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Lecture 11

Lecture 11

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Matthias Niemeier

PSYB51 th November 26 , 2010 Lecture 11: Touch - Acoustic energy in a sound for a speech (i.e. vowels) - Formants: they’re peaks in the frequency spectrum of that sound. Vowels are harmonic sounds with these very regular intervals of high energy frequency levels going in regular steps (e.g. 200 Hz, 300 Hz...& so on)  At least 3 formants for a vowel! = 3 peaks where you’ve maximum energy  A vowel is not identified by the pitch, so not by the fundamental frequency itself but rather where these formants are relative to the fundamental frequency and relative to each other - Formants are good for distinguishing between different vowels; helps us with perceiving speech essentially! - Touch: e.g. such as vibrations - Proprioception: kinaesthetic receptors in our muscles, tendons, and joints; these receptors are also sensing mechanical displacements essentially - Haptics: when you use touch in an active way! PSYB51 November 26 , 2010 - Attributes: Receptive field: for which 1 receptor would be responsible/sensitive for Rate of adaptation: slow or fast depending on the receptor – so we pick out diff. information that way What are mechanoreceptors? Mechanoreceptors are sensory receptors that are responsive to mechanical stimulation, such as pressure and vibration. - So all these receptors have the same type of stimulation: mechanical displacements - BUT –> they have diff. receptive fields and diff. rates of adaptation FA I: the Meissner corpuscles sense skin slip; if you hold a cup (surface of it) and it’s sliding through your hands b/c you aren’t holding it tight enough = these cause low-frequency vibrations So that’s what these receptors are most sensitive to! FA II: Pacinian corpuscle – these receptors sense quick changes in terms of vibrations (e.g. your finger hits a surfae) so the first impact is coded as high frequency = first contact PSYB51 November 26 , 2010 SA I: Merkel complex senses spatial details, textures...etc [other’s listed on slide] = they’re sensitive to lower frequencies! = someone that reads Braille will mostly rely on these receptors! SA II: Ruffini endings sense lateral stretch (when your skin gets stretched – e.g. when you grasp for something); gives you an idea about what the shape of the hand is! Not useful for reading Braille This lateral stretch is very important for you to control so as to be able to grasp stably! - These receptors don’t sit in the skin itself...they’re found within muscles, tendons and joints! What is the role of the muscle spindle? The muscle spindle is a sensory receptor located in a muscle that senses its tension. The sensory response from the spindle is sent back to the central nervous system, conveying information about muscle length and thus regulating muscle tension. - Based on if a muscle is contracting or relaxing, muscle spindles give you an idea about position of the body part is in space (e.g. arm) relative to rest of the body - Neurons (alpha and gamma motor fibres) innervate the muscles, making it contract/relax - Additional fibres: Sensory fibres respond quite well to vibrations - So these receptors (muscle spindle) found in muscles, tendons, and joints! Name and describe the two types of thermoreceptors: The two types of thermoreceptors are warmth fibers and cold fibers. Warmth fibers are sensory nerves that fire when skin temperature increases, and cold fibers are sensory nerves that fire when skin temperature decreases. PSYB51 November 26 , 2010 - A-delta fibres: myelinated so info about pain travels fast! - C fibres: unmyelinated so info about pain travels slowly! - 2 phases of pain: so that is why you feel the heat faster than the cold - Hansen’s Disease: person has reduced or absence of pain perception - These ppl can’t notice anymore when something damages their body [i.e. don’t get away quickly enough from noxious stimuli] How does tactile information travel from the spinal cord to the brain? Tactile information travels from the spinal cord to the brain via two pathways: 1. The spinothalamic pathway 2. Dorsal column–medial lemniscal (DCML) pathway. - The spinothalamic pathway carries most of the information about skin temperature and pain, while the DCML pathway carries signals from skin, muscles, tendons, and joints. - All info travels through spinal cord: there’s one exception though! - Exception = cranial nerve fibres go into the brain directly through parts of the central nervous system that sit on top of the spinal cord! - Nerve trunks = info. highways - Spinal cord ends at : there are nerve fibres extending from this point! - 2 major pathways for somatosensory sensation in the spinal cord PSYB51 November 26 , 2010 - Many more synapses: more relays at each synapse = so you lose time - Why is pain slow? When you encounter pain and other stimuli = what you do is you get away from it  this is a REFLEX [it happens locally] = you don’t need to get that info. to the brain; so we’re still okay [as it happens quickly] somatosensation A collective term for sensory signals from the body. - So it runs through the medulla  then ventral posterior nucleus of thalamus  then S1 & then S2 - Patients...: these ppl can’t feel their muscles stretch when you move their hands and they can’t feel that you touched their hand; yet they might be able