Alpine marmots freeze their memry during hibernation [Les marmottes alpines gelent leur mémoire pendant l'hibernation].

Résumé

Alpine marmots (Marmota marmota) hibernate 6-8 month each winter in order to survive unfavorable conditions. Since a negative impact of hibernation on memory is debated, we examined learning behavior and memory of a marmot colony housed and bred at the University of Marburg. During their active season (May-September), the marmots were trained in an operant and spatial learning task. Animals firstly learned to walk through a tube and to jump on two boxes to obtain a food reward. After six months of hibernation in a climate chamber with Ta of 6° C, performance was tested again. In both tasks, skills were found to be unimpaired after hibernation (boxes: first training day: 890.3 ± 91.8 s, before hibernation: 298.0 ± 35,7 s, after hibernation: 299.3 ± 14.4 s; tube: first training day: 330.8 ± 52.9 s, before hibernation/ 158.4 ± 9.0 s, after hibernation: 137.7 ± 6.3 s). We further investigated habitation during repeated open field exposure. In the first run, all animals showed a high locomotor activity (61.4 ± 8.6 crossed squares), whereas in the second run, animals immediately moved into one corner and remained there (7.2 ± 1.6 crossed squares). This habituation was not altered even after the 6 month of hibernation (6.1 ±1.1 crossed squares). Despite the unimpaired performance after hibernation, we observed that memory was less fixed during the summer period, since changes in test procedure or prolonged gaps between training sessions resulted in a slight impairment of test performance. We thus conclude that Alpine marmot freeze their memory during hibernation and retain skills entirely after arousal.