TMS investigations into the task-dependent functional interplay between human posterior parietal and motor cortex

Area of Science:

• Neuroscience
• Motor Control
• Cognitive Neuroscience

Background:

• Cortical control of reach and grasp movements is complex.
• Understanding the temporal dynamics of motor cortical circuits is crucial.

Purpose of the Study:

• To review how transcranial magnetic stimulation (TMS) investigates the role of cortical areas in human reach/grasp movements.
• To examine the time course of parallel intracortical circuits and cortico-cortical connections.

Main Methods:

• Utilizing TMS to create 'virtual lesions' in specific cortical areas during tasks.
• Employing a twin-coil TMS design to assess motor cortex excitability.
• Analyzing conditioning stimulus (CS) and test stimulus (TS) interactions to probe pathway excitability.

Main Results:

• Virtual lesions identified contributions of ventral premotor cortex (PMv), dorsal premotor cortex (PMd), and anterior intraparietal sulcus (aIPS) to reaching and grasping.
• Twin-coil TMS demonstrated task- and time-dependent changes in the excitability of connections to the primary motor cortex (M1).
• Functional interplay between PMd, PMv, posterior parietal cortex (PPC), and M1 is not fixed but dynamically modulated.

Conclusions:

• TMS is a valuable tool for dissecting the functional contributions of cortical areas to motor control.
• The excitability of cortico-cortical connections involved in reach and grasp is highly dynamic.
• Motor cortical networks exhibit flexible, task-specific operational timings.