The Modulation of Cortical Excitability by Observation and/or Imagery of Action

Objective: To better delineate the changes in cortical excitability that accompany perceptual to motor transformations when people are asked to observe and/or image two kinds of action. Method: Twenty right handed young adult without neurological deficit were included. Motor evoked potentials (MEPs) from transcranial magnetic stimulation were recorded in the abductor pollicis brevis of the dominant hand in six different conditions: (1) passive observation (PO) of the slow (1 Hz) action (abduction of right thumb); (2) imagery of the slow action; (3) active observation (AO) of the slow action; (4) PO of the fast (4 Hz) action; (5) imagery of the fast action; and (6) active observation of the fast action. MEPs were also recorded at resting state. Results: The mean amplitude of MEPs at rest condition was 0.85 +/- 0.84 mV; PO of the slow action, 1.27 +/- 1.13 mV; imagery of the slow action, 1.76 +/- 1.49 mV; AO of the slow action, 2.46 +/- 2.02 mV; PO of the fast action, 1.90 +/- 1.31 mV; imagery of the fast action, 2.35 +/- 1.32 mV; and AO of the fast action, 3.44 +/- 1.85 mV. And at a constant speed of action, AO produced the largest amplitude of MEPs. A comparison between the slow and fast action revealed the latter produced larger amplitude of MEPs than the former during each task. Conclusion: The observed and/ or imagined action can alter cortical excitability without actual execution of movement. And active observation of the fast action might be more useful for facilitating cortical excitability.