SENSORIMOTOR LEARNING IN BUMBLEBEES - LONG-TERM RETENTION AND REVERSAL TRAINING

Bumblebees were trained in biologically realistic sensorimotor tasks t o test how learnt information from more than a single task is organise d in memory, Bees (Bombus impatiens and Bombus occidentalis) learned t o collect sucrose solution from the arms of small T-mazes. The reward was offered in the right arm of a maze when the entrance was marked bl ue, and in the left arm when the entrance was yellow, Bees were traine d on either one or both of these tasks until after they had reached sa turation in terms of speed and accuracy, One group of bees (Bombus imp atiens) was evaluated for long-term retention by retesting (a) on the day after training and (b) between 3 and 4 weeks after training, Perfo rmance did not decline overnight but, when bees were tested after a de lay of several weeks, an increase in error scores and times taken to n egotiate mazes occurred, However, bees started out at a better level t han during the initial training, indicating that information acquired during initial training had not been entirely erased from memory, A se cond group of bees (Bombus occidentalis) was tested to see whether it was possible to reverse the association between colour and direction, so that blue entrances now meant that the reward was on the left side, and yellow entrances meant that it was on the right, Bees reached sat uration on both tasks as rapidly as they had during the initial traini ng, However, after a second reversal, bees chose directions randomly f or several hundred trials, indicating that the first-learnt colour-dir ection associations had not been forgotten as a consequence of the fir st reversal: instead, information from the initial training must have been retained, but actively suppressed, causing difficulties in reesta blishing the appropriate sensorimotor associations during the second r eversal, Finally, a single Bombus impatiens worker was trained on only a single task, but with multiple reversals, The bee went through an i ntermediate phase when performance was poor until, after more than sev en reversals, it required only three trials to assess that a reversal had taken place, This indicates that bees can learn actively to suppre ss irrelevant information, but only with an extended training schedule , Taken together, these results suggest that sensorimotor information is rarely lost from long-term memory, either during extended lay-offs or during interfering reversal training sessions, Organizing, correctl y retrieving and suppressing information accumulated in memory seems t o be more of a challenge than storing new information.