Memory duration and effect of serotonin on butanone enhancement. A, Experimental scheme of memory duration experiments. Three conditions for the interval period were tested, while animals were normally preexposed to butanone and food but to food only in control experiments. B, Memory duration of butanone enhancement. Wild-type animals were exposed to 12 μl of butanone with food (filled squares; butanone enhancement experiment) or food only (open rhombuses; control experiment), washed, kept on NGM plates without butanone and food for the time lengths indicated on the graph, and tested for chemotaxis to 1:10 butanone. The results showed that animals retained the memory for 4 h but not for 8 h. Five to six plates were used for all data. C, “Unlearning” of butanone enhancement. Wild-type animals were exposed to 12 μl of butanone and food (filled squares; butanone enhancement) or food only (open rhombuses; control), washed, kept on NGM plates with food but without butanone for the time lengths indicated on the graph, washed, and tested for chemotaxis to 1:10 butanone. Triangles show the results of the experiment in which wild-type animals were exposed to 12 μl of butanone and food, washed, kept on NGM plates with 12 μl of butanone without food, washed, and tested for chemotaxis to 1:10 butanone. The control experiment for the latter was not conducted. Animals lost the memory quicker in both cases than in experiments shown in B. Six plates were used for all data. D, The effects of the serotonin synthesis mutation tph-1 and exogenous serotonin on butanone enhancement. “+5HT” means that exogenous serotonin (5 mm) was contained in the preexposure plates. Four to 15 plates were used for all data. *p < 0.005, **p < 0.05, comparing “conditioning with butanone and food” with “conditioning with butanone and serotonin.” The error bars indicate SEM.