Larry A. Palmer, Ph.D
Department of Neuroscience
School of Medicine
University of Pennsylvania
Philadelphia, PA 19104-6060
B.S. (Electrical Engineering)
Drexel University, 1967.
University of Pennsylvania, 1972.
Description of Research ExpertiseRESEARCH INTERESTS
Cortical circuits mediating direction and orientation selective responses and responses from outside the classical receptive field in visual cortex.
visual cortex, context dependency, extracellular recording, intracellular recording
Single and multiple spike train analysis, crosscorrelation techniques, intracellular recording in vivo.
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.
Selected PublicationsNafziger, JS, Finkel, LH, and Palmer, LA: The effect of Gabor element orientation and spatial frequency bandwidth on contour detection. Soc. for Neuroscience Abstracts 25: 1052, 1999.
Palmer, LA and McLean, J: Motion effects from the surround in visual cortical receptive fields. Investig. Ophtal. And Vis. Science 40: 201, 1999.
Palmer, LA and McLean, J: Motion effects from the surround in visual cortical receptive fields. Investig. Ophthal. And Vis. Science 40: 201, 1999.
Wolfe J., Palmer LA.: Temporal diversity in the lateral geniculate nucleus of cat. Visual Neuroscience 15(4): 653-75, Jul-Aug 1998.
McLean J., Palmer LA.: Plasticity of neuronal response properties in adult cat striate cortex. Visual Neuroscience 15(1): 177-96, Jan-Feb 1998.
Wollman, D. and L.A. Palmer: Inhibitory processes in visual cortex. The Neuroscientist 4: 45-52, 1998.
McLean J., Palmer LA.: Contrast adaptation and excitatory amino acid receptors in cat striate cortex. Visual Neuroscience 13(6): 1069-87, Nov-Dec 1996.
Wollman DE., Palmer LA.: Phase locking of neuronal responses to the vertical refresh of computer display monitors in cat lateral geniculate nucleus and striate cortex. Journal of Neuroscience Methods 60(1-2): 107-13, Aug 1995.
Rowe MH., Palmer LA.: Spatio-temporal receptive-field structure of phasic W cells in the cat retina. Visual Neuroscience 12(1): 117-39, Jan-Feb 1995.
McLean J., Palmer LA.: Organization of simple cell responses in the three-dimensional (3-D) frequency domain. Visual Neuroscience 11(2): 295-306, Mar-Apr 1994.