139 EFFECTS OF ACUTE ADMINISTRATION OF ZOLPIDEM ON A NON-ASSOCIATIVE MEMORY TASK: OPEN-FIELD HABITUATION

Abstract

Objective: Free recall of word lists is a commonly used paradigm to investigate learning during sleep deprivation. Here, we studied whether sleep deprivation alters the pattern of recall based on serial positions of words in word lists, which enables the determination of: a) long-term episodic memory learning, or recall of the first words on the lists (primacy effect); b) shortterm learning, or recall ofwords in the last serial positions (recency effect); c) working memory processes involved in transferring information to and from long-term memory. Method: Twenty-four young, healthy male volunteers were randomly allocated to two groups: total sleep deprivation for 48 h or normal sleep (control group). All volunteers took part in 4 test sessions at: baseline, 24 h, 48 h and 72 h (corresponding to a session after one night of recovery sleep in the sleep-deprived group). Five word-lists were presented per session and immediate serial recall was assessed. Each list was composed of 15 unrelated concrete nouns. Results: The sleep-deprived group, both after 24 and 48 h, recalled fewer words in the serial positions following the primacy portion of the list in comparison to the control group. At 72 h, after one night of recovery sleep in the sleep-deprived group, performance of both groups no longer differed, but recall was larger than at baseline in serial positions between the primacy and recency portions of the list, indicating that both groups benefited from the repeated exposure to the task. Conclusions: One and two nights of sleep deprivation impairs memory for words in the serial positions following the primacy portion of the list, possibly due to an extension of primacy in the control group. Because transfer of information to long-term memory is thought to involve secondary processes of active rehearsal and chunking of word sequences, our data indicates that sleep-deprivation impairs the functioning of the episodic buffer of working memory, which is responsible for these cognitive processes. One night of recovery sleep restores these working memory processes to normal. Financial Support: Fundacao de Amparo a Pesquisa do Estado de Sao Paulo (FAPESP-2008/089210) and Associacao Fundo de Incentivo a Psicofarmacologia (AFIP).