Precision Neuromodulation for Psychiatric Disorders: A Narrative Review of Brain State-Dependency, Phase-Locked Stimulation, and Behavioral Context

Results

State-Dependent Effects: TMS effects consistently varied as a function of pre-stimulation neural state. Stimulation delivered during active network engagement produced different physiological and behavioral outcomes compared to stimulation at rest [4,5]. Baseline cortical excitability, indexed by pre-stimulus alpha power and phase, significantly predicted TMS-evoked responses, with high-power states in some contexts acting as a gating mechanism that attenuated stimulation effects [8,9]. In depression, elevated frontal alpha asymmetry and altered excitability-inhibition balance represent pathological states that may differentially modulate treatment response [10,11].

Phase-Locked and EEG-Guided TMS: Aligning stimulation with endogenous oscillatory rhythms enhanced modulation of cortical excitability and reduced response variability [6]. Zrenner et al. demonstrated that rTMS triggered at the mu-rhythm negative peak (high-excitability state) induced LTP-like plasticity, while stimulation at the positive peak produced no change [6]. In clinical translation, Sun et al. reported that closed-loop phase-locked rTMS synchronized to individual alpha frequency yielded an 85.7% response rate in biomarker-selected patients with TRD, with increased neural entrainment and decreased cortical excitability predicting treatment efficacy [12,13]. In a sham-controlled trial, EEG-synchronized TMS (sTMS) at individual alpha frequency achieved a 48.5% symptom reduction versus 19.3% for sham (p=0.001), with a 53.3% response rate versus 12.5% sham [14]. Phase-synchronized 40 Hz stimulation combining iTBS with tACS produced the most significant increase in gamma oscillatory activity, with effects persisting up to 2 hours post-stimulation [15].

Concurrent Behavioral Interventions: Neuromodulation delivered concurrently with psychotherapy yielded response rates substantially exceeding monotherapy. Donse et al. reported 66% response and 56% remission rates when rTMS was combined with simultaneous CBT-based psychotherapy in 196 MDD patients, with 65% of responders maintaining gains at 6-month follow-up [16]. In PTSD, a 2026 RCT (n=119) demonstrated that navigated TMS combined with intensive prolonged exposure significantly outperformed sham plus exposure on PTSD severity (CAPS-5 difference -6.03, p=0.008), with durable gains at 3-month follow-up [17]. A systematic review of 31 TMS-for-PTSD studies confirmed that memory provocation and exposure protocols enhance response across stimulation parameters [18]. However, combinations with general cognitive training yielded mixed results, suggesting that task specificity is critical for synergistic effects [7,19].

Emerging Modalities: Transcranial focused ultrasound (tFUS) offers millimeter-scale spatial resolution at depths exceeding TMS capacity. Sanguinetti et al. demonstrated that tFUS targeting the right prefrontal cortex modulated default mode network connectivity and improved mood [20]. Folloni et al. confirmed subcortical neuromodulation capability in primates [21]. Emerging closed-loop architectures combining real-time EEG with optimized triggering systems achieve sub-millisecond latency, enabling phase-locking even for gamma-band oscillations [22,23]. The Stanford Neuromodulation Therapy (SNT) protocol, using fMRI-guided connectivity targeting with accelerated dosing, achieved approximately 79% remission in a recent RCT, demonstrating the clinical potential of spatially precise, individualized approaches [24].