Transcranial magnetic stimulation (TMS) interventions could feasibly strengthen residual
corticospinal connections and enhance recovery of paretic upper extremity function after
stroke. To maximize the therapeutic effects of such interventions, they must be delivered
during poststroke brain activity patterns during which TMS best activates the residual
corticospinal tract and enhances neural transmission within it (i.e., brain
state-dependent TMS). In this study, the investigators will test the feasibility of
real-time, personalized brain state-dependent TMS in chronic stroke survivors. The
investigators will also quantify the relationship between personalized poststroke brain
state-dependent activation of the residual corticospinal tract and upper extremity motor
impairment; results will inform future clinical trial inclusion criteria.
Participants will visit the laboratory for two days of testing that are separated by at
least one night of sleep. On Day 1, participants will provide their informed consent. The
MacArthur Competence Assessment Tool and the Frenchay Aphasia Screening Test will be used
to evaluate consent capacity and confirm the presence of expressive aphasia as needed.
Afterwards, the investigators will complete eligibility screening and clinical assessment
of upper extremity motor impairment using the Upper Extremity Fugl-Meyer Assessment,
measurements of grip and pinch strength, and a dexterity measurement that requires
participants to place small pegs into round holes. Participants will then be screened for
the presence of residual corticospinal connections from the lesioned hemisphere to an
affected upper extremity muscle at rest. Recording electrodes will be attached to
multiple affected arm muscles in order to record TMS-evoked twitches in these muscles.
During this screening procedure, single-pulse TMS will be applied to each point of a 1 cm
resolution grid covering primary and secondary motor areas of the lesioned hemisphere at
maximum stimulator output. If TMS reliably elicits a muscle twitch in any of the recorded
muscles, that participant will be considered to have residual corticospinal connections
and will be eligible for the full study. If no muscle twitch can be elicited in any of
these muscles, that participant will not be eligible for the full study. Afterwards, all
recording electrodes will be removed and the participant will leave the laboratory.
On Day 2, participants will return to the laboratory. The investigators will place
recording electrodes on the scalp using a swim-type cap. The investigators will also
place recording electrodes on the most distal affected arm muscle in which a twitch was
most reliably observed during Day 1 as well as four additional muscles of the affected
arm. After determining the location at which TMS best elicits muscle twitches, the
investigators will determine the lowest possible intensity at which TMS elicits muscle
twitches at least half of the time. Then, they will deliver 6 blocks of 100 single TMS
pulses while the participant rests quietly with their eyes open; stimulation will be
delivered at an intensity that is 20% greater than the lowest possible intensity at which
TMS elicits muscle twitches at least half of the time. Afterwards, the investigators will
use the muscle and brain activity recordings acquired during these 6 blocks to build a
personalized mathematical model that identifies which patterns of brain activity
correspond to the largest TMS-evoked muscle twitches. The investigators will then use
this model to detect the occurrence of these brain activity patterns in real-time; when
these patterns are detected, single TMS pulses will be delivered. For comparison, the
investigators will also deliver single TMS pulses during random brain activity patterns.
Afterwards, all recording electrodes will be removed, participation will be complete, and
the participant will leave the laboratory.
The investigators will recruit a total of 37 chronic stroke survivors for this study. The
number of participants needed for this study was determined from their preliminary
studies and previous studies that explored the relationship between variability in
corticospinal tract activation (a necessary component of building robust personalized
mathematical models) and corticospinal tract integrity (a correlate of motor impairment
and recovery potential).
