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J. Patrick Mayo, Marc A. Sommer; Encoding of brief time interval judgments in single neurons. Journal of Vision 2010;10(7):934. doi: 10.1167/10.7.934.
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© ARVO (1962-2015); The Authors (2016-present)
Our knowledge of the psychophysics of brief interval time perception currently outweighs our knowledge of its neuronal basis. Of particular interest are the neuronal mechanisms for temporal judgments in frontal cortex, the region of the brain thought to underlie conscious perception. One ubiquitous neuronal phenomenon, adaptation, is intimately tied to temporal processing and could play a role in perceiving time intervals. Neuronal adaptation results when two visual stimuli are presented in close succession, yielding a normal first neuronal response but a diminished second response. The amount of time between the first and second stimuli governs the magnitude of the second response, with longer interstimulus intervals resulting in less adaptation and therefore larger second responses. In previous work (Mayo and Sommer, 2008), we quantified the dynamics of neuronal adaptation during passive fixation at two stages of visual processing in the brain: the frontal eye fields (FEF) in prefrontal cortex, and the superficial superior colliculus (SC) in the midbrain. We found robust neuronal adaptation in both areas with a similar time to recovery, even in the superficial SC located one synapse away from the retina. Here, we ask if the relative magnitude of successive neuronal responses contains useful information about the amount of time between successively-presented stimuli at naturalistic time intervals (<500 ms). Monkeys were trained to decide whether the amount of time between two brief, identical flashes was greater or less than a learned reference interval (300 ms). They reported their decision by making a saccade to one of two choice targets. Stimuli were presented in the receptive field of a single isolated FEF or SC neuron. We compare neuronal activity in correct versus incorrect trials in both brain areas to determine what role, if any, the magnitude of sensory responses (as opposed to latency alone) plays in temporal processing.
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