PSY106 Fall 2024 Lecture 10 Notes (PDF)

WEEK 6, NOV 4TH – 10TH Two in-person lectures (Mon & Wed) Read Week 6 Readings on Canvas Complete Quiz 5 on Canvas by Sunday at 11:59pm Available at 5pm on Wednesday Optional: Attend a ULA session Optional: Participate in Week 6 Discussion by Sunday at 11:59pm WRITING ASSIGNMENT...

WEEK 6, NOV 4TH – 10TH Two in-person lectures (Mon & Wed) Read Week 6 Readings on Canvas Complete Quiz 5 on Canvas by Sunday at 11:59pm Available at 5pm on Wednesday Optional: Attend a ULA session Optional: Participate in Week 6 Discussion by Sunday at 11:59pm WRITING ASSIGNMENT Assignment page on Canvas contains all relevant details, including prompt, example, and a detailed rubric You can find this in the Week 7 module You will be writing about a sensation and an action using the neurobiology that we are covering in this unit I recommend working on the sensory part of this now, and then finishing up the action part after next Wednesday’s lecture Assignment is due Friday November 15th by 11:59pm Today’s Topics: 10A: Other Visual Pathways 10B: Auditory Transduction 10C: Auditory Pathways 10D: Olfactory Transduction 10E: Olfactory Pathways DR. SCUDDER PSY106 INTRODUCTION TO BIOPSYCHOLOGY FALL 2024 LECTURE 10A: OTHER VISUAL PATHWAYS DR. SCUDDER PSY106 GOALS OF THIS SECTION Define blindsight and explore the basis of this phenomenon Describe the pathway that sends information to the hypothalamus BLINDSIGHT Some individuals are “cortically blind” – damage to the back of the brain (primary visual cortex) have left them unable to consciously perceive visual stimuli Hold a basketball up in front of them and ask them what it is, and they wouldn’t even be able to tell you that you’re holding something up Some of these “blind” individuals can still react to an incoming object, or avoid obstacles when walking – we call this blindsight BLINDSIGHT He wouldn’t be able to describe the obstacles in front of him, but has no problem moving around them – what could explain this? ANOTHER ROAD FOR RGC AXONS About 10% of RGCs send their axons to a different brain region after reaching the optic chiasm – the superior colliculus (also called optic tectum in some animals), located in the midbrain This retinotectal pathway allows for rapid and somewhat automatic (non-conscious) movements of our eyes, head, and limbs If the retina -> LGN -> cortex pathway is damaged, retina -> superior colliculus pathway will be intact and can allow for some basic visually guided movements Mystery #2 = Solved! MYSTERY #2 A man has been blind from birth – if you show him a picture of a ball, he would not even be able to tell that you are holding up a picture, much less tell you what the picture is of. However, you toss a ball at his face, and he grabs it from the air. Was he lying about being blind? How could he do this? This man likely has damage to his visual cortex, and thus cannot consciously perceive any visual information. However, his retinotectal pathway is intact, allowing him to react to some types of visual stimuli VISUAL PATHWAYS The eye (retina) Photoreceptors (rods & cones) Bipolar One final visual Cells pathway! Retinal Ganglion Cells Retina -> Thalamus = “retinofugal” Thalamus Tectum (Midbrain) Lateral Superior Geniculate Colliculus Nucleus Retina -> Superior Cortex Colliculus = “retinotectal” Primary Visual Extrastriate Cortex Cortex CIRCADIAN RHYTHMS Many biological functions (and our wakefulness) vary throughout the course of a 24-hour day These fluctuations are known as circadian rhythms External light is used to “tune” these rhythms and keep them in sync with daytime vs nighttime Light information is passed from the retina to the suprachiasmatic nucleus (SCN) in the hypothalamus  VISUAL PATHWAYS The eye (retina) Retina -> Hypothalamus= Photoreceptors This pathway supports “retinohypothalamic” (rods & cones) conscious visual perception, but Hypothalamus our brain also does some visual Bipolar processing that we’re not Suprachiasmatic Cells consciously aware of nucleus (SCN) Retinal Ganglion Cells Retina -> Thalamus = Thalamus Tectum (Midbrain) “retinofugal” Lateral Superior Geniculate Colliculus Nucleus Retina -> Superior Cortex Colliculus = “retinotectal” Primary Visual Extrastriate Cortex Cortex INTRODUCTION TO BIOPSYCHOLOGY FALL 2024 LECTURE 10B: AUDITORY TRANSDUCTION DR. SCUDDER PSY106  SENSORY SYSTEMS Audition and Light somatosensation: sensory neurons Energy Sound respond to physical movement or Somatosensation pressure applied to Touch them Self (body) Ion channels get physically pushed open, causing a Odors depolarizing inward Chemicals flow of ions Tastes GOALS OF THIS SECTION Describe what sound is and how it affects our nervous system Explore the components of the inner ear Describe the process of auditory transduction SOUNDWAVES Sounds are audible variations in air pressure Fluctuations in pressure cycle up and down, and the number of cycles per second is called the frequency (measured in Hertz (Hz)) Human range of frequency detection is 20 Hz - 20,000 Hz (20 kHz) Different species have different ranges – for example, mice