title: Functional organization of sound direction and sound pressure level in primary auditory cortex of the cat.
abstract: 1. The functional organization of neuronal tuning to the azimuthal location and sound pressure level (SPL) of noise bursts was studied in high-frequency primary auditory cortex (AI) of barbiturate-anesthetized cats. Three data collection strategies were used to map neural responses: 1) electrode penetrations oriented normal to the cortical surface provided information on the radial organization of neurons' responses; 2) neurons' responses were examined at a few points in the middle cortical layers in multiple normal penetrations across AI to produce fine-grain maps of azimuth and level selectivity; and 3) electrode penetrations oriented tangential to the cortical surface provided information on neurons' responses along the isofrequency dimension. 2. An azimuth-level data set was obtained for each single- or multiple- (multi-) unit recording; this consisted of responses to noise bursts at five SPLs (0-80 dB in 20-dB steps) from seven azimuthal locations in the frontal hemifield (-90 to +90 degrees in 30 degrees steps; 0 degree elevation). An azimuth function was derived from these data by averaging response magnitude over all SPLs at each azimuth tested. A preferred azimuth range (PAR; range of azimuths over which the response was > or = 75% of maximum) was calculated from the azimuth function and provided a level-independent measure of azimuth selectivity. Each PAR was assigned to one of four azimuth preference categories (contralateral-, midline-, ipsilateral-preferring, or broad/multipeaked) according to its location and extent. A level function obtained from the data set (responsiveness averaged over all azimuths) was classified as monotonic if it showed a decrease of < or = 25% (relative to maximum) at the highest SPL tested (usually 80 dB), and nonmonotonic if it showed a decrease of > 25%. The percentage reduction in responsiveness, relative to maximum, at the highest level tested (termed nonmonotonic strength) and the preferred level range (PLR; range of SPLs over which responsiveness was > or = 75% of maximum) of each response was also determined. 3. Normal penetrations typically showed a predominance of one azimuth preference category and/or level function type. The majority of penetrations (26/36: 72.2%) showed statistically significant azimuth preference homogeneity, and approximately one-half (17/36: 47.2%) showed significant level function type homogeneity. Over one-third (13/36) showed significant homogeneity for both azimuth preference and level function type. 4. Mapping experiments (n = 4) sampled the azimuth and level response functions at two or more depths in closely spaced normal penetrations that covered several square millimeters of AI.(ABSTRACT TRUNCATED AT 400 WORDS)
authors.affiliation: Department of Physiology, University of Kansas Medical Center, Kansas City 66160-7401.
authors.forename: J C
authors.initials: JC
authors.lastname: Clarey
authors.forename: P
authors.initials: P
authors.lastname: Barone
authors.forename: T J
authors.initials: TJ
authors.lastname: Imig
mesh_terms: D000818:Animals; D001143:Arousal / Q000502:physiology; D001288:Attention / Q000502:physiology; D001303:Auditory Cortex / Q000502:physiology*; D001306:Auditory Pathways / Q000502:physiology; D001309:Auditory Threshold / Q000502:physiology; D001931:Brain Mapping; D002415:Cats; D004292:Dominance, Cerebral / Q000502:physiology; D005072:Evoked Potentials, Auditory / Q000502:physiology; D008144:Loudness Perception / Q000502:physiology*; D009474:Neurons / Q000502:physiology; D010898:Pitch Perception / Q000502:physiology; D013017:Sound Localization / Q000502:physiology*; D009435:Synaptic Transmission / Q000502:physiology*; D000159:Vestibulocochlear Nerve / Q000502:physiology