Vestibular and corticospinal control of human body orientation in the gravitational field
Bibliographic record
Abstract
Body orientation with respect to the direction of gravity changes when we lean forward from upright standing. We tested the hypothesis that during upright standing, the nervous system specifies the referent body orientation that defines spatial thresholds for activation of multiple muscles across the body. To intentionally lean the body forward, the system is postulated to transfer balance and stability to the leaned position by monotonically tilting the referent orientation, thus increasing the activation thresholds of ankle extensors and decreasing their activity. Consequently, the unbalanced gravitational torque would start to lean the body forward. With restretching, ankle extensors would be reactivated and generate increasing electromyographic (EMG) activity until the enhanced gravitational torque would be balanced at a new posture. As predicted, vestibular influences on motoneurons of ankle extensors evaluated by galvanic vestibular stimulation were smaller in the leaned compared with the upright position, despite higher tonic EMG activity. Defacilitation of vestibular influences was also observed during forward leaning when the EMG levels in the upright and leaned position were equalized by compensating the gravitational torque with a load. The vestibular system is involved in the active control of body orientation without directly specifying the motor outcome. Corticospinal influences originating from the primary motor cortex evaluated by transcranial magnetic stimulation remained similar at the two body postures. Thus, in contrast to the vestibular system, the corticospinal system maintains a similar descending facilitation of motoneurons of leg muscles at different body orientations. The study advances the understanding of how body orientation is controlled. NEW & NOTEWORTHY The brain changes the referent body orientation with respect to gravity to lean the body forward. Physiologically, this is achieved by shifts in spatial thresholds for activation of ankle muscles, which involves the vestibular system. Results advance the understanding of how the brain controls body orientation in the gravitational field. The study also extends previous evidence of empirical control of motor function, i.e., without the reliance on model-based computations and direct specification of motor outcome.
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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) | 0.001 | 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".