Limits...
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.

Show MeSH
Phase value distributions were nonuniform and tuned to fingertip stimulation.Distributions of voxels (r≥0.3) are summed across digits (D1 and D2) and subjects, and are shown cumulatively for areas 4, 3a, 3b, and 1 along a linearized axis aligned with the digit surface. In the distributions for both tip-to-base (top; ordinate flipped) and base-to-tip (bottom) stimulation, there was a strong response coincident with stimulation across the fingertip jets. The peak of this response appeared to shift in phase as a function of stimulation direction.
© Copyright Policy
Related In: Results  -  Collection


getmorefigures.php?uid=PMC2200828&req=5

pone-0001505-g002: Phase value distributions were nonuniform and tuned to fingertip stimulation.Distributions of voxels (r≥0.3) are summed across digits (D1 and D2) and subjects, and are shown cumulatively for areas 4, 3a, 3b, and 1 along a linearized axis aligned with the digit surface. In the distributions for both tip-to-base (top; ordinate flipped) and base-to-tip (bottom) stimulation, there was a strong response coincident with stimulation across the fingertip jets. The peak of this response appeared to shift in phase as a function of stimulation direction.

Mentions: The D1/D2 phase value distributions appeared to peak near the delay corresponding to stimulation of the digit tips (Fig. 2). Moreover, while the peaks of the tip-to-base and base-to-tip distributions were both within the phase delay range corresponding to fingertip stimulation, they were also significantly different from each other (p<0.01). Recall that each fingertip was stimulated at two locations (Fig. 1C). When the cyclical stimulation window proceeded in a tip-to-base fashion—i.e. when it contacted the most distal fingertip location before more proximal digit locations—the cortical sensorimotor activation appeared to correlate predominantly with stimulation at the more distal of the two fingertip jets (Fig. 2, top). Conversely, when the stimulation window approached the fingertip in a base-to-tip direction, the greater part of the sensorimotor activation appeared to correlate with stimulation at the base of the fingertip (Fig. 2, bottom). It thus appeared that there was an enhanced population BOLD response limited to the part of the fingertip initially contacted in each cycle of stimulation.


Symmetric sensorimotor somatotopy.

Overduin SA, Servos P - PLoS ONE (2008)

Phase value distributions were nonuniform and tuned to fingertip stimulation.Distributions of voxels (r≥0.3) are summed across digits (D1 and D2) and subjects, and are shown cumulatively for areas 4, 3a, 3b, and 1 along a linearized axis aligned with the digit surface. In the distributions for both tip-to-base (top; ordinate flipped) and base-to-tip (bottom) stimulation, there was a strong response coincident with stimulation across the fingertip jets. The peak of this response appeared to shift in phase as a function of stimulation direction.
© Copyright Policy
Related In: Results  -  Collection

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

pone-0001505-g002: Phase value distributions were nonuniform and tuned to fingertip stimulation.Distributions of voxels (r≥0.3) are summed across digits (D1 and D2) and subjects, and are shown cumulatively for areas 4, 3a, 3b, and 1 along a linearized axis aligned with the digit surface. In the distributions for both tip-to-base (top; ordinate flipped) and base-to-tip (bottom) stimulation, there was a strong response coincident with stimulation across the fingertip jets. The peak of this response appeared to shift in phase as a function of stimulation direction.
Mentions: The D1/D2 phase value distributions appeared to peak near the delay corresponding to stimulation of the digit tips (Fig. 2). Moreover, while the peaks of the tip-to-base and base-to-tip distributions were both within the phase delay range corresponding to fingertip stimulation, they were also significantly different from each other (p<0.01). Recall that each fingertip was stimulated at two locations (Fig. 1C). When the cyclical stimulation window proceeded in a tip-to-base fashion—i.e. when it contacted the most distal fingertip location before more proximal digit locations—the cortical sensorimotor activation appeared to correlate predominantly with stimulation at the more distal of the two fingertip jets (Fig. 2, top). Conversely, when the stimulation window approached the fingertip in a base-to-tip direction, the greater part of the sensorimotor activation appeared to correlate with stimulation at the base of the fingertip (Fig. 2, bottom). It thus appeared that there was an enhanced population BOLD response limited to the part of the fingertip initially contacted in each cycle of stimulation.

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