Longitudinal Changes in Intracortical Excitability During Ramadan Fasting: A Paired-Pulse Transcranial Magnetic Stimulation Study

Abstract

Ramadan fasting represents a natural model of prolonged daily intermittent fasting associated with metabolic and circadian alterations. This study investigated longitudinal changes in intracortical excitability across pre-, mid-, and post-Ramadan timepoints in healthy adults observing Ramadan fasting. Thirty fasting participants underwent paired-pulse transcranial magnetic stimulation at three timepoints (pre-, mid-, and post-Ramadan). A non-fasting control group (n = 11) was assessed at pre- and mid-Ramadan. Conditioned motor-evoked potentials were recorded at interstimulus intervals of 2-10 ms and normalized to unconditioned responses. A linear mixed-effects model assessed effects of Timepoint and interstimulus interval (ISI). Secondary outcomes included blood glucose, cognitive performance, sleep duration, and reaction time. A significant main effect of Timepoint (p < 0.001) indicated longitudinal modulation of intracortical excitability, with increased MEP ratios at mid-Ramadan and partial persistence post-Ramadan. The ISI effect confirmed the inhibition-facilitation gradient (p < 0.001). The Timepoint x ISI interaction was not significant (p = 0.566), indicating a global shift in excitability without ISI-specific modulation. Blood glucose and sleep duration decreased significantly at mid-Ramadan. Ramadan fasting is associated with a time-dependent increase in intracortical excitability, most appropriately interpreted as a generalized shift rather than selective modulation of inhibitory or facilitatory circuits. These changes occur in the context of concurrent metabolic and sleep alterations and may reflect combined influences of fasting-related metabolic state and reduced sleep duration; however, these factors cannot be disentangled within the present design.