Programs for action in superior parietal cortex: a triple-pulse TMS investigation

Area of Science:

• Neuroscience
• Motor Control
• Cognitive Neuroscience

Background:

• The posterior parietal cortex (PPC), particularly the left hemisphere, is implicated in planning and controlling goal-directed reaching movements.
• Existing research lacks consensus on the specific contributions of different PPC subregions to movement programming and online control.

Purpose of the Study:

• To investigate the distinct roles of the inferior parietal lobule (IPL) and superior parietal lobule (SPL) in reach programming.
• To differentiate the functions of SPL and IPL in movement programming versus online movement control.

Main Methods:

• Utilized MRI-guided event-related triple-pulse transcranial magnetic stimulation (tp-TMS) on the left IPL and SPL.
• Applied tp-TMS at different time points: target onset (programming) and movement onset (online control).
• Participants (n=16) performed pointing movements to peripheral targets without visual feedback of hand position.

Main Results:

• Stimulation of the SPL, but not the IPL, significantly increased endpoint errors when applied during the programming phase (target onset).
• No significant increase in errors was observed when tp-TMS was applied during the online control phase (movement onset).

Conclusions:

• The superior parietal lobule (SPL) plays a critical role in the real-time programming of reaching movements.
• These findings delineate specific functional contributions of PPC subregions to distinct phases of motor control.