Psychology 2115A/B Lecture Notes - Olfactory Bulb, Olfactory Mucosa, Piriform Cortex

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Published on 21 Apr 2013
School
Western University
Department
Psychology
Course
Psychology 2115A/B
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of 8
Chapter 15 Review: The Chemical Senses
By the end of this section, you should know:
Functions of smell and taste
Physiology of smell and taste
Flavour perception: sensory interaction of smell and taste
The Chemical Senses
Smell and taste as “gatekeepers”
o Identify things that need to be absorbed for survival
o Detect bad things in our environment (smell of decay, etc.)
o Smell and taste are the initial ways of our defense system to determine if something should be
approached and later be absorbed into our system or if something is bad and should avoid it so it
doesn‟t get absorbed into your system
Neurogenesis of receptors (rebirth)
o In the other systems, if you damage or destroy the receptors, they are gone (neural conductive
deafness, etc.)
o This is not the case for taste and smell in the sense that these receptors have constant
neurogenesis: reborn over and over again after a cycle of several weeks
5-7 week cycle for olfactory receptors
1-2 week cycle for taste receptors
o Due to their direct one-to-one contact with a chemical substance absorbing a chemical and
using that chemical for the basic sensation
o As a result, they become quite damaged over a short period of time
The Chemical Senses
Taste (gustation)
Smell (olfaction)
Sensory interaction (flavour)
Taste and smell are phyogenetically old receptor systems in our bodies
The sensory systems that allow us to detect and discriminate tiny molecules in the environment and
help us link external environmental cues and internal needs (thirst, hunger, etc.)
Unlike vision and auditory, taste and smell are emotionally vivid and perceptually vivid
Very much related to memory and cognition
Interactions with limbic activity
We have pretty good memories for smell and taste can bring back memories of the past
The Olfactory System
Macrosmatic vs. Microsmatic animals
o Macrosmatic: certain animals have a very keen sense of smell that is critical to their survival
(rats, dogs, etc.)
o Microsmatic: humans have a relatively good sense of smell but is not as keen as other animals
and not as crucial to survival
The role of pheromones: chemical signals released by an individual that affect the physiology and
behaviour of other individuals
o Olfactory cues that are not largely consciously detectable
o Play a big role in animal mating practices
o Not known whether we do the same in order to signal certain biological events
Stern & McClintock (1998)
Underarm secretions and menstrual synchrony
Thought that maybe women are secreting pheromones in the environment that other women are
picking up on, causing menstrual synchrony
Thought that this is a hold over our evolutionary past
Collected underarm secretions from 9 different women
Took the secretions and wiped them on the upper lip of recipient female subjects
Wanted to know whether the recipients would have synched menstrual cycles with the donor
participants
Found that menstrual synchrony occurred because secretions taken from the beginning of the cycles
shortened the length of the recipient‟s cycles
Suggests that the pheromones were part of the secretion even though the women did not report any
sort of odor detection and yet the changes still occurred
This suggests that perhaps human women are in fact secreting pheromones that are altering the
physiology of the women around them
How do we Measure Odor Detection?
Yes/no procedure
o Basic detection present or not present
o Given trials with odors and no odors
o Say yes or no if they do or don‟t smell anything
Forced choice
o Give participants two trials, one that has an odor and one that doesn‟t
o The participant has to indicate whether trial one or tow contains the smell
Both these procedures can be used to measure the detection threshold OR the different threshold
Detection Thresholds
Detection threshold: the minimum amount of a stimulus required to know that something is there
for the participant to indicate that they detect the presence of the stimulus
Dog odor sensitivity > rat odor sensitivity
Rat odor sensitivity > human odor sensitivity
Why?
o Sensitivity receptors? NO
Maybe the types of receptors we have for smell just aren‟t sensitive
However humans and animals have the same receptors with equal sensitivity
o Number of receptors? YES
The biggest difference seems to be the number of receptors they possess
Whereas the receptors themselves are the same, and therefore the sensitivity is the same, the
number of receptors that dogs have in comparison to humans is enormous
Difference Thresholds
Difference threshold: the smallest amount of difference that an individual can detect in the stimulus
o In the case of odor, it is the smallest difference in chemical concentration that can be detected
between two different samples
Olfactomer
o Device used to precisely present specific concentrations of olfactory stimuli
Human difference threshold is approximately 11%
o We can detect a difference at about 11% of chemical concentration can detect differences that
are 11% different
o Tells us that we are not sensitive
How do we Identify Odors?
Recognition threshold: concentration needed to determine quality of an odorant
o How much of that chemical is necessary for us to be able to identify a particular odor
Humans can discriminate among 100,000 odors, but they cannot label them accurately
o Our ability to recognize smells is very good, but our ability to label an individual odor is terrible
o Due to our relatively bad memory system in terms of labeling smells (cognition)
How do we Organize/Categorize Odor?
What is the physical property of odor that is linked into our sensory system?
Very difficult to map perceptual experience onto physical attributes to a stimulus/chemicals
We don‟t have language to describe the quality of odors other than that it is good/you like it or it is
bad/you don‟t like it
Some molecules that have a similar structure smell different and some molecules that have different
structures smell the same
The Olfactory System
Can be broken down into 3 parts
Olfactory mucosa (OM)
o Located at the top of the nasal cavity
o The chemicals comes into the system and are trapped in the mucosa
Olfactory receptor neurons (ORNs)
o Once it gets to the mucosa, the chemicals flow over the mucosa and come in contact with the
ORN
o The signal is transformed into an electrical signal that is eventually transferred to the brain
o Several types of ORNs around 350 different types in humans
Olfactory bulb
o Large amounts of convergence from ORN to olfactory bulb
Unlike vision or audition or even touch, the olfactory system is compromised of a whole bunch of
receptors that is particularly specialized for a particular chemical type
How do ORNs Respond to Different Smells?
Calcium imaging method
o Increase of Ca+ inside ORN
o Detect the amount of Ca+ inside ORN
o When an ORN is active, Ca+ decreases inside the ORN
o More Ca+ = less glow of ORN, therefore decrease in glow means higher strength of activation
o Less glow, more activity
Smells are coded by recognition profiles
o Has been used to determine that we encode smell neurally by sing a distributed code at the level
of the ORN
o Suggests that odorants are encoded by patterns of activation of ORNs depending on what the
stimulus is recognition profile
Activating the Olfactory Bulb
ORN sends signals to the Glomeruli in the olfactory bulb
Olfactory bulb considered part of the brain by some but not others (mid/low brain)
ORNs sends their signal to one, maybe two, of the glomeruli
How do Glomeruli Respond to Different Smells?
Two methods:

Document Summary

By the end of this section, you should know: Flavour perception: sensory interaction of smell and taste. Taste and smell are phyogenetically old receptor systems in our bodies. The sensory systems that allow us to detect and discriminate tiny molecules in the environment and help us link external environmental cues and internal needs (thirst, hunger, etc. ) Unlike vision and auditory, taste and smell are emotionally vivid and perceptually vivid. Very much related to memory and cognition. We have pretty good memories for smell and taste can bring back memories of the past. Thought that maybe women are secreting pheromones in the environment that other women are picking up on, causing menstrual synchrony. Thought that this is a hold over our evolutionary past. Collected underarm secretions from 9 different women. Took the secretions and wiped them on the upper lip of recipient female subjects. Wanted to know whether the recipients would have synched menstrual cycles with the donor participants.