layer I and there is slight terminal degeneration in this site and in layer V. Electron microscopy shows that degenerating terminals are recognizable in the visual cortex at several stages according to survival period, but that most stages can exist simultaneously in any one site, and that all are associated with asymmetrical membrane thickenings. Mapping of electron microscopic sections confirms the laminar pattern seen with the light microscope. In area 17 of the cat and monkey and in area 19 of the cat over 80% of degenerating terminals end on dendritic spines, the rest making synaptic contact mainly with dendritic shafts, and very few with the soma of stellate cells, but in area 18 some 10 % are related to stellate cell bodies. In layer IV of all areas degenerating terminals tend to occur in clusters which are separated by approximately 100μm. Where degenerating thalamic afferents end on cell somata or varicose dendrites almost all are identifiable as derived from stellate cells. Although it is difficult to identify positively the parent dendrites bearing the spines which receive the majority of the thalamo-cortical afferents, it is suggested that some, at least, of them may also originate from stellate cells.