to perceive that their hand is moving - So why? When you move your hands in the air:  then you feel air resistance/air molecules hitting the surface of the skin [but these ppl can’t feel touch]  but the wind also makes the surface of the hand cooler = so the temperature receptors there sense that [as these ppl still have the sense of temperature which is conveyed through another pathway!] How are touch sensations represented in area S1? Touch sensations are represented in area S1 somatotopically. This means that the representations are mapped in correspondence to the skin, so that adjacent areas in the skin are ultimately connected to adjacent areas in the brain. What is a homunculus? A homunculus is a maplike representation of regions of the body in the brain. PSYB51 November 26 , 2010 - larger hand in picture means that many more neurons are representing it; the nose is smaller  So S1 has a very large hand area - So basically, the homunculus is designed so that the size of diff. body parts reflect how many neurons are representing certain parts of that body The Sensory Homunculus Careful experimentation (and cooperative subjects!) allowed Penfield to map out most of the somatosensory cortex (S1), not just the few areas marked in the figure at left. Penfield discovered two important qualities of S1:  The mapping from body areas to sub-areas in S1 is not arbitrary or haphazard. Rather, Penfield found an orderly somatotopic map of the body on S1. That is, areas that are close to each other in S1 represent body parts that are close to each other. You can see this in our probed locations: Starting from the third red circle up from the bottom, we move along S1 from the thumb to the forearm to the neck to the leg to the toes.  The sizes of the sub-areas of S1 do not correlate well with the sizes of the body parts driving the brain areas. For example, the lips occupy more space in S1 than do the legs! Slide 22: These two qualities of S1 are cleverly represented by the sensory homunculus, now shown curling around our diagram of S1. The homunculus’s body parts are shown lying on top of their corresponding receptive areas S1, and the sizes of the body parts are distorted in proportion to the extent of their representation in S1. - Topography preserved across these several areas - The brain re-organizes itself: connections between neurons is re-structured!; these neurons at once used to respond to the limb that is now missing = so although they do some other work now, they still remember to respond to the limb that they used to before Brain is plastic; it learns to re-use neurons in different ways! PSYB51 November 26 , 2010 - Pain perception is regulated/modulated! - 2 types of modulation - What is the role of the endogenous opiates? Endogenous opiates are chemicals released by the body in order to block the release or uptake of neurotransmitters necessary to transmit pain sensations to the brain, thus creating an analgesic effect - When you play sports –> if you hurt yourself a little bit = you might not even notice it b/c you experience analgesia! SG = substantia gelatinosa The SG has interneuron’s that sit in between motor neurons and sensory neurons = they’ve a gate function (gate neurons) So these neurons sitting in the SG, block the pain transmission system = neural control More on this theory in BIOB30 NOTES – LEC 13; SLIDE #4 - the SG is activated  which then dampens down pain perception - Gate control theory = BOTTOM-UP PAIN REGULATION! Central control = top-down regulation (from your brain) - Pain is modulated by higher level processes: including emotions and cognitions - Pain perception has a social context in regulation! In an experiment where male participants had to hold their hands in buckets full of ice cold water; they hold those hands longer if the experimenter is female versus male; gender of experimenter = independent variable! PSYB51 November 26 , 2010 - Experience of pain will be different depending on the social context - This will actually have very much top- down effect all the way down to the spinal cord; it has been shown! - It does have an effect on cerebral cortex as well! Example: ppl under hypnosis while they were participating under a PET study; they looked at how ppl experienced pain  Increase in the activity of S1 when ppl touched HOT WATER; but you also get activity in other parts of the brain (Anterior cingulate cortex)  Hypnotic suggestion: suggesting HOT WATER is hot when it is actually hot versus suggesting the that it’s not hot when it actually was  So the pain perception (activity) in S1 is the same no matter what the suggestion is BUT the activity in the anterior cingulate cortex changes!; so if in hypnosis you’re being told that you’re touching lukewarm water rather than HOT WATER (although it is hot)  then there is less activity in the anterior cingulate cortex (ACC) suggesting that the ACC is rather associated with negative experience of pain - What kind of function is the anterior cingulate cortex associated with? The anterior cingulate cortex is associated with the perceived unpleasantness of a pain sensation. - What kind of function is the prefrontal cortex associated with? The prefrontal cortex is associated with cognition and executive control. PSYB51 November 26 , 2010 - Absolute thresholds can be tested using Frey hairs - Human and horse h
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