Regional and age-dependent Effects of Cortical Magnetic Stimulation on Unconstrained Reaching Behavior
Bibliographic record
Abstract
Abstract Background The specific and dynamic contributions of premotor and supplementary motor areas to reaching movements in aging humans are not well understood. Objective To better understand the role of cortical motor regions and age on the control of unconstrained reaches against gravity by neurologically intact, younger and older adults. Methods Double pulse transcranial magnetic stimulation (TMS) was applied at locations targeting primary motor cortex (M1), dorsal premotor area (PMA), supplementary motor area (SMA), or dorsolateral prefrontal cortex (DLPFC). Paired stimuli were delivered before or after a visual cue was presented to initiate self-paced right-handed reaches to one of three, vertically oriented target locations. Results Regional stimulation effects on movement amplitude were observed both early and late in the reach. PMA stimulation increased reach distance to a greater extent than M1, SMA, and DLPFC stimulation. M1 and PMA stimulation increased deviation from the straight-line path around the time of peak velocity to an extent that was greater than SMA and DLPFC stimulation. Cortical stimulation increased the time that elapsed after, but not before, peak velocity. Despite stronger effects of stimulation on reaches in the younger group, this group had shorter times to reach the target after reaching peak velocity. Conclusion These results provide support for a role of PMA in visually guided movement after movement initiation. For older subjects, the increased time to arrive at the target after peak velocity despite weaker stimulation effects suggests an age-related reduction in sensorimotor processing flexibility for online control of unconstrained reaching. Highlights Dorsal premotor area stimulation at any time during the reaction-time period and early reaching affected early reach kinematics at least as much as stimulation of primary motor cortex. Older individuals had more stimulation-related interference in the late components of reaching despite having less early effect of stimulation, suggesting a reduction in flexibility of dynamic motor control due to aging. The antigravity component of unconstrained reaching did not have special aspects for regional cortical effects of stimulation.
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How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.002 | 0.000 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one source (direct Gemma or distilled Codex), not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".