Left Prefrontal Cortex Contributes to Motor Imagery: A Pilot Study

Transcranial magnetic stimulat ion (TMS) over the motor cortex during motor imagery results in increased amplitudes of motor evoked potentials (MEPs) in muscles specific to the imagined movement. Functional MRI studies demonstrate that motor imagery involves a widespread neural network including prefrontal and parietal areas. The purpose of this pilot TMS study was to explore whether the left prefrontal cortex (PFC) is an active part of the motor imagery network. MEPs were recorded in 5 healthy subjects in t ibialis anterior (TA) muscles during the imagined right ankle dorsiflexion while the neural processes in the left PFC were disturbed by a single TMS pulse 300ms prior to the leg area stimulat ion with TMS. Motor imagery alone significantly increased MEP amplitudes in the target TA muscle compared to rest(440% on average, p=0.004). The left PFC stimulat ion prior to test stimulus significantly reduced the facilitat ion of MEPs during motor imagery (326%, p=0.031) butleft PFC stimulat ion had no effect when delivered during rest (103%). Th is suggests a functional link between the left PFC and sensorimotor cortex actively involved in motor imagery. Appropriately timed TMS over the left PCF most likely disturbed the kinesthetic working memory required for maintaining motor imagery.