Submitted on June 13, 2006
Accepted on October 19, 2006
BOLD adaptation in vibrotactile stimulation: Neuronal networks involved in frequency discrimination
Yiwen Li Hegner1*, Ralf Saur2, Ralf Veit3, Raymond Butts4, Susanne Leiberg5, Wolfgang Grodd2, and Christoph Braun6
1 Institute of Medical Psychology and Behavioral Neurobiology, University of Tuebingen, Tuebingen, Germany; MEG-Center, University of Tuebingen, Tuebingen, Germany; Graduate School of Neural & Behavioural Sciences, International Max Planck Research School, University of Tuebingen, United States
2 Neuroradiology, University Clinics Tuebingen, T®bingen, Germany
3 Institute of Medical Psychology and Behavioural Neurobiology, University of Tuebingen, T®bingen, Germany
4 Graduate School of Neural & Behavioural Sciences, International Max Planck Research School, University of Tuebingen, United States
5 Department of Psychiatry and Psychotherapy, University Hospital Aachen, Aachen, Germany
6 Institute of Medical Psychology and Behavioral Neurobiology, University of Tuebingen, Tuebingen, Germany; MEG-Center, University of Tuebingen, Tuebingen, Germany
* To whom correspondence should be addressed. E-mail: yiwen.li{at}med.uni-tuebingen.de.
The present functional magnetic resonance imaging (fMRI) study investigated human brain regions subserving the discrimination of vibrotactile frequency. An event-related adaptation paradigm (Grill-Spector et al. 1999) was used in which blood-oxygen-level-dependent (BOLD) responses are lower to same compared to different pairs of stimuli (BOLD adaptation). This adaptation effect serves as an indicator for feature-specific responding of neuronal subpopulations. Subjects had to discriminate two vibrotactile stimuli sequentially applied with a delay of 600 ms to their left middle fingertip. The stimulus frequency was in the flutter range of 18 to 26 Hz. In half of the trials the two stimuli possessed identical frequency (SAME) while in the other half a frequency difference of ± 2 Hz was used (DIFF). As a result, BOLD adaptation was observed in the contralateral primary somatosensory cortex (S1), precentral gyrus, superior temporal gyrus (STG); ipsilateral insula as well as bilateral secondary somatosensory cortex (S2) and supplementary motor area (SMA). When statistically comparing the BOLD time courses between SAME and DIFF trials in these cortical areas, it was found that the vibrotactile BOLD adaptation is initiated in the contralateral S1 and STG simultaneously. These findings suggest that the cortical areas responsive to the frequency difference between two serially presented stimuli sequentially process the frequency of a vibrotactile stimulus, and constitute a putative neuronal network underlying human vibrotactile frequency discrimination.