make and hear ultrasonic vocalizations at 20 kHz – 50 kHz We lose our high-frequency sensitivity as we age – many of you can hear frequencies that I cannot! A TEEN REPELLANT? https://www.youtube.com/watch?v=iN3PBpInNJM STRUCTURE OF THE EAR Outer ear: Gathers and funnels the environmental soundwaves towards the middle ear Middle ear: converts changes in air pressure into movement of tiny bones called ossicles, which push fluid in the inner ear around Inner ear: converts movement of fluid into neural signals Let’s skip over the outer and middle ear and jump straight into the inner ear  INNER EAR The final ossicle of the middle ear (the stapes) is pushed in and out of an opening called the oval window, which disturbs fluid in the cochlea Cochlea – a long, fluid-filled, multi- chambered spiral that contains the basilar membrane The basilar membrane is a long strip of tissue covered with several types of cells (including neurons called hair cells) that get physically pushed by the moving fluid within the cochlea BASILAR MEMBRANE Sitting just on top of the basilar membrane is a slab of cells called the Organ of Corti, which contains neurons called hair cells Kim et al., 2018, Scientific Reports HAIR CELLS When the basilar membrane wiggles up and down, protrusions on hair cells called stereocilia are pushed around Hair cells are neurons, though they don’t have action potentials, axons, or dendrites What is the transduction mechanism for sound – how do these physical movements become neural signals? HAIR CELLS The physical bending of stereocilia opens up potassium channels The fluid (endolymph) is unusually high in K+, so K+ ions have a strong inward driving force here K+ influx causes depolarization of hair cells, which allows for the We don’t have time to release of glutamate (no cover it, but the action potentials here) vestibular system uses very similar hair cells to detect head movements  A NEW TYPE OF GATED CHANNEL Now we know three types of gated ion channels: Voltage-gated channels, which open up at a specific membrane potential (such as voltage-gated sodium channels and voltage- gated calcium channels) Ligand-gated channels, which open up in the presence of a specific compound (such as AMPA receptors and GABA receptors) Mechanically-gated channels, which open up due to the physical movement of the cell (K+ channels in hair cells) Our sense of touch relies on mechanically-gated channels as well – pressure applied to our skin causes depolarization of mechanoreceptive cells AUDITORY TRANSDUCTION 1. Outer ear & middle ear gather soundwaves and convert them into physical movement, pushing on the oval window of the inner ear 2. Fluid in the cochlea of the inner ear is pushed around in a way that causes the basilar membrane to wiggle up and down in various places 3. The movement of the basilar membrane causes the stereocilia of hair cells to move back and forth 4. Stereocilia movement causes mechanically-gated potassium channels to open up, allowing potassium to enter hair cells and depolarize them 5. Depolarized hair cells release glutamate onto nearby spiral ganglion neurons Where does this information go? INTRODUCTION TO BIOPSYCHOLOGY FALL 2024 LECTURE 10C: AUDITORY PATHWAYS DR. SCUDDER PSY106 GOALS OF THIS SECTION Describe the main circuit involved in processing auditory information Describe the tonotopic organization of auditory cortex AUDITORY PATHWAY Depolarization of hair cells causes them to release glutamate onto neurites from neurons in the nearby spiral ganglion This glutamate triggers action potentials in those spiral ganglion neurons, which have axons that enter the brain and contact neurons in the medulla Spiral Ganglion Medulla  We likely consciously hear a sound when the information reaches auditory cortex Primary Auditory Thalamus Cortex (A1) is located along the Tectum side of the (Midbrain) temporal lobe Medulla Remember this pathway: Cortex Thalamus Inferior Colliculus (midbrain) Nuclei in the medulla Spiral Ganglion TONOTOPIC MAP Wiggled by high Wiggled by low frequencies frequencies When the hair cells here are When the hair cells here are activated by the wiggling, the activated by the wiggling, the auditory system knows that a high auditory system knows that a low frequency sound has been detected frequency sound has been detected Most sounds will wiggle the membrane in many different locations, so the set of neurons that end up activated encodes the soundwave TONOTOPIC MAP This separation of various frequencies in a complex sound occurs early (in the cochlea) And persists through the pathway, apparent in the organization of primary auditory cortex AUDITORY CORTEX Apart from the fact that tonotopic maps exist in auditory cortex, much of the organization of these areas is a huge mystery We know very little about what determines the response properties of various neurons in this region (how their spiking relates to the characteristics of the sound stimulus) Visual cortex has been far more deeply studied AUDITORY CORTEX Our auditory system relies on lots of contextual information to make sense of a noisy world