Figure 3.

Left column: Diagram illustrating the proposed hypothesis by Murase et al: enhanced interhemispheric inhibition (IHI) from the intact hemisphere to the M1 in the lesioned hemisphere in patients with subcortical stroke relative to healthy controls. IHI was evaluated in the process of generation of a voluntary movement in a simple reaction time (RT) paradigm. Subjects responded with a brisk voluntary index finger movement to a Go signal. The onset of the electromyogram (EMG) response from first dorsal interosseus (FDI) characterized the RT. IHI in the paretic hand was studied applying a conditioning stimulus to the M1 of the intact hemisphere of patients (right hemisphere of controls) 10 ms preceding a test stimulus applied to M1 of the lesioned hemisphere of patients (or left hemisphere of controls). Right column: IHI targeting the moving hand in a RT paradigm in a healthy volunteer (A) and a stroke patient (B). The abscissa shows the timing (milliseconds) of application of the test stimulus relative to the Go signal. The ordinate shows the magnitude of IHI targeting the moving hand (1 indicates absence of facilitation or inhibition; >1 indicates facilitation; and <1 indicates inhibition). Note the deep maximum IHI (single arrow, <1) that progressively became less prominent in intervals close to movement onset in both subjects. Around movement onset, IHI at movement onset (double arrow) and IHI before movement (open circles) turned to facilitation in the control subject but remained inhibited in the patient. The gray lines in the top right corner indicate mean ±1 SD of RTs in unstimulated trials. Modified, with permission, from Murase N, Duque J, Mazzocchio R, et al. Influence of interhemispheric interactions on motor function in chronic stroke. Ann Neurol. 2004;55:400–409. Copyright © 2004 by Wiley InterScience.