Motion-selective recruitment of MT+ by tactile apparent motion stimuli
Konkle, Bedny, Saxe, & Moore
The human MT+ complex is defined by its relative selectivity for visual motion stimuli. However, several other kinds of stimuli can drive activity in this region, including tactile input. Previous imaging studies have demonstrated that tactile motion stimuli and stationary vibratory stimuli can activate a tactile region of the MT+ complex (tMT+). However, tactile stimuli used in previous experiments often vary in several dimensions other than only the motion percept.
To more carefully examine tactile motion, we created 3 kinds of stimuli from bursts of high-frequency input (200 msec bursts at 100 Hz) applied to the middle and distal pads of the right hand 3rd digit. These stimuli varied only in inter-burst interval (IBI). Stimuli applied at an IBI of 70ms created an illusory percept of smooth motion across the skin, while simultaneously applied stimuli and those at a longer IBI (0ms and 400ms respectively) did not induce a motion percept. Data were acquired in a 3-T Seimens magnet while stimuli were applied in 10s blocks with interleaved 10s rest periods. Significant activation of MT+ was observed for apparent motion compared to either simultaneous or oscillating tactile stimuli in 4 of 5 Ss. These results demonstrate that the MT+ complex or subregions within this area are ‘tuned’ for tactile motion.
This study indicates that the response of MT+ to tactile stimuli is similar to that observed for visual stimuli: In human fMRI and monkey electrophysiolgical studies, visual flicker can drive MT+, but a stronger response is observed for moving stimuli, and contrasting moving with flickering stimuli is often used as a selective contrast for identifying human MT+. Similarly, our findings indicate greater relative drive for moving versus stationary vibrating tactile inputs, and that these stimuli in combination may be employed to localize tMT+.
Konkle, T., Bedny, M., Saxe, R. R., & Moore, C. I. Motion-selective recruitment of MT+ by tactile apparent motion stimuli. Program No. 852.11. 2008 Neuroscience Meeting Planner. Washington, DC: Society for Neuroscience, 2008. Online.