Afferent bases of spatial- and temporal-frequency processing by neurons in the cat's posteromedial lateral suprasylvian cortex: effects of removing areas 17, 18, and 19

Abstract

1. We investigated whether spatial- and temporal-frequency processing by neurons in the cat's posteromedial lateral suprasylvian (PMLS) extrastriate cortex depends on inputs from ipsilateral areas 17, 18, and 19 (visual cortex; VC) or occurs in parallel with those cortical areas. 2. Single neurons were recorded in PMLS cortex of normal adult cats and adult cats that had ipsilateral VC removed within 24 h before recording. Receptive-field properties were characterized, and responses to sine-wave gratings of different spatial frequencies, contrasts, and temporal frequencies were measured and Fourier analyzed. 3. As in previous studies, removing inputs from VC led to a reduction in the proportion of direction-selective PMLS cells. In addition there were statistically significant reductions in response amplitude and variability, although signal-to-noise ratios were unchanged. Contrast sensitivity also was reduced at all spatial frequencies. Spatial resolution was reduced slightly; however, this reduction appears to be secondary to the overall reduction in response amplitude and sensitivity. 4. The shape of the spatial-frequency contrast-sensitivity functions and the distribution of optimal spatial frequencies were unaffected by removing inputs from VC. In addition, once response threshold was reached, the slope of the contrast-response function (contrast gain) at the optimal spatial frequency was similar for PMLS cells in normal cats and cats with a VC lesion. 5. When tested at the optimal spatial frequency, temporal-frequency bandwidths, high and low temporal-frequency cutoffs, and optimal temporal frequencies were similar for PMLS cells in normal cats and cats with VC removed. 6. The results thus indicate that inputs from VC are important for the elaboration of direction selectivity and affect response amplitude and contrast sensitivity among PMLS neurons. However, visual-cortical inputs have little or no influence on spatial- and temporal-frequency processing by PMLS neurons. These properties depend on inputs from other cortical areas or the thalamus and are processed in parallel with areas 17, 18, and 19.