Are neurons in cat posteromedial lateral suprasylvian visual cortex orientation sensitive? Tests with bars and gratings

Abstract

There is controversy in the literature concerning whether or not neurons in the cat's posteromedial lateral suprasylvian (PMLS) visual cortex are orientation selective. Previous studies that have tested cells with simple bar stimuli have found that few, if any, PMLS cells are orientation selective. Conversely, studies that have used repetitive stimuli such as gratings have found that most or all PMLS cells are orientation selective. It is not known whether this difference in results is due to the stimuli used or the laboratories using them. The present experiments were designed to answer this question by testing individual PMLS neurons for orientation sensitivity with both bar and grating stimuli. Using quantitative response measures, we found that most PMLS neurons respond well enough to stationary flashed stimuli to use such stimuli to test for orientation sensitivity. On the basis of these tests, we found that about 85% of the cells with well-defined receptive fields are orientation sensitive to flashed gratings, and a similar percentage are orientation sensitive to flashed bars. About 80% of the cells were orientation sensitive to both types of stimuli. The preferred orientations typically were similar for the two tests, and they were orthogonal to the preferred direction of movement. The strength of the orientation sensitivity (measured as the ratio of discharge to the preferred and nonpreferred orientations) was similar to both types of stimuli. However, the width of the orientation tuning curves was systematically broader to bars than to gratings. Several hypotheses are considered as to why previous studies using bars failed to find evidence for orientation sensitivity. In addition, a mechanism for the difference in orientation tuning to bars and gratings is suggested.

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

“…Neurons within the region (Fig. 1a) are particularly sensitive to movement, movement direction, and line orientation (11)(12)(13)(14), and send a prominent projection to area 18 (15)(16)(17). Therefore, these neurons could contribute significantly to the emergence of both direction of movement and orientation selectivity in this area.…”

Spatial organization of receptive fields and dynamic peculiarities of neurons of the extrastriate area 21a of the cat cerebral cortex

“…Inhibitory components in the responses of visually sensitive neurons were recently studied in detail by some researchers, but mainly in the primary visual cortex [21][22][23][24]. The effects of inhibition in the response of neurons of the extrastriate associative cortical structures, in particular of the area 21а, were examined mostly in the context of formation of specialized neuronal responses (e.g., of those that determine the orientation selectivity) [11,25].…”

Visual Pathways Serving Motion Detection in the Mammalian Brain

“…Contrary to the PMLS, which receives inputs from area 17 and other structures which also get input from the primary visual cortex (areas 18 and 19, and the lateral division of the lateral posterior nucleus) and projects to areas 17, 18, 19 and 20a and other LS areas, the PLLS receives only sparse input from striate-recipient structures, but instead it is driven mainly by tectal inputs from the medial division of the lateral posterior nucleus and projects to more remote extrastriate areas such as theAEV [74,137–140]. The reciprocal connection between the PMLS and the PLLS is weak [74,132–134]. We do not have as much as information about the PLLS as we have about the PMLS.…”