Spatial and temporal properties of neurons of the lateral suprasylvian cortex of the cat

Abstract

Neurons in the posteromedial lateral suprasylvian cortex (PMLS) of cats were recorded extracellularly to investigate their response to stimulation by bars and by sinusoidal gratings. Two general types of cells were identified: those that modulated in synchrony with the passage of drifting bars and gratings and those that responded with an unmodulated increase in discharge. Both types responded to contrast reversed gratings with a modulation of activity: the cells that modulated to drifting gratings modulated to the first harmonic of contrast reversed gratings (at appropriate spatial phase and frequency), whereas those that did not modulate to drifting gratings always modulated to the second harmonic of contrast reversed gratings. No cell had a clear null point. Nearly all cells were selective for spatial frequency. The preferred frequency ranged from 0.1 to 1 cycles per degree (cpd), and selectivity bandwidths (full width at half height) were around two octaves. Preferred spatial frequency was not correlated with receptive field size, but bandwidth and receptive field size were positively correlated. Preferred spatial frequency decreased with eccentricity, at about 0.05 octaves/deg. The response of all cells increased as a function of grating contrast up to a saturation level. The contrast threshold for response to a grating of optimal parameters was approximately 1% for most cells and the saturation contrast approximately 10%. The contrast gain was approximately 25 spikes/s per log unit of contrast. All cells were tuned for temporal frequency, preferring frequencies from approximately 3 to 10 Hz, with a selectivity bandwidth approximately 2 octaves. For some cells, the spatial selectivity did not depend on the temporal frequency and vice versa. Others were spatiotemporally coupled, with the preferred temporal frequency being lower at high than at low spatial frequencies, and the preferred spatial frequency lower at high than at low temporal frequencies. Previous results showing broad velocity tuning to a bar were replicated and found to be predictable from the combined spatial and temporal tuning of PMLS cells and the Fourier spectrum of a bar. Preferred temporal frequency steadily decreased with eccentricity, at 0.025 octaves/deg. The results for PMLS cells are compared with those of other visual areas. Acuity and spatial preference and selectivity bandwidth is comparable to all areas except area 17, where they are a factor of about two higher. Temporal selectivity in PMLS is as fine as observed in other areas. The possibility that PMLS cells may be involved with motion detection and detection of motion in depth is discussed.

The role of feedback in shaping neural representations in cat visual cortex

“…In designing our stimuli, we needed to ensure that large numbers of both MS and area 18 neurons were activated well. However, the values selected (2 Hz and 16°per sec) may not be fully optimal for every MS and every area 18 neuron (11,49,50). We acknowledge that if we had used a fully comprehensive set of stimuli, we may have shown that the direction selectivities of every neuron in the upper layers of primary visual cortex was influenced by signals fed back from higher-motion cortices.…”

Motion Tuned Spatio-Temporal Quality Assessment of Natural Videos

“…Evidence indicates that the receptive field profiles of simple cells in the mammalian visual cortex are well modeled by Gabor filters [52]. The Gabor filters that we use in the algorithm we develop later are separable in the spatial and temporal coordinates and several studies have shown that neuronal responses in Area V1 are approximately separable [54], [55], [56]. Gabor filters attain the theoretical lower bound on uncertainty in the frequency and spatial variables and thus, visual neurons approximately optimize this uncertainty [52].…”

Neurons in V1, V2, and PMLS of Cat Cortex Are Speed Tuned But Not Acceleration Tuned: The Influence of Motion Adaptation

“…The convolution operations provide a stimulus with lowpass spatial frequency content, with little or no power in spatial frequencies Ͼ1 cpd. The spatial frequency content of these aperiodic stimuli is known to cover the sensitivity range of most cells in V1, V2, and PMLS (Casanova et al 1995;Hamada 1987;Merabet et al 2000;Morrone et al 1986;Movshon et al 1978;Zumbroich and Blakemore 1987). However, as in previous studies, we found that only ϳ70 -80% of neurons in each area responded to the motion of visual noise or random stripes (Casanova et al 1995;Hamada 1987;Merabet et al 2000), and only the responses of these neurons are reported here.…”

“…These differences with earlier reports may relate to the large texture elements used in our stimuli (0.8°) compared with previous reports (e.g., 0.04 -0.64°in Casanova et al 1995), because a neuron's preferred speed tends to be higher when larger texture elements are used. Technically, when tested with spatial sine-wave gratings, cells in V1, V2, and PMLS do not always show speed tuning but are tuned to the spatial or temporal frequencies contained within a stimulus (Morrone et al 1986;Movshon et al 1978;Zumbroich and Blakemore 1987). Although many cells only respond to a narrow range of spatial frequencies, they should still be stimulated by our stimuli, which contain a broad range of spatial frequencies.…”

“…The majority of neurons in these areas respond better to moving rather than stationary stimuli and have strong orientation or direction preferences and spatiotemporal-frequency or speed tuning (e.g., Morrone et al 1986;Movshon 1975;Movshon et al 1978). We studied the responses of neurons in V1, V2, and PMLS in anesthetized cats to constant speed steps and linear speed ramps comprising constant rates of acceleration and deceleration.…”