Representation of facial muscles in human motor cortex
Bibliographic record
Abstract
Whether there is a projection from the primary motor cortex (M1) to upper facial muscles and how the facial M1 area is modulated by intracortical inhibitory and facilitatory circuits remains controversial. To assess these issues, we applied transcranial magnetic stimulation (TMS) to the M1 and recorded from resting and active contralateral (C-OOc) and ipsilateral orbicularis oculi (I-OOc), and contralateral (C-Tr) and ipsilateral triangularis (I-Tr) muscles in 12 volunteers. In five subjects, the effects of stimulating at different scalp positions were assessed. Paired TMS at interstimulus intervals (ISIs) of 2 ms were used to elicit short interval intracortical inhibition (SICI) and ISI of 10 ms for intracortical facilitation (ICF). Long interval intracortical inhibition (LICI) was evaluated at ISIs between 50 and 200 ms, both at rest and during muscle activation. The silent period (SP) was also determined. C-OOc and I-OOc responses were recorded in all subjects. The optimal position for eliciting C-OOc responses was lateral to the hand representation in all subjects and MEP amplitude markedly diminished when the coil was placed 2 cm away from the optimal position. For the I-OOc, responses were present in more scalp sites and the latency decreased with more anterior placement of the coil. C-Tr response was recorded in 10 out of 12 subjects and the I-Tr muscle showed either no response or low amplitude response, probably due to volume conduction. SICI and ICF were present in the C-OOc and C-Tr, but not in the I-OOc muscle. Muscle activation attenuated SICI and ICF. LICI at rest showed facilitation at 50 ms ISI in all muscles, but there was no significant inhibition at other ISIs. There was no significant inhibition or facilitation with the LICI protocol during muscle contraction. The SP was present in the C-OOc, C-Tr and I-OOc muscles and the mean durations ranged from 92 to 104 ms. These findings suggest that the I-OOc muscle response is probably related to the first component (R1) of the blink reflex. There is M1 projection to the contralateral upper and lower facial muscles in humans and the facial M1 area is susceptible to cortical inhibition and facilitation, similar to limb muscles.
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How this classification was reachedexpand
Full frame distilled prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. Learned from the 10,348 direct Codex labels and 10,348 direct Gemma labels. Candidate is the union of thresholded teacher heads; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels or direct frontier model labels.
Codex and Gemma teacher scores by category
| 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) | 0.000 | 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 teacher head, 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".