Does the sedation resulting from sleep deprivation and lorazepam cause similar cognitive deficits?

It is notoriously difficult to assess the contribution of the sedative effects of benzodiazepines to the cognitive impairments that they produce. The purpose of the present experiment was to determine whether a similar pattern of cognitive impairment would be seen in conditions when subjects felt equally sleepy as the result of sleep deprivation. The effects of a sedative dose of lorazepam (2.5 mg) in healthy volunteers was therefore compared with the effects of acute sleep deprivation (a night on-call) in a group of junior doctors and the effects of chronically disturbed sleep due to snoring. Lorazepam, acute sleep deprivation, and chronic sleep disturbance all significantly increased subjective sedation. In addition, lorazepam significantly impaired performance in two tests of psychomotor speed and caused significant anterograde amnesia. Semantic and short-term memory were not impaired by lorazepam, nor was there any impairment in executive function. The only deficit found following acute sleep deprivation was in a test of semantic memory, generating examples from a difficult category. The only significant deficit in the group suffering from chronically disturbed sleep, compared with age-matched controls, was in executive function, and there was a nearly significant impairment in sustained attention. These results suggest that, despite the common factor of increased subjective sedation, the profile of cognitive impairment in the two sleep deprivation groups are neither similar to each other nor to that seen following an acute dose of lorazepam.