THE USE OF M-SEQUENCES IN THE ANALYSIS OF VISUAL NEURONS - LINEAR RECEPTIVE-FIELD PROPERTIES

We have used Sutter's (1987) spatiotemporal m-sequence method to map t he receptive fields of neurons in the visual system of the cat. The st imulus consisted of a grid of 16 x 16 square regions, each of which wa s modulated in time by a pseudorandom binary signal, known as an m-seq uence. Several strategies for displaying the m-sequence stimulus are p resented. The results of the method are illustrated with two examples. For both geniculate neurons and cortical simple cells, the measuremen t of first-order response properties with the m-sequence method provid ed a detailed characterization of classical receptive-field structures . First, we measured a spatiotemporal map of both the center and surro und of a Y-cell in the lateral geniculate nucleus (LGN). The time cour ses of the center responses was biphasic: OFF at short latencies, ON a t longer latencies. The surround was also biphasic-ON then OFF-but som ewhat slower. Second, we mapped the response properties of an area 17 directional simple cell. The response dynamics of the ON and OFF subre gions varied considerably; the time to peak ranged over more than a fa ctor of two. This spatiotemporal inseparability is related to the cell 's directional selectivity (Reid et al., 1987, 1991; McLean & Palmer, 1989; McLean et al., 1994). The detail with which the time course of r esponse can be measured at many different positions is one of the stre ngths of the m-sequence method.