PSYCH 109 PDF Lecture Notes

- Proportion of slow wave sleep decreases from 40 years onwards. Children sleep more because they have to learn more - Less slow wave sleep (deep) when older so sleep is less satisfying - Without a strong theory of consciousness questions about consciousness in other animals or in...

- Proportion of slow wave sleep decreases from 40 years onwards. Children sleep more because they have to learn more - Less slow wave sleep (deep) when older so sleep is less satisfying - Without a strong theory of consciousness questions about consciousness in other animals or in machines remain uncertain. In later life slow wave sleep and overall time sleeping decreases Brain Lecture 24 - Some strokes damage in the limbic system of the brain will lead to uncontrollable laughter - Dopamine transmitter is responsible for the chills we get up our spine - Neuron parts: dendrites, axons, cell body, axon terminal and myelin function - Neurons perform computations inside the brain called thought. There were lots of neurons, 10-100 billion neurons in humans. Neurons form complex connections with other neurons - Dendrites: receive nerve impulses from other neurons, tree like branches off the cell body - Main function is to receive messages from another neurons - Axons: transmit nerve impulses, the long thin part of the neuron that carries the action potential and always for communication - Cell body/soma: has dendrites attached and contains a nucleus. Responsible for the cell maintenance and metabolism and can receive messages from other neurons, but this mainly occurs in the dendrites. Dendrites send the messages to the cell body - Cell body is about 5-100 microns in diameter and dendrites are short, few 100 microns - Myelinated axons: some neurons are coated in myelin, part protein and fat and if an axon is myelinated it shows up as white matter in brain scans - If the axon is unmyelinated it appears as grey matter. Myelin makes the nerve impulse or action potential travel faster. The nerve impulse travels at about 20 metres per second - If the neuron is unmyelinated the impulse will travel about 1 metre per second - The end of the neuron is the axon terminals that secrete neurotransmitters, chemical substances into the synapse - Motoneurons: begin in the central nervous system, exit through the spinal cord and end on muscle fibre. Responsible for movement and motor actions - Sensory neurons: bein at the sense organ (retina, skin, tongue) convey sensory information to the brain via the spinal cord - Interneurons: interposed between other neurons do most of computation in the brain - Glial cells are about 9-% of cells in the brain, acting as scaffolding and support for growing neurons. Later in development provide supportive scaffolding for mature neurons and can assist in repair processes when the tissue is damaged - When the neuron is in the resting state, not communicating, the inside of the axon is negative with respect to the surface by about -70 millivolts. This is the resting potential - When a pulse is applied that exceeds the excitation threshold by about -55 millivolts for the action potential to take place. The action potential is an abrupt short lived reversal in the electrical charge of an axon. Action potentials is much slower than electricity - This causes the inside to swing positive relative to the outside of the neuron. Positive charge travels down the axon until it reaches the axon terminals similar to a Mexican wave - Resting potential depends on positive sodium ions on the outside of the cell membrane - Ion channels let charged ions in and out of the cell - In the resting state sodium ions are kept on the outside by a sodium pump but in going ion channels remain closed in the resting state  - When a pulse is applied, ingoing channels open and sodium ions pour into the cell, reversing the voltage difference (positive). Sodium channels close and K+ ions go outside the cell - Sodium is pushed outside the cell and potassium ions are drawn inside. Inside and outside concentrations are returned to their original concentration - Dendrites receive the message from another neuron, the message goes to the soma and the action potential moves down the axon causing the inside to be more positive, all the way down the axon to the end of the neuron to terminal buttons where the synapse occurs - The synapse is where one neuron meets another. Transmission of an action potential along one neuron may cause the next neuron to fire (excitation) or it may inhibit firing (inhibition) - The dendrites between neurons to not touch, they have a small gap called the synapse - Governed by the release of neurotransmitters with many different roles. Neurotransmitters in a synapse or synaptic vesicle will move to the presynaptic membranes of the endfoot of the sending neuron and spill the neurotransmitter out to the synaptic gap between the sending and receiving dendrites and neurotransmitter bind to receptors on the postsynaptic membrane of the receiving dendrite of the receiving neuron via the lock and key model - Lock and key model: neurotransmitter molecules will only affect the postsynaptic membrane if the molecule shape fits into certain synaptic receptors - Within axon terminals there are synaptic vesicles filled with neurotransmitters and those synaptic vesicles come to the presynaptic membrane and spill the neurotransmitters into the synaptic gap. Depending on the shape, those neurotransmitters will bind onto the postsynaptic report of the receiving neurons dendrite to inform what to do - After the synapse has