High Spectral and Temporal Acuity in Primary Auditory Cortex of Awake Cats

Abstract

Most accounts of single- and multi-unit responses in auditory cortex under anesthetized conditions have emphasized V-shaped frequency tuning curves and low-pass sensitivity to rates of repeated sounds. In contrast, single-unit recordings in awake marmosets also show I-shaped and O-shaped response areas having restricted tuning to frequency and (for O units) sound level. That preparation also demonstrates synchrony to moderate click rates and representation of higher click rates by spike rates of non-synchronized tonic responses, neither of which are commonly seen in anesthetized conditions. The spectral and temporal representation observed in the marmoset might reflect special adaptations of that species, might be due to single- rather than multi-unit recording, or might indicate characteristics of awake-versus-anesthetized recording conditions. We studied spectral and temporal representation in the primary auditory cortex of alert cats. We observed V-, I-, and O-shaped response areas like those demonstrated in awake marmosets. Neurons could synchronize to click trains at rates about an octave higher than is usually seen with anesthesia. Representations of click rates by rates of non-synchronized tonic responses exhibited dynamic ranges that covered the entire range of tested click rates. The observation of these spectral and temporal representations in cats demonstrates that they are not unique to primates and, indeed, might be widespread among mammalian species. Moreover, we observed no significant difference in stimulus representation between single- and multi-unit recordings. It appears that the principal factor that has hindered observations of high spectral and temporal acuity in the auditory cortex has been the use of general anesthesia.

Neural processing in the primary auditory cortex following cholinergic lesions of the basal forebrain in ferrets

“…Our results indicate that under medetomidine/ketamine anesthesia, spontaneous activity of cortical neurons is low and not particularly affected by loss of cholinergic inputs from the nucleus basalis, other than a higher proportion of bursting units in the control group than in the NB ACh - group. There is growing evidence that spontaneous activity and aspects of stimulus coding in the auditory cortex can be affected by general anesthesia ( Zurita et al, 1994 ; Banks et al, 2018 ; Filipchuk et al, 2022 ; Middlebrooks et al, 2023 ), but since both groups of animals were anesthetized in the same way during the recordings, the key difference would have been the loss of most of the cholinergic innervation of the cortex in the NB ACh- group.…”