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[PhD Thesis] Integration and temporal processing in the inferior colliculus: Neural coding of duration and novelty of sound
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David Perez Gonzalez
Dept. of Cell Biology and Pathology.Institute of Neuroscience of 'Castilla y Leon'
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The present work reports certain forms of temporal processing in the inferior colliculus of the rat, by means of extracellular recordings of single units during auditory stimulation. Study I deals with the sensibility to sound duration. Neurons with that kind of sensibility were found in the inferior colliculus of the rat, and were more frequent in the cortical areas than in the central nucleus. The most common kind of duration sensibility found was long pass, and the ranges of sensitivity were compatible with the duration of a wide range of calls. The results were similar to the data published for other species of non-echolocating mammals, but differed from those about echolocating bats. This suggests that while duration sensitivity at the level of the IC seems to be a common feature across mammals, some species may present adaptations to suit their specific needs. The results of Study II indicate that a population of neurons in the inferior colliculus of the rat show stimulus-specific adaptation, allowing them to respond selectively to changes in the stimulus, and being able to detect novel sounds, even at slow repetition rates (less than 2 stimuli per second). Those neurons were typically onset responders with little spontaneous activity, and were found exclusively in the external and dorsal cortical areas of the inferior colliculus. The dense cortical projection to those areas suggest a possible cortical contribution to the generation of these responses. The stimuli evoking these responses was similar to those eliciting mismatch negativity, a component of the event-related potentials related to the detection of changes in the stimuli. The neurons described here could be a neuronal correlate of those potentials.
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