Crossmodal influences in somatosensory cortex: Interaction of vision and touch

Abstract

Previous research has shown that information from one sensory modality has the potential to influence activity in a different modality, and these crossmodal interactions can occur early in the cortical sensory processing stream within sensory-specific cortex. In addition, it has been shown that when sensory information is relevant to the performance of a task, there is an upregulation of sensory cortex. This study sought to investigate the effects of simultaneous bimodal (visual and vibrotactile) stimulation on the modulation of primary somatosensory cortex (SI), in the context of a delayed sensory-to-motor task when both stimuli are task-relevant. It was hypothesized that the requirement to combine visual and vibrotactile stimuli would be associated with an increase in SI activity compared to vibrotactile stimuli alone. Functional magnetic resonance imaging (fMRI) was performed on healthy subjects using a 3T scanner. During the scanning session, subjects performed a sensory-guided motor task while receiving visual, vibrotactile, or both types of stimuli. An event-related design was used to examine cortical activity related to the stimulus onset and the motor response. A region of interest (ROI) analysis was performed on right SI and revealed an increase in percent blood oxygenation level dependent signal change in the bimodal (visual + tactile) task compared to the unimodal tasks. Results of the whole-brain analysis revealed a common fronto-parietal network that was active across both the bimodal and unimodal task conditions, suggesting that these regions are sensitive to the attentional and motor-planning aspects of the task rather than the unimodal or bimodal nature of the stimuli.

Figure 1

Timing of experimental task. (A) shows timing for the bimodal visual + tactile condition; (B) depicts the timing for trials in the unimodal task conditions.

Figure 2

Region of interest (ROI) results for right somatosensory cortex (R SI). White bar/line represents the unimodal tactile task, green bar/line represents the bimodal visual + tactile task, and the gray line represents the unimodal visual task. Error bars depict SEM, asterisk indicates a significant difference (P < 0.05).

Figure 3

Group activation maps and event‐related average plots for the stimulus presentation relative to baseline. Panel A depicts areas with greater activity during the 4‐s stimulus “on” time compared to baseline, shown on orange color scale, significant at P < 0.001 with a cluster threshold of 14 voxels. Panel B shows event‐related averaging plots for clusters of interest, illustrating the BOLD response of each task condition; gray lines represent the visual task, white lines show the tactile task, and green lines depict the visual + tactile task. Bars represent SEM, and asterisks indicates a significant difference (P < 0.05).

Figure 4

Group activation maps for the motor response relative to baseline. Orange color scale depicts areas with greateer activity during the motor response compared of baseline, significant at P < 0.001 with a cluster threshold of 14 voxels.

Figure 5

Behavioral results. Bars depict mean percent accuracy of all subjects in each task condition. Error bars represent standard error of the mean.