The cortical representation of visual field is divided between the two hemispheres in the early visual cortex with only a slight overlap along the vertical meridian. Therefore, when an object lies on the vertical meridian, visual information about it must be stitched together between the two halves. Within a given hemisphere, the continuity of visual representation on the cortical surface is assured by the retinotopy and the columnar organization for stimulus parameters such as orientation. Does this continuity extend across the hemispheric boundary? Specifically, for example, do a pair of neurons separated across hemispheres tend to have similar tuning properties if their receptive field positions overlap?
To address these questions, we measured receptive field positions and tuning properties of multiple cortical neurons recorded simultaneously across the two hemispheres in anesthetized and paralyzed cats. Reverse correlation method was used for analyzing the activities of these neurons in response to ternary dynamic dense noise stimuli. The degree of overlap of receptive fields for each pair of neurons was used as a metric of the proximity of receptive fields. The similarity of tuning properties of the pair was evaluated by the correlation coefficient in the 2-D spectral domain, i.e., in the joint spatial-frequency and orientation domain, using the strongest maps at the optimal correlation delay from the local spectral reverse correlation (LSRC) analysis (Nishimoto et al., 2006).
Our results show that hemispherically-separated pairs of neurons with greater degree of receptive fields overlap tended to be more similar in their tuning properties in the spatial frequency and the orientation domain. Pairs with distant receptive fields tended to have dissimilar tuning properties.
We therefore conclude that the continuity of cortical representation in the early visual cortex is maintained not only within a hemisphere, but also across the hemispheric boundary. Such cross-hemispheric continuity of the cortical representation may be of great importance in binding the two halves of the visual field into a coherent and accurate single visual map.
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