Presynaptic inhibition is a widespread mechanism for regulating transmitter release in the CNS. Presynaptic inhibitors act as a high-pass filter, but the functional consequence of this filtering during the synaptic processing of behaviorally relevant activity remains unknown. Here we use analytical approaches to examine the effects of presynaptic inhibition on synaptic output in response to activity patterns from CA3 pyramidal cells during the performance of a complex behavioral task. We calculate that presynaptic inhibition enhances the contrast between background activity and responses to environmental cues and that neuronal responses to location are subject to stronger contrast enhancement than neuronal responses to olfactory information. Our analysis suggests that presynaptic inhibition also enhances the importance of integrative inputs that respond to many behavioral cues during the task at the expense of specific inputs that respond to only a few of these cues.
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