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1 Biomedical Engineering, Boston University, Boston, MA, USA
* To whom correspondence should be addressed. E-mail: kamalsen{at}bu.edu.
Although, auditory cortex is thought to play an important role in processing complex natural sounds such as speech and animal vocalizations, the specific functional roles of cortical receptive fields (RFs) remain unclear. Here, we investigate the relationship between a behaviorally important function: the discrimination of natural sounds, and the structure of cortical RFs. We examine this problem in the model system of songbirds, using a computational approach. First, we construct model neurons based on the Spectral Temporal Receptive Field (STRF), a widely used description of auditory cortical RFs. We focus on delayed inhibitory STRFs, a class of STRFs experimentally observed in primary auditory cortex (ACx) and its analog in songbirds (field L), which consist of an excitatory subregion and a delayed inhibitory subregion co-tuned to a characteristic frequency. We then quantify the discrimination of birdsongs by model neurons, examining both the dynamics and temporal resolution of discrimination, using a recently proposed Spike Distance Metric (SDM). We find that single model neurons with delayed inhibitory STRFs, can discriminate accurately between songs. Discrimination improves dramatically when the temporal structure of the neural response at fine timescales is considered. When we compare discrimination by model neurons with and without the inhibitory subregion, we find that the presence of the inhibitory subregion can improve discrimination. Finally, we model a cortical microcircuit with delayed synaptic inhibition, a candidate mechanism underlying delayed inhibitory STRFs, and show that blocking inhibition in this model circuit degrades discrimination.
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