Relating Motor Cortical Oscillations to Motor γ-Aminobutyric Acid (GABA)

Abstract

The human motor cortex exhibits characteristic beta (15 – 30 Hz) and gamma oscillations (60-90 Hz) in the context of transient finger movement tasks. The functional significance of these oscillations, such as post-movement beta rebound (PMBR) and movement-related gamma synchrony (MRGS), remain unclear. Considerable animal and human non-invasive studies suggest that the networks supporting these motor cortex oscillations depend critically on the inhibitory neurotransmitter γ-Aminobutyric acid (GABA). However, a direct relation between MEG measured motor cortex oscillation power and frequency with resting GABA concentrations in adult human participants has not been demonstrated.

In the present study, motor cortical responses were measured from 8 healthy adults participating in a cued button-press task using the right index finger. PMBR and MRGS measures were obtained using beamformer differential source localization. In particular, PMBR and MRGS measures were obtained from the time-frequency plots obtained from beamformer localized primary motor (MI) sources. For each participant, complimentary magnetic resonance spectroscopy (MRS) GABA measures from the motor hand knob of the left central sulcus were also obtained. GABA concentration was estimated as the ratio of the motor cortex GABA integral to a reference GABA phantom.

A significant linear relation was observed between MI GABA concentration and PMBR power (R² = 0.42, p=0.04), with no such relation observed for GABA and PMBR frequency. Conversely, a significant correlation was observed between MI GABA concentration and MRGS frequency (R² = 0.67, p=0.01), with no correlation observed between GABA concentration and MRGS power.

Present findings support a role for GABA in the generation and modulation of endogenous motor cortex rhythmic activity.