The posterior parietal cortex mediates early offline-rather than online-motor sequence learning

Area of Science:

• Neuroscience
• Motor Learning
• Cognitive Science

Background:

• Motor skill acquisition occurs both during training (online) and after (offline).
• The posterior parietal cortex (PPC) is a potential sensory-motor interface, but its role in motor learning is not fully understood.
• While the primary motor cortex is known to be involved in online and early offline learning, the PPC's contribution remains less clear.

Purpose of the Study:

• To investigate the causal role of the left posterior parietal cortex (PPC) in motor sequence learning.
• To determine if transcranial direct current stimulation (tDCS) applied at different time points affects online and offline motor learning.

Main Methods:

• Fifty-four healthy volunteers performed a serial reaction time task (SRTT).
• Transcranial direct current stimulation (tDCS) was applied over the left PPC immediately before, during, or after SRTT training.
• Reaction times were measured during training (online learning) and 30 minutes post-training (offline learning).

Main Results:

• No significant modulation of reaction times was observed during SRTT training (online learning).
• Cathodal tDCS applied over the left PPC significantly decelerated reaction times for learned sequences 30 minutes after training (offline learning).
• Anodal and sham tDCS did not produce significant effects on offline learning.

Conclusions:

• The left posterior parietal cortex (PPC) appears to be involved in the offline consolidation or reproduction of motor sequences.
• Cathodal tDCS over the left PPC may interfere with the processes underlying offline motor learning.
• These findings highlight the PPC's functional significance in motor learning beyond immediate task performance.