Comparison of Orientational Tuning and Its Dynamics in Neurons in Different Functional Domains of the Primary Visual Cortex

Abstract

We report here studies of orientational tuning and its dynamics during generation of responses in neurons located in orientation columns and the centers of orientation pinwheels in the primary visual cortex of the cat. Intrinsic signal optical mapping was used to define the position of the working module on functional and vascular maps of the cortical surface. Both maps were used for targeted implantation of microelectrodes. The dynamics of orientational tuning were studied using a time slice method. Neurons whose preferred orientations were stable during response generation were observed in pinwheel centers and in orientation columns, accounting for 14.5% of cells, along with neurons in which the preferred orientation sequentially shifted by an average of 102 ± 5° (40.8%) and neurons with mixed-type dynamics (44.7%). Neurons with stable tuning in pinwheel centers differed from neurons with unstable tuning by producing greater responses to the preferred orientation, while those in orientation columns were characterized by later onset of responses to all orientations, including the preferred and non-preferred orientations. The orientational qualities of detection in stable neurons in these functional modules were better than those of cells with unstable tuning. Comparison of neurons with the same type of preferred orientation dynamics but different locations showed that stable neurons in pinwheel centers had shorter latent periods and larger responses than neurons in orientation columns. The width and selectivity of orientation tuning in these cells showed no differences. In unstable neurons, the characteristics of orientation tuning and responses to the preferred orientation were independent of location and were essentially identical. The functional significance of neurons with stable and unstable tuning during response generation in pinwheel centers and orientation columns in the primary visual cortex is discussed