Hand function and motor cortical output poststroke: are they related?

OBJECTIVES

To characterize hand function and cortical excitability in chronic and subacute stages of stroke recovery and to describe the relations between these measures.

DESIGN

Observational, case-control, and cohort pre-post inpatient rehabilitation.

SETTING

Motor performance laboratory.

PARTICIPANTS

Fourteen community-living chronic and 14 subacute inpatient stroke survivors volunteered. Fourteen similarly aged healthy subjects served as a control group.

INTERVENTIONS

Not applicable.

MAIN OUTCOME MEASURES

Finger tapping, peg placing, and strength were measured as indicators of hand function. The amplitude and latency of motor-evoked potentials (MEPs) and the duration of the silent period in the first dorsal interosseous muscle elicited by transcranial magnetic stimulation (TMS) reflected the integrity of excitatory and inhibitory cortical circuits.

RESULTS

Diminished hand function, small MEPs, and prolonged silent-period durations were evident in stroke compared with control subjects. Longer MEP latencies and smaller amplitudes distinguished subacute from chronic stroke. Side-to-side asymmetries were greatest in the subacute group for all TMS outcomes, although this lessened over time based on the subsample retested at discharge. Greater side-to-side MEP amplitude symmetry and lower motor threshold (lesioned side) were associated with better hand function in subacute and chronic stroke, respectively.

CONCLUSIONS

Cortical excitability is an important determinant of hand function poststroke and evolves with the time elapsed since the stroke event. The unique neural correlates of hand function evident in subacute and chronic stroke may reflect different phases of neuromuscular recovery.