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The Chemical Senses
• Olfaction detects airborne chemicals
– Our sense of smell
• Gustation detects chemicals in solution
that come into contact with receptors
inside the mouth
– Our sense of taste
Figure 4.22: The Olfactory System
Ramachandran V.S.& Hubbard, E.M. (2001), Psychosocial Investigations into the Neural Basis of Synaesthesia,"
from Proceeding of the Royal Society of London B Biological Sciences, 268, 979-983 (figure #3) (2001).
Olfactory System
• Employs about 1,000 different types of
receptors
• Only sense that does not send its
messages through the thalamus
• Processing in several brain regions
including frontal lobe and amygdala
• Strong relationship between olfaction and
emotional memory
Olfactory System (cont’d)
• Only sense that does not send its
messages through the thalamus
• Pathways from olfactory bulb sends
information on for further processing in
several brain regions
– Including frontal lobe and amygdala
• Strong relationship between olfaction and
emotional memory
Pheromones
• Chemicals released by one animal, and
when detected by another, can shape the
second animal’s behavior or physiology
• Role of pheromones in humans not clear
Smell, Taste, and Flavor
• Smell and taste act together to form
system known as flavor.
• Tastes and odors can prompt strong
emotional responses.
• Nutritional state can affect taste and flavor
of food and motivation to eat particular
foods.
• Flavor includes other characteristics of
food.
Somatic Senses and the
Vestibular System
• Somatosensory systems are spread
throughout the body
• Somatic senses include:
– Skin senses of touch, temperature, and pain
– Kinesthesia
• Vestibular system tells the brain about
the position and movement of the head
Touch
• Energy detected is physical pressure on
tissue.
• Many nerve endings in the skin act as
touch receptors.
• Touch is both an active and passive
sense.
• Changes in touch provide most important
sensory information.
Coding of Touch Information
• Intensity of the stimulus is coded by:
– Firing rate of individual neurons
– The number of neurons stimulated
• Location is coded by the location of the
neurons responding to the touch.
Temperature
• Some of the skin’s sensory neurons
respond to a change in temperature.
– “Warm” and “cold” fibers
• Sensations of touch and temperature
sometimes interact.
• Stimulation of the touch sense can have
psychological and physiological effects.
Pain
• Pain provides information about impact of
world on body.
• Information-carrying aspect of pain very
similar to that of touch and temperature.
• Two types of nerve fibers carry pain
signals from skin to the spinal chord.
• Pain pathways
• Cerebral cortex plays role in the
Continue
experience of pain.
Figure 4.24: Pain Pathways
Return
Emotional Aspects of Pain
• Specific pathways carry an emotional
component of the painful stimulus to
several areas of the brain.
• Overall emotional response depends
greatly on cognitive factors.
– Knowing about the pain
– Use of pain-reducing cognitive strategies
Modulating Pain
• Gate Control Theory
• Natural Analgesics
– Serotonin
– Endorphins
Thinking Critically:
Does Acupuncture Relieve Pain?
• What am I being asked to believe or
accept?
– Twirling a needle in the skin can relieve pain
• What evidence is available to support the
assertion?
– MRI studies
– Positive results in patients treated by
acupuncture for various kinds of pain
– Acupuncture associated with release of
endorphins
Thinking Critically:
Does Acupuncture Relieve Pain?
(cont’d)
• Are there alternative ways of interpreting
the evidence?
– Might simply confirm that the body’s
painkilling system can be stimulated by
external means
• What additional evidence would help to
evaluate the alternatives?
– More placebo-controlled studies of
acupuncture
– What is the general relationship between
internal painkilling systems and external
Thinking Critically:
Does Acupuncture Relieve Pain?
(cont’d)
• What conclusions are most reasonable?
– In some circumstances, acupuncture does
relieve pain, but it is not a cure-all.
– No evidence that acupuncture is better than
other painkilling procedures.
– Quality of future studies of acupuncture will
determine whether acupuncture finds a more
prominent place in Western medicine.
Proprioceptive Senses
• Sensory systems that provide information
to the brain about:
– The position of the body
– What each of part of the body is doing
• Vestibular sense indicates the position of
the head in space and its general
movements.
– Sense of balance
Vestibular Sense
• Organs:
– Vestibular sacs
– Otoliths
– Semicircular canals
• Neural connections
to:
– The cerebellum
– The autonomic
nervous system
– The eye muscles
Kinesthesia
• Sense that indicates where the parts of
the body are with respect to one another.
– Necessary guide for movement
• Kinesthetic information comes primarily
from the joints as well as muscles.
Focus on Research Methods:
The Case of the Mysterious Spells
• What was the researcher’s question?
– Is there a specific brain region that, when
activated by a seizure, causes the sensation
of orgasm?
• How did the researcher answer the
question?
– Used the case study method of research
– Studied person’s brain activity while she was
actually having a spell
Focus on Research Methods:
Mysterious Spells (cont’d)
• What did the researcher find?
– EEG showed seizures in right temporal lobe.
– MRI revealed small area of abnormal tissue.
– Seizures stopped after removal of tissue.
• What do the results mean?
– Person was having “localization-related
epilepsy.”
– Right temporal lobe may play a special role in
creating the sensory experience of orgasm.
Focus on Research Methods:
Mysterious Spells (cont’d)
• What do we still need to know?
– How specific is the linkage between activity
in this brain region and the sensory
experience of orgasm?
– Did person continue to experience orgasms
during sexual activity?