End-zone region in receptive fields of hypercomplex and other striate neurons in the cat

Abstract

The lengthwise organization of receptive fields was studied quantitatively using an optimally oriented narrow (.ltoreq. 0.29.degree.) light-bar stimulus to prepare length-response curves from 60 orientation-sensitive striate cells (simple, 16; hypercomplex I, 24; complex, 6; hypercomplex II, 10; atypical, 4) from 10 anesthetized (N2O/O2) and paralyzed cats. Unilateral length-response curves from 11 cells (hypercomplex I, 9; hypercomplex II, 2) showed that, in every case, end-zone inhibitory areas were present at both ends of the discharge region. Bilateral length-response curves give a reasonably good approximation to the length-wise organization of cells in the simple and complex families. Length-response curves for the non-preferred direction of stimulus motion were studied in 56 cells. The end-zone inhibitory regions of hypercomplex I cells are usually not directionally sensitive and have properties that are very similar in the 2 directions of stimulus motion. Only 2 of 14 hypercomplex I cells showed a simple-type length-response curve in the nonpreferred direction. Cells (4) had atypical length-response curves. With continued lengthening of the stimulus, 2 cells showed a late onset of inhibition after a clear reponse plateau had been achieved, and 2 cells showed a late recovery of responsiveness after a period of inhibition. For any given cell in the simple or complex families, the length-response curves were similar whether the stimulus was a moving or a stationary flashing bar. The lengths of the discharge region and of the end-zone inhibitory areas were the same whichever stimulus was used for the length-response curve. Interactive effects of stimulus length and orientation on the response of a hypercomplex I cell showed that, like simple cells, the orientation tuning curve progressively sharpens as stimulus lengthens. With hypercomplex II cells, the sharpness of the orientation tuning curve is relatively unaffected by stimulus length. Cells with receptive-field centers near or over the vertical midline may have the boundaries of their fields extending up to 4.1.degree. into the wrong hemifield. The fields that extend over the midline appear not to be truncated or to have their organization altered in any way.