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The Journal of Neuroscience, October 3, 2007, 27(40):10751-10764; doi:10.1523/JNEUROSCI.0482-07.2007

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Behavioral/Systems/Cognitive
Neural Correlates of Tactile Detection: A Combined Magnetoencephalography and Biophysically Based Computational Modeling Study

Stephanie R. Jones,¹ Dominique L. Pritchett,² Steven M. Stufflebeam,¹ Matti Hämäläinen,¹ and Christopher I. Moore^1,2

¹Athinoula A. Martinos Center for Biomedical Imaging, Massachusetts General Hospital, Charlestown, Massachusetts 02129, and ²McGovern Institute for Brain Research, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139

Correspondence should be addressed to Stephanie R. Jones, Massachusetts General Hospital, Athinoula A. Martinos Center for Biomedical Imaging, 149 13th Street, Suite 2301, Charlestown, MA 02129. Email: srjones{at}nmr.mgh.harvard.edu

Previous reports conflict as to the role of primary somatosensory neocortex (SI) in tactile detection. We addressed this question in normal human subjects using whole-head magnetoencephalography (MEG) recording. We found that the evoked signal (0–175 ms) showed a prominent equivalent current dipole that localized to the anterior bank of the postcentral gyrus, area 3b of SI. The magnitude and timing of peaks in the SI waveform were stimulus amplitude dependent and predicted perception beginning at 70 ms after stimulus. To make a direct and principled connection between the SI waveform and underlying neural dynamics, we developed a biophysically realistic computational SI model that contained excitatory and inhibitory neurons in supragranular and infragranular layers. The SI evoked response was successfully reproduced from the intracellular currents in pyramidal neurons driven by a sequence of lamina-specific excitatory input, consisting of output from the granular layer (25 ms), exogenous input to the supragranular layers (70 ms), and a second wave of granular output (135 ms). The model also predicted that SI correlates of perception reflect stronger and shorter-latency supragranular and late granular drive during perceived trials. These findings strongly support the view that signatures of tactile detection are present in human SI and are mediated by local neural dynamics induced by lamina-specific synaptic drive. Furthermore, our model provides a biophysically realistic solution to the MEG signal and can predict the electrophysiological correlates of human perception.

Key words: computational model; magnetoencephalography; dendritic processes; conscious perception; network dynamics; somatosensory cortex

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Received Feb. 2, 2007; revised Aug. 16, 2007; accepted Aug. 19, 2007.

Correspondence should be addressed to Stephanie R. Jones, Massachusetts General Hospital, Athinoula A. Martinos Center for Biomedical Imaging, 149 13th Street, Suite 2301, Charlestown, MA 02129. Email: srjones{at}nmr.mgh.harvard.edu

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