(operant and classical components)
As described when explaining the Drosophila
flight simulator, in this paradigm the rotational speed of the arena
is made proportional to the fly's recorded yaw torque around its vertical
body axis. This enables the fly to stabilize the rotational movements of
the panorama (i.e. to fly straight) and to adjust certain flight directions
with respect to particular visual landmarks. Usually, the landmarks are
4 patterns of alternating shapes evenly spaced at the periphery of the
arena. Whenever one of the two pattern types is in the frontal position,
the fly is punished by an infrared lightbeam, focussed onto its abdomen.
Drosophila quickly learns to avoid the heat and stabilize the arena
with the 'cold' pattern in the frontal position, with short excursions
into the heated sectors. The perfomance increases during the training period,
suggesting that some learning occurs during the flight. If the heat is
permanently switched off, the flies keep their pattern preference towards
the previously 'cold' pattern for at least several minutes.
Flies are unable to develop a pattern preference if they fly in 'open
loop' and the movements of the arena (together with the heating schedule),
recorded from a previously trained fly, are played back to them. However,
Drosophila can be trained classically as described when explaining
the Drosophila flight simulator.
Thus, in this paradigm, it is not solely the sequence of patterns associated
with heat that determine learning performance, but some operant component
is required as well.
Pattern avoidance learning is an operant process. The flight
simulator establishes normal negative feedback between angular velocity
and yaw torque. Instead of a single stripe the panorama consists of 4 equally
spaced patterns as shown when describing the Drosophila
flight simulator. Flies are trained to avoid every second pattern by
being heated with the IR beam whenever the respective pattern is in the
frontal quadrant of the visual field (pattern width (max.) d = 40°;
height (max.) theta = +- 20°). Each experiment lasts 9 x 2 min. After
2 x 2 min of training (light shaded bars) a test period (hatched bars)
without heat is introduced; this whole sequence is repeated once; during
the last three 2-min intervals the fly is trained twice for 2 min to avoid
the alternative patterns and is subsequently tested. In (a) all training
periods are digitally recorded and one day later flies are subjected to
the identical sequence of pattern motion and heating as during the original
experiment. The subsequent test shows that in this passive manner flies
do not learn to avoid the heat-associated patterns (black bars). Controls
ruling out fatigue not shown. In (b) the patterns are distinguished only
by their position in the arena which is not a cue for associative learning
in this paradigm. The avoidance index is defined as (t2-t1)/(t2+t1)
with t2 being the time during which the patterns not associated
with heat were kept in the frontal quadrant of the visual field. Error
bars are SEMs. |
