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S. E. Boehnke, D. J. Berg, R. A. Marino, P. F. Baldi, L. Itti, D. P. Munoz, Adaptation, habituation and dishabituation of visual responses in the superior colliculus, In: Collaborative Research in Computational Neuroscience Annual Meeting, Los Angeles, California, Jun 2008.
Abstract: When stimuli are repeatedly flashed into the receptive field of visual neurons in the superior colliculus (SC), the response magnitude decreases (e.g., in a cue-target task). This effect could be due to 'adaptation' - a lower level mechanism like pupil constriction, or 'habituation' - the non-associative learning mechanism by which an organism stops responding to an irrelevant stimulus but recovers the response (dishabituates) after a change in stimulus properties. We sought to characterize the changes in responses that could be attributed to adaptation and habituation in superficial (SCs, n=18) and intermediate (SCi, n=36) layer neurons using a paradigm adopted from the ideas of Sokolov (1963). Two monkeys (Macaca mulatta) were rewarded for fixating a central fixation point while a series of 7 successive stimuli were flashed briefly (55 ms duration; 75-800 ms interstimulus interval (ISI)) in the receptive field of the neuron. On 70% of trials all flashed stimuli were identical, while on others, the 4th stimulus was either brighter, dimmer or absent (10% each). If reduced neural responsiveness is due to habituation, some recovery of the response (dishabituation) should occur to any oddball stimulus. However, if the reduced response is due to adaptation, the response should be further reduced after the brighter stimulus, but recover after the dimmer or absent stimulus. For the typical ISI of 200ms, the largest decrease in response magnitude (> 60% in SCs and ~50% in SCi) was to the second stimulus, and subsequent stimuli resulted in only small further reductions. The shorter the ISI the greater these reductions, with responses to stimuli 2-7 often being obliterated at very short ISIs (<100ms). The onset latency of the visual response increased with each stimulus so that on average the 7th stimulus response initiated nearly 20ms later than the 1st. These patterns were globally similar in SCs and SCi, but there were greater changes to the 3-7th stimuli in many SCi neurons. Responses to oddball stimuli in SCs neurons were suggestive only of sensory adaptation, while responses in SCi neurons showed features of both adaptation and habituation because a dishabituation signature in response to brighter or dimmer stimuli was present in the late visual response, and in the subsequent interstimulus interval. The adaptation responses of neurons in the SCs were more homogenous compared to those in the SCi, which showed considerable diversity in adaptation and habituation response properties.
Themes: Model of Top-Down Attentional Modulation, Computational Modeling, Human Psychophysics
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