Journal of Neurophysiology, Vol 51, Issue 2 294-324, Copyright © 1984 by APS

ARTICLES

Mechanism of directional selectivity in simple neurons of the cat's visual cortex analyzed with stationary flash sequences

L. Ganz and R. Felder

The properties of simple neurons showing selectivity to direction of motion in area 17 of the cat cortex were examined. We analyzed in particular a sample of cells receiving a projection from 0 to 10 degrees in visual angle from the area centralis of the cat retina. Three categories of simple neurons were examined: directionally asymmetric (DA) neurons, directionally selective neurons of the unimodal type (DS1), and bimodal types (DS2). Poststimulus time histograms (PSTH) were obtained to moving white and black bars as well as to static onset sequences and static offset sequences. Our analysis involves a comparison of responses to single static flashes at various receptive-field locations with responses to sequence pairs of static flashes at those same locations. We find that DA neurons are not sensitive to the direction in which a pair of stimuli are presented. Inhibitory and excitatory responses show properties of linear summation whatever the direction of the stimulus sequence. Their behavior is reminiscent of retinal and LGN neurons. The synergy model accounts well for a DA neurons's directional asymmetry. If pairs of stimuli are close enough (usually an interstimulus distance of 20' or less for the central 10 degrees of the cat's visual field), then DS neurons show striking departures from linear summation. Specifically, this departure entails an anisotropic distribution of inhibition. The directional selectivity of DS neurons cannot be explained on the basis of a simple linear combination of their on and off region's responses. Directional selectivity is produced entirely within an on-excitatory discharge region or entirely within an off-excitatory discharge region. The excitatory discharge center of even the simplest unimodal DS neuron can be shown to be decomposable into subunits smaller than that discharge center. The fact that the spread of this anisotropy of inhibition is often much more restricted than the entire extent of the DS neuron's excitatory discharge center argues strongly that underlying subregions or modules are contributing their inputs to DS neurons. A DS neuron does not analyze motion as an isolated unit; to the contrary, it is probably embedded in a pool of mutually "cooperative" DS neurons. The basic module of directional analysis is responsive either to an on-on sequence or an off-off sequence but not to both. It is not selective to an on-off sequence. Therefore, unimodal DS neurons (DS1) are performing an analysis of single moving edges.(ABSTRACT TRUNCATED AT 400 WORDS)

This article has been cited by other articles:

				C. Rivadulla, J. Sharma, and M. Sur Specific Roles of NMDA and AMPA Receptors in Direction-Selective and Spatial Phase-Selective Responses in Visual Cortex J. Neurosci., March 1, 2001; 21(5): 1710 - 1719. [Abstract] [Full Text] [PDF]

				M. Brosch, A. Schulz, and H. Scheich Processing of Sound Sequences in Macaque Auditory Cortex: Response Enhancement J Neurophysiol, September 1, 1999; 82(3): 1542 - 1559. [Abstract] [Full Text] [PDF]

				R. M. Glantz Directionality and Inhibition in Crayfish Tangential Cells J Neurophysiol, March 1, 1998; 79(3): 1157 - 1166. [Abstract] [Full Text] [PDF]

				B. Jagadeesh, H. S. Wheat, L. L. Kontsevich, C. W. Tyler, and D. Ferster Direction Selectivity of Synaptic Potentials in Simple Cells of the Cat Visual Cortex J Neurophysiol, November 1, 1997; 78(5): 2772 - 2789. [Abstract] [Full Text] [PDF]

				R. Douglas, C Koch, M Mahowald, K. Martin, and H. Suarez Recurrent excitation in neocortical circuits Science, August 18, 1995; 269(5226): 981 - 985. [Abstract] [PDF]

				B Jagadeesh, H. Wheat, and D Ferster Linearity of summation of synaptic potentials underlying direction selectivity in simple cells of the cat visual cortex Science, December 17, 1993; 262(5141): 1901 - 1904. [Abstract] [PDF]