Aging-related changes in motor response-related theta activity.

It has been suggested that a distributed oscillatory system in the brain operating in the theta (3.5-7 Hz) frequency range plays a major role in coordinating motor actions. The major objective of the present study was to explore the effects of human aging on the neurodynamics of motor-related EEG theta activity during correct motor response generation. Response-related potentials of young and older adults elicited in auditory and visual four-choice sensorimotor tasks were analyzed in the time-frequency domain. The phase-locking factor and total power were computed at motor cortical regions contra- and ipsilateral to the movement and at the midline to reflect phase synchronization and power of motor theta oscillations. Major results demonstrated that in both young and older adults, a pronounced response-locked theta activity (3.5-7 Hz) was generated at premotor, motor and sensorimotor cortical regions contra-lateral to the responding hand. Aging was associated with a decreased lateral asymmetry in the phase synchronization of only the left-hand responses. Also, there was a strong aging-related suppression of theta power at the medial fronto-central region that was specifically enhanced and correlated with response speed only in young adults. These results confirm the involvement of theta oscillations in movement generation in relation to action coordination in humans. Also, they show that aging is associated with a dysfunction of the oscillatory theta system for motor action regulation due to a strong suppression of a medial frontal integrating mechanism and an impaired balance in the functional control of responses with the right and the left hand.