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Symmetric sensorimotor somatotopy.

Overduin SA, Servos P - PLoS ONE (2008)

Bottom Line: Using high-resolution functional magnetic resonance imaging in human subjects, we found a widely distributed cortical response in both primary somatosensory and motor cortex upon pneumatic stimulation of the hairless surface of the thumb, index and ring fingers.In considering functional activation that is not somatotopically or anatomically restricted as in monkey electrophysiology studies, our methodology reveals finger-related activation that is not organized in a simple somatotopic manner but is nevertheless as structured as it is widespread.Our findings suggest a striking functional mirroring in cortical areas conventionally ascribed either an input or an output somatotopic function.

View Article: PubMed Central - PubMed

Affiliation: Department of Brain and Cognitive Sciences and McGovern Institute for Brain Research, Massachusetts Institute of Technology, Cambridge, Massachusetts, USA.

ABSTRACT

Background: Functional imaging has recently been used to investigate detailed somatosensory organization in human cortex. Such studies frequently assume that human cortical areas are only identifiable insofar as they resemble those measured invasively in monkeys. This is true despite the electrophysiological basis of the latter recordings, which are typically extracellular recordings of action potentials from a restricted sample of cells.

Methodology/principal findings: Using high-resolution functional magnetic resonance imaging in human subjects, we found a widely distributed cortical response in both primary somatosensory and motor cortex upon pneumatic stimulation of the hairless surface of the thumb, index and ring fingers. Though not organized in a discrete somatotopic fashion, the population activity in response to thumb and index finger stimulation indicated a disproportionate response to fingertip stimulation, and one that was modulated by stimulation direction. Furthermore, the activation was structured with a line of symmetry through the central sulcus reflecting inputs both to primary somatosensory cortex and, precentrally, to primary motor cortex.

Conclusions/significance: In considering functional activation that is not somatotopically or anatomically restricted as in monkey electrophysiology studies, our methodology reveals finger-related activation that is not organized in a simple somatotopic manner but is nevertheless as structured as it is widespread. Our findings suggest a striking functional mirroring in cortical areas conventionally ascribed either an input or an output somatotopic function.

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Sliding window paradigm.(A) Pneumatic stimulation was delivered to D1, D2, or D4, via a restricted set of jets within a sliding window of stimulation. (B) Voxels correlated to the reference waveform were assigned one of 12 colors, according to the phase delay giving the maximal correlation. Because the number of jet positions was only four (D1) or six (D2/D4), the color values included interpolated phase lags. (C) The colors corresponded to locations on the digit surface, although the mapping from phase delay to location differed depending on stimulation direction.
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pone-0001505-g001: Sliding window paradigm.(A) Pneumatic stimulation was delivered to D1, D2, or D4, via a restricted set of jets within a sliding window of stimulation. (B) Voxels correlated to the reference waveform were assigned one of 12 colors, according to the phase delay giving the maximal correlation. Because the number of jet positions was only four (D1) or six (D2/D4), the color values included interpolated phase lags. (C) The colors corresponded to locations on the digit surface, although the mapping from phase delay to location differed depending on stimulation direction.

Mentions: Our experimental paradigm adapted the phase analysis method used previously to identify retinotopic maps in visual cortex [7]. A reference time course consisting of periods of stimulation interspersed with non-stimulation intervals was created by a “sliding window” [8], [9] of stimulation that cycled repeatedly over the digit surface (Fig. 1). Any location on the digit surface experienced alternating windows of stochastic stimulation and silence. Neighboring locations were stimulated in like fashion, but with a stimulation time course that was staggered in time. This design was not strictly a block design, except with respect to individual locations on the digit surface. Any correlated cortical activity should have been driven by an on/off stimulation time course, but one whose particular phase lag would indicate its sensitivity to a certain location on the digit surface. The relatively slow progression of the stimulation window over the digit, and the random nature of the jet activations within any stimulation window, mitigated any “cutaneous rabbit” illusions of movement [10]. As a within-digit control, we varied the general direction of stimulation, from the base of the finger to the fingertip, or from the tip to the base.


