Memory of a choice direction in a T maze as measured by spontaneous alternation in mice: Effects of intertrial interval and reward.

Spontaneous alternation in a T maze was studied as a one trial learning paradigm in mice of the BALB/c strain. In the first experiment the combined effects of time interval between the first and second trial (intertrial interval: ITI), food deprivation and feeding given during the first trial, were shown to affect performance. Thus, on the one hand, the percentage of spontaneous alternation decreased as ITI increased; on the other hand, food reward dramatically improved spontaneous alternation for the 24-h ITI, but had no significant effect for 30-sec and 1-h ITI. Since the effect of feeding might be due either to an increase of arousal, thus favoring input of informations associated with the first choice, or to an improvement in memory consolidation, a second experiment was aimed at testing the effect of food given after the first trial. It was shown that, as in the first experiment, post-trial feeding improved spontaneous alternation on the second trial given 24 hours later with a temporal gradient of effect less than 30 min. These results clearly showed that the reinforcement of run to one side (first trial) increased the tendency to go to the other side 24 hours later. It is concluded that reinforcement might have two distinct effects: (i) according to SR theory, reinforcement increases conditioned responses and (ii), as shown here, acts on memory processes by preventing memory traces from fading. The fact that this last effect was only observed for long ITI suggests that short-term or transient memory and long-term memory are two relatively independent processes.