Comparison of Response Characteristics in Auditory Cortex of the Awake and Anesthetized Ferret

摘要

We recently developed an awake preparation for chronic physiological recording in the ferret (ARO Abstracts. Fritz et al, 2001) and described neural responses in auditory cortex in the awake animal to a variety of acoustic stimuli including tomes, noise, ripples and their combinations. Previous neurophysiological studies of the ferret auditory cortex in our laboratory (Depireux et al, 2001) have used an anesthetized preparation which has yielded valuable insight into auditory function but may have caused depression of neural activity and inhibit cortico-cortical interactions. Hence we have continued to explore responses in auditory cortex of the awake animal in order to understand the full range of dynamic information flow, and have recorded from over 300 single units. We characterized and correlated the activity of single units from neighboring cells in a cortical column in response to these stimuli. As we have shown in previous research, units in auditory cortex are well characterized by their responses to the envelope of moving ripples. An important property of a spectro-temporal receptive field (STRF) is its separability, i.e. whether it can be decomposed into the product of two 1- dimensional functions (temporal and spectral). We have characterized the STRFs from cortical neurons in the awake and the anesthetized preparation analyzing separability in the two populations and found an overall similarity of the STRFs in both conditions. However, we observed differences in the response pattern to pure tones in the awake vs anesthetized ferret (increased sustained on-responses and vigorous off-responses in the awake preparation) and so discuss the apparent disparity in the effects of anesthesia on cortical responses to pure tone and dynamic ripples.