Symmetric sensorimotor somatotopy.

Overduin SA, Servos P - PLoS ONE (2008)

Sliding window paradigm.(A) Pneumatic stimulation was delivered to D1, D2, or D4, via a restricted set of jets within a sliding window of stimulation. (B) Voxels correlated to the reference waveform were assigned one of 12 colors, according to the phase delay giving the maximal correlation. Because the number of jet positions was only four (D1) or six (D2/D4), the color values included interpolated phase lags. (C) The colors corresponded to locations on the digit surface, although the mapping from phase delay to location differed depending on stimulation direction.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC2200828&req=5

pone-0001505-g001: Sliding window paradigm.(A) Pneumatic stimulation was delivered to D1, D2, or D4, via a restricted set of jets within a sliding window of stimulation. (B) Voxels correlated to the reference waveform were assigned one of 12 colors, according to the phase delay giving the maximal correlation. Because the number of jet positions was only four (D1) or six (D2/D4), the color values included interpolated phase lags. (C) The colors corresponded to locations on the digit surface, although the mapping from phase delay to location differed depending on stimulation direction.
Mentions: Our experimental paradigm adapted the phase analysis method used previously to identify retinotopic maps in visual cortex [7]. A reference time course consisting of periods of stimulation interspersed with non-stimulation intervals was created by a “sliding window” [8], [9] of stimulation that cycled repeatedly over the digit surface (Fig. 1). Any location on the digit surface experienced alternating windows of stochastic stimulation and silence. Neighboring locations were stimulated in like fashion, but with a stimulation time course that was staggered in time. This design was not strictly a block design, except with respect to individual locations on the digit surface. Any correlated cortical activity should have been driven by an on/off stimulation time course, but one whose particular phase lag would indicate its sensitivity to a certain location on the digit surface. The relatively slow progression of the stimulation window over the digit, and the random nature of the jet activations within any stimulation window, mitigated any “cutaneous rabbit” illusions of movement [10]. As a within-digit control, we varied the general direction of stimulation, from the base of the finger to the fingertip, or from the tip to the base.

Bottom Line: Using high-resolution functional magnetic resonance imaging in human subjects, we found a widely distributed cortical response in both primary somatosensory and motor cortex upon pneumatic stimulation of the hairless surface of the thumb, index and ring fingers.In considering functional activation that is not somatotopically or anatomically restricted as in monkey electrophysiology studies, our methodology reveals finger-related activation that is not organized in a simple somatotopic manner but is nevertheless as structured as it is widespread.Our findings suggest a striking functional mirroring in cortical areas conventionally ascribed either an input or an output somatotopic function.

View Article: PubMed Central - PubMed

Affiliation: Department of Brain and Cognitive Sciences and McGovern Institute for Brain Research, Massachusetts Institute of Technology, Cambridge, Massachusetts, USA.

ABSTRACT

Background: Functional imaging has recently been used to investigate detailed somatosensory organization in human cortex. Such studies frequently assume that human cortical areas are only identifiable insofar as they resemble those measured invasively in monkeys. This is true despite the electrophysiological basis of the latter recordings, which are typically extracellular recordings of action potentials from a restricted sample of cells.

Methodology/principal findings: Using high-resolution functional magnetic resonance imaging in human subjects, we found a widely distributed cortical response in both primary somatosensory and motor cortex upon pneumatic stimulation of the hairless surface of the thumb, index and ring fingers. Though not organized in a discrete somatotopic fashion, the population activity in response to thumb and index finger stimulation indicated a disproportionate response to fingertip stimulation, and one that was modulated by stimulation direction. Furthermore, the activation was structured with a line of symmetry through the central sulcus reflecting inputs both to primary somatosensory cortex and, precentrally, to primary motor cortex.

Conclusions/significance: In considering functional activation that is not somatotopically or anatomically restricted as in monkey electrophysiology studies, our methodology reveals finger-related activation that is not organized in a simple somatotopic manner but is nevertheless as structured as it is widespread. Our findings suggest a striking functional mirroring in cortical areas conventionally ascribed either an input or an output somatotopic function.

Show MeSH