Biomedical Engineering Reference
In-Depth Information
2.3.5
Memory Retention Test
Memory retention tests are performed to test for PER to two odors (CS, the
conditioned odor, and NO, the novel odor) delivered by two different odor syringes.
The order of presentations of the two odors should be randomized between bees to
avoid sequential effects. Thus, ten subjects (bee A-J) are fi rst tested with CS1 fi rst
and NO second, while the next ten subjects (bee K-T) are tested with the reversed
odor of presentation. As for conditioning, the ITI between odor stimulations is
10 min. Thus, proceeding like during the conditioning trials (see above) but without
US delivery is recommended.
2.3.6
Response Check for Sucrose Solution
At last, i.e., following the last retention test, the unconditioned response (PER to
sucrose) should be tested in all animals by applying sucrose solution to the anten-
nae. Bees that do not show the unconditioned response should be discarded from the
data, as their lack of response to the odors cannot be necessarily ascribed to a lack
of memory but could be due to a low physical condition.
2.3.7
Unpaired Conditioning
To ensure that honeybees acquired associative memory by absolute conditioning
(paired conditioning), several kinds of experimental controls can be performed in
parallel to normal conditioning. One of them is the explicitly unpaired conditioning
that has to be performed with a number of bees equivalent to that used in the
absolute-conditioning group. The results of both groups, ran in parallel, are com-
pared to determine whether increases in conditioned responses in the absolute-
conditioning group are the consequence of real associative learning. In the explicitly
unpaired group, bees receive unpaired presentations of the CS and of the US (fi ve
odor-only and fi ve sucrose-only presentations, 5 min apart in a pseudorandomized
sequence; Fig.
2.2b
). Thus, both the absolute-conditioning (the paired group) and
the unpaired group have exactly the same sensory experience (fi ve CS and fi ve US
presentations), the difference being in the pairing or absence of pairing between
odor and sucrose. An additional factor that needs to be controlled is the fact that the
number of placements in the setup is twice as higher (if not controlled) in the
unpaired group compared to the absolute-conditioning group. This can be balanced
by inserting between conditioning trials fi ve blank trials in the absolute-conditioning
group, in which the bee will be simply located in the setup without stimulation.
As responses to sucrose solution and learning performance may vary accord-
ing to the season and climate conditions (Ray and Ferneyhough
1997a
,
b
), the
same number of experimental and control animals should always be conditioned
every day.
