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First published online March 31, 2005
Journal of Experimental Biology 208, 1525-1536 (2005)
Published by The Company of Biologists 2005
doi: 10.1242/jeb.01545

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Boosting intermediate-term into long-term memory

Kashif Parvez, Ory Stewart, Susan Sangha and Ken Lukowiak^*

Department of Physiology and Biophysics, Hotchkiss Brain Institute, University of Calgary, 3330 Hospital Drive NW, Calgary, Alberta, Canada T2N 4N1

View larger version (21K): [in a new window]   Fig. 2. `Changing memory'. (A) A second bout of ITM-training (TS3 and TS4) 24 h after the first bout can cause LTM formation even if the behavioural phenotype of memory is absent. Yoked control snails (Yoked), given tactile stimuli at the same times as trained snails, did not exhibit LTM. (B) A 48 h interval between the two bouts of ITM-training does not result in LTM. *Significant difference in number of openings from control TS1 and TS3.

View larger version (19K): [in a new window]   Fig. 3. Immediate cooling after training session 2 (TS2) blocks memory boosting. (A) Cooling snails immediately after ITM-training prevents the establishment of an ITM memory trace sufficient for a second bout of ITM-training to produce LTM. (B) When the cooling was administered after the consolidation process had occurred (i.e. 2 h after TS2) LTM was apparent 24 h later (MT). *Significant difference in number of openings from control TS1 and TS3.

View larger version (19K): [in a new window]   Fig. 4. Cooling applied after ITM consolidation has occurred extends the persistence of the residual memory trace for at least 48 h. Cooling snails to 4°C for 2 h after TS2 extends the period of time effective to produce LTM to 48 h between bouts of ITM-training. *Significant difference in number of openings from control TS1.

View larger version (18K): [in a new window]   Fig. 5. Change of context and memory boosting. (A) A change in context on Day 2 ITM-training prevents the establishment of LTM. White bars, standard training context; black bars, carrot training context. See text for details. (B) Training in the standard context on Day 1 and then training in the carrot context on Day 2 does not produce a LTM on Day 3 in the carrot context. (C) Similar results were found as in B if we reversed the presentation of the contexts used for ITM-training.

View larger version (23K): [in a new window]   Fig. 6. Extinction training and the ability to `boost' memory. (A) Extinction training (E1 and E2) in the same context (hypoxic water; white bars) prevents LTM formation. (B) Extinction training in a different context (carrot-odorant containing hypoxic water; black bars) allows LTM formation. See text for details. *Significant difference in number of openings from control TS1 and TS3.

View larger version (25K): [in a new window]   Fig. 7. Altering the sequence of operant conditioning and extinction training in different contexts did not alter the observed results. (A) The interposition of extinction training (E1 and E2) in the standard context (white bars) on Day 2 did not prevent LTM formation as a result of a second bout of ITM-training in a carrot context (black bars). (B) The interposition of extinction training in the carrot context on Day 2 prevents LTM formation as a result of a second bout of ITM-training in a carrot context. *Significant difference in number of openings from control TS1 and TS3.

View larger version (21K): [in a new window]   Fig. 8. The somata of RPeD1 is necessary for memory boosting. Snails had either the somata of RPeD1 (R) or LPeD1 (L) ablated and were given 2 days to recover from the procedure. Both cohorts were given 2 days of ITM-training (TS1, TS2, TS3 and TS4) but only the snails that had the somata of LPeD1 ablated were able to form LTM. RPeD1 somata ablation but not LPeD1 somata ablation prevented memory `boosting'. *Significant difference in number of openings from control TS1 and TS3.

View larger version (24K): [in a new window]   Fig. 1. Intermediate-term and long-term memory in Lymnaea. (A) An interval of 0.5 h between training sessions TS1 and TS2 results in an intermediate-term memory (ITM) that persists for 3 h but not 24 h as observed during memory tests (MT). (B) An interval of 1 h between the 30 min training sessions TS1 and TS2 results in a long-term memory (LTM) that persists for 3 h and at least 24 h after the last training session (TS2). Yoked controls (see text for details) in A and B did not show ITM or LTM. *Significant difference in number of openings from control TS1.