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The Journal of Neuroscience, December 27, 2006, 26(52):13567-13575; doi:10.1523/JNEUROSCI.3990-06.2006

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Behavioral/Systems/Cognitive
Receptive Field Properties of the Macaque Second Somatosensory Cortex: Nonlinear Mechanisms Underlying the Representation of Orientation Within a Finger Pad

Pramodsingh H. Thakur,^1,3 Paul J. Fitzgerald,^1,2 John W. Lane,¹ and Steven S. Hsiao^1,2,3

¹Zanvyl Krieger Mind/Brain Institute, ²Departments of Neuroscience, and ³Biomedical Engineering, The Johns Hopkins University, Baltimore, Maryland 21218

Correspondence should be addressed to Dr. Steven Hsiao, Zanvyl Krieger Mind/Brain Institute, Johns Hopkins University, 338 Krieger Hall, 3400 North Charles Street, Baltimore, MD 21218. Email: steven.hsiao{at}jhu.edu

We investigate the position invariant receptive field properties of neurons in the macaque second somatosensory (SII) cortical region. Previously we reported that many SII region neurons show orientation tuning in the center of multiple finger pads of the hand and further that the tuning is similar on different pads, which can be interpreted as position invariance. Here we study the receptive field properties of a single finger pad for a subset (n = 61) of those 928 neurons, using a motorized oriented bar that we positioned at multiple locations across the pad. We calculate both vector fields and linear receptive fields of the finger pad to characterize the receptive field properties that give rise to the tuning, and we perform an additional regression analysis to quantify linearity, invariance, or both in individual neurons. We show that orientation tuning of SII region neurons is based on a variety of mechanisms. For some neurons, the tuning is explained by simple excitatory regions, simple inhibitory regions, or some combination of these structures. However, a large fraction of the neurons (n = 20 of 61, 33%) show position invariance that is not explained well by their linear receptive fields. Finding invariance within a finger pad, coupled with the previous result of similar tuning on different pads, indicates that some SII region neurons may exhibit similar tuning throughout large regions of the hand. We hypothesize that invariant neurons play an important role in tactile form recognition.

Key words: somatosensory cortex; tactile; SII; orientation; receptive field; vector field

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Received Sept. 13, 2006; revised Oct. 31, 2006; accepted Nov. 21, 2006.

Correspondence should be addressed to Dr. Steven Hsiao, Zanvyl Krieger Mind/Brain Institute, Johns Hopkins University, 338 Krieger Hall, 3400 North Charles Street, Baltimore, MD 21218. Email: steven.hsiao{at}jhu.edu

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				P. H. Thakur, A. J. Bastian, and S. S. Hsiao Multidigit Movement Synergies of the Human Hand in an Unconstrained Haptic Exploration Task J. Neurosci., February 6, 2008; 28(6): 1271 - 1281. [Abstract] [Full Text] [PDF]

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