We have used Sutter's (1987) spatiotemporal m-sequence method to map the receptive fields of neurons in the visual system of the cat. The stimulus consisted of a grid of 16 X 16 square regions, each of which was modulated in time by a pseudorandom binary signal, known as an m-sequence. Several strategies for displaying the m-sequence stimulus are presented. The results of the method are illustrated with two examples. For both geniculate neurons and cortical simple cells, the measurement of first-order response properties with the m-sequence method provided a detailed characterization of classical receptive-field structures. First, we measured a spatiotemporal map of both the center and surround of a Y-cell in the lateral geniculate nucleus (LGN). The time courses of the center responses was biphasic: OFF at short latencies, ON at longer latencies. The surround was also biphasic—ON then OFF—but somewhat slower. Second, we mapped the response properties of an area 17 directional simple cell. The response dynamics of the ON and OFF subregions varied considerably; the time to peak ranged over more than a factor 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 response can be measured at many different positions is one of the strengths of the m-sequence method.

In the absence of a direct and specific marker for basket cells, the aim of this paper was to use available data to estimate the density of basket cell synaptic input to smooth and spiny neurons within layer IV of cat striate visual cortex (area 17). A linear quantitative analysis of layer IV basket cell connectivity data suggests that on average basket cells (1) comprise 25–35% of all GABAergic neurons in layer IV (3552–4736 cells mm−3), (2) account for 30–41% of all putative inhibitory dendritic synapses of layer IV spiny stellate cells (145–195 synapses cell−1) and a similar proportion of layer IV basket cells (25–37%, 71–107 synapses cell−1), and (3) provide each layer IV spiny cell with 13–45 axons and each layer IV basket cell with 6–29 axons. These estimates suggest that basket cells may be less common and provide a smaller proportion of the dendritic synaptic input to layer IV spiny and smooth neurons than previously thought. In addition, the analysis indicates that a layer IV spiny stellate cell may receive on average as many synapses and axons from layer IV basket cells as from lateral geniculate relay cells. Based on this potential numerical similarity, a geniculate-basket synaptic pairing in a spine-shaft microcircuit is hypothesized. This microcircuit could implement a type of local (dendritic) push–pull interaction underlying subfield antagonism.

We characterized the chromatic and temporal properties of a sample of 177 red–green parvocellular neurons in the LGN of Macaca nemestrina, using large-field stimuli modulated along different directions through a white point in color space. We examined differences among the properties of the four subclasses of red–green P-cells (on- and off-center, red and green center). The responses of off-center cells lag the stimulus more than do those of on-center cells. At low temporal frequencies, this causes the phase difference between responses of the two kinds of cells to be considerably less than 180 deg. For isoluminant modulations the phases of on- and off-responses were more nearly 180 deg apart. A cell's temporal characteristics did not depend on the class of cone driving its center. Red center and green center cells have characteristically different chromatic properties, expressed either as preferred elevations in color space, or as weights with which cells combine inputs from L- and M-cones. Red center cells are relatively more responsive to achromatic modulation, and attach relatively more weight to input from the cones driving the center. Off-center cells also attach relatively more weight than do on-center cells to input from the class of cone driving the center.

We studied the interaction between the chromatic and temporal properties of parvocellular (P) neurons in the lateral geniculate nucleus (LGN) of macaque monkeys. We measured the amplitudes and phases of responses to stimulation by spatially uniform fields modulated sinusoidally about a white point in a three-dimensional color space, at a range of temporal frequencies between 1 and 25 Hz. Below about 4 Hz, temporal frequency had relatively little effect on chromatic tuning. At higher frequencies chromatic opponency was weakened in almost all cells. The complex interactions between temporal and chromatic properties are represented by a linear filter model that describes response amplitude and phase as a function of temporal frequency and direction in color space along which stimuli are modulated. The model stipulates the cone inputs to center and surround, their temporal properties, and the linear combination of center and surround signals. It predicts the amplitudes and phases of responses of P-cells, and the change of chromatic properties with temporal frequency. We used the model to investigate whether or not the chromatic signature of the surround in a red–green cell could be estimated from the change in the cell's chromatic properties with temporal frequency. Our findings could be equally well described by mixed cone surrounds as by pure cone surrounds, and we conclude that, with regard to temporal properties, there is no benefit to be gained by segregating cone classes in center and surround.