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The Journal of Neuroscience, May 16, 2007, 27(20):5474-5483; doi:10.1523/JNEUROSCI.0764-07.2007

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Behavioral/Systems/Cognitive
Learning-Induced Plasticity in Auditory Spatial Representations Revealed by Electrical Neuroimaging

Lucas Spierer,¹ Eric Tardif,¹ Holger Sperdin,¹ Micah M. Murray,^1,2,3 and Stephanie Clarke¹

¹Neuropsychology and Neurorehabiliation Service and ²Radiology Service, The Functional Electrical Neuroimaging Laboratory, Vaudois University Hospital Center, and ³EEG Core, Center for Biomedical Imaging of Lausanne and Geneva, Lausanne, 1011 Switzerland

Correspondence should be addressed to either of the following: Lucas Spierer or Dr. Stephanie Clarke, Division Autonome de Neuropsychologie, Hôpital Nestlé, 5 Avenue Pierre Decker, Centre Hospitalier Universitaire Vaudois, 1011 Lausanne, Switzerland. Email: Lucas.spierer{at}chuv.ch or Email: stephanie.clarke{at}chuv.ch

Auditory spatial representations are likely encoded at a population level within human auditory cortices. We investigated learning-induced plasticity of spatial discrimination in healthy subjects using auditory-evoked potentials (AEPs) and electrical neuroimaging analyses. Stimuli were 100 ms white-noise bursts lateralized with varying interaural time differences. In three experiments, plasticity was induced with 40 min of discrimination training. During training, accuracy significantly improved from near-chance levels to 75%. Before and after training, AEPs were recorded to stimuli presented passively with a more medial sound lateralization outnumbering a more lateral one (7:1). In experiment 1, the same lateralizations were used for training and AEP sessions. Significant AEP modulations to the different lateralizations were evident only after training, indicative of a learning-induced mismatch negativity (MMN). More precisely, this MMN at 195–250 ms after stimulus onset followed from differences in the AEP topography to each stimulus position, indicative of changes in the underlying brain network. In experiment 2, mirror-symmetric locations were used for training and AEP sessions; no training-related AEP modulations or MMN were observed. In experiment 3, the discrimination of trained plus equidistant untrained separations was tested psychophysically before and 0, 6, 24, and 48 h after training. Learning-induced plasticity lasted <6 h, did not generalize to untrained lateralizations, and was not the simple result of strengthening the representation of the trained lateralizations. Thus, learning-induced plasticity of auditory spatial discrimination relies on spatial comparisons, rather than a spatial anchor or a general comparator. Furthermore, cortical auditory representations of space are dynamic and subject to rapid reorganization.

Key words: electroencephalography (EEG); auditory-evoked potential (AEP); electrical brain imaging; spatial; interaural time difference (ITD); training; plasticity; sound localization; mismatch negativity (MMN)

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Received Nov. 1, 2006; revised March 20, 2007; accepted April 16, 2007.

Correspondence should be addressed to either of the following: Lucas Spierer or Dr. Stephanie Clarke, Division Autonome de Neuropsychologie, Hôpital Nestlé, 5 Avenue Pierre Decker, Centre Hospitalier Universitaire Vaudois, 1011 Lausanne, Switzerland. Email: Lucas.spierer{at}chuv.ch or Email: stephanie.clarke{at}chuv.ch

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