Interhemispheric facilitation of gesturing: A combined theta burst stimulation and diffusion tensor imaging study

Area of Science:

• Neuroscience
• Cognitive Science
• Neurology

Background:

• Gestures have distinct neural underpinnings for posture (finger vs. hand) and domain.
• Theta burst stimulation (TBS) can modulate gesture performance, potentially via interhemispheric disinhibition.

Purpose of the Study:

• To investigate the effects of dual-site continuous TBS over the left inferior frontal gyrus (IFG-L) and right inferior parietal gyrus (IPL-R) on gesture pantomime and imitation.
• To determine if dual cTBS improves hand gesture imitation and if this correlates with callosal connectivity.

Main Methods:

• A randomized sham-controlled study involving 46 healthy subjects.
• Application of continuous TBS (cTBS) at baseline, sham, single IFG-L, dual IFG-L/IPL-R, and single IPL-R sites.
• Assessment of gestures using the Test for Upper Limb Apraxia (TULIA) and Postural Imitation Test (PIT), with callosal connectivity analyzed via diffusion tensor imaging (DTI).

Main Results:

• Dual cTBS significantly improved overall TULIA scores, driven by cTBS over IPL-R enhancing TULIA imitation.
• No significant effect was observed on TULIA pantomime.
• TULIA imitation scores positively correlated with the fractional anisotropy of the splenium, indicating a link with white matter microstructure.

Conclusions:

• Inhibition of the right inferior parietal gyrus (IPL-R) appears to be the primary driver of improved gesturing, potentially via transcallosal facilitation of the left IPL.
• Findings suggest potential relevance for treating apraxic stroke patients.
• Gesture pantomime and postural gestures were not modulated by dual cTBS, indicating broader or more variable neural representations.