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C. Casanova, D. Dumbrava, J. Faubert; Complex motion integration in the cat's LP-pulvinar. Journal of Vision 2001;1(3):398. doi: 10.1167/1.3.398.
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We have previously shown that neurons in the cat's lateral posterior-pulvinar (LP-pulvinar) complex are involved in higher-order visual processing (Merabet et al., Nature, 396, 1998). To further investigate this issue, we examined whether neurons in the LP-pulvinar complex can integrate local motion cues into a coherent percept. Experiments were performed on anesthetized normal adult cats. The cells' sensitivity to complex motion was studied using moving random dot kinematograms (RDKs) consisting of a two frame random dot motion sequence, in which each dot survived for a brief period of time (16–160 ms) before being replaced by its partner dot (the dots moved only once before being randomly repositioned). The influence of spatial and temporal intervals between partner dots, stimulus area, relation between global and pattern-motion selectivity were studied. We recorded from 76 direction-selective cells. Out of these, 38% cells responded to the coherent direction of the complex RDKs pattern. Responses varied as a function of spatial and temporal characteristics of the stimulus: cell discharges were generally optimal for short temporal intervals (16 ms) and for large displacements (>2 deg). These observations indicate that the processing of global motion by LP-pulvinar neurons involves higher-order spatiotemporal integration. We have also found that neurons sensitive to complex RDKs were not pattern-selective when tested with drifting plaids, suggesting that the nature of integration underlying responses to the two kind of patterns differs. These findings demonstrates that thalamic cells can integrate local signals into a global percept, further indicating that the extrageniculate thalamus may actively participate in higher-order visual processing. Furthermore, these results provide evidence that there may be specialized mechanisms for different types of complex motion within the LP-pulvinar complex.
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