Dynamics of spectro-temporal tuning in primary auditory cortex of the awake ferret.
We previously characterized the steady-state spectro-temporal tuning properties of cortical cells with respect to broadband sounds by using sounds with sinusoidal spectro-temporal modulation envelope where spectral density and temporal periodicity were constant over several seconds. However, since speech and other natural sounds have spectro-temporal features that change substantially over milliseconds, we study the dynamics of tuning by using stimuli of constant overall intensity, but alternating between a flat spectro-temporal envelope and a modulated envelope with well defined spectral density and temporal periodicity. This allows us to define the tuning of cortical cells to speech-like and other rapid transitions, on the order of milliseconds, as well as the time evolution of this tuning in response to the appearance of new features in a sound. Responses of 92 cells in AI were analyzed based on the temporal evolution of the following measures of tuning after a rapid transition in the stimulus: center of mass and breadth of tuning; separability and direction selectivity; temporal and spectral asymmetry. We find that tuning center of mass increased in 70% of cells for spectral density and in 68% of cells for temporal periodicity, while roughly half of cells (47%) broadened their tuning, with the other half (53%) sharpening tuning. The majority of cells (73%) were initially not direction selective, as measured by an inseparability index, which had an initial low value that then increased to a higher steady state value. Most cells were characterized by temporal symmetry, while spectral symmetry was initially high and then progressed to low steady-state values (61%). We demonstrate that cortical neurons can be characterized by a lag-dependent modulation transfer function. This characterization, when measured through to steady-state, becomes equivalent to the classical spectro-temporal receptive field.
Shechter
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B
Department of Anatomy and Neurobiology, School of Medicine, University of Maryland, Baltimore, MD 21201, USA. barak.shechter@gmail.com
Dobbins
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HD
Marvit
P
P
Depireux
D A
DA
D000161:Acoustic Stimulation; D000818:Animals; D001303:Auditory Cortex / Q000166:cytology / Q000502:physiology*; D001307:Auditory Perception; D001309:Auditory Threshold; D005289:Ferrets / Q000502:physiology*; D005583:Fourier Analysis; D008959:Models, Neurological; D009474:Neurons / Q000502:physiology*; D012815:Signal Processing, Computer-Assisted; D013018:Sound Spectrography; D013998:Time Perception; D014851:Wakefulness