Stimulus dependence of orientation and direction sensitivity of cat LGNd relay cells without cortical inputs: A comparison with area 17 cells

Abstract

The cortical contribution to the orientation and direction sensitivity of LGNd relay cells was investigated by recording the responses of relay cells to drifting sinusoidal gratings of varying spatial frequencies, moving bars, and moving spots in cats in which the visual cortex (areas 17, 18, 19, and LS) was ablated. For comparison, the spatial-frequency dependence of orientation and direction tuning of striate cortical cells was investigated employing the same quantitative techniques used to test LGNd cells. There are no significant differences in the orientation and direction tuning to relay cells in the LGNd of normal and decorticate cats. The orientation and direction sensitivities of cortical cells are dependent on stimulus parameters in a fashion qualitatively similar to that of LGNd cells. The differences in the spatial-frequency bandwidths ofLGNd cells and cortical cells may explain many of their differences in orientation and direction tuning. Although factors beyond narrowness of spatial-frequency tuning must exist to account for the much stronger orientation and direction preferences of cells in area 17 when compared to LGNd cells, the evidence suggests that the orientation and direction biases present in the afferents to the visual cortex may contribute to the orientation and direction selectivities found in cortical cells.

Concomitant sensitivity to orientation, direction, and color of cells in layers 2, 3, and 4 of monkey striate cortex

“…The foregoing findings combined with the observation that most cortical cells appear to be less orientation sensitive when tested with sinusoidal gratings of relatively low spatial frequency ( Fig. 1; Hammond and Pomfret, 1990;Thompson et al, 1994) can explain why color-sensitive cells appear less orientation sensitive than broad-band cells in response to moving bars. In particular, a bar or edge stimulates a cell over its full range of spatial frequencies but a sinusoidal grating does not.…”

“…However, this is not always the case ( Fig. 1; see also Hammond and Pomfret, 1990;Thompson et al, 1994). When the test stimuli were optimized to best reveal the cell's selectivity, the degree of orientation and direction sensitivity was observed to vary continuously among cortical cells.…”

“…1, 3). In general, orientation sensitivity was clearest when the test stimuli were gratings of relatively high spatial frequency and direction sensitivity was clearest when gratings of relatively low spatial frequency were employed (see also Blasdel and Fitzpatrick, 1984;Hammond and Pomfret, 1990;Thompson et al, 1994). However, this is not always the case ( Fig.…”

“…LGNd relay cells , and visual cortical cells to moving stimuli (W&getter and Eysel, 1987;WGrgGtter et al, 1990;Thompson et al, 1994).…”

“…In particular, a bar or edge stimulates a cell over its full range of spatial frequencies but a sinusoidal grating does not. As a result, cells that respond better to low spatial frequencies such as LGNd cells, layer 4Cp cells, and color-sensitive cells in layers 2 and 3 tend to appear less orientation sensitive in response to bar stimuli than to sinusoidal gratings of the appropriate spatial frequency (Thompson et al, 1994). The reason for this is that the responses of these cells are especially dependent upon the relatively unoriented, low spatial frequency component of bar stimuli.…”