0062 Diurnal Variation in Somatosensory Information Processing in Chronic Insomnia

Abstract Introduction Increased somatosensory information processing is component of neurobiological model of chronic insomnia. Insomnia patients are highly sensitive to sensory stimuli, particularly at night. Our hypothesis is that insomnia patients have lower threshold for somatosensory information processing at night as compared to daytime. Methods In this study, 15 healthy controls and 12 insomnia patients were recruited. Quantitative sensory testing was used to assess peripheral somato sensory information processing before day-time nap and before night time sleep. Threshold levels of thermal detection, pain and pain tolerance in hot and cold modalities were determined. Results In healthy controls group, no significant difference was observed between night and afternoon time points for detection threshold for hot (37 ± 2.3 °C & 36 ± 0.86°C, p = >0.9999), cold (28 ± 2.0°C & 28 ± 1.4°C, (p=0.2061), pain threshold of cold (18±5.3°C & 21±4.2°C, p=0.2618) and pain tolerance for hot (47±3.3°C & 47±1.5°C, p=0.7695), cold (9.5 ± 6.2°C & 12±5.5 °C, p=0.1055). Significant difference was observed between night (43 ± 3.4°C) and afternoon (41 ± 2.4°C) time points for pain threshold for hot (p=0.0174), pain onset is at a higher temperature for hot at night. In insomnia patients group, no significant difference is observed between night and afternoon for detection threshold for hot (36±3.7°C&36±3.7°C,p=0.7344),cold (27±3.4°C&28±2.9°C,p=0.4691), pain threshold for hot (44±3.1°C&45±3.0°C,p=0.7894),cold (15±6.3°C&15±6.3°C,p=0.8117), pain tolerance for hot (48±1.4°C&49±0.93°C,p=0.1591),cold (8.1±4.9°C&8.3±4.3°C,p=0.7610). Conclusion Healthy controls exhibit a circadian modulation of thermal nociceptive threshold (night ↑ threshold), consistent with intact nocturnal endogenous analgesic tone. Insomnia patients lack this diurnal modulation and show an altered sensory–affective pain profile: elevated hot-pain detection thresholds (hyposensitivity to nociceptive onset) combined with reduced suprathreshold tolerance at night, indicating preserved or enhanced central amplification of suprathreshold signals (impaired descending inhibitory control / exaggerated affective amplification) despite raised detection thresholds. Support (if any) This study is supported by Intramural grant from All India Institute of Medical Sciences, New Delhi