Antagonist tendon vibration dampens estimates of persistent inward currents in motor units of the human lower limb
Bibliographic record
Abstract
ABSTRACT We can readily measure motoneuron discharge patterns in humans due to the one-to-one spike relation between motoneuron and muscle fiber action potentials, which allows us to make inferences about motor commands. Persistent inward currents (PICs), which provide gain control of motoneuronal output, are facilitated by monoaminergic input from the brainstem. This monoaminergic input is greatly diffuse, but resulting PICs are highly sensitive to inhibitory inputs. Antagonist muscle stretch, and thus Ia input from the antagonist decreases PIC magnitudes in the decerebrate cat. In the present study, we explored whether estimates of PICs are altered with vibratory input to antagonist muscles in humans. MUs of the tibialis anterior (TA), soleus (SOL), and medial gastrocnemius (MG) were discriminated using high-density surface electromyography and convolutive blind source separation. We estimated PICs using the paired MU analysis technique, which quantifies discharge rate hysteresis (ΔF) by comparing the discharge rate of a lower-threshold MU at the onset and offset of a higher-threshold MU. Participants performed isometric plantarflexion and dorsiflexion contractions to a peak of 30% of maximal voluntary contraction, with 10 s ascending and descending phases. In half of the trials, we applied vibration to the antagonist tendon and found that ΔF in agonist MUs decreased in the presence of vibration. These findings suggest that inhibition from the antagonist muscle, most likely Ia reciprocal inhibition, can reduce discharge rate hysteresis. This provides insights about non-invasive methods potentially capable of dampening PICs in hyperexcitable motoneurons, which are manifest in some neurological impairments. KEY POINTS Persistent inward currents in motoneurons amplify synaptic inputs and thus have a major impact on motor unit firing patterns. We show that sustained vibration to the antagonist tendon reduces estimates of persistent inward currents (ΔF) of the contracting muscle in both the plantarflexors and dorsiflexors. These findings provide evidence for the important role of sensory input in the control of persistent inward currents in the human. Reciprocal inhibition may help refine neuromodulatory commands to tailor motor unit activation to diverse movement patterns and specific tasks, and loss of inhibition may exacerbate symptoms of neurological impairment.
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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 | 0.001 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.001 |
| 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".