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Wei Song Ong, James W. Bisley; A study of peri-saccadic remapping in area MT. Journal of Vision 2010;10(7):557. doi: https://doi.org/10.1167/10.7.557.
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Area MT has traditionally been thought to operate in a retinotopic reference frame; however, there has been recent fMRI evidence that human MT has some spatiotopic properties (d'Avossa et al, 2007). Also, we have presented psychophysical evidence that area MT plays a spatiotopic role in the memory for motion process (Ong et al, 2009).
Here, we recorded from area MT in animals performing visually guided saccades during which a moving dot stimulus (100% coherence) or a circular stimulus was presented. The dot stimulus moved in the preferred direction of the recorded neuron in the pre-saccadic or post–saccadic receptive field for 500 ms; its onset occurring 80 ms before the saccade target appeared. The luminance-matched circle was flashed for 50 ms in the pre- or post-saccadic receptive field at random time intervals between 100ms before the saccade target appeared to 350 ms after. Mean saccadic latency was 192 ± 35 ms.
We recorded from 31 neurons and none of them showed pre-saccadic remapping with either stimulus. With the flashed circle, approximately 1/3 of the neurons showed late post-saccadic remapping, defined as when stimuli flashed shortly before the beginning of the saccade induced a neural response after the saccade in the post-saccadic receptive field.
We found that the post-saccadic response latencies of the moving dots were similar to onset latencies for most neurons, consistent with saccadic suppression. A subpopulation had shorter latencies, but none were pre-saccadic. These neurons were more likely to show late post-saccadic remapping of the flashed circle.
Although no neurons exhibited pre-saccadic remapping, the presence of the late post-saccadic response to a stimulus flashed entirely prior to the saccade indicates that a remapping mechanism may act on MT neurons and could explain results showing spatiotopic processing in area MT.
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