Differences in Hebbian stimulation effects between biceps and triceps brachii in humans

Area of Science:

• Neuroscience
• Motor Control
• Neuroplasticity

Background:

• Monosynaptic corticospinal connections differ between biceps and triceps motoneurons.
• Hebbian stimulation targets corticospinal-motoneuronal connections.

Purpose of the Study:

• To investigate if Hebbian stimulation differentially enhances corticospinal excitability in biceps versus triceps brachii.
• To test the hypothesis that Hebbian stimulation would yield greater corticospinal excitability in biceps due to more prevalent corticospinal connections.

Main Methods:

• Transcranial magnetic stimulation (TMS) assessed motor-evoked potential (MEP) size.
• Hebbian stimulation involved paired pulses (TMS preceding electrical stimulation).
• MEP size was measured at resting motor threshold (MEP-RMT) and maximum output (MEP-100%), and a control intensity (MEP-Control).

Main Results:

• Both MEP-RMT and MEP-100% increased in biceps and triceps post-stimulation.
• The increase in MEP-RMT was significantly greater in biceps compared to triceps.
• Hebbian stimulation produced a greater increase in MEP-Control in biceps than triceps, irrespective of baseline MEP size.

Conclusions:

• Hebbian plasticity enhances corticospinal excitability more in elbow flexors (biceps) than extensors (triceps).
• Muscle-specific innervation patterns influence the efficacy of Hebbian stimulation.
• Therapeutic strategies utilizing Hebbian stimulation should consider these muscle-specific differences.