Neurophysiological and Cognitive Changes Induced by the Acute Head-Down Tilt
INTRODUCTION: In space, under weightlessness conditions, human brain activity is changed due to the shifting of body fluid and blood toward the cephalic region. This shifting leads to changes in cerebral hemodynamics and, consequently, neurophysiological function, which impacts mental functions like cognition and decision-making capabilities of space travelers. The present study reports the effect of acute exposure to simulated microgravity on cognitive functions and event-related potentials. METHODS: There were 18 healthy human subjects who participated in a 1-h 6° head-down tilt (HDT) bed rest to simulate physiological conditions during microgravity. Subjects were instructed to perform event-related potential tasks and cognitive tasks with a simulator sickness questionnaire to evaluate their performance, attention, and alertness during weightlessness, at baseline, after microgravity exposure, and after a recovery of 30 min. RESULTS: A significant change was found in the latency of P300 as compared to the baseline. The amplitude of the P300 wave was changed during HDT. The mean reaction time of contingent negative variation increased significantly as compared to the baseline. A significant increase in choice reaction time was observed during HDT vs. baseline. The values recovered partially after 30 min of exposure. DISCUSSION: It was concluded that simulated microgravity impacts mental functions as evidenced by alterations in choice reaction time and event-related potential latencies and reaction time. The study has applied value for understanding neurophysiological responses and optimization of cognitive performance in space conditions. Sharma M, Gaur S, Pawar H, Yadav N, Thondala B, Kumar S, Kishore K, Ray K, Panjwani U. Neurophysiological and cognitive changes induced by the acute head-down tilt. Aerosp Med Hum Perform. 2025; 96(1):45–52.
Schematic representation of the study design including study time points and parameters.
Effect of head-down tilt (HDT) on P300: A) the representative waveform of baseline P300 showing prominent peaks (N1, P2, N2, P3, N3); B) the representative waveform of P300 after 6° HDT for 1 h, demonstrating an increase in latency and decrease in amplitude (N1, P2, N2, P3, N3); and C) the representative waveform of P300 after 30 min of recovery from HDT, demonstrating an improvement in latency and amplitude in comparison to the HDT group.
Exposure to 6° head-down tilt (HDT) alters the P300 latency and amplitude: A) statistical comparison of P300 latency between control, HDT, and recovery groups (****P < 0.0001; *P < 0.01; repetitive measure ANOVA; N = 18); and B) statistical comparison of P300 amplitude between control, HDT, and recovery groups (P < non-significant; P > non-significant; repetitive measure ANOVA; N = 18).
Effect of head-down tilt (HDT) on contingent negative variation (CNV): A) representative tracing of baseline CNV showing mean reaction time and amplitude; B) representative tracing of CNV after 6° HDT for 1 h, demonstrating an increase in mean reaction time; and C) representative tracing of CNV after 30 min of recovery from HDT, depicting a shorter mean reaction time in comparison to HDT group.
Exposure to 6° head-down tilt (HDT) alters the contingent negative variation (CNV) mean reaction time and amplitude: A) statistical comparison of CNV mean reaction time between control, HDT, and recovery groups (*P < 0.01; repetitive measure ANOVA; N = 18); and B) statistical comparison of CNV amplitude between control, HDT, and recovery groups (*P < 0.01; P < non-significant; repetitive measure ANOVA; N = 18). The error bar indicates the SD of subjects.
Exposure to 6° head-down tilt (HDT) alters the latency of choice reaction time (CRT) and scoring of spatial working memory (SWM): A) statistical comparison of latency of CRT between control, HDT, and recovery (****P < 0.0001; ***P < 0.001; P < non-significant; repetitive measure ANOVA; N = 18); and B) statistical comparison of scoring of SWM between control, HDT, and recovery (P < non-significant; P < non-significant; repetitive measure ANOVA; N = 18).
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