Motor imagery (MI) can improve motor performance, but standardized objective measures of MI quality remain lacking. The authors aimed to determine whether changes in corticospinal excitability, quantified by motor evoked potentials (MEPs) elicited with transcranial magnetic stimulation, might serve as an objective index of MI quality. The investigation used an explicit serial reaction time task (SRTT) to evaluate whether MEP changes during MI correlate with performance improvements following MI practice.
Experiment 1 was designed to validate the SRTT and confirm an appropriate practice volume. Ten participants (n = 10) performed physical practice under two conditions: a sequential condition and a random condition. Reaction time (RT) during physical execution was measured to assess sequence-specific learning. The goal of this experiment was to confirm that the SRTT and the chosen number of practice trials produced measurable RT improvements for sequential learning compared with a random control.
Experiment 2 recruited 18 participants (n = 18) and used only the sequence condition of the SRTT. The primary behavioral outcome was RT during physical execution measured before and after MI practice. Neurophysiological assessment focused on MEP amplitudes recorded from the first dorsal interosseous muscle during task-related MI, obtained both before and after MI practice. MEPs at rest were also recorded to compare baseline excitability with MI-related facilitation.
In Experiment 1, RT decreased only in the sequential condition (padj < 0.001), validating that the task and practice volume produced sequence-specific improvements. In Experiment 2, RT improved significantly following MI practice (padj < 0.001), indicating that motor imagery of the explicit sequence yielded measurable behavioral learning.
Neurophysiologically, MEP amplitudes measured during MI were significantly larger than at rest both before and after the MI practice (padj < 0.001), demonstrating consistent facilitation of corticospinal excitability during MI relative to rest. However, comparisons of MEP amplitudes obtained during MI before versus after practice did not reach significance (padj = 0.054). Thus, while MI elicited elevated MEPs versus rest, the MI training employed did not produce a statistically significant change in MEP amplitude across the pre- to post-practice interval.
The authors examined whether individual differences in behavioral improvement (RT change) were associated with MEP-related variables. No significant correlations were found between changes in RT and any MEP-related measures (correlation coefficients r < 0.411, p > 0.163). These results indicate that, within this dataset and task context, modulation of corticospinal excitability during MI did not predict the magnitude of explicit sequence learning assessed by RT.
The combined findings show a dissociation between behavioral gains from motor imagery and changes in corticospinal excitability as indexed by MEP amplitude in an explicit SRTT. MI produced behavioral learning and consistently higher MEPs during imagery compared with rest, but MEPs did not change significantly with MI practice and did not correlate with RT improvements. From the data reported in the abstract, MEP amplitude during MI does not appear to be a reliable objective index of MI quality for explicit SRTT sequence learning.
These findings are relevant for researchers and clinicians seeking objective physiological markers to monitor or dose MI interventions. The lack of a predictive relationship between MEP modulation and behavioral gains suggests caution in using single-muscle MEP amplitude as a standalone quality metric for MI-driven explicit sequence learning.
The summary above is based on the published abstract. Reported sample sizes were n = 10 for Experiment 1 and n = 18 for Experiment 2. Statistical outcomes reported in the abstract include padj values for behavioral and neurophysiological comparisons and correlation statistics (r and p thresholds). The abstract reports no conflicts of interest.
Details beyond the abstract—such as full methodological parameters for TMS (stimulation intensity, coil orientation), exact MI instructions, timing and number of MEP trials, demographic breakdown beyond adult participants, or effect size estimates—were not reported in the source text provided here. According to the authors' abstract-level conclusions, MEPs are unlikely to be a useful index of motor imagery quality in the context of an explicit SRTT.
Overall, the study supports the behavioral efficacy of MI for sequence learning but questions the utility of MEP amplitude changes as an objective quality measure for MI in this task context.