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Alan B. Saul, Yamei Tang, Elsie Wong; Timing aftereffects in alert monkey V1. Journal of Vision 2006;6(6):407. doi: 10.1167/6.6.407.
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© ARVO (1962-2015); The Authors (2016-present)
The importance of adaptation aftereffects lies largely in their specificity. One of the most specific examples of an aftereffect occurs in single cells of visual cortex, consisting of a delayed response onset to each cycle of a periodic stimulus, without any change in the offset. These timing aftereffects were previously reported in anesthetized cats (Saul 1995, 1999). They also occur in anesthetized monkeys, and could in principle be due to anesthesia.
We recorded from single neurons of alert monkey V1, and measured responses to gratings drifting continuously during 5 s trials. Control responses were taken from the first 2 s of each trial, and adapted responses from the final 2 s. Across trials, contrast and spatial and temporal frequencies varied. Timing aftereffects occurred in nearly all cells whose response was modulated by the grating stimuli, including complex cells that gave first harmonic responses at low spatial frequencies. On average, adapted responses were shifted by about 0.03 cycles relative to control responses (P<0.01, N=57), as in anesthetized animals. Onsets were shifted by about 0.04 cycles whereas offsets were not changed. Amplitudes were decreased by a factor of 0.92 (geometric mean, not significantly different from 1). Amplitude aftereffects had a slight negative correlation with timing aftereffects.
Adaptation may potentiate inhibition that is out of phase with the excitation to a cell, inducing these timing aftereffects. This process appears to operate in awake behaving monkeys as well as in anesthetized cats.
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