Is High IQ Protective Against Cognitive Dysfunction in Narcoleptic Patients?

BACKGROUND AND PURPOSE: The aims of this study were to elucidate the cognitive functions of narcoleptics and determine whether intelligence protects against cognitive dysfunction and depressive mood in these patients. METHODS: Sixty-six subjects (33 narcoleptics, 33 controls) were administered a battery of neuropsychological tests and an individual standardized intelligence test. The cognitive functions of the narcoleptic patients and the healthy controls were compared, as were those of high-IQ and mid-to-low-IQ narcoleptic patients. RESULTS: Narcoleptics exhibited significantly lower scores in the Corsi Block-Tapping Test forward and backward, and the digit symbol tests, and significantly higher Beck Depression Inventory scores than the controls. However, verbal attention, verbal-visual long-term memory, and executive function task scores did not differ significantly between patients and controls. The mid-to-low-IQ patient group had lower mean digit span backward test, phonemic and semantic fluency Controlled Oral Word Association Test and Korean version of the Boston Naming Test scores, and a higher total score and general depressive symptoms subscales Beck Depression Inventory score than the high-IQ patient group. However, controls exhibited no IQ-related differences in cognitive performance or depressive mood. Patients in the high-IQ group exhibited impaired visual attention and working memory as compared with controls. CONCLUSIONS: The findings of the present study show that narcolepsy patients have deficits in visual attention and visual working memory, and tend to feel more general depressive symptoms but not somatic symptoms than their control, nonnarcoleptic counterparts. In addition, it appears that higher intelligence protects against cognitive dysfunction and depressive mood.

The Relationship between Hippocampal Volume and Cognition in Patients with Chronic Primary Insomnia

BACKGROUND AND PURPOSE: Differences in hippocampal volume (HV) were compared between chronic primary insomniacs (PIs) and good sleepers (GSs), and the relationship between HV and memory function in PIs was investigated to clarify the effect of chronic sleep deprivation on brain structure and cognition. METHODS: Twenty PIs (mean age, 50 years; 18 females) and 20 age-, gender-, and education-matched GSs were enrolled. Brain magnetic resonance imaging (MRI) was performed on a 1.5-T MRI scanner. Left and right HV and intracranial volume (ICV) were measured manually. Nighttime polysomnography and neuropsychological testing were also applied to all subjects. Group differences in HV were analyzed and the relationships between HV and sleep questionnaire data, nighttime polysomnography, and neuropsychological findings were evaluated. RESULTS: Compared to GSs, PIs exhibited significantly increased sleep latency and arousal index and a decreased percentage of REM sleep in nighttime polysomnography, as well as impaired verbal and visual memory, and frontal lobe function. Absolute HV and ICV did not differ significantly between PIs and GSs. In the PIs, right and left HVs were negatively correlated with the duration of insomnia and the arousal index, and positively correlated with the recognition of visual memory. In addition, free recall in verbal memory was positively correlated with left HV in PIs. CONCLUSIONS: These findings suggest that chronic sleep deprivation impairs memory and frontal lobe function, and that a long duration of insomnia and poor sleep quality contribute to a bilateral reduction in HV.