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Temporal determinants of long-term retention of olfactory memory in the cricket Gryllus bimaculatus

Yukihisa Matsumoto¹ and Makoto Mizunami^1,2,*

¹ Research Institute for Electronic Science, Hokkaido University, Sapporo 060-0812, Japan
² PRESTO, Japan Science and Technology Corporation (JST), Japan

View larger version (20K): [in a new window]   Fig. 1. (A) Experimental arrangement for conditioning. A syringe containing water or saline solution was used for conditioning. A filter paper soaked with peppermint or vanilla essence was attached to the needle of the syringe 10mm from its tip (see left). The filter paper was placed within 1 cm of the cricket's head so as to present a particular odour, and water or saline was then presented to the mouth (right). (B) The apparatus used for the odour preference test. WCH, waiting chambers; TCH, training chamber; CH, container holder; RA, rotating axle; OS, odour source; N, gauze net; SD, sliding door; H, holes connecting the chamber with two of three odour sources. (C) Typical time schedule for training and testing; preference tests (PTs, open columns) were performed before (PT-0) and 2 h (PT-1), 1 day (PT-2) and 4 days (PT-3) after training (Tr, filled column). The white and black parts of the time bar indicate photophase (12 h) and scotophase (12 h), respectively. A typical stimulus schedule for training is illustrated at the bottom, in which the hatched and shaded bars above the line indicate the presentation of peppermint or vanilla odour, and the white and black squares below the line indicate the presentation of water or saline solution, respectively. For appetitive conditioning, peppermint odour was associated with water (reward); for aversive conditioning, vanilla odour was associated with saline solution (punishment).

View larger version (19K): [in a new window]   Fig. 2. Effects of two-trial conditioning. (A) Stimulus schedules (see Fig. 1C for key to shading). Groups 1, 2 and 3 were subjected to two trials of differential conditioning (P+/V-) and elementary aversive (V-) and appetitive (P+) conditioning, respectively. (B) The preferences (PPIs) for peppermint of groups 1 (N=29), 2 (N=15) and 3 (N=18) before training and 2 h after training. Values are means + S.E.M. (C) Performance index (PI) of groups 1, 2 and 3 measured 2 h, 1 day and 4 days after training. Values are means + S.E.M.

View larger version (21K): [in a new window]   Fig. 3. Effects of four-trial conditioning. (A) Stimulus schedules (see Fig. 1C for key to shading). Groups 1, 4 and 5 were subjected to four differential conditioning peppermint-rewarded and vanilla-punished (P+/V-) trials, vanillapunished and peppermint-unpunished (V-/P0) trials, and peppermint-rewarded and vanilla-unrewarded (P+/V0) trials, respectively. Groups 2 and 3 were subjected to four trials of aversive (V-) and appetitive (P+) conditioning, respectively. (B) Performance indices of groups 1-5 (N=45, 22, 26, 22 and 23, respectively) 2 h, 1 day and 4 days after training. Values are means + S.E.M.

View larger version (20K): [in a new window]   Fig. 4. Effects of different numbers of differential conditioning trials. (A) Stimulus schedules (see Fig. 1C for key to shading). Groups 1, 2 and 3 were subjected to one, two and three sets of P+/V- conditioning trials, respectively. Group 4 crickets were subjected to two elementary appetitive (P+) conditioning trials followed by two aversive (V-) conditioning trials. (B) Performance indices of groups 1-4 (N=29, 45, 24 and 22, respectively) 2 h, 1 day and 4 days after training. Values are means + S.E.M.

View larger version (18K): [in a new window]   Fig. 5. Non-associative controls and the effects of inter-stimulus interval. (A) Stimulus schedules (see Fig. 1C for key to shading) for three nonassociated control groups (CS alone, US alone and CS/US unpaired groups) and for five differential conditioning groups with different relationships between CS and US (backward, coincident and forward 5, 10 and 20 s groups). (B) Performance indices of eight groups at 2 h after training. Values are means + S.E.M. (N=26, 21, 27, 25, 25, 23 and 20 from left to right). CS, conditioned stimulus; US, unconditioned stimulus.

View larger version (21K): [in a new window]   Fig. 6. Effects of inter-trial interval. (A) Stimulus schedules (see Fig. 1C for key to shading). Five groups of crickets were subjected to two sets of differential conditioning trials with inter-trial intervals (ITIs) of 30s (group 1), 1 min (group 2), 2 min (group 3), 5 min (group 4) and 10 min (group 5). (B) Performance indices of groups 1-5 (N=39, 40, 39, 45 and 47, respectively) 2 h, 1 day and 4 days after training. Values are means + S.E.M.

View larger version (14K): [in a new window]   Fig. 7. Effects of anaesthetic treatment with CO2. (A) The time schedule for the preference test (PT, open column) and training (Tr, filled column). In the training session, crickets were subjected to four trials of differential conditioning with an inter-trial interval (ITI) of 2 min. Crickets were anaesthetized with CO2 for 60s before and at various times after training (striped bar on the time schedule). Odour preference was tested before (PT-1) and 5 h after (PT-2) training. (B) Performance indices of 14 groups of crickets 5 h after training. Values are means ± S.E.M. The open circle indicates the performance of the group that received training but no anaesthetic treatment (N=38), and the open square indicates the performance of the group that received anaesthetic treatment 1 h before training (N=17). Filled squares show the performances of 12 groups (N=21-27) that received anaesthetic treatment immediately (0 min) or 1-60 min after training.