James, C R (1975) Pattern evoked potentials and single unit responses in the visual cortex of the cat. Doctoral thesis, Keele University.

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Abstract

In this dissertation,experiments are described which investigated the properties of 51 cells in area 17 of the visual cortex of the cat. Simple and complex cells were distinguished by their responses to moving stimuli, and the level of their spontaneous activity. Using these criteria, simple cells showed narrower orientation tuning; responded with fewer action potentials to an optimal moving stimulus; exhibited greater directional sensitivity and had smaller receptive fields. Simple and complex cells are affected similarly by changes in stimulus contrast and blurring of the retinal image by defocussing.
Experiments are also described in which attempts were made to record potentials at depth within the cortex which reflected the orientation preference and receptive field location of cells in the vicinity of the electrode (orientation column potentials). In the absence of clear results from these experiments, a study of the surface recorded pattern-related visual evoked potential (PKVEP) was made to establish the existence of such potentials in the cat visual cortex. In experiments where PRVEPs were recorded, the following questions were asked:-
1. How do PRVEPs compare with potentials evoked by equivalent blank stimuli?
2. How does the form of the stimulus pattern affect the PKVEP? Do discontinuous pattern elements evoke larger potentials?
5, Does a reduction in the pattern dimensions and contrast affect the PRVEP? How is the response changed by defocussing?
4. Is the PRVEP sensitive to pattern pre-exposure? How does the form and orientation of the pre-exposed pattern affect this sensitivity?
5. Is the retinotopic organisation of the cortex reflected in the distribution of components of the PRVEP over the cortical surface? Does this distribution differ from that of potentials evoked by blank stimuli?
6. How does the PRVEP relate to potentials evoked by pattern reversal?
PRVEPs in the cat showed a wide variety of waveforms in different experiments and were often similar to those evoked by equivalent blank stimuli. Increasing the discontinuity of the stimulus pattern elements did not have a marked effect on the PRVEP, in contrast to the results of analogous experiments in man. The cat PRVEP is attenuated by a reduction in pattern contrast and dimensions but is not as sensitive to defocussing as the human PRVEP. Pre-exposure of the stimulus pattern can cause a selective attenuation of some components of the PRVEP. This attenuation was dependent on the orientation of the pre-exposed stimulus and was different from that caused by pre-exposure of a blank field. Components of the PRVEP in the cat do not show a clear retinotopic distribution resembling the wide cortical spread of the later components of potentials evoked by diffuse stimuli. Potentials evoked by pattern reversal appear to contain components present In potentials evoked by both pattern appearance stimuli and blank stimuli.
In general the properties of the cat PKVEP has some similarities with Cl of the human PRVEP but differs markedly in certain respects, notably the lack of a clear retinotopic distribution of its components on the cortical surface.

Item Type: Thesis (Doctoral)
Subjects: R Medicine > RC Internal medicine > RC0321 Neuroscience. Biological psychiatry. Neuropsychiatry
Divisions: Faculty of Natural Sciences > School of Life Sciences
Depositing User: Lisa Bailey
Date Deposited: 03 May 2019 13:25
Last Modified: 03 May 2019 13:25
URI: http://eprints.keele.ac.uk/id/eprint/6270

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