A novel TMS framework for assessing neurophysiological recovery at the subacute stage after stroke

OBJECTIVE: To use peri-threshold transcranial magnetic stimulation (TMS) intensities to elicit motor evoked potentials (MEPs) during the subacute stage after stroke and assess their association with upper limb motor recovery. METHODS: Twenty-five MEP+ patients participated in three sessions at 1, 3, and 6 months post-stroke. Single-pulse TMS across a range of stimulation intensities was used to elicit MEPs in four muscles of the paretic and non-paretic upper limb. At each timepoint, threshold matrices were constructed based on MEP amplitude and persistence. A matrix element was suprathreshold if five out of ten stimulations elicited MEPs ≥ 50 μV. A subthreshold element produced MEPs below this criterion. Dexterity was assessed using the nine hole peg test. RESULTS: There were fewer suprathreshold, and more subthreshold elements on the paretic compared to the non-paretic side. The number of suprathreshold elements on the paretic side increased between 1 and 6 months post-stroke. Neither sub- nor supra-threshold elements were associated with dexterity recovery. CONCLUSION: The proportion of sub- and supra-threshold elements reflect neurophysiological recovery during the subacute stage after stroke. A threshold matrix framework can identify patients with stable versus dynamic neurophysiology post-stroke. SIGNIFICANCE: A compositional analysis framework can quantify neurophysiological recovery after stroke.