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Jessy D. Dorn, Dario L. Ringach; Long-range interactions in macaque primary visual cortex. Journal of Vision 2002;2(7):108. doi: https://doi.org/10.1167/2.7.108.
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We examined long-range interactions (cross-correlations) between neuronal pairs in macaque V1. Recordings were performed in the anesthetized and paralyzed M. fascicularis. The physical distance between neural pairs in our population ranged from of 800µm to about 3mm, and their receptive fields were located within 6deg of the fovea. Simultaneous responses of cells to a fast sequence of sinsusoidal gratings of varying orientation, spatial frequency and spatial phase were obtained using a four-electrode micropositioner. This stimulus is advantageous because it simultaneously drives neurons with differing orientation and/or spatial frequency preferences. In addition, the increased firing rate of the population makes it easier to detect inhibitory interactions between neurons. Shuffle-corrected cross-correlations in response to repeated stimuli sequences were calculated. The strength of the cross-correlations were measured as the height of the peak or trough, normalized by the largest correlation magnitude one could theoretically expect given the firing rates of the neurons. We studied cross-correlation magnitude as a function of the difference in preferred orientation of the cells. Large positive cross-correlations are more likely to occur between cells of similar orientation preference, while large negative cross-correlations are less dependent on the orientation preferences of the cells. These results suggest that excitatory and inhibitory interactions in V1 do not share the same orientation tuning. Inhibition, as a function of orientation difference, appears to be much broadly tuned than excitation. These data may help to discriminate among different models of orientation selectivity in V1.
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