Reading and Modulating Cortical β Bursts from Motor Unit Spiking Activity

Area of Science:

• Neuroscience
• Motor Control
• Human Physiology

Background:

• Beta (β) oscillations (13-30 Hz) are common in the human motor nervous system but their origin and function remain unclear.
• Traditionally, β activity was viewed as a continuous signal, but recent findings suggest it occurs in transient bursting events.
• Understanding the source of muscle β activity is crucial for deciphering its role in motor control.

Purpose of the Study:

• To investigate whether muscle β activity primarily originates from cortical projections.
• To characterize the temporal dynamics of β activity at both cortical and motor unit (MU) levels.
• To explore the possibility of volitionally modulating MU β activity and its cortical correlates.

Main Methods:

• Two experiments were conducted on healthy human participants (N=15 and N=13) during isometric contractions of the tibialis anterior muscle.
• Cortical and motor unit (MU) β activity were recorded and analyzed for bursting patterns, duration, and rate.
• A novel operant conditioning paradigm was employed to assess volitional modulation of MU β activity and its effect on cortical β.

Main Results:

• β rhythms at both cortical and MU levels were confirmed to occur in synchronized bursting events.
• These bursts exhibited comparable durations (40-80 ms) and rates (3-4 Hz) and appeared time-locked between cortical and MU recordings.
• Volitional modulation of MU β activity was achieved with minimal learning and was paralleled by corresponding changes in cortical β activity.

Conclusions:

• The findings strongly support the hypothesis that muscle β activity is predominantly driven by cortical projections.
• This study demonstrates a direct link between cortical β activity and peripheral motor output at the level of individual motor units.
• The results open avenues for decoding cortical activity from peripheral recordings and developing novel neural interfaces.