To establish differences in intracortical facilitation (ICF) and intracortical inhibition (ICI) between survivors of stroke and healthy individuals.
Fourteen chronic stroke survivors and 19 healthy subjects were investigated using single- and paired-pulse transcranial magnetic stimulation. Transcranial magnetic stimulation was applied over the motor cortex in the lesioned (stroke survivors) or left (healthy subjects) hemisphere. Motor evoked potentials were collected from the contralateral first dorsal interosseus. Subjects received 40 pseudo-randomized trials consisting of 10 trials for each: conditioning stimulus, test stimulus, ICF, and ICI. Between the groups, we compared motor evoked potential amplitudes for test stimulus, ICF, and ICI, motor threshold, and ICF/ICI ratio.
Compared with healthy individuals, the stroke group exhibited higher motor threshold and lower ICI; the difference ICF neared significance. The ICF/ICI ratio was significantly lower in the stroke group and close to 1, indicating little difference between ICF and ICI responses. These differences demonstrate that motor cortex excitatory and inhibitory mechanisms are impaired for individuals in the chronic poststroke recovery phase.
Compared with healthy individuals, both global and intracortical transcranial magnetic stimulation measures reveal reduced motor cortex excitability in survivors of stroke. Interventions that normalize motor cortex excitability may promote better neurophysiological conditions for motor recovery to occur.