A 2021 multisite study (Zhao et al., Molecular Psychiatry) reported that in 156 abstinent men with methamphetamine use disorder (MUD), cue-induced craving, sleep disturbance, and medial prefrontal cortex (MPFC) beta-band source synchrony — driven by beta-band connectivity between MPFC and orbital gyrus — all peak at 1–3 months of abstinence, and proposed neuromodulation of frontal beta activity as a future therapy. Because the study was cross-sectional and correlational, two linked questions remain open: (1) whether the 1–3-month peak reflects a true within-subject time-dependent incubation process rather than between-cohort differences, and (2) whether MPFC beta synchrony causally maintains incubated craving. A 2023 sham-controlled 10 Hz rTMS trial targeting MPFC/anterior cingulate reduced cue-induced craving with correlated MPFC beta decreases, but was small, stimulated at alpha frequency, included only men, and had no relapse follow-up. No longitudinal within-subject EEG study of the craving/sleep/beta trajectory exists, and generalization to female patients and active (non-abstinent) users is untested.

Background

Methamphetamine use disorder (MUD) is a substance-use disorder with high relapse rates and no approved pharmacotherapy. Relapse is strongly driven by cue-induced craving — the subjective urge to use triggered by drug-related stimuli. Preclinical work beginning in 2001 established 'incubation of craving': in rats, cue-induced drug-seeking behavior increases over the first weeks to months of forced abstinence before declining, a time-dependent phenomenon now demonstrated for cocaine, methamphetamine, opioids, and nicotine (reviewed by Chow et al. 2025). Human analogues are thinner: cue-induced craving changes across abstinence have been reported in cigarette smokers (Bedi et al. 2011), alcohol-dependent inpatients (Li et al. 2015), and, using electroencephalography (EEG), in cocaine-dependent adults (Parvaz et al. 2016), but a 2024 systematic review found that across 20 clinical studies opioid craving does not increase over abstinence (Bergeria et al. 2024), so the translational status of incubation in humans is contested.

Zhao et al. (2021) provided the first human neurophysiological data on methamphetamine craving incubation. In 156 men with MUD in long-term residential rehabilitation, recruited at five abstinence durations (<1, 1–3, 3–6, 6–12, 12–24 months), they collected self-report measures (cue-induced craving after a methamphetamine video, sleep quality, impulsivity, anxiety, depression) and 128-channel high-density resting-state EEG. Key electrophysiology terms: source localization estimates the brain generators of scalp EEG using a head model; current source density (CSD) is the estimated current flowing in cortical patches; the beta band (here 16.5–26.5 Hz) is an oscillation frequency range; synchronization or functional connectivity measures statistical coupling between activity in different brain regions. Compared with the other abstinence windows, the 1–3-month group showed higher cue-induced craving and worse sleep quality (anxiety, depression, and impulsivity did not show this pattern), globally decreased theta/alpha and increased beta power, and — in source space — increased MPFC beta synchronization associated with craving, apparently driven by beta-band connectivity between the MPFC and bilateral orbital gyrus (ORB). The authors concluded that frontal beta hyper-synchrony is a neurophysiological signature of the incubation period, usable to identify relapse-susceptible individuals, and suggested future therapeutic intervention 'via neuromodulation of beta activity'.

Two classes of non-invasive neuromodulation are relevant: repetitive transcranial magnetic stimulation (rTMS), which uses repeated magnetic pulses to modulate a targeted cortical region (deep TMS with H-coils can reach medial frontal structures), and transcranial alternating current stimulation (tACS), which applies weak oscillating currents intended to entrain brain rhythms at a chosen frequency, permitting frequency-specific tests of an oscillatory marker. The 2021 study was cross-sectional (different participants at each abstinence duration), so its peak could reflect cohort differences rather than a within-person trajectory; and it was correlational, so MPFC beta synchrony could be a downstream consequence of incubation-related neuroadaptations rather than a causal contributor. These design limitations — together with the abstract's own proposal of 'future therapeutic interventions for MUD via neuromodulation of beta activity' — frame the unresolved questions addressed here: within-subject longitudinal confirmation of the 1–3-month peak in craving, sleep disturbance, and frontal beta synchrony; and whether MPFC beta synchrony is a causal driver testable by frequency-specific modulation of MPFC beta activity. The all-male, abstinent residential cohort additionally limits the population scope of the reported signature.

Problem Statement

Establish whether the neurophysiological 'incubation' signature reported in methamphetamine use disorder (MUD) — the apparent peak of cue-induced craving, sleep disturbance, and medial prefrontal beta-band source synchrony (with MPFC–orbital beta connectivity) at 1–3 months of abstinence — reflects a true within-person time-dependent process, and whether MPFC beta synchrony causally maintains incubated craving. Concretely, two linked components, left open by the source study's cross-sectional, correlational design: (1) within-subject longitudinal confirmation — track the same individuals with MUD across abstinence (covering the first months through at least the 1–3-month window and beyond), with repeated cue-induced craving ratings, sleep measures, and high-density EEG source-space beta metrics, to determine whether the trajectory shows true time-dependent incubation or reflects cohort effects; and (2) causal interventional test — test whether interventions that change local MPFC beta activity at beta frequency alter cue-induced craving, to determine whether MPFC beta synchrony — the beta-band coupling between MPFC and orbital gyrus that is the reported marker — is a causal driver of incubated craving or a downstream correlate of other neurobiological changes. A rigorous within-subject study that fails to find the peak (e.g., showing monotonic craving decline or no beta-trajectory change) would answer component (1) negatively; this is an admissible answer to component (1), not a failure, and does not by itself settle component (2), so the task is resolved only when both components have been answered.

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