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, (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.

Continue 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 experience of pain.

Return Figure 4.24: Pain Pathways

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 methods for stimulating them?

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?