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Larry
A. Palmer, Ph.D.
Professor, Department of Neuroscience
School of Medicine
121 Johnson Pavilion/6060
(215) 898-0992 FAX: 215-573-9050
email: palmerl@mail.med.upenn.edu
RESEARCH INTERESTS
Cortical circuits mediating direction and orientation selective responses and responses from outside the classical receptive field in visual cortex.RESEARCH TECHNIQUES
Single and multiple spike train analysis, crosscorrelation techniques, intracellular recording in vivo.RESEARCH SUMMARY
Studies are on-going in two, related major areas: extracellular studies of the context dependency of responses elicited from the classical receptive fields (CRF) of neurons in cat primary visual cortex and intracellular studies of lateral, horizontal inputs to these same cells.
We have found that the responses of about half of the direction selective cells in primary visual cortex can be strongly influenced, sometimes even overwhelmed, by moving stimuli situated entirely outside the CRF. The centers and surrounds have an opponent organization--surround motion in the null direction facilitates the center response and surround motion in the preferred direction inhibits the center response. By estimating spatiotemporal receptive field structure both with and without effective surround stimuli, we have determined that the surround effects are effected by changes in gain of the CRF mechanism rather than changes in RF structure. Thus the filters are scalable but not tunable.
In the intracellular studies, we are using spike-triggered averaging
of membrane potential locked to extracellular activity of groups of neurons
recorded extracellularly at various distances in visual space and as a
function of orientation difference. With this approach, we hope to establish
patterns of connectivity and to explore the synaptic mechanisms underlying
context dependency in visual cortex.
KEY WORDS:
visual cortex, context dependency, extracellular recording, intracellular recording
