Ethanol-induced impairments in spatial working memory are not due to deficits in learning

Acute ethanol administration impairs spatial reference memory and spatial working memory. However, the experimental designs previously used to test spatial working memory fail to make a distinction between the acquisition, or learning, of spatial information and the retention of this information. This study demonstrates that acute ethanol administration impairs spatial working memory, by using a novel experimental design that eliminates the confound between the learning of new spatial information and the testing of this information.

Long-Evans male rats received three forced trials to the same place for food reward on an elevated radial arm maze. Subjects were then given six free-choice trials in the first acquisition session, followed by a 30-min consolidation period before an additional six free-choice trials were administered-the retention session. Animals were trained to a criterion of five of six correct in both the acquisition and retention over 2 consecutive days. Once criteria were obtained, subjects received either saline or one of three ethanol doses immediately after the acquisition session to investigate whether ethanol alters retention of the learned spatial information.

Acute ethanol administration impaired spatial working memory. Rats tested under saline and low-dose ethanol (1.0 g/kg) made significantly more place choices than rats tested under moderate- or high-dose ethanol (1.5 and 2.0 g/kg, respectively). Ethanol produced a temporary impairment in that no significant differences were found when subjects were retrained and retested 24 hr after initial testing.

These results demonstrate that acute ethanol administration impairs spatial working memory and that such a deficit is not contingent on a learning impairment. These results support earlier findings that acute ethanol administration impairs spatial working memory but provide a significant advance by validating a novel training procedure that allows for direct investigation of working memory. Ethanol's impairment of both spatial working memory and spatial reference memory strengthens the similarities between memory impairments due to ethanol administration and memory impairments due to hippocampal lesions.