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Bilateral representation of oral structures in anterior parietal somatosensory fields
Neurolmage U, Number
b,
ZUUl, Part 2 01 2 Parts 10 EbL”
SENSORIMOTOR
Bilateral representation of oral structures in anterior parietal somatosensoryfields E. A. Diibrow*t,
L. Hinkley*,
T. P. L. Roberts*
*UCSF Biomagnetic Imaging Lab j-UCD Center for Neuroscience Oral structures in mammals, especially in primates, are unique in that information from peripheral receptors must be particularly well integrated across the midline. Body part representations in anterior parietal fields (3a, 3b, 1, 2) are generally exclusively contralateral, however, there is evidence that the face representation in area 3b of monkeys contains a bilateral representation of the tongue and teeth (l-3). We used MEG to examine the cortical representations of oral structures in humans to determine if they had a similar organization. Stimuli consisted of pneumatically driven mechanical taps applied to a single location on the right or left sides of the tongue or lips with a balloon diaphragm with a lcm diameter (4D Neuroimaging, San Diego, CA). Stimulus intensity was set to be just detectable in order to avoid inadvertent stimulation of ipsilateral skin receptors. The stimulus intensity range was 24psi, duration was 30 ms, and interstimulus interval was pseudo randomly varied from 3.5 to 4.5s. Neuromagnetic fields were recorded bilaterally from 10 subjects using a twin 37chamtel biomagnetometer system (Magnesm, BTi, San Diego, CA). 250 epochs of 5OOmsduration were acquired with a l.OHz high-pass cutoff and a sampling rate of 1 kHz, and time locked dam were averaged and bandpass filtered (8-4OHz). The position and strength of the estimated current source was computed using a single equivalent current dipole model, and a model-data correlation of 0.97 was required for the definition of a dipole source. As controls, the stimulus was administered to the to the right index finger and the right skin below the nose in 3 subjects. Due to subject fatigue, recordings were not made for all stimulation sites in all subjects. Overall, ipsilateral dipoles were identified in 78% of recordings, specifically 67% for the upper lip, 85% for the lower lip and 87% for the tongue. No ipsilateral current sources were detected in response to control stimuli on the face or finger. Modeled current sources were located in the inferior central sulcus, and there were no significant differences in ipsi- vs. contralateral source location for a particular stimulus in a given hemisphere. There were no significant differences (paired t-test) for contralateral vs. ipsilateraJ latency of activation (range of means=31.7 to 39.5). In some casesboth the M20 and M30 were apparent for both ipsi- and contralateral activation. There were also no significant differences in estimated dipole strength @MS), however the variance was large. Humans clearly have bilateral representations of the lips and tongue in anterior parietal cortex. While both monkeys and humans have bilateral representation of the tongue in anterior somatosensory cortex, humans differ in that they have a bilateral representation of the lips as well. This difference in cortical organization may be related to the precise articulation necessary for language production. References 1. Dreyer, D. A. et al. (1975) J Neurophysiol. 38:714-734. 2. Jain, N. et al. (2001) J Comp Neurol. 429:455-468. 3. Manger, P. R. et al. (1995) J Comp Neurol. 363:597-607.
Sll56
b,
ZUUl, Part 2 01 2 Parts 10 EbL”
SENSORIMOTOR
Bilateral representation of oral structures in anterior parietal somatosensoryfields E. A. Diibrow*t,
L. Hinkley*,
T. P. L. Roberts*
*UCSF Biomagnetic Imaging Lab j-UCD Center for Neuroscience Oral structures in mammals, especially in primates, are unique in that information from peripheral receptors must be particularly well integrated across the midline. Body part representations in anterior parietal fields (3a, 3b, 1, 2) are generally exclusively contralateral, however, there is evidence that the face representation in area 3b of monkeys contains a bilateral representation of the tongue and teeth (l-3). We used MEG to examine the cortical representations of oral structures in humans to determine if they had a similar organization. Stimuli consisted of pneumatically driven mechanical taps applied to a single location on the right or left sides of the tongue or lips with a balloon diaphragm with a lcm diameter (4D Neuroimaging, San Diego, CA). Stimulus intensity was set to be just detectable in order to avoid inadvertent stimulation of ipsilateral skin receptors. The stimulus intensity range was 24psi, duration was 30 ms, and interstimulus interval was pseudo randomly varied from 3.5 to 4.5s. Neuromagnetic fields were recorded bilaterally from 10 subjects using a twin 37chamtel biomagnetometer system (Magnesm, BTi, San Diego, CA). 250 epochs of 5OOmsduration were acquired with a l.OHz high-pass cutoff and a sampling rate of 1 kHz, and time locked dam were averaged and bandpass filtered (8-4OHz). The position and strength of the estimated current source was computed using a single equivalent current dipole model, and a model-data correlation of 0.97 was required for the definition of a dipole source. As controls, the stimulus was administered to the to the right index finger and the right skin below the nose in 3 subjects. Due to subject fatigue, recordings were not made for all stimulation sites in all subjects. Overall, ipsilateral dipoles were identified in 78% of recordings, specifically 67% for the upper lip, 85% for the lower lip and 87% for the tongue. No ipsilateral current sources were detected in response to control stimuli on the face or finger. Modeled current sources were located in the inferior central sulcus, and there were no significant differences in ipsi- vs. contralateral source location for a particular stimulus in a given hemisphere. There were no significant differences (paired t-test) for contralateral vs. ipsilateraJ latency of activation (range of means=31.7 to 39.5). In some casesboth the M20 and M30 were apparent for both ipsi- and contralateral activation. There were also no significant differences in estimated dipole strength @MS), however the variance was large. Humans clearly have bilateral representations of the lips and tongue in anterior parietal cortex. While both monkeys and humans have bilateral representation of the tongue in anterior somatosensory cortex, humans differ in that they have a bilateral representation of the lips as well. This difference in cortical organization may be related to the precise articulation necessary for language production. References 1. Dreyer, D. A. et al. (1975) J Neurophysiol. 38:714-734. 2. Jain, N. et al. (2001) J Comp Neurol. 429:455-468. 3. Manger, P. R. et al. (1995) J Comp Neurol. 363:597-607.
Sll56