Monday, April 14, 2008

TB Journal Club: New paper in J. Neurosci on auditory cortex asymmetries

Well, here is a must-read for the TB Journal Club:

Right-Hemisphere Auditory Cortex Is Dominant for Coding Syllable Patterns in Speech

The paper by Daniel A. Abrams, Trent Nicol, Steven Zecker, and Nina Kraus appears in the latest issue of J. Neuroscience (2008;28 3958-3965)

Looks like confirmation that auditory cortex in the right hemisphere is tracking speech envelope information (i.e., slow temporal features in the 3-5 Hz range). See abstract below. So in addition to the Mirror Neuron readings for our SimulCourse, let's read this one and "discuss" next week. BTW, is anyone else reading these papers, or am I the only one? :-)

Cortical analysis of speech has long been considered the domain of left-hemisphere auditory areas. A recent hypothesis poses that cortical processing of acoustic signals, including speech, is mediated bilaterally based on the component rates inherent to the speech signal. In support of this hypothesis, previous studies have shown that slow temporal features (3–5 Hz) in nonspeech acoustic signals lateralize to right-hemisphere auditory areas, whereas rapid temporal features (20–50 Hz) lateralize to the left hemisphere. These results were obtained using nonspeech stimuli, and it is not known whether right-hemisphere auditory cortex is dominant for coding the slow temporal features in speech known as the speech envelope. Here we show strong right-hemisphere dominance for coding the speech envelope, which represents syllable patterns and is critical for normal speech perception. Right-hemisphere auditory cortex was 100% more accurate in following contours of the speech envelope and had a 33% larger response magnitude while following the envelope compared with the left hemisphere. Asymmetries were evident regardless of the ear of stimulation despite dominance of contralateral connections in ascending auditory pathways. Results provide evidence that the right hemisphere plays a specific and important role in speech processing and support the hypothesis that acoustic processing of speech involves the decomposition of the signal into constituent temporal features by rate-specialized neurons in right- and left-hemisphere auditory cortex.

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