Page 106 - Zoo Animal Learning and Training

78 Box A3 Makinng Sense oouScents: loactorry erception inuAnimals

VetBooks.ir considerably depending on the particular signals from potential prey (Gillingham and
Clark 1981), and elephants transfer potential
message being sent, and olfactory signals
have been shown to convey a staggering
(Rasmussen and Schulte 1998). In fact, the
amount of information on factors such as signals there using the tip of their trunk
sex, age, condition, reproductive status, typical ‘flehmen’ response of cats and many
group membership and even individual iden- ungulates, whereby they lift and curl the nose
tity (e.g. see Epple et al. 1987). But how are whilst raising and contorting their lips, relates
these olfactory signals perceived? to the stimulation of the vomeronasal organ
with urine from conspecifics. Overall, the
vomeronasal organ appears to be particularly
Scent Perception important in modulating reproduction and
social behaviour, and many neurons are acti-
Successful olfactory communication relies on vated by urinary‐borne chemicals signalling
the receipt and accurate discrimination of physiological state.
scent signals, all of which is handled by spe-
cialised olfactory processing equipment,
which is divided into two discrete systems. Perception and Learning
The first, the main olfactory system, is the
olfactory bulb, and this receives information Using this olfactory equipment, receivers
passed along millions of olfactory receptor must be able to extract and categorise the rel-
neurons travelling from the nose to the brain. evant olfactory information from encoun-
Neurons expressing the same olfactory recep- tered odours, all within environments infused
tor are clustered together in individual glo- with irrelevant and potentially confusing
meruli in the olfactory bulb, forming a kind of smells. Correct categorisation, or recognition,
layer that has been described as a spatial of different odours may be important in many
odour map (Uchida et al. 2000). Importantly, aspects of social life, including the modulation
in the context of learning and perception, the of competitive relationships and the mainte-
olfactory bulb appears to exhibit enormous nance of stable social groups, navigation and
plasticity in response to experience with reproduction. Although innate responses to
scents, and exposure to odours can modify some chemical signals are known, novel
the perceptions of those odours enormously odours are generally more difficult to discrim-
(e.g. Wilson and Stevenson 2003). In the sec- inate than familiar ones (Rabin 1988). In fact,
ond system, the accessory olfactory system, learning is perhaps the most important com-
the vomeronasal organ or Jacobson’s organ ponent of olfactory perception. Unsurprisingly,
(Keverne 1999), is responsible for scent detec- human adults and older children perform bet-
tion and is usually found in the main nasal ter at odour discrimination tasks than young
chamber of many but not all amphibians, rep- children (Lehrner et al. 1999), but importantly
tiles, and mammals. Neurons from the vome- improvement in the discrimination often
ronasal organ connect it to the accessory improves after exposure to that odour, whilst
olfactory bulb in the brain, which ultimately discrimination of other odours remains poor
feeds the hypothalamus via the amygdala. As (Rabin 1988). This suggests that maturity of
in the olfactory bulb, odours are detected fol- the receptor system itself is not driving the
lowing binding to receptors, but in this case observed odour improvement in discrimina-
the signals are non‐volatile and so are received tion with age. Rather it is specific experience
in the liquid phase. Additionally, animals may or learning that enhances olfactory percep-
exhibit various specialist behaviours in order tion. In fact, under conditions where a per-
to transfer signals to the vomeronasal organ. son’s capability for memory is reduced, such
For example, snakes touch their tongue to the as is the case in Alzheimer’s disease, the ability
vomeronasal organ after ‘tasting’ the air for to perceive odour quality is itself lost or