Phase-dependent adaptation of emotional reactivity during prolonged complete fasting: longitudinal ERP evidence from a human metabolic challenge

Prolonged fasting exposes individuals to sustained energy deficits and psychological stress. Such adversity may alter emotional reactivity and impair the ability to process negative and threatening stimuli. The current study aimed to characterize neural signatures of emotional reactivity adaptation under metabolic deprivation and to evaluate whether these readouts may inform candidate neurobehavioral monitoring strategies and the timing of countermeasures in metabolic-stress contexts. We adopted a 15-day complete fasting protocol and longitudinally measured event-related potentials (ERPs) elicited by a negative emotional picture Oddball task. As supplementary evidence for emotional flexibility, photoplethysmograms (PPG) and respiration (RSP) were collected in a resting state before each Oddball task and were subsequently used to estimate respiratory sinus arrhythmia (RSA). Nineteen healthy adults completed the task at four phases: baseline (BL), day 7 (CF7) and day 14 (CF14) of complete fasting, and day 2 of complete recovery (R2). Across phases, ERP dynamics indicated phase-dependent shifts in emotional reactivity: an early phase (CF7) with heightened salience-evaluation (parietal P3), followed by a later phase (CF14) with attenuated attentional orienting to unexpected information (fronto-central N2). During complete fasting (CF7, CF14), participants showed increased attentional resource recruitment (occipital N1) in response to the explicit task. These changes returned to the baseline level at R2. PPG-derived RSA also supported the reduction in emotional context flexibility during complete fasting. Prolonged fasting was associated with phase-dependent changes in ERP indices of emotionally laden deviant-event processing in healthy adults. These findings are hypothesis-generating and require replication in larger controlled studies before the identified neural and autonomic patterns can be considered for neurobehavioral monitoring or countermeasure planning.