Date of Completion

4-16-2015

Embargo Period

4-16-2015

Keywords

auditory cortex, encoding, spike timing, temporal sound cues

Major Advisor

Heather L. Read

Co-Major Advisor

Maxim Volgushev

Associate Advisor

Monty A. Escabi

Associate Advisor

James J. Chrobak

Associate Advisor

Shigeyuki Kuwada

Field of Study

Psychology

Degree

Doctor of Philosophy

Open Access

Open Access

Abstract

Virtually all animals use time-varying (temporal) cues to categorize sounds, communicate and act appropriately within their environments. In mammals, the auditory cortices are essential for behavioral discrimination of temporal cues and yet the neural mechanisms underlying this ability remain unknown. Primary (A1) and ventral non-primary auditory cortical fields are physiologically and anatomically organized and specialized to represent distinct spectral and spatial cues in sound. The current study investigates cortical field differences for encoding envelope shape and periodicity in sound. We use shuffled correlation analysis to quantify reliability, precision (jitter), and temporal coding fraction of single neuron spike timing responses to periodic noise sequences with variations in shape and modulation frequency. In all three fields, we find that spike-timing precision (jitter) and reliability change systematically and proportionally with sound envelope shape and modulation frequency, respectively. However, A1 responses are primarily sound onset driven with low spike timing jitter indicating more precise temporal coding than ventral fields. In contrast, ventral fields had sustained responses to repetitive noise trains. Across regional neuron populations, average spike timing jitter is rank ordered A1 < VAF < cSRAF. Reliability and vector strength modulation transfer functions are lowpass or bandpass in three fields. Both reliability and synchrony upper cutoff frequencies show a rank order decrease progressing from A1 to more ventral fields. Together, these differences suggest a functional hierarchy whereby later developing ventral auditory cortical fields encode sound shape with spike timing jitter, and respond reliably over a reduced range of modulation frequencies, possibly due to slower integration times. This could serve to better encode sound shape cues important for perception of attack and timbre and used to discriminate and categorize sound objects.

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