Introduction to Physiological Psychology Psych 260 Kim Sweeney [email protected] cogsci.ucsd.edu/~ksweeney/psy260eve.html Today… n Gustation and Olfaction n Somatosensation 1 Gustation Different modalities are encoded by different receptor types Somatosensation Proprioception Olfaction Gustation Audition Vision 2 Gustation n Taste receptors are scattered around surface of the tongue in clusters (taste buds) – NB- this means high convergence at very lowest level! Taste buds and papillae n Average person has ~5,000 taste buds, but exceptional individuals may have 500… or 20,000! (supertasters) n An individual taste receptor w/in a taste bud lives ~2 weeks 3 Gustation n 4 primary tastes (sweet, sour, salty, bitter) n 5th is umami, meat or savory (MSG) ? Gustation n Transduction of taste is similar to the chemical transmission that takes place at synapses. n The tasted molecule binds with the receptor and produces changes in membrane permeability that cause receptor potentials. n Different substances bind with different types of receptors, producing different taste sensations. 4 Receptors n Two different receptors are responsible for detection of sweet tastes. n Bitterness is detected by members of a family of about thirty different receptors. n The existence of so many different bitterness receptors suggests that although different bitter compounds share a common taste quality, they are detected by different means. Gustation salt n Most taste receptors (~90%) sweet respond to at least 2 basic tastes… sour bitter Ogawa et al., 1968 5 Gustation n If a given receptor does not respond exclusively to one kind of taste… n A given gustatory axon doesn’t either. Sucrose Salt Sour Bitter Gustation n We respond to many tastes that can not be created by combining primaries … – So how do we distinguish between chocolate and banana… and cilantro? 6 Population coding! The neural pathways of taste 7 The neural pathways of taste /(Solitary Nucleaus) VPM nucleus (thalamus) GUSTATORY, Top-down processing matters n Culture n Current experience – Information from other sensory modalities n Past experience 8 Top-down processing matters Peter Menzel, photography Taste and Smell work together n Try eating a jelly bean while holding your nose! 9 Smell and Vision work together Brochet, 2001 Taste and Sound work together! Spence et al., 2009 10 What could possibly go wrong? n Ageusia – inability to taste – Rare, because multiple pathways carrying taste information… but can occur after stroke or tumor damage to VPM thalamus or gustatory cortex The Chemical Senses: Smell and Taste n Gustation (taste) – Responds to chemicals in the mouth n Olfaction (smell) – Detects airborne chemicals n Food acts on both systems to produce flavor! 11 Olfaction- Broadly Speaking n Odorants enter through the nose, hit olfactory receptors, which have axons that enter the olfactory bulbs. n From the olfactory bulb, the olfactory tract projects to many, many brain areas, including amygdala and piriform cortex. The human olfactory system Remember: Olfaction is the only one of our senses to have direct access to the brain, without going through the thalamus first! But… it makes it to the thalamus eventually. 12 Olfactory bulb n Receives sensory information from olfactory receptor cells n Sends information to olfactory (piriform) cortex (among other places) n Also receives top-down information from cortex, amygdala, hippocampus Olfaction n Receptors are embedded in the olfactory mucosa of the nose – ~40,000,000 receptors in humans, – ~2,000,000,000 in a German Shephard! 13 Olfactory receptor cells n Like auditory receptor cells, they terminate in cilia n Transduction occurs when an odorant binds to the cilia n 6- Olfactory receptor cells n 5- Glomeruli n 4- Olfactory mucosa n 3- Cribriform plate n 2- (mitral cells) n 1- Olfactory Bulb n Glomeruli each contain many axons (~2,000!) from olfactory receptors… but any given glomerulus receives input from only one kind of receptor! 14 Another way of looking at it n There is high convergence: – Many receptor neurons converge onto few glomeruli (~150:1) – Many glomeruli converge onto a single neuron of the olfactory tract (~25:1) n This convergence increases the sensitivity of the olfactory signal sent to the brain! Olfaction n In humans there are (only!) several hundred different olfactory receptors n How can a (relatively) small amount of receptors lead to such a vast array of smells? – A particular odorant binds to more than one receptor, thus different odorants produce different patterns of activity in different glomeruli 15 The human olfactory system Vomeronasal organ Pheromones n Chemicals that influence that behavior of conspecifics (members of the same species) n Evidence of human pheromones – Changes in olfactory