Intrinsic excitation-inhibition imbalance in major depressive disorder.

In people with major depressive disorder, the balance between excitation and inhibition across the brain's cortex is disrupted, particularly in the parietal and prefrontal-cingulate regions. Using resting-state functional magnetic resonance imaging data from 254 patients and 451 healthy controls, the Hurst exponent—a proxy for excitation-inhibition balance—was found to be significantly reduced in patients. This imbalance was linked to specific gene expression related to neuronal structure, metabolism, and mitochondrial function, as well as to neurotransmitter systems including GABA, opioid, serotonin, and synaptic density. In a separate trial of 32 patients with treatment-resistant depression, ketamine increased the Hurst exponent in the anterior cingulate and medial prefrontal cortices, suggesting that restoring excitation-inhibition balance may underlie ketamine's antidepressant effects.

Study at a glance

Abstract

Major depressive disorder (MDD) ranks among the foremost contributors to disability worldwide, yet its neurophysiological mechanisms remain poorly understood. Excitation-inhibition (E/I) imbalance has been implicated in MDD pathophysiology, but cortex-wide E/I ratio and its molecular substrates in MDD remain unknown. Resting-state functional magnetic resonance imaging data from 254 MDD patients and 451 healthy controls (HCs) across six sites were analyzed. The Hurst exponent, a biophysically confirmed proxy of E/I balance, was estimated using a fractionally integrated process framework. Neurobiological decoding analyses were performed to map the transcriptomic and neurochemical signatures of cortical E/I imbalance in MDD. An independent ketamine clinical trial dataset (32 treatment-resistant depression patients and 21 HCs) was used to examine ketamine-induced changes in cortical E/I balance. Patients with MDD demonstrated significantly reduced Hurst exponent values, predominantly encompassing the parietal and prefrontal-cingulate cortices. Transcriptomic analysis identified enrichment for neuronal structural organization, nucleic acid metabolism, and mitochondrial function, with preferential overlap with excitatory and inhibitory neuron-specific gene sets. Neurochemically, Hurst exponent alterations were spatially associated with GABAergic, opioidergic, serotonergic, and synaptic density distributions. Divergent group-by-treatment effects were observed in the anterior cingulate and medial prefrontal cortices, with ketamine-induced increases in TRD patients. These findings highlight that prefrontal-cingulate E/I imbalance, anchored to specific transcriptional and neurochemical substrates, may underlie the pathophysiology of MDD and the antidepressant effects of ketamine. The Hurst exponent offers a promising neuroimaging approach for probing E/I imbalance and identifying potential treatment targets in depression.