Sleep apnea-related cognitive deficits and intelligence: an implication of cognitive reserve theory MANOS ALCHANATIS 1 , NIKOLAOS ZIAS 1 , NIKOLAOS DELIGIORGIS 1 , ANASTASIA AMFILOCHIOU 2 , GIORGOS DIONELLIS 1 and D O R A ORPHANIDOU 1 1 Sleep Laboratory, Respiratory Medicine Department, Athens University Medical School, Sotiria Hospital for Chest Diseases and 2 Sleep Laboratory, ÔSismanoglioÕ Hospital, Athens, Greece Accepted in revised form 22 October 2004; received 6 February 2004 SUMMARY Cognitive deficits in patients with obstructive sleep apnea syndrome (OSAS) are well demonstrated, but the pathophysiology of these deficits is still controversial, as the relationship between OSA severity and cognitive deficits is usually weak. Our study considers the possible relationship between OSA-related cognitive deficits and the overall intellectual function of OSA patients. Forty-seven OSA patients and 36 normal individuals underwent a neuropsychological battery test assessing attention and alertness. According to the resulting IQ score, patients and controls were divided into a high-intelligence group (IQ ‡ 90th percentile) and a normal-intelligence group (50 £ IQ < 90%ile). Between the two patient groups there were no significant differences noticed, regarding OSA severity or sleepiness. High-intelligence patients showed the same attention/alertness performance compared with the high-intelligence controls. On the contrary, patients with normal-intelligence showed attention/alertness decline compared with the normal-intelligence control group. The two patient groups were re-examined with the same battery test after at least 1 year of CPAP treatment. At re-examination neither patient group showed any differences regarding attention and alertness compared with the control groups. We assume that high-intelligence may have a protective effect against OSA-related cognitive decline, perhaps due to increased cognitive reserve. keywords cognitive function, intelligence, IQ, obstructive sleep apnea syndrome INTRODUCTION Obstructive sleep apnea syndrome (OSAS) exhibits a relatively high prevalence, occurring in 5% of the general adult population (Young et al., 2002). Patients with OSAS often develop neurocognitive deficits, which are related to decreased work performance, increased rate of road traffic accidents and diminished quality of life (Barbe et al., 1998; Bennet et al., 1999; D’Ambrosio et al., 1999). The areas frequently affected by OSAS are selective attention (or concentration), sustained attention (or vigilance), short-term and working memory, and executive and motor functioning (Adams et al., 2001; Decary et al., 2000). Most of these deficits are corrected after CPAP therapy, whereas executive dysfunction, as well as some degree of somnolence may persist (Decary et al., 2000; Ferini-Strambi et al., 2003). The pathophysiology of these deficits is still controversial. The main contributing factors are supposed to be daytime somnolence due to sleep fragmentation, and the effect of intermittent hypoxemia on brain function. Excessive daytime somnolence is related to attention and memory deficits, while hypoxemia contributes to deficits in executive and motor function (Bedard et al., 1991; Decary et al., 2000; Engleman et al., 2000). However, these relationships are sometimes weak and have limited predictive power (Engleman et al., 2000). In addition, some researchers have failed to establish a significant correlation between cognitive function Correspondence: Nikolaos Zias, Karatza 8, Papagou, 15669, Athens, Greece. Tel.: +302106515667; fax: +302105758411; e-mail: nikoszias@ yahoo.gr J. Sleep Res. (2005) 14, 69–75 Ó 2005 European Sleep Research Society 69