Hebbian-type stimulation during robot-assisted training in patients with stroke.

BACKGROUND: Training-related improvements in motor function are associated with changes in movement representation of the primary motor cortex (M1). In healthy individuals, transcranial magnetic stimulation (TMS) of M1 delivered in a strict temporal relationship (Hebbian-type stimulation) during execution of movements enhances these effects and is superior to random stimulation. OBJECTIVE: The authors tested whether training combined with Hebbian-type M1 stimulation enhances M1 reorganization in patients with stroke. METHODS: Six patients with chronic stroke participated in the study. Patients executed robot-assisted wrist extension movements at 0.2 Hz frequency while subthreshold repetitive TMS was applied over M1 in a strict temporal relationship to the training movements. TMS was applied to either the affected hemisphere (contralateral M1) or the nonaffected hemisphere (ipsilateral M1) at 0.1 Hz. Intervention-related changes in motor maps and intracortical excitability were measured using TMS. RESULTS: Training alone or combined Hebbian-type stimulation of either M1 resulted in differential effects on motor maps and intracortical inhibition. Shifts in motor maps were associated with increases in intracortical excitability. In contrast to previous results for healthy participants, the inhibitory effect of ipsilateral M1 Hebbian-type stimulation was not present, and the facilitatory effect of contralateral M1 stimulation was more subtle. CONCLUSIONS: Hebbian-type stimulation is feasible in patients poststroke and induces map reorganization and associated decreases in GABAergic inhibition. However, because TMS protocols have a different effect on motor reorganization in the injured brain and may depend on location of the lesion, protocols need to be tailored to the patient's pathology.

Distinct cortico-cerebellar activations in rhythmic auditory motor synchronization.

We investigated the role of the cerebellum in differential aspects of temporal control of rhythmic auditory motor synchronization using positron emission tomography (PET). Subjects tapped with their right index finger to metronome tones at a mean frequency of .8 Hz during 5 conditions: (1) an isochronous rhythm condition, (2) random changes in interval durations, and while the duration of rhythmic intervals was continuously time-modulated following a cosine-wave function at (3) 3%, (4) 7%, and (5) 20% of base interval. Anterior lobe cerebellar neuronal populations showed similar motor-associated activity across all conditions regardless of rhythmic time structure in vermal and hemispheric parts ipsilateral to the movements. Neuronal populations in bilateral anterior posterior lobe, especially in the simple lobule, increased their activity stepwise with each increase in tempo modulation from a steady beat. Neuronal populations in other parts of the posterior lobe showed an increase of activity only during the 20% condition, which involved conscious monitoring of rhythmic pattern synchronization, especially on the left side contralateral to the movements. Differential cerebellar activation patterns correspond to those in contralateral primary (primary sensorimotor), ipsilateral secondary (inferior parietal close to the intraparietal sulcus) and bilateral tertiary (dorsolateral prefrontal cortex) sensorimotor areas of the cerebral cortex, suggesting that distinct functional cortico-cerebellar circuits subserve differential aspects of rhythmic synchronization in regard to rhythmic motor control, conscious and subconscious response to temporal structure, and conscious monitoring of rhythmic pattern tracking.