The multisensory representation of tactile space

How does our brain refer tactile sensations on the skin to our extra-personal space?

"Figure from Ruzzoli & Soto-Faraco, Current Biology, 2014"

When we notice a mosquito on our forearm, we direct our gaze in order to find its exact position and quickly try to swat it or brush it away to prevent its bite.  This apparently simple, instantaneous reaction is the result of a mental process that is much more complex than it may seem. It requires the brain to align the tactile sensation on the skin with spatial information about our surroundings and our body posture, in a process called external mapping of touch. The aim of this line of research is to disentangle how spatial information belonging to different coordinate systems is integrated and mapped in our brain. To do this we have used ERP/EEG, eye-tracking, and rhythmic transcranial magnetic stimulation (TMS) combined with MRI-based neuronavigation. In one of our last TMS studies, we found evidence for the frequency of coding of one of these coordinate systems in the parietal cortex. In particular, we observed facilitation for detecting a touch to the finger tip after 10Hz TMS stimulation at the Posterior Parietal Cortex of the cerebral hemisphere ipsialteral (same side) as the hand. Remarkably, we observed how this facilitation completely reversed to inhibition as a function of the posture of the limbs in external coordinates (when the same hand was now crossed about the body midline). This study managed to reveal a causal link between neural activity of a specific kind (10 Hz oscillation) and the externally-based representation of space in the human parietal cortex.  

 

Representative publications:

Ruzzoli M, Soto-Faraco S.  2014.  Alpha Stimulation of the Human Parietal Cortex Attunes Tactile Perception to External Space. Current Biology. 24(3):pages329-332.

Azañón E, Longo MR, Soto-Faraco S, Haggard P.  2010.  The Posterior Parietal Cortex Remaps Touch into External Space. Current Biology. 20(14):1304–1309.

Azañón E, Soto-Faraco S.  2008.  Changing reference frames during the encoding of tactile events. Current Biology. 18(16):1044–1049.