occurred the neurotransmitters do not sit in the synapse because we do not want activity all the time. They must be inactivated by cleanup enzymes or reused in synaptic reuptake, neurotransmitters are repackaged in vesicles through the presynaptic membrane and are reused in another synapse - How drugs and the synapse can interact: stimulate or inhibit neurotransmitter releases, stimulate or block postsynaptic receptor molecules or inhibit reuptake in vesicles Brain Lecture 25 - Divisions of the nervous system: CNS, peripheral nervous system and somatic/autonomic - The Hindbrain: pons, medulla and cerebellum - Forebrain: cortex, subcortical structures, thalamus, basal, ganglia, limbic and hypothalamus - Central nervous system: brain and spinal cord - The peripheral nervous system can be divided into the somatic nervous system and the autonomic nervous system. Somatic contains: afferent, efferent and cranial nerves - Afferent: takes information from sense organs to the brain, information is arriving - Efferent: exits, taking information from the brain to the sense organs - Autonomic nervous system is based on automatic processes: regulation of viscera (heart, lungs, dilation/constriction blood vessels, digestion and responses of sex organs) - Afferent nerves (sensory) transmit information from sense organs to brain and spinal cord - Efferent nerves (motor) transmit information from CNS to effectors (muscles/glands) that are the organs of action - 12 pairs of cranial nerves that enter and exist the hindbrain (pons/medulla) - Poke through holes in the skull with afferent and efferent functions. Control movements depending on the nerve and carry sensations from the head and neck - Regulate the glandular secretions in the head (tears and saliva) and control visceral functions - Olfactory nerves tracks lie under the prefrontal cortex in relation to smell  - Bell's Palsy: droopy side of the face and does not move as expected or the person may not be able to close one of their eyes. Large lifestyle and self esteem effects - Trigeminal neuralgia: affect trigeminal nerves, incredible pain in the face where traditional pain relief does not work - Photic sneezing: sneezing when looking at a bright light, a genetic quirk - Animal brain similarities/differences: all have two sides or hemispheres of the brain - Language production and comprehension occurs in the left side of the brain - Left and right hemispheres are split apart by a long fissure, the longitudinal fissure (no psychological function) that separates each side - Rats and rabbits have olfactory bulbs that protrude from the brain in relation to smell - Humans have a large part of the brain associated with sight (occipital lobe) our main sense - Structure at the back of the brain (hindbrain) are common across most animal species - Humans have convoluted cerebral cortices and in other species in more cognitively intelligent species compared to rat/rabbit which have smooth hemispheres - Hemispheres are anatomically similar but hemisphere function differently - Left hemisphere dominant for language, right for spatial awareness - Brain divided into three major parts, the hindbrain, midbrain and forebrain (cortex) Brain Lecture 26 - Pons is a structure of the hindbrain to do with conscious arousal with a relay role, relaying sensory information between cerebellum, cerebrum and other parts of the brain - Pons: regulates respiration and involved in sleep and dreaming, pons shuts down involuntary muscles during sleep so we do not move around - Medulla is involved in regulation of heart rate, blood pressure and rate of respiration, vomiting, defecation, reflexes and swallowing, all automatic processes - Simpler animals: crawling and swimming motions (not humans) - Strokes in the medulla region can cause patients to struggle swallowing, easy to choke - Cerebellum (cauliflower or coral looking at the back of the brain) knows what each part of the body is doing. Receives information from frontal lobes involved in movement - Knows what movements this lobe intends to accomplish before movement has occurred - Monitors information about posture/balance, coordination, produces eye movements that compensate for changes in head position so we do not fall over or become dizzy - Cerebellum is well developed in humans and primates due to our coordinated movements - May play a role in learning of new movements and movement skills - Cerebellum controls overall bodily balance. Damage due to injury, disease or alcohol (temporary) results in wild stance (feet far apart to balance) and staggering gait (walk) - Sequencing and timing of precise skilled movements. Damage leads to tremors during movement and inability to perform rapidly alternating movements - Influences thinking: damage impairs performance of tasks requiring exact sequencing - The midbrain is involved with auditory and visual stimuli: eye movement, large in birds of prey. Control movements used in sexual behaviour, fighting and decrease pain sensitivity - The forebrain (everything above the midbrain), cerebral cortex, thalamus, corpus callosum - Mammals (primates) have the largest forebrains, it surrounds and hides from view all the midbrain and half the hindbrain, it is very large - The part that is wrinkled is the cortex, the outer shell of the brain with the most important function for psychology. Covered in a film to protect the brain containing the spinal fluid - Three layers of meninges: dura, arachnoid and pia mater (innermost thin layer)  - 80% of the brain’s volume is the cerebral cortex and makes us humans with flexibility - Cortex is 2-3 mm thick made possible by convolution to fit in the brain by folding - Tasks performed by the limbic system or midbrain in non mammals are performed by the cortex in mammals. Over the course of evolution the cortex enlarged and subcortical structures such as the midbrain started to act as relay stations for that information - Gyri is a ridge with psychological function. The precentral gyrus is at the back of the frontal lobe and the postcentral gyrus is at the start of the parietal lobe - Sulcus is the groove between the ridges known as a fissure, no function - Cerebral cortex is grey matter - Thalamus is deep in the brain involved in receiving and relay station for sensory input - Receives sensory information from sense organs, performs simple analysis and passes results on to the primary sensory cortex. Except for one sense: smell - Hypothalamus: below the thalamus involved in homeostasis and species typical behaviour - Feeding, drinking, body temperature, sex. Controls much of the ability of autonomic system - Hypothalamus is a very small part of the brain but is crucial. Involved in the four F’s: fleeing, feeding, fighting, procreation. Also controls the pituitary gland in the forebrain Brain Lecture 28 - Lecture 27 was cancelled btw for the strike - Basal ganglia: regulation and smoothing of movement (beside the thalamus). Involved in balance and coordination. Allows movement to not be jerky - Parkinson’s disease is a progressive neurological disease impacting movement, small movements and jerky movements with lack of expression in face (lack of muscle movement) - Huntington’s disease is a neurological degenerative genetic disease that, in later stages, have no control over movement. Wildly out of control movement, difficult to swallow - Foreign accent syndrome also implicates the basal ganglia, usually a stroke or other brain injury leads to people speaking in a different accent following the stroke - Limbic system: hippocampus (memory) and amygdala (expression of emotion), deep in the brain close to the temporal lobe in the middle of the brain - The amygdala responds to a scary experience and also allows us to interpret fear in others - Amygdala allows us to form the expression of fear and interpret it in others - Damage - do not respond physiologically to fear or recognise fear - Fusiform gyrus has a role in recognising faces. Unlike other syndromes, Capgras syndrome the facial recognition is intact but believe that their loved one is an imposter - Damage to parts of the brain that connect the emotional response to a face of a loved one with a loss of connection between the limbic system and the fusiform gyrus - There is a physiological response to looking at a loved one: sweaty palms, dilated pupils etc - Occipital lobe: back of the brain that receives input from the eyes via the thalamus - Parietal lobe: important for spatial perception. Postcentral gyrus: receiving area for skin senses (touch, cold, warmth and movement) tissue part of the parietal lobe - Temporal lobe: receiving area for auditory information, also part of smell (olfactory) - Also thought to have a role in migraine premonitions, such as certain smell → stroke - Frontal lobe: most recently evolved and the largest lobe of the brain that is responsible for motor output and motor planning - Precentral gyrus: maps onto movements of different parts of the body, strip of tissue found towards the back of the lobe. Map movements clearly through specific areas  - Primary areas: basic input (sensory), primary motor and auditory with basic input and output no perception or cognition. The complex behaviour and interpretation occurs in the association areas of the cortex, usually in a different area to the primary areas, high function - Primary motor area: discovered in the 1860s stimulating the cortex by mild electric currents applied to parts of the cortex in animals with specific effects - For example a paw moved every time when a specific area of the motor area is touched - Evidence of contralateral control - operates in all nervous systems - The right hemisphere controls the left hand side, and vice versa. Used to determine which side of the brain is affected dependent on which side of the body does not work - Canadian neurosurgeon Wilder Penfiled confirmed that the primary motor area lies in the frontal lobe and stimulation there led to movement of specific parts of the body - Homunculus: Map out body surface areas onto the motor cortex, mapped upside down - Only mapped out a male not females - Toes movement are located at the top of the motor cortex - Areas that have fine movement and dextris control have a larger area due to the sensitive area Brain Lecture 29 - Strip in the parietal lobe called the post central gyrus, also known as the somatosensory primary projection area that is involved with skin sense - Parts of the body that are most sensitive to touch receive more cortical space - Is the mind just a mechanical function of the brain? - Can consciousness be reduced to the firing of neurons in the brian? - Are we really just machines or robots? - Damage to primary visual cortex causes scotoma - hole in the visual field like a blind spot - Part of the vision has a black spot compared to the brain just filling in the blind spot - Primary areas have specific functions and damage to these have clear cut effects - Removal of primary visual cortex on one side leads hemianopia on the opposite side - Damage to primary motor cortex: hemiplegia - paralysis of one side of the body - Due to damage to the contralateral motor