Inter-session delay and its effects on performance and retention of spatial learning on a radial maze with mice.

Spatial learning on the radial maze was studied in two inbred strains of mice (C57BL/6 and DBA/2). Five different periods of delay (no delay, 40 min, 2, 8, and 24 h) were inserted between sessions in order to analyze the role of this inter-session delay on training and on retest 1 month later. Results showed that learning profiles and performance levels varied widely with inter-session delay. When the delay was very short (no delay and 40 min), mice of both strains were incapable of learning the task but when the delay was more than or equal to 2 h, the mice succeeded very quickly. The inter-session delay also influenced the performance of mice in the 1-month retention test. C57BL/6 mice obtained good performances in the procedure including a 2-h inter-session delay, while DBA/2 mice obtained good performances with 2- and 8-h delays. These results demonstrate the importance of the procedure in complex spatial learning.