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James Schummers, Mriganka Sur; Orientation selective responses to the offset of grating stimuli. Journal of Vision 2003;3(9):370. doi: 10.1167/3.9.370.
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It is well established that the responses of neurons in primary visual cortex (V1) are not static, but rather are influenced by recent stimulus exposure. Previous work has demonstrated strong effects of preceding stimuli on responses to subsequent ones (Nelson, 1991; Dragoi et al, 2000). We have examined the activity of neurons in V1 during the period after the removal of a grating stimulus, when no explicit stimulus was present (the screen was uniform gray). We find that orientation tuning curves taken during this interval (referenced to the previous stimulus) are generally tuned orthogonal to the tuning during the grating presentation (∼66% of cells within 90+/−10 degrees). This orthogonal tuning is shaped by both a decrease in firing following the preferred orientations, and surprisingly, in ∼30% of cells, by an increase in firing following orthogonal stimuli. This “offset response” has a similar latency to the grating onset response, and typically lasts longer than 500 msec, and can be more than half as large as the response to the grating itself. Interestingly, this behavior is more pronounced in complex cells than in simple cells. The selectivity of the tuning curve during the blank period was positively correlated with the selectivity during the grating period (r = .76). There is not a simple inverse relationship between the number of spikes fired during the two epochs; for many sharply tuned neurons, in which several grating orientations fail to elicit any response, only those orthogonal to the optimal elicited an offset response. This phenomenon may provide a means for highlighting temporal orientation contrast, and may be related to psychophysical phenomena such as orthogonal percepts following extended viewing, which have been attributed to a rebound from inhibition (Vidyasagar et al 1999).
NelsonSBJ Neurosci 1991 Feb;11(2):344–356; DragoiVNeuron 2000 Oct;28(1):287–298; VidyasagarTRNature 1999 Jun 3;399(6735):422–423
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