cortex. Paralysis is worse at the extremities, may lose finger movement but movement of the arm may be maintained - Primary areas take up less than ¼ of the cortex so are much smaller. The association areas take up more space but do not show fixed mapping, implicated in higher mental functions - Cannot point to a particular brain location and say this is the centre for planning, higher tasks depends on control exerted from many locations - Prosopagnosia: agnosia means to know. Damage to the association areas in the temporal/occipital lobes. Difficulty recognising faces. Some can’t recognise familiar faces (less severe cases) and some can’t even recognise that a face is a face such as a hat - Case of an old man in the Oliver Sacks book, who used to pat children’s heads but after he sustained brain injury of prosopagnosia and patted fire hydrants on the head instead - Phineas Gage would pack holes full of explosives and push down with a rod. Rod sparked against the rod and the rod went through the frontal lobe and he survived - Phineas’ behaviour changed dramatically: kind, well spoken, not aggressive, could plan ahead and got on with others. Became out of control, engage in profanity, stubborn, mind changed - Taught people the function of the prefrontal cortex and the frontal lobe, must be involved in personality. Frontal lobes are the most recently evolved and the largest - Prefrontal cortex: deficiency in response inhibition. Our behaviour is moderated to social norms and appropriate behaviour. Their behaviour becomes inhibited, unacceptable  - Alcohol makes a temporary change in the inhibition of responses, inhibition inaction - Damage to prefrontal cortex: inability to plan lack of foresight for the consequences of actions - Under of the age of 25, frontal lobe connections and prefrontal cortex are not fully developed - Neural connections are still forming so cannot plan ahead and consider their consequences Brain Lecture 30 - Following a brain injury, Michelle notices that she can’t feel when a mosquito has landed on her left index finger. What areas are damaged? Post central gyrus in the primary sensory cortex and this is on the right hemisphere towards the bottom/middle. Upper body = bottom - Damage to prefrontal cortex: people are uninvolved, depressed and apathetic while other may appear psychopathic acting crudely and engaging in criminal conduct - Problems with initiating behaviour and changing strategies (such as tasks with steps in order) - Prefrontal lobotomy is permanent brain damage as a method to control behaviour - 1940-1950s surgery to at least 20,000 people disconnected prefrontal areas. Helped some people and families used indiscriminately, on people that it should not have happened to - Patients were docile but cognitively disabled, apathetic (not violent or out of control) - Easy surgery to perform a prefrontal lobotomy, with many people gathering around the patient - GPs would watch the learn how to perform the surgery (while the patient was still awake) - Controlled wiggled after piercing through the fine part of the skull and cause the damage - Apraxia: there are many forms affecting the frontal lobe. Serious disturbances in initiation or organisation of voluntary action. Unable to form well known actions or actions become fragmented or disorganised for complex motor behaviours - Soldiers in the military could not perform the solute which requires specific motor actions - Neglect syndrome occurs when people with right sided parietal damage tend to neglect the left side of space (seldom vice versa). Can be visual, auditory or tactural (might think they do not have the left side of the body and cannot dress themselves properly) - Do have vision, not blind but do not pay attention to what they can see on the left side - An emotional component: denial of any deficit (anosognosia) - Left neglect is brain damage to the right side of the brain and right neglect does also occur with has left brain damage, but does go away after a while (transient) - Process the picture but fail to pay attention to the left hand side - Why is neglect asymmetrical? Right hemisphere of the brain (parietal lobe) controls attention to both sides of space. Left hemisphere controls attention to the right side of space only - Therefore damage to the right hemisphere causes neglect of the left side - Left hemisphere is restricted because of invasive presence of language maybe - Damage to the right hemisphere will have intense left neglect but the other way round has backup where the other hemisphere can help out - Right hemisphere is dominant for spatial attention, with damage have neglect syndromes - Right for melody, damage leads to amusia (relates to the musical side of language, we do not talk in a monotone, we talk in a certain tone etc and distinguish when there is a question) - Facial recognition, damage to right hemisphere prosopagnosia - Recognition of natural objects, damage is agnosia - Left hemisphere is dominant for language, damage is aphasia. Recognition of manufactured objects, damage causes agnosia and voluntary action causes apraxia when damaged - Tools are represented in the left hemisphere and animals in the right shown in a fMRI Brain Lecture 31 - The intact corpus callosum prevents us from being able to write well in both hands - Split brain surgery: relief of intractable (not controlled by drugs), multifocal epilepsy - Separates left and right hemispheres and prevents seizures spreading in the brain - Largest cerebral commissure (largest communicating pathway) between left and right hemisphere with 200 