The broad objective of this project is to elucidate neural mechanisms associated with complex sound processing relevant for the perception of speech, music and auditory scene analysis by examining electrophysiological responses within both monkey and human auditory cortex. There are many similarities between monkeys and humans in their auditory cortex organization and in their ability to perform phonetic and complex sound discriminations, highlighting the utility of primates as a reasonable electrophysiological model. Direct recordings in monkey auditory cortex offer the opportunity to investigate neural bases of complex sound encoding with a detail that is unobtainable by non-invasive studies in the human. Our studies clarify normal mechanisms of speech and other complex sound encoding, and serve as a benchmark for evaluating hypotheses regarding dysfunctional processes associated with abnormal speech and hearing development. Through our unique collaborative work with the University of Iowa, we have identified that neural responses reflecting the processing of phonetic and musical sounds are similar in both human and monkey auditory cortex. Additional collaborative work at Albert Einstein has translated these basic science studies to address issues that may be crucial for developmental language disorders.
Recent speech-related work has focused on the cortical processes involved in the encoding of the voice onset time and place of articulation phonetic parameters. Music-related studies have concentrated on auditory cortical encoding of pitch and timbre, as well as the neural response features associated with consonance and dissonance of musical intervals. Temporal and spectral streaming relevant for auditory scene analysis are also being actively investigated. Cortical responses are described using 4 complementary, concurrently recorded measures of neuronal ensemble activity, (1) multiunit activity (MUA), (2) auditory evoked potentials (AEPs), (3) the derived current source density (CSD), and (4) frequency-specific changes in the EEG, including those in the gamma range (>30 Hz). CSD analysis characterizes the temporal and laminar distributions of current sources and sinks that reflect net synaptic activation and inhibition, whereas phasic MUA patterns determine changes in the net firing rate of neuronal ensembles. Gamma-band activity is envisioned to play a central role in the perceptual binding of sensory attributes crucial for object recognition. These recording procedures yield stable measures of the synchronized neuronal activity required for complex sound encoding. Parallel studies performed through both direct and indirect recordings are using frequency-specific changes in the EEG to identify the informational flow within human auditory cortex.
Fishman, Y.I., Volkov, I.O., Noh, M.D., Garell, P.C., Bakken, H., Arezzo, J.C., Howard, M.A. and Steinschneider, M. Consonance and dissonance of musical chords: Neural correlates in auditory cortex of monkeys and humans. J. Neurophysiol., 86 (2001) 2761-2788.
Steinschneider, M. and Dunn, M. Electrophysiology in developmental neuropsychology. In: Segalowitz, S. and Rapin, I., (Eds.), Handbook of Neuropsychology, 2nd Edition, Volume 8, Part 1, Elsevier Science B.V., Amsterdam, 2002, Chapter 5, pp. 91-146.
Steinschneider, M, Fishman, YI, and Arezzo, JC, Representation of the voice onset time (VOT) speech parameter in population responses within primary auditory cortex of the awake monkey. J. Acoust. Soc. Am., 114 (2003) 307-321.
Fishman, Y.I., Arezzo, J.C. and Steinschneider, M. Auditory stream segregation in monkey auditory cortex: effects of frequency separation, presentation rate, and tone duration. J. Acoust. Soc. Am., 116 (2004) 1656-1670.
Steinschneider, M, Volkov, I.O., Fishman, Y.I., Oya, H., Arezzo, J.C., and Howard, M.A., III, Intracortical responses in human and monkey primary auditory cortex support a temporal processing mechanism for encoding of the voice onset time (VOT) phonetic parameter. Cerebral Cortex, 15 (2005) 170-186.
Sussman, E. and Steinschneider, M., Neurophysiological evidence for context-dependent encoding of sensory input in human auditory cortex. Brain Research, 1075 (2006) 165-174.
Fishman, Y.I. and Steinschneider, M., Spectral resolution of monkey primary auditory cortex (A1) revealed with two-noise masking. J. Neurophysiology, in press.
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