sensitivity across and menstrual cycle – Synchronization of menstrual cycles – Sex identification by smell (especially by women… and healthy mixes preferred) – Men can identify menstrual stage by smell 16 What can possibly go wrong? n Anosmia- the inability to perceive smells – A strong blow to the head can sever those axons that pass through the cribriform plate! – Old age is also often accompanied by a decreased ability to smell n Olfactory agnosia- inability to identify smells n Olfactory hallucinations n … among other things! The cutaneous senses n What kinds of things can we feel with our skin? n Pressure, vibration, heat, cold, pain 17 Transduction! n In the visual system, rods and cones transduce light to neural signals… n In the auditory system, hair cells transduce sound waves to neural signals… n In the olfactory and gustatory systems, receptors transduce chemicals into neural signals n In the somatosensory system, sensory neurons in skin, joints, organs transduce pressure (or heat, or location, or…) into neural signals… Receptor cells transduce stimuli into neural activity Stimulus Receptor Cell Response 18 Sensing and Moving/Responding n The two most basic nervous system functions! – Even single cell organisms can sense nutrients and toxins, and respond by moving towards or away n Complex organisms have specialized cells and systems to carry out these functions – our simplest but most crucial behaviors involve reflexive responses to sensory stimuli § pain reflex to avoid damage § increased breathing stimulated by blood CO2 Sensation and Perception n Generally speaking, the brain is sensitive to to change – when there is no change, no sensation 19 Somatosensation: Touch and Pain ` n Somatosensory system is three separate and interacting systems: – Exteroceptive – external stimuli – Proprioceptive and kinesthetic – body position and motion – Interoceptive – body conditions (e.g., temperature and blood pressure) Somatosensation: Touch and Pain n Exteroceptive System- specialized receptors respond to various stimuli – Touch (mechanical stimuli) – Temperature (thermal stimuli) – Pain (nociceptive stimuli) 20 A sensory stimulus presents different kinds of information n Modality – What kind? n Intensity – How much? n Duration – How long? n Location – Where? Your skin n Skin is the largest, heaviest organ of the body n Humans have both hairy and glabrous (hairless) skin. 21 Hairy and Glabrous n Hairy skin – Free nerve endings –painful stimuli, changes in temperature – Ruffini corpuscles –indentation of skin – Pacinian corpuscles –rapid vibrations – (Hair Follicles) n Glabrous skin – Free nerve endings, Ruffini and Pacinian corpuscles – Meissner’s corpuscles – stroking, fluttering, small bumps – Merkel’s disk – compression Touch and Pain Five cutaneous receptors that occur in the human skin 22 Somatosensation: Touch and Pain n Cutaneous Receptors: – Free nerve endings unmyelinated § temperature and pain – Merkel’s disks § gradual skin indentation – Meissner corpuscles § low frequency vibration – Pacinian corpuscles myelinated § sudden displacements of the skin – Ruffini endings § gradual skin stretch 23 Somatosensory Receptors n Deep receptors: large receptive fields (big patches of skin); - low spatial resolution. n Superficial receptors: small receptive fields (small patches of skin). – high spatial resolution: e.g. for reading Braille. Deep Receptors n (subcutaneous) (large RF): – Pacinian corpuscles: § Rapidly adapting § responds to rapid indentation of skin; vibration; motion (of object across skin). – Ruffini endings: § Slowly adapting § sense stretch of skin or bending of fingernails: this compresses the nerve endings. Perception of shape of objects. 24 Different receptors adapt at different rates Rapid Slow Very Rapid Slow Shallow receptors n (in superficial layers of skin) (small RF): – Meissner’s corpuscles: § Rapidly adapting § stroking, fluttering; detecting small bumps – Merkel disks: § Slowly adapting § give sustained responses to skin compression; pressure 25 Different receptors adapt at different rates Rapid Slow Very Rapid Slow Different receptors adapt at different rates Rapid Slow Slow Very Rapid 26 Receptive fields and adaptation of mechanoreceptors The intensity of a stimulus is transmitted by the frequency of the neural response Maximum response (Saturation) Sigmoidal response function/curve Firing Rate Firing Rate Threshold Stimulus Intensity 27 Characteristics of sensory receptors in the skin Receptor Stimulus Sensation Adaptation Location Steady Merkel's disk Pressure Slow Shallow indentation Meissner's Low frequency Gentle fluttering Rapid Shallow corpuscle vibration Ruffini's Rapid Stretch Slow Deep corpuscle indentation Pacinian Vibration Vibration Rapid Deep corpuscle Hair