Cerebral Cortex Advance Access originally published online on October 12, 2005
Cerebral Cortex 2006 16(8):1142-1156; doi:10.1093/cercor/bhj056
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Central Signals Rapidly Switch Tactile Processing in Rat Barrel Cortex during Whisker Movements
1 Department of Cognitive Neurology, Hertie-Institute for Clinical Brain Research, University of Tübingen, Germany and 2 Section of Experimental Anaesthesiology, Department of Anaesthesiology, University of Tübingen, Germany
Address correspondence to Cornelius Schwarz, Abteilung für Kognitive Neurologie, Hertie-Institut für Klinische Hirnforschung, Eberhard Karls Universität Tübingen, Otfried Müller Str. 27, 72076 Tübingen, Germany. Email: cornelius.schwarz{at}uni-tuebingen.de.
Palpatory movements (‘active’ touch) are an integral part of tactile sensing. It is known that tactile signals can be modulated in certain behavioral contexts, but it is still unresolved to what degree this modulation is related to movement kinematics and whether it stems from tactile receptors or from central sources. Using awake, head-fixed rats, trained to contact an object, we measured trajectories of muscle-propelled whisker movement precisely and compared tactile responses to contacts thus accomplished with ‘passive’ contacts (motionless whisker contacted by object). Multielectrode extracellular recordings in deep layers of barrel cortex revealed that when the animals moved their whiskers actively, tactile processing switched from high response amplitudes, wide cortical representation and low background firing, to low response amplitudes, narrow spatial representation and elevated background firing. Switching was fast (<100 ms) and unrelated to the degree of alertness as assessed by spectral analysis of pre-contact field potentials. Switching persisted when information about whisker kinematics was interrupted by transection of the infraorbital nerve and contacts were mimicked by peripheral electrical stimulation. Taken together, these characteristics render central signals derived from the motor system a likely contributor to the processing of active touch.
Key Words: active sensing • neural coding • primary somatosensory cortex • sensorimotor integration • vibrissae • whisking
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