Comparing Tactile Pattern and Vibrotactile Frequency Discrimination: A Human fMRI Study

We investigated to which extent the discrimination of tactile patterns and vibrotactile frequencies share common cortical areas. An adaptation paradigm has been used to identify cortical areas specific for processing particular features of tactile stimuli. Healthy right-handed subjects performed a delayed-match-to-sample (DMTS) task discriminating between pairs of tactile patterns or vibrotactile frequencies in separate functional MRI sessions. The tactile stimuli were presented to the right middle fingertip sequentially with a 5.5 s delay. Regions of interest (ROIs) were defined by cortical areas commonly activated in both tasks and those that showed differential activation between both tasks. Results showed recruitment of many common brain regions along the sensory motor pathway ( such as bilateral somatosensory, premotor areas, and anterior insula) in both tasks. Three cortical areas, the right intraparietal sulcus (IPS), supramarginal gyrus (SMG)/parietal operculum ( PO), and PO, were significantly more activated during the pattern than in the frequency task. Further BOLD time course analysis was performed in the ROIs. Significant BOLD adaptation was found in bilateral IPS, right anterior insula, and SMG/PO in the pattern task, whereas there was no significant BOLD adaptation found in the frequency task. In addition, the right hemisphere was found to be more dominant in the pattern than in the frequency task, which could be attributed to the differences between spatial ( pattern) and temporal ( frequency) processing. From the different spatio-temporal characteristics of BOLD activation in the pattern and frequency tasks, we concluded that different neuronal mechanisms are underlying the tactile spatial and temporal processing.