Biomedical Engineering Reference
In-Depth Information
Keywords
Absolute
conditioning
•
Classical
conditioning
•
Differential
conditioning
•
Honeybee
•
Learning
•
Memory
•
Olfactory
conditioning
• Proboscis extension refl ex (PER)
2.1
Introduction
Associative learning is a fundamental property of nervous systems, which is gov-
erned by conserved rules both across species and across modalities. In a classical
conditioning procedure, the animal is presented with two types of stimuli, the
unconditioned stimulus (US) and the conditioned stimulus (CS). The US is a stimu-
lus which innately evokes a certain response, while the CS is usually a neutral
stimulus without any initial connection with a response. Through forward pairing
of CS and US, the animal learns that the CS predicts US delivery and starts respond-
ing to the CS. The response evoked by the CS is termed conditioned response.
Classical conditioning is also called “Pavlovian conditioning,” after the work by
Ivan Pavlov who laid the foundations of this conditioning by studying conditioned
salivation in dogs, which resulted from pairings between sounds (CS) and meat
(US) (Pavlov
1927
).
Insects have good learning abilities subtended by a more simple neural system
and lower numbers of neurons than vertebrates (Mizunami et al.
2004
; Giurfa
2007
).
For this reason, several species of insects have become mainstream models for
research on learning and memory (Mizunami et al.
2004
). Thus, insect species as
diverse as honeybees, fruit fl ies, crickets, cockroaches, ants, and moths have been
shown to possess robust learning abilities, using behavioral experiments (Bitterman
et al.
1983
; Tully and Quinn
1985
; Matsumoto and Mizunami
2000
,
2002
;
Balderrama
1980
; Dupuy et al.
2006
; Daly and Smith
2000
). Among these insects,
honeybees (
Apis mellifera
) are reported to have the highest and broad range of
learning abilities (e.g., Menzel
1999
; Giurfa
2007
; Avarguès-Weber et al.
2011
;
Sandoz
2011
).
Honeybees are able to associate odors, colors, visual patterns, or tactile stimuli
with a food reward (Menzel et al.
1993
; Menzel
1999
; Giurfa
2007
). However, stud-
ies on learning and memory in honeybees have mostly used visual learning proto-
cols when the focus was on the performances of free-fl ying honeybees and olfactory
learning protocols when the goal was a full control of behavior in harnessed bees.
The latter are based on the conditioning of the proboscis extension refl ex (PER), a
case of classical conditioning which is relatively easy to carry out in the laboratory
(Giurfa
2007
; Giurfa and Sandoz
2012
).
The PER is a refl exive response which is part of the bee's feeding behavior while
foraging or within the hive (Frings
1944
). It is observed when the antennae, tarsi, or
mouthparts of a hungry honeybee come in contact with sugar solution; the bee then
automatically extends its proboscis to reach the sucrose solution (PER) and drink it.
In naïve bees, odors generally do not evoke the PER. During conditioning, an odor
(CS) is presented in close temporal association with a sucrose solution reward (US).
