Biomedical Engineering Reference
In-Depth Information
2.3.8
Differential Classical Conditioning
Differential conditioning is an associative conditioning procedure in which animals
have to learn the difference between two or more stimuli, based on their differen-
tial outcome in terms of reinforcement. In the case of olfactory PER conditioning,
differential conditioning is achieved by using two odors, one (the CS+) that is
paired with sucrose solution and the other (the CS−) that is presented explicitly
without reinforcement (Fig.
2.2c
). Compared to the absolute-conditioning proto-
col, differential conditioning has the advantage of providing the researcher with an
internal control of the associative nature of the established memory, as bees have
to learn to respond to the CS+ but not to the CS−. Yet its use depends on the ques-
tion raised by the experimenter. Note, for instance, that differential conditioning
may boost discrimination capabilities as in the former case, bees are trained to
discriminate stimuli while in the later case, they are trained to respond to a unique
stimulus. Perceptual measures derived from one protocol or the other may, there-
fore, differ.
2.3.9
Data Collection and Making Graphs
For each conditioning trial, the percentage of conditioned responses (%CR) is cal-
culated as the number of bees showing PER to the conditioned odor with respect to
the total number of bees assayed. Typical results of absolute olfactory classical
conditioning of PER are shown in Fig.
2.3a-c
. In Fig
2.3a
, plotted CR (%) during
conditioning trials corresponds to an acquisition curve. Given the dichotomous
nature of the response measured (PER: 1 or 0), it is obvious that the gradually
changing acquisition curve does not necessarily refl ect the stepwise nature of indi-
vidual bee responses; yet it provides a basis to assess populational learning and to
promote analyses of individual performances with respect of group ones (Pamir
et al.
2011
). In Fig.
2.3a
, we see that bees from the paired group increased their
responses to the CS, while bees from the unpaired group do not show such increase,
thus showing the associative nature of performance variation in the paired group.
For memory retention tests, the percentage of PER both to the learned odor (CS)
and to the novel odor (NO) has to be plotted (Fig.
2.3b
). In the tests after 60 min,
which corresponds to a midterm memory (MTM), paired bees responded to the CS
but not to the NO, thus showing the presence of CS-specifi c MTM (Fig.
2.3b
). To
give a more precise measure of odor-specifi c memory, the percentage of bees that
showed PER to the CS+ but not to the NO can be plotted (specifi c response: %SR)
(Fig.
2.3c
). Figure
2.3d,e
show typical results of a differential-conditioning proce-
dure. Bees increased their responses to the CS+ but not to the CS− (Fig.
2.3d
).
Likewise, in the 60 min retention tests, bees responded to the CS+ and not to the
CS− (Fig.
2.3e
).
