Elevated primary motor cortex GABA in Parkinson's disease: 7T MR spectroscopy evidence.

INTRODUCTION Cortical inhibitory-excitatory imbalance may contribute to motor dysfunction in Parkinson's disease (PD), but in vivo primary motor cortex (M1) neurochemistry remains incompletely characterized.

Methods

We used 7T proton MR spectroscopy to quantify γ-aminobutyric acid (GABA) and glutamate (Glu) in M1 in patients with mild-to-moderate PD and healthy controls. The inhibitory/excitatory ratio (I/E ratio, GABA/Glu) was derived as an exploratory measure. After quality control, baseline analyses included 32 patients and 28 controls. A self-paced bilateral handgrip task was conducted in a subgroup with15 patients and 14 controls.

Results

At rest, patients with PD showed higher GABA concentrations than controls, but this did not survive FDR correction across the two primary metabolites (pFDR = 0.06). There was no difference in Glu between the two groups. The I/E ratio was also higher in PD. Higher GABA showed nominal associations with greater MDS-UPDRS III scores, but these did not survive correction. During the motor task, Glu increased across groups, with no significant group × condition interaction for GABA, Glu. Task findings were preliminary given limited power.

Conclusions

Ultra-high-field MRS preliminary evidence for altered resting M1 GABAergic neurochemistry in mild-to-moderate PD. Task-related findings require validation in larger cohorts. These findings support the utility of 7T MRS for probing motor-cortical neurochemistry in PD.