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Forgetting and the extension of memory in Lymnaea

Susan Sangha^*, Chloe McComb^* and Ken Lukowiak

Department of Physiology and Biophysics, Faculty of Medicine, University of Calgary, 3330 Hospital Drive NW, Calgary, Alberta, Canada T2N 4N1

View larger version (16K): [in a new window]   Fig. 1. The 30 min training procedure results in a 1-day, but not a 3-day memory. A cohort of snails (N=24) received operant conditioning training of two 30 min training sessions separated by a 1 h interval (Sessions 1 and 2). In the first randomly picked group (N=12), we tested for long-term memory (LTM) 1 day later (Session 3). There was a significant effect between Sessions 1 and 2 (ANOVA; Fisher's LSD protected t-test, P<0.01), demonstrating learning (asterisk). As can be seen, LTM was also demonstrated, i.e. there was no significant difference (NS; Fisher's LSD protected t-test, P>0.05) between Session 2 and the 1-day memory test Session 3, and the significant difference from Session 1 remained (asterisk). The second group of snails, was tested 3 days later (3 days) and LTM was not demonstrated, i.e. there was a significant difference (Fisher's LSD protected t-test, P<0.01) between Session 2 and the 3-day memory-test Session 3, but not between this session and Session 1.

View larger version (18K): [in a new window]   Fig. 2. Preventing aerial respiration for 3 days does not alter subsequent aerial respiratory behaviour in the hypoxic training/testing apparatus. 12 snails were tested (Before) in the hypoxic testing apparatus as described in Materials and methods. 1 day following training they were placed for 3 days in a eumoxic aquarium with a barrier that prevented them from reaching the surface of the water, so that they could not perform aerial respiration. After 3 days the snails were tested (After) in the hypoxic training/testing apparatus and responded no differently (paired t-test; NS, P>0.05) than they did before being placed in a situation where they were not able to perform aerial respiration.

View larger version (18K): [in a new window]   Fig. 3. Submerging in the same context after operant training prolongs the memory for operant conditioning. (A) Two 30 min sessions separated by 1 h in the standard context were followed by 3 days of submersion in the standard context. The test session in standard context was significantly different (asterisk; Fisher's LSD protected t-test, P<0.01) from Session 1, demonstrating a 3-day memory. A change of context test (carrot, CC) was not significantly different from Session 1 (Fisher's LSD protected t-test, P>0.05, N=14). (B) Two 30 min sessions separated by 1 h in carrot context were followed by 3 days of submersion in carrot context. The test session in carrot context was significantly different (asterisk; Fisher's LSD protected t-test, P<0.01) from Session 1, demonstrating 3-day memory. A change of context test (standard; CC) was not significantly different from Session 1 (Fisher's LSD protected t-test, P>0.05, N=14).

View larger version (20K): [in a new window]   Fig. 4. Submerging snails in a different context does not prolong the memory for operant conditioning. (A) Two 30 min operant conditioning training sessions separated by 1 h in standard context were immediately followed by 3 days of submersion in carrot context. The test session in standard context was significantly different (paired t-test, P<0.01, N=14) from Session 2 but not from Session 1, showing that memory was no longer present. (B) Two 30 min operant conditioning training sessions separated by 1 h in the carrot context were immediately followed by 3 days of submersion in the standard context. The test session in the carrot context was significantly different (paired t-test, P<0.01, N=14) from Session 2 but not from Session 1, showing that memory was no longer present.