Proboscis extension reflex
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Proboscis extension reflex (PER) is when a bee extends her proboscis (sticks out her tongue) as a reflex to antennal stimulation. It is evoked when a sugar solution is touched to a bee's antenna. This reflex response can be used to study bee learning and memory.
Use of PER
The PER paradigm is most commonly used in associative learning experiments in honeybees and bumblebees because of the ease in using PER in simple Pavlovian conditioning[1].
How PER works
As in classical conditioning, there are two steps in a PER experiment. The first step trains the individual to associate an unconditioned stimulus (US), such as a sugar reward, with a conditioned stimulus (CS), such as odor. The two stimuli are paired in such a fashion that the bee associates the presentation of the US with the CS. The bee is presented with an odor (CS) and an application of the sugar (US) solution to its antennae. She reflexively extends her proboscis, and she is immediately rewarded with the sugar to reinforce her response. After some number of reinforcements, the bee should have made the association between the odor and the sugar. The second step in the PER paradigm tests whether or not the association is learned. If the association of the US and CS has been learned, then a conditioned response (CR) should be elicited in the presence of the CS, even if the US is absent. This time, the odor (CS) is presented to the bee in the absence of the sugar solution (US). If the bee has learned the association, then she will extend her proboscis (CR) regardless of whether the sugar solution (US) is applied to her antennae.
PER in honeybees
The PER paradigm has been successfully used to investigate olfactory learning in honeybees. Individual honeybees show first-order conditioning by associating an odor with a sugar reward and extending its proboscis even in the absence of a reward[1]. In addition, honeybees are also capable of second-order conditioning by learning to associate a second odor with the original odor[1]. The PER paradigm has also been used in honeybees to study motion learning[2], thermal learning[3], habituation, and reversal learning[4].
PER in bumblebees
Although the majority of PER studies are performed on honeybees, there is at least one successful study of using PER on bumblebees. Although bumblebees are slower than honeybees at learning through a PER paradigm, they are still able to associate odor with a food reward by eliciting the proboscis extension even in the absence of a food reward[5].
PER and learning asymmetry
Recently, interesting findings in PER studies show there is an asymmetry in olfactory learning between the two antennae i.e., one antenna is better at associative learning than the other antenna. In honeybees, individuals had either their right or their left antenna covered with a silicone sleeve, leaving the other antenna exposed. The bees that had their right antenna exposed were better at associating an odor with a food reward than bees that had their left antenna exposed[6]. The same study also found that the right antenna has more olfactory receptors than the left antenna, a possible cause for this laterilized PER learning[6]. However, other causes such as internal differences in the actual olfactory pathway or the central nervous system must not be ruled out just yet.
External Links
Picture diagram of PER on a honeybee
Picture of a honeybee sticking out her proboscis
References
- ^ a b c Bitterman et al. 1983. Classical Conditioning of Proboscis Extension in Honeybees (Apis mellifera). J. Comp. Psych. 97: 107-119.
- ^ Hori et al. 2007. Associative learning and discrimination of motion cues in the harnessed honeybee, Apis mellifera L. J. Comp. Physiol. A 193:825-833.
- ^ Hammer et al. 2009. Thermal learning in the honeybee, Apis mellifera. J. Experiment. Bio. 212:3928-3934.
- ^ Komischke et al. 2002. Successive Olfactory Reversal Learning in Honeybees. Learn. Mem. 9:122-129.
- ^ Riveros and Gronenberg. 2009. Olfactory learning and memory in the bumblebee, Bombus occidentalis. Naturwissenschaften 96:851-856.
- ^ a b Letzkus et al. 2006. Lateralization of Olfaction in the Honeybee Apis mellifera. Current Biology 16:1471-1476.