Total sleep deprivation can increase vestibulo-ocular responses G. QUARCK 1 , J. VENTRE 2 , O. ETARD 1 and P. DENISE 1 1 UPRES EA no. 3917– attention, orientation et fonctions exe´cutives, Faculte´ de Me´decine, Universite´ de Caen – Basse Normandie, Caen Cedex, France and 2 INSERM and CNRS-Cognitive Sciences Institute – UMR 5015, Bron, France Accepted in revised form 11 July 2006; received 18 January 2005 SUMMARY The effect of sleep deprivation on the vestibular function is largely unknown. Some studies have found that postural balance or vestibular reflexes are decreased in sleep- deprived subjects while others found no change. The aim of this study was to evaluate the effect of sleep deprivation on the vestibulo-ocular reflex (VOR). Horizontal eye movements were recorded in healthy subjects during earth vertical axis rotation in darkness once after an ordinary night sleep and once after 26–29 h of sleep deprivation. In the first experiment (n ¼ 8), for which rotation was a 60° s )1 velocity step, sleep deprivation induced a significant increase in VOR gain. In the second experiment (n ¼ 12), for which rotation was sinusoidal (0.2 Hz ± 25° s )1 ), sleep deprivation induced no significant modification in VOR gain. The difference between the two studies was the abrupt onset of the step stimulation in comparison with the sinusoidal rotation. Because of its unexpected onset and the potential threat to postural balance, the step stimulation may activate the system specialized in reorienting attention towards salient or behaviourally relevant events. This system includes the right temporoparietal cortex, an area also involved in VOR control. A number of studies have found that sleep deprivation alters the activity of this cortical area during attentional tasks. It is therefore our hypothesis that the difference between the effects of these two vestibular stimulations results from a sleep deprivation-induced modulation of the right temporoparietal cortex. keywords attention, eye movements, sleep deprivation, vestibulo-ocular reflex INTRODUCTION The vestibular apparatus is composed of semicircular canals and otolith organs which detect angular and linear acceleration of the head respectively. The afferent vestibular activity combined with visual and somatosensory inputs is used to maintain a stable representation of space during change in body position or motion. In this context, any vestibular malfunctioning can result in a misperception of the body position or movements relative to external space. The effects of sleep deprivation on vestibular responses have been the subject of a very few studies. If sleep deprivation induces impairments in vestibular function, we can expect repercussions on postural balance, driving, piloting aircraft, etc. We know that sleep deprivation alters daytime cognitive and psychomotor functioning (review in Bonnet, 2002), including increased sleepiness or reduced alertness and alterations of more localized cortical function (Wu et al., 1991; Horne, 1993; Drummond et al., 2000, 2001; Thomas et al., 2000; Drum- mond and Brown, 2001). Especially, it has been shown that sleep deprivation in humans can induce an alteration in the posterior parietal cortex (Drummond and Brown, 2001) that plays a crucial role in the processing of vestibular information in relation with space representation. Anatomical studies provide evidence in primates of direct reciprocal connections between the vestibular nuclei and a number of vestibular-related cortical areas extending from the posterior parietal cortex to the frontal regions (Ventre and Faugier-Grimaud, 1988; Akbarian et al., 1993; Fukushima, 1997). The parietotemporal and the retroinsular cortices (PIVC) receive projections from vestibular nuclei and are activated during vestibular stimulation in monkey (Guldin and Grusser, 1998). Using unilateral cortical lesions, it has been Correspondence: Gae¨lle Quarck, UPRES EA no 3917– attention, orientation et fonctions exe´cutives, Faculte´ de Me´decine, Universite´ de Caen – Basse Normandie, 14032 Caen Cedex, France. Tel.: +02 31 06 82 14; fax: +02 31 06 82 19; e-mail: gaelle.quarck@wanadoo.fr J. Sleep Res. (2006) 15, 369–375 Ó 2006 European Sleep Research Society 369