Visual information helps us make sense of ambiguous speech (McGurk Effect) Expectation can strongly influence our conscious perception of an ambiguous auditory signal (auditory illusions – “Yanny/Laurel”) https://www.youtube.com/watch?v=2k8fHR9jKVM https://www.youtube.com/watch?v=7X_WvGAhMlQ https://www.tiktok.com/@keg_has_stiles/video/6970367683615395077  COCHLEAR IMPLANTS If the stimulating electrodes are threaded through the cochlea, but the inner hair cells there are damaged or nonfunctional, what are they directly stimulating? A) Primary auditory cortex neurons B) Thalamic neurons C) Spiral ganglion neurons D) Medulla neurons https://forms.office.com/r/cL3dy3ED45  COCHLEAR IMPLANTS If the stimulating electrodes are threaded through the cochlea, but the inner hair cells there are damaged or nonfunctional, what are they directly stimulating? A) Primary auditory cortex neurons B) Thalamic neurons C) Spiral ganglion neurons D) Medulla neurons  COCHLEAR IMPLANTS If the stimulating electrodes are threaded through the cochlea, but the inner hair cells there are damaged or nonfunctional, what are they directly stimulating? A) Primary auditory cortex neurons B) Thalamic neurons C) Spiral ganglion neurons D) Medulla neurons INTRODUCTION TO BIOPSYCHOLOGY FALL 2024 LECTURE 10D: OLFACTORY TRANSDUCTION DR. SCUDDER PSY106 GOALS OF THIS SECTION Describe the neurons responsible for sensing odorants in the environment Explore the organization of the olfactory epithelium and olfactory bulbs WHY DO WE TASTE AND SMELL THINGS? We have two chemical senses: our sense of smell (olfaction) and our sense of taste (gustation) These are the original senses – even extremely basic organisms can sense chemicals around them Enable us to find and assess potential food sources, avoid dangerous substances, and (sometimes) find compatible mating partners Tightly connected to our emotional system (more on that in Unit 3) – evoke strong, rapid responses that guide our behavior SENSE OF SMELL: OLFACTION Humans don’t heavily rely on this sense: only 0.01% of our brain volume is devoted to circuits for processing smell information Much higher in rodents: about 2% of mouse brain Our sense of smell strongly contributes to what we consider to be the flavor of food – it works with our sense of taste to generate flavor Odorants are chemicals in the air we breathe that cause the generation of neural signals in our olfactory neurons: chemical transduction mechanism SENSE OF SMELL: OLFACTION Odorants are chemicals in the air that pass over the olfactory epithelium and are absorbed into the mucus layer Odorants can then contact the cilia of olfactory receptor cells (neurons) The cilia are small protrusions off of the single dendrite that extends from the cell body Exploring the Brain (Bear, Connors, Paradiso) OLFACTORY RECEPTOR NEURONS Cilia are coated with G-protein- coupled-receptors which use odorants as their ligands G-protein cascade opens cation channels (don’t worry about specifics), causing depolarization Depolarization can initiate action potentials that travel down the axon The bundles of axons from olfactory receptor neurons are collectively called the olfactory nerve – they will carry information to the olfactory Similar to an EPSP! bulb Exploring the Brain (Bear, Connors, Paradiso) POPULATION CODING Each neuron expresses a single receptor type, but that receptor can respond to multiple odorants (has multiple ligands) Estimated to be more than 400 receptor types, which means 400 unique olfactory receptor neuron types – mice have more than 1000 unique types! A single odor does not activate a single type of ORN, but each neuron will be differently sensitive to specific odorants based on the receptor type it has Our perception of a smell is created by a unique pattern of activity across a population of receptors Exploring the Brain (Bear, Connors, Paradiso) OLFACTORY BULBS Olfactory Olfactory epithelium will contain Nerve many ORNs of each of the ~400 types Approximately 10-20 million ORNs in total Neurons expressing the same type of receptor all send their axons to the same glomerulus (bundle within the olfactory bulb) Within glomeruli, ORN axons make contact with dendrites of nearby olfactory bulb neurons called mitral Human Mouse cells Size of olfactory bulb varies wildly between species – ours are tiny Exploring the Brain (Bear, Connors, Paradiso)  GLOMERULI Olfactory bulb Olfactory nerve Olfactory epithelium Exposed to the environment and therefore can be damaged Open Neuroscience Initiative ANOSMIA: LOSS OF SENSE OF SMELL Very few individuals are anosmic from birth, but many more can permanently lose sense of smell from injuries and illnesses Poses many problems: smell can allow us to assess safety of situations or food products Also linked to high rates of depression – tight link between olfactory system and emotion Covid can induce a transient anosmia – have you experienced this? INTRODUCTION TO BIOPSYCHOLOGY FALL 2024 LECTURE 10E: OLFACTORY PATHWAYS DR. SCUDDER PSY106 GOALS OF THIS SECTION Describe the brain circuits that enable conscious perception of smells and emotional responses to smells Discuss the existence of pheromones and their behavioral importance OLFACTORY PATHWAYS Orbitofrontal cortex The olfactory bulb neurons (mitral cells) primarily send their axons (olfactory tract) to an area called piriform cortex, which can trigger emotional responses to smells Piriform cortex also sends information to the thalamus, which relays it to other areas in the frontal Piriform cortex is found on the ventral lobe, generating conscious (bottom) surface of the brain and is perception of the smell very closely intertwined with emotional regions like the amygdala Wilson, 2012 OLFACTORY PATHWAYS Olfactory receptor Axons in the olfactory tract carry neurons (olfactory epithelium) information from the olfactory bulb directly Olfactory nerve to olfactory cortex, also known as piriform cortex Mitral cells in the Doesn’t need thalamus to get to cortex! olfactory bulb Emotional response: information from Olfactory tract olfactory cortex goes to diffuse limbic areas (more in Unit 3) Olfactory cortex (piriform cortex) Conscious perception: from olfactory cortex to thalamus (different nucleus from LGN) and other areas of frontal cortex Thalamus Emotion regions (limbic system) Frontal cortex PHEROMONES Organisms can secrete compounds called pheromones that influence the behavior of other organisms In mammals, pheromones are typically detected by the vomeronasal organ, though humans generally do not have this Pheromones can stimulate aggression, defensive behaviors, and influence mating decisions Humans seem sensitive to some pheromones through our olfactory system, but much of the data is inconclusive MARIJUANA AND THE SENSE OF SMELL THC is the psychoactive component of marijuana (the chemical that makes you feel high when you ingest/inhale marijuana products) THC affects neurons by binding to receptors called cannabinoid receptors throughout the brain The olfactory bulbs have lots of cannabinoid receptors (in rodents, at least), and THC appears to enhance olfactory processing – it boosts the sense of smell This seems to stimulate the appetite, causing the animal to seek out and ingest more food Scientific American: “Why Marijuana Gives People the Munchies” MYSTERY #3 A group of friends go out for dinner, then head back to their apartment to responsibly use some legal recreational substances. Soon after, the smell of wings wafts into the room and they suddenly feel extremely hungry – they decide to order WingStop, even though they just ate. Why would they feel this way? The THC in the marijuana they consumed activated cannabinoid receptors on neurons in their olfactory bulbs, heightening their sensitivity to smell and stimulating their appetites  KEY CONCEPTS, PART 1 Bipolar neurons react Information is passed from differently to the presence photoreceptors to bipolar cells of light based upon their to retinal ganglion cells, which expression of glutamate send axons out of the retina as receptors the optic nerve Visual information is processed in the dorsal RGC axons get reorganized and ventral streams, at the optic chiasms to allow allowing us to build a mental picture of the Some visual information is for the segregation of visual world around us sent to the midbrain and hemifields to the hypothalamus  KEY CONCEPTS, PART 2 Inner hair cells transduce soundwaves into neural signals through depolarization caused by mechanically All levels of the auditory system Soundwaves are the gated potassium are tonotopically organized, result of fluctuations channels meaning that similar in air pressure frequencies will be processed by nearby neurons Emotional responses to Olfactory receptor neurons smells arise from the in olfactory epithelium activation of olfactory cortex detect odorants using by olfactory bulb neurons, GPCRs and pass information while conscious perception to the olfactory bulbs requires additional connections to frontal cortex via the thalamus WEEK 6 KEY TAKEAWAYS By the end of this week, you should be able to: Explain how ON and OFF bipolar cells differ from each other Describe the path that retinal axons take through the optic chiasm in order to reach the LGN Differentiate between the optic nerve and the optic tract and the organization of each Differentiate between the dorsal and ventral streams of visual processing Provide one explanation for the phenomenon of blindsight Trace the flow of visual information through three distinct pathways from the retina Explain what sound is and how it becomes transduced into neural signals List the major components of the auditory system and describe its tonotopic organization at multiple levels Describe how odorants lead to neural signals in our olfactory system Identify the major components of the olfactory pathways that enable conscious perception of odors and emotional responses to them WEEK 6, NOV 4TH – 10TH Two in-person lectures (Mon & Wed) Read Week 6 Readings on Canvas Complete Quiz 5 on Canvas by Sunday at 11:59pm Available at 5pm on Wednesday Optional: Attend a ULA session Optional: Participate in Week 6 Discussion by Sunday at 11:59pm