The Journal of Neuroscience, May 24, 2006, 26(21):5819-5824; doi:10.1523/JNEUROSCI.5536-05.2006
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Behavioral/Systems/Cognitive
Transient Suppression of Ipsilateral Primary Somatosensory Cortex during Tactile Finger Stimulation
Yevhen Hlushchuk1,2 and
Riitta Hari1,2,3
1Brain Research Unit, Low Temperature Laboratory, and 2Advanced Magnetic Imaging Centre, Helsinki University of Technology, 02150 TKK, Espoo, Finland, and 3Neuroscience Center, University of Helsinki, 00014 Helsinki, Finland
Correspondence should be addressed to Dr. Yevhen Hlushchuk, Brain Research Unit, Low Temperature Laboratory, Helsinki University of Technology, P.O. Box 2200, FIN 02015 HUT, Espoo, Finland. Email: yevhen{at}neuro.hut.fi
The whole human primary somatosensory (SI) cortex is activated by contralateral tactile stimuli, whereas its subarea 2 displays neuronal responses also to ipsilateral stimuli. Here we report on a transient deactivation of area 3b of the ipsilateral SI during long-lasting tactile stimulation.
We collected functional magnetic resonance imaging data with a 3 T scanner from 10 healthy adult subjects while tactile pulses were delivered at 1, 4, or 10 Hz in 25 s blocks to three right-hand fingers. In the contralateral SI cortex, activation [positive blood oxygenation level-dependent (BOLD) response] outlasted the stimulus blocks by 20 s, with an average duration of 45 s. In contrast, a transient deactivation (negative BOLD response) occurred in the ipsilateral rolandic cortex with an average duration of 18 s. Additional recordings on 10 subjects confirmed that the deactivation was not limited to the right SI but occurred in the SI cortex ipsilateral to the stimulated hand. Moreover, the primary motor cortex (MI) contained voxels that were phasically deactivated in response to both ipsilateral and contralateral touch.
These data indicate that unilateral touch of fingers is associated, in addition to the well known activation of the contralateral SI cortex, with deactivation of the ipsilateral SI cortex and of the MI cortex of both hemispheres. The ipsilateral SI deactivation could result from transcallosal inhibition, whereas intracortical SIMI connections could be responsible for the MI deactivation. The shorter time course of deactivation than activation would agree with stronger decay of inhibitory than EPSP at the applied stimulus repetition rates.
Key words: fMRI; BOLD; somatosensory cortex; motor cortex; tactile; human
Received Dec. 24, 2005;
revised March 31, 2006;
accepted April 18, 2006.
Correspondence should be addressed to Dr. Yevhen Hlushchuk, Brain Research Unit, Low Temperature Laboratory, Helsinki University of Technology, P.O. Box 2200, FIN 02015 HUT, Espoo, Finland. Email: yevhen{at}neuro.hut.fi
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