Biomedical Engineering Reference
In-Depth Information
One way to get rid of this effect is to discard those bees that exhibit spontaneous
PER upon the fi rst olfactory stimulation (fi rst conditioning trial).
We recommend always using two different odors in any experiment in which an
absolute-conditioning protocol will be used. In absolute conditioning animals learn
that a unique CS is reinforced. Yet, to show that the acquisition evinced in a learning
experiment is stimulus specifi c (here odor specifi c), it is recommendable to run the
experiments with two parallel groups, one group trained with a CS1 paired with the
US and another group trained with a CS2 paired with the US. Using two odors has
the additional advantage of allowing a test of memory specifi city: each bee is trained
with one odor (say CS1) and will be tested afterwards with two odors, the condi-
tioned odor (CS1) and the other odor (the CS2 used for the other group) which will
be novel to it (NO). In this way, it is possible to distinguish between memories that
are odor specifi c (CS specifi c), and which should be only evoked by the CS1, and
unspecifi c PER responses which are elicited by the NO. The difference between
these two response categories (to the CS and to the NO) provides an assessment of
the CS-specifi c memory. As mentioned above, to balance the effect of the two cho-
sen odorants in the experiments, half the bees should be conditioned with CS1 and
the other half with CS2. The use of two odors that are well distinguished from each
other and are easily associated with sucrose solution is recommended (e.g.,
1-nonanol and 2-hexanol) (Guerrieri et al.
2005a
).
2.2.6
Odor Ventilation
When carrying out olfactory learning experiments, the odors presented should be
exhausted from the experimental system as soon as the stimulation ends. This
ensures that the temporal properties of the stimulus are well controlled. Therefore,
a ventilation system should be made with duct hose, one end being set at the experi-
mental setup and the other end connected to a standard air extraction. During con-
ditioning and test trials, honeybees are set individually in front of the odor stimulation
device, with the exhaust at their back. Ventilation should not be too strong, as unin-
tended mechanical stimulations from the ventilation may interfere with olfactory
learning.
2.2.7
Olfactory Stimulation (CS)
In the laboratory, researchers use computer-controlled odor stimulation devices
(Galizia et al.
1997
) to deliver the CS to antennae of the conditioned bees. Although
such systems allow well-controlled olfactory stimulation, PER conditioning can be
also performed using simple plastic syringes. With gloves on, take two 20 mL
