Neural correlates of detection and decision in auditory cortex during frequency discrimination

This dissertation presents the results of a series of experiments designed to expand our understanding of the role that auditory cortex plays in threshold-level frequency discrimination. The unifying hypothesis of this dissertation is that auditory cortex is involved in discrimination of fine-grained frequency differences. Recording neural responses to auditory stimuli during performance of a difficult frequency discrimination task opens the door to investigating possible neural mechanisms which may encode frequency change detection. Additionally, simultaneous recording of neural and psychophysical data allows for insight into the rats' perception of or lack of perception of a frequency change (as inferred from the behavioral response to the stimuli).;Briefly, the results of these studies show that rats are capable of performing a frequency discrimination task and that their thresholds are comparable to those found in other mammals, including humans, making them a suitable candidate for studying how fine grain frequency differences are processed. Post-surgery psychophysical results show that implantation of a chronic recording device in the rat's auditory cortex did not have a large effect on frequency discrimination thresholds or other behavioral measures. Recordings from rat auditory cortex revealed a neural correlate of the frequency discrimination ability in the onset response of cortical neurons to the target tone. Additionally, the onset latency of auditory cortex responses was shown to be correlated with behavioral reaction times. The results document an increase in firing rate (facilitation) relative to the reference tone based on whether the rat made a decision to respond or not to respond to the presentation of a target tone. This facilitation was not stimulus specific, as was shown to be correlated with behavior, but not the frequency or frequency shift. Finally, the response strength of auditory cortex to frequency changes was shown to be modulated according to the relevance to task performance. Facilitation to the frequency change was not seen when the frequency change was irrelevant to the task the despite correct performance of the task.;The results of this series of experiments implicate auditory cortex as an important component in the resolution of small frequency differences and suggest that signals from auditory cortex may play a significant role in the perception of frequency changes as well as in the decision to respond to those frequency changes. Future studies in this field could help to elucidate how neural codes from sensory cortex relate to perception and how they contribute towards the formation of decisions while performing a detection task such as the one presented here.