Cerebral Cortex Advance Access originally published online on March 24, 2006
Cerebral Cortex 2007 17(2):492-499; doi:10.1093/cercor/bhj165
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Hemispheric Asymmetry for Auditory Processing in the Human Auditory Brain Stem, Thalamus, and Cortex
1 Faculty of Biosciences, Pharmacy and Psychology, University of Leipzig, Leipzig, Germany, 2 Department of Cognitive Neurology, Max-Planck-Institute for Human Cognitive and Brain Sciences, Leipzig, Germany, 3 Department of Cognitive Neurology, Institute of Medicine, Research Centre Jülich, Jülich, Germany, 4 Nottingham University Section, Medical Research Council Institute of Hearing Research, Nottingham, UK, 5 Department of NeurologyCognitive Neurology, University Hospital, Rheinisch-Westphälische Technische Hochschule Aachen, Aachen, Germany
Address correspondence to Marc Schönwiesner, Montreal Neurological Institute, McGill University, 3801 rue University, H3A 2B4 Montreal, Quebec, Canada. Email: marc.schoenwiesner{at}mcgill.ca.
We report evidence for a context- and not stimulus-dependent functional asymmetry in the left and right human auditory midbrain, thalamus, and cortex in response to monaural sounds. Neural activity elicited by left- and right-ear stimulation was measured simultaneously in the cochlear nuclei, inferior colliculi (ICs), medial geniculate bodies (MGBs), and auditory cortices (ACs) in 2 functional magnetic resonance imaging experiments. In experiment 1, pulsed noise was presented monaurally to either ear, or binaurally, simulating a moving sound source. In experiment 2, only monaural sounds were presented. The results show a modulation of the neural responses to monaural sounds by the presence of binaural sounds at a time scale of tens of seconds: In the absence of binaural stimulation, the left and right ICs, MGBs, and ACs responded stronger to stimulation of the contralateral ear. When blocks of binaural stimuli were interspersed in the sound sequence, the contralateral preference vanished in those structures in the right hemisphere. The resulting hemispheric asymmetry was similar to the asymmetry demonstrated for spatial sound processing. Taken together, the data demonstrate that functional asymmetries in auditory processing are modulated by context. The observed long time constant suggests that this effect results from a "topdown" mechanism.
Key Words: auditory spatial processing corticofugal system FMRI hemisphere dominance lateralization subcortical auditory system
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