BEHAVIORAL-CORRELATES OF SINGLE UNITS IN THE MEDIAL SEPTAL AREA - THEEFFECT OF ETHANOL

Experimental manipulations that compromise the medial septal area cons istently and selectively impair working memory. The electrophysiologic al and pharmacological properties of medial septal neurons have been s tudied extensively, but the relation between medial septal neuronal ac tivity and ongoing behavior has not been systematically analysed. Work ing memory was assessed in a continuous conditional discrimination tas k, and behavioral performance was correlated with medial septal single unit activity. Operant performance and the activity of rhythmically a ctive neurons were continuously monitored during a 90 min test session , and peri-event time histograms of unit activity were constructed aro und relevant task events. Rats received intraperitoneal injections of either saline or ethanol (0.75 g/kg) 5 min before testing. Of the 52 m edial septal neurons recorded under saline conditions, approximately 8 0% had significant behavioral correlates. Thirty-five per cent of thes e neurons were selectively activated at the time of the response and 6 5% at the time of the reward. Response-related activity was not select ive for responses to the right or left lever, or to a particular type of trial, but in 61% of the cases was correlated with the accuracy of the response. In ethanol-treated rats, working memory was impaired, si ngle unit activity was disrupted, and the behavioral correlates were l ess frequent and robust, especially the response-related correlates th at were accuracy-sensitive. The results suggest that the medial septal area is involved in guiding accurate responses and processing rewards , and may contribute to the ethanol-induced impairments in working mem ory.