Brain mechanisms and outcomes of electroconvulsive therapy in treatment-resistant depression

Treatment-resistant depression (TRD) represents a challenge in the clinical practice of any psychiatrist. It is estimated that 30% of patients diagnosed with major depressive disorder will not respond to at least two adequate antidepressant trials, meeting criteria for treatment-resistant depression (TRD). Electroconvulsive therapy (ECT) is a therapeutic procedure based on the controlled induction of seizure activity through electrical stimulation and the oldest and most effective nonpharmacological treatment currently available for depression. In fact, ECT is the first-line treatment for TRD, with a response rate of around 70-80% and a rate of complete remission of symptoms in around 50% of patients. Despite its established efficacy, the underlying neurobiological mechanisms of ECT and clinical outcomes are still subject to active investigation. This paper aims to synthesize current evidence on the brain mechanisms involved in this neuromodulatory procedure and its clinical outcomes in patients with TRD.

A systematic search was conducted in PubMed using MeSH terms and free-text keywords, including “electroconvulsive therapy”, “treatment-resistant depression”, “neuroplasticity”, “mechanisms”, and “outcomes”, restricted to systematic reviews and meta-analyses published from 2020 to the present. From an initial pool of 35 records, 12 were excluded: 8 did not specifically address ECT, 2 did not evaluate ECT as a treatment for depression, and 2 assessed ECT in combination with other treatments. A final set of 23 articles was included for qualitative synthesis.

ECT was shown to modulate dysfunctional brain circuits involved in the pathophysiology of depression, particularly frontolimbic circuits involving the hippocampus, amygdala, and temporal cortex. These changes were accompanied by increased Brain-Derived Neurotrophic Factor (BDNF) levels and hippocampal volume, supporting the neurotrophic hypothesis of depression [1]. Furthermore, evidence suggests an increase in synaptic density in patients achieving remission, supporting the role of synaptic remodeling in ECT’s therapeutic effects. Glutamatergic modulation, particularly in the prefrontal cortex, was observed in treatment responders [2]. Additionally, ECT modulated neuroinflammatory markers and functional connectivity, notably normalizing the Default Mode Network [3]. Elevated baseline inflammatory markers were found to predict better clinical response to ECT [4], with further evidence of hypothalamic-pituitary-adrenal (HPA) axis regulation through epigenetic mechanisms. ECT demonstrated high clinical efficacy in TRD, consistently outperforming pharmacotherapy in speed and magnitude of response. Cognitive side effects, particularly short-term autobiographical memory impairment, were common but largely transient, with most deficits resolving within two weeks and long-term improvements in executive function observed post-remission [5]. Without continuation treatment, relapse rates reached 84% within six months, highlighting the importance of maintenance strategies. Overall, ECT showed a favorable safety profile and a significant short-term reduction in suicide risk.

In conclusion, ECT is a highly effective and safe intervention for TRD, with a well-supported neurobiological evidence base involving neuroplasticity, glutamatergic modulation, neuroinflammation and HPA axis regulation. Despite transient cognitive side effects, long-term functional outcomes are favorable. These findings reinforce ECT as an evidence-based first-line option in the management of TRD, highlighting the need for structured maintenance protocols to sustain its therapeutic benefits.

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