| Abstract: | Orientation tuning (OT) of 225 cat neurons of the primary visual cortex (field 17) to the flashing of a light bar in the discharge centers of their receptive field (RFs) were investigated. It was found that 43% of the cells investigated were monomodally tuned, i.e., were primarily detecting horizontal and vertical orientations. The remaining 57% of the neurons exhibited double OT, i.e, exhibited, in addition to a main preferred orientation (PO), an additional preferred orientation (aPO) at a right or acute angle to the main orientation (the mean angle between the two OT maxima equalled 71.4±2.4°). In bimodal cells, the additional maximum of OT was comparable in magnitude to the main maximum (averaging 0.7±0.03 of the PO) in half the cases. The orientational properties of the main and additional maxima were almost indistinguishable. Under light or moderate anesthesia, approximately half the neurons with double OT became monomodal; at the same time, a small fraction of monomodal cells (12%) manifested double OT. Under anesthesia, the angle between two the preferred orientations decreased, while the ratio of amplitude characteristics remained unchanged. Monomodal neurons frequently exhibited simple RFs and OTs unaffected by anesthesia. Neurons with double OT, on the other hand, exhibited simple and complex types of RFs just as often and their OT changed under the influence of anesthesia. It is suggested that neurons with double OT can function as detectors of angles and angles of intersecting lines; such angles, together with line orientation, are important attributes of images. In contrast, monomodal neurons may provide a benchmark for a stable reference system of orientation coordinates. The interaction of the two neuronal systems mentioned may allow effective analysis of image attributes at the level of the primary visual cortex.Institute of Higher Nervous Activity and Neurophysiology, Russian Academy of Sciences Moscow. Translated from Neirofiziologiya, Vol. 24, No. 3, pp. 260–269, May–June, 1992. |
