Inhibitory and excitatory motor cortex dysfunction persists in the chronic poststroke recovery phase.

PURPOSE: To establish differences in intracortical facilitation (ICF) and intracortical inhibition (ICI) between survivors of stroke and healthy individuals. METHODS: 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. RESULTS: 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. CONCLUSIONS: 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.

Biomechanical contributions of the trunk and upper extremity in discrete versus cyclic reaching in survivors of stroke.

BACKGROUND: Stroke rehabilitation interventions and assessments incorporate discrete and/or cyclic reaching tasks, yet no biomechanical comparison exists between these 2 movements in survivors of stroke. OBJECTIVE: To characterize the differences between discrete (movements bounded by stationary periods) and cyclic (continuous repetitive movements) reaching in survivors of stroke. METHODS: Seventeen survivors of stroke underwent kinematic motion analysis of discrete and cyclic reaching movements. Outcomes collected for each side included shoulder, elbow, and trunk range of motion (ROM); peak velocity; movement time; and spatial variability at target contact. RESULTS: Participants used significantly less shoulder and elbow ROM and significantly more trunk flexion ROM when reaching with the stroke-affected side compared with the less-affected side (P < .001). Participants used significantly more trunk rotation during cyclic reaching than discrete reaching with the stroke-affected side (P = .01). No post hoc differences were observed between tasks within the stroke-affected side for elbow, shoulder, and trunk flexion ROM. Peak velocity, movement time, and spatial variability were not different between discrete and cyclic reaching in the stroke-affected side. CONCLUSIONS: Survivors of stroke reached with altered kinematics when the stroke-affected side was compared with the less-affected side, yet there were few differences between discrete and cyclic reaching within the stroke-affected side. The greater trunk rotation during cyclic reaching represents a unique segmental strategy when using the stroke-affected side without consequences to end-point kinematics. These findings suggest that clinicians should consider the type of reaching required in therapeutic activities because of the continuous movement demands required with cyclic reaching.

Kinematic motion analysis and muscle activation patterns of continuous reaching in survivors of stroke.

Coordinated reaching requires continuous interaction between the efferent motor output and afferent feedback; this interaction may be significantly compromised following a stroke. The authors sought to characterize how survivors of stroke generate continuous, goal-directed reaching. Sixteen survivors of stroke completed functional testing of the stroke-affected side and a continuous reaching task between 2 targets with both sides. Motion analysis and electromyography data were collected to determine segmental contributions to reach (e.g., amount of compensatory trunk), spatiotemporal parameters (e.g., peak velocities), and muscle activation patterns (MAP). Repeated measures analyses of variance compared how survivors of stroke reach with the stroke-affected versus less affected sides. Correlations were determined between kinematic outcomes and functional ability. Participants used significantly more trunk movement and less shoulder flexion and elbow extension when reaching with the stroke-affected side. This corresponded with less muscle activity in the proximal musculature including the anterior, middle, and posterior deltoid on the stroke-affected side. There were significant correlations between the segmental contributions to reach, functional ability, and MAPs. Survivors of stroke generate reduced MAPs in the stroke-affected side corresponding to altered segmental kinematics and function ability. These findings suggest that impairments in the ability to generate sufficient MAPs may contribute to the difficulty in generating continuous reaching motions.