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Journal ArticleDOI

Relationship between responses to contra- and ipsilateral stimuli in the human second somatosensory cortex SII.

01 Oct 1999-NeuroImage (Neuroimage)-Vol. 10, Iss: 4, pp 408-416

TL;DR: The results suggest that neuronal activations due to contra- and ipsilateral stimuli overlap strongly in the human SII cortex.

AbstractWe studied the interaction between responses to contra- and ipsilateral stimuli in the human second somatosensory cortex SII by recording somatosensory evoked magnetic fields (SEFs) from 8 healthy subjects with a 122-channel whole-scalp SQUID magnetometer. Right (R) and left (L) median nerves were electrically stimulated at the wrists at intensities exceeding the motor threshold. In each stimulus sequence, the four equiprobable pairs (L-L, R-R, L-R, R-L) were presented in a random order once every 2 s, with a 300-ms interstimulus interval within the pair. The responses were modelled with a four-dipole model, with current dipoles located in the SI and SII cortices of both hemispheres. The SII responses peaked around 85-120 ms and responses to the 1st (2nd) stimulus on the pair were on average 2 (12) ms earlier and about 3 (2.5) times stronger for contralateral than ipsilateral stimuli. Independently of the condition, the 2nd response always peaked later than the 1st; the mean delay was 16 ms. The responses to the 2nd stimulus depended only slightly on the type of the 1st: the latency increased more and the amplitude decreased less after different than identical 1st stimuli. These results suggest that neuronal activations due to contra- and ipsilateral stimuli overlap strongly in the human SII cortex.

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Citations
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Journal ArticleDOI
TL;DR: MEG patterns following stimulation of different peripheral nerves indicate activation of an extensive cortical network and the serial versus parallel processing in the cortical somatosensory network is still under debate.
Abstract: Magnetoencephalography (MEG) is a totally non-invasive research method which provides information about cortical dynamics on a millisecond time-scale. Whole-scalp magnetic field patterns following stimulation of different peripheral nerves indicate activation of an extensive cortical network. At the SI cortex, the responses reflect mainly the activity of area 3b, with clearly somatotopical representations of different body parts. The SII cortex is activated bilaterally and it also receives, besides tactile input, nociceptive afference. Somatically evoked MEG signals may also be detected from the posterior parietal cortex, central mesial cortex and the frontal lobe. The serial versus parallel processing in the cortical somatosensory network is still under debate.

331 citations


Journal ArticleDOI
TL;DR: The findings based on optical imaging are in agreement with results in the literature obtained with positron emission tomography and functional magnetic resonance imaging.
Abstract: We have performed a noninvasive bilateral optical imaging study of the hemodynamic evoked response to unilateral finger opposition task, finger tactile, and electrical median nerve stimulation in the human sensorimotor cortex. This optical study shows the hemoglobin-evoked response to voluntary and nonvoluntary stimuli. We performed measurements on 10 healthy volunteers using block paradigms for motor, sensory, and electrical stimulations of the right and left hands separately. We analyzed the spatial/temporal features and the amplitude of the optical signal induced by cerebral activation during these three paradigms. We consistently found an increase (decrease) in the cerebral concentration of oxy-hemoglobin (deoxy-hemoglobin) at the cortical side contralateral to the stimulated side. We observed an optical response to activation that was larger in size and amplitude during voluntary motor task compared to the other two stimulations. The ipsilateral response was consistently smaller than the contralateral response, and even reversed (i.e., a decrease in oxy-hemoglobin, and an increase in deoxy-hemoglobin) in the case of the electrical stimulation. We observed a systemic contribution to the optical signal from the increase in the heart rate increase during stimulation, and we made a first attempt to subtract it from the evoked hemoglobin signal. Our findings based on optical imaging are in agreement with results in the literature obtained with positron emission tomography and functional magnetic resonance imaging.

281 citations


Cites background from "Relationship between responses to c..."

  • ...In fact, MEG and fMRI studies have shown that during median nerve stimulation only the contralateral primary sensorimotor cortex is activated (Simoes & Hari, 1999; Spiegel et al., 1999)....

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Journal ArticleDOI
TL;DR: Somatotopy in SII seems to be less fine-grained than in primary somatosensory cortex (SI), as, in contrast to SI, no separate representations of the two fingers in S II were observed.
Abstract: This fMRI study investigated the human somatosensory system, especially the secondary somatosensory cortex (SII), with respect to its potential somatotopic organization. Eight subjects received electrical stimulation on their right second finger, fifth finger and hallux. Within SII, the typical finding for both fingers was a representation site within the contralateral parietal operculum roughly halfway between the lip of the lateral sulcus and its fundus, whereas the representation site of the hallux was found more medially to this position at the fundus of the lateral sulcus, near the posterior pole of the insula. Somatotopy in SII seems to be less fine-grained than in primary somatosensory cortex (SI), as, in contrast to SI, no separate representations of the two fingers in SII were observed. A similar somatotopic representation pattern between fingers and the hallux was also observed within ipsilateral SII, indicating somatotopy of contra- as well as ipsilateral SII using unilateral stimulation. Further areas exhibiting activation were found in the superior and inferior parietal lobule, in the supplementary and cingulate motor area, and in the insula.

262 citations


Cites methods from "Relationship between responses to c..."

  • ...…stimulation have been reported in several neuroimaging studies in humans using magnetoencephalography (MEG) (Hari et al., 1983, 1984, 1993; Simoes and Hari, 1999), PET (Seitz and Roland, 1992; Burton et al., 1993; Ledberg et al., 1995) or fMRI (Maldjian et al., 1999a; Polonara et al.,…...

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Journal ArticleDOI
TL;DR: It is argued that the decline in tactile discrimination performance when the hands are crossed reflects a failure to represent appropriately near simultaneous bimanual tactile stimuli, and stands in marked contrast to many recent observations of efficient remapping of singly-presented tactile stimuli.
Abstract: Observers made temporal order judgements (TOJs) regarding which of two tactile stimuli presented to either hand (at stimulus onset asynchronies of up to 200 ms) occurred first. When the observers' hands were placed in an uncrossed posture (i.e., each hand in its own hemispace), performance was accurate, with a just noticeable difference (JND; the smallest interval which produces 75% correct performance) of 34 ms. By contrast, when the hands were crossed over the midline, performance declined such that 124 ms was needed for accurate performance. In a second experiment, we presented visual instead of tactile stimuli to evaluate the relative contribution of motor and perceptual confusions to the effect. While performance with crossed hands was significantly worse than with uncrossed hands (JND=36 vs. 31 ms, respectively), this difference was negligible compared to that with tactile stimuli. In a third experiment, experienced observers showed a robust crossed-hands deficit which was not improved by using different fingers on either hand. We argue that the decline in tactile discrimination performance when the hands are crossed reflects a failure to represent appropriately near simultaneous bimanual tactile stimuli, and stands in marked contrast to many recent observations of efficient remapping of singly-presented tactile stimuli.

262 citations


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