Musical beat influences corticospinal drive to ankle flexor and extensor muscles in man

Body movements in man are frequently observed in relation to musical rhythms. In this study we have investigated the effect of strongly rhythmic music on corticospinal drive to the ankle extensor and flexor muscles involved in foot tapping. Surface electromyographic (EMG) recordings were made from tibialis anterior (TA) and lateral gastrocnemius (LGN) muscles in 12 normal subjects. Rock music with a strong rhythmic beat or white noise was played. Transcranial magnetic stimulation (TMS) was delivered to the motor cortex in time with the music to produce motor evoked potentials (MEPs) in both muscles while relaxed. During white noise trials nine subjects showed a significant correlation of MEP areas in TA with LGN, compared with only three subjects during music. Overall, there was a significant decrease in the correlation coefficient during music. We conclude that correlated variations in MEP areas between the muscles seen during white noise can be destroyed in the presence of music. This may be due to sub-threshold variations in corticospinal excitability to ankle extensors and flexors, which are time-locked to the musical beat but out of phase with one another.