Noninvasive Brain Stimulation to Evaluate Neural Plasticity After Stroke

Long-term potentiation-like plasticity was measured using paired associative stimulation (PAS). PAS consists of repeated peripheral electric stimulation paired with Transcranial Magnetic Stimulation (TMS) applied to the motor cortex at varying interstimulus intervals. Participants received 180 paired stimuli at 0.25 hertz (Hz) for 12 minutes. Impaired long-term potentiation-like plasticity points towards reduced excitatory synaptic connectivity and deficits in sensorimotor integration. Decrease or no change in the amplitudes of motor-evoked potentials (MEPs) indicates impaired long-term potentiation-like plasticity.

Electroencephalography (EEG) data were recorded using a 64-channel TMS-compatible electrode cap (Easy Cap). Signals were collected at 2000 hertz (Hz) during pre- and post-transcranial magnetic stimulation epochs (-100ms to 200ms). Up to fifty suprathreshold (120% AMT) transcranial magnetic stimulation pulses were applied to motor cortex while the subject was seated quietly with eyes open. This procedure was conducted bilaterally. Data epochs (-1000 to 4000 ms with respect to TMS delivery) were extracted for subsequent imaginary phase coherence analysis. Post-TMS coherence values between electrodes overlying M1 bilaterally (C3 and C4) were calculated within the beta frequency range (15 to 30 Hz). EEG data values are unit-free that can range from 0 to 1. Higher values represent greater coherence which is thought to indicate stronger connectivity.

Three items of the Wolf Motor Function Test (WMFT) were used to evaluate functional motor performance. The 3 items were selected based on task difficulty ranging from easiest (hand to table) to most difficult (stack checkers) along with a task of moderate difficulty (lift can). Each task has different control demands and number of actions required to complete successfully. Task performance is timed in seconds, with a maximum time of 120 seconds.

The arm function in subjects in the subcortical stroke group was evaluated by the Wolf Motor Function Test (WMFT). The test consists of timed and functional tasks and has 17 items. It is composed of 3 parts: Time, functional ability and strength and includes 15 function-based tasks and 2 strength based tasks. Items 1-6 involve timed functional tasks, items 7-14 are measures of strength, and the remaining 9 items consist of analyzing movement quality when completing various tasks. The examiner will test the less affected upper extremity followed by the most affected side. Scores are based on time taken to complete each task. The median time to complete all tasks will be be used to evaluate motor function. Larger values indicate greater upper extremity motor dysfunction.

Three items of the WMFT were used to evaluate functional motor performance. The 3 items were selected based on task difficulty ranging from easiest (hand to table) to most difficult (stack checkers) along with a task of moderate difficulty (lift can). Each task has different control demands and number of actions required to complete successfully. Task performance will be timed, with a maximum time of 120 seconds.

Long-term potentiation-like plasticity was measured using paired associative stimulation (PAS). PAS consists of repeated peripheral electric stimulation paired with Transcranial Magnetic Stimulation (TMS) applied to the motor cortex at varying interstimulus intervals. Participants receive 180 paired stimuli at 0.25 Hz for 12 minutes. Impaired long-term potentiation-like plasticity points towards reduced excitatory synaptic connectivity and deficits in sensorimotor integration. Decrease or no change in the amplitudes of motor-evoked potentials (MEPs) indicates impaired long-term potentiation-like plasticity.

Electroencephalography (EEG) data were recorded using a 64-channel TMS-compatible electrode cap (Easy Cap). Signals were collected at 2000 hertz (Hz) during pre- and post-transcranial magnetic stimulation epochs (-100ms to 200ms). Up to fifty suprathreshold (120% AMT) transcranial magnetic stimulation pulses were applied to motor cortex while the subject was seated quietly with eyes open. This procedure was conducted bilaterally. Data epochs (-1000 to 4000 ms with respect to TMS delivery) were extracted for subsequent imaginary phase coherence analysis. Post-TMS coherence values between electrodes overlying M1 bilaterally (C3 and C4) were calculated within the beta frequency range (15 to 30 Hz). EEG data values are unit-free that can range from 0 to 1. Higher values represent greater coherence which is thought to indicate stronger connectivity.

The SRTT involves pressing a key that corresponds to a target square positioned on a screen in front of the participant as quickly and accurately as possible. The response time for repeated and random sequences evaluate SRTT performance and skill is measured as the difference in response times between repeated and random sequences. Lower response times indicate better performance and a larger positive difference in response times represents greater sequence-specific skill. Negative values represent better performance on random sequences compared to repeated sequences.