Motor system contributions to verbal and non-verbal working memory

Area of Science:

• Cognitive Neuroscience
• Neuroscience
• Psychology

Background:

• Working memory (WM) involves maintaining and manipulating information.
• Neuroimaging suggests secondary motor areas are active during verbal WM, potentially for inner speech.
• The causal role of the motor system in WM remains unclear.

Purpose of the Study:

• To investigate the causal relationship between motor system activity and WM processing.
• To determine if disrupting motor activity specifically impacts verbalizable vs. non-verbalizable information in WM.
• To explore the mechanisms underlying motor system involvement in WM.

Main Methods:

• Used transcranial magnetic stimulation (TMS) to disrupt motor cortex activity.
• Tested WM performance for verbalizable (words, pseudowords) and non-verbalizable (Chinese characters) stimuli.
• Compared TMS effects to sham stimulation and TMS over visual cortex (VC).

Main Results:

• TMS over motor cortex slowed response times (RTs) for verbal WM, particularly with high phonological load (pseudowords).
• Non-verbal WM trials were also significantly slowed by motor cortex TMS.
• WM performance was unaffected by sham TMS or VC TMS.
• Self-reported motor strategy use correlated with the degree of disruption.

Conclusions:

• The motor system contributes to both verbal and non-verbal WM processing.
• Motor system involvement in WM may involve creating motor traces for rehearsed information.
• These findings provide causal evidence for the motor system's role in WM maintenance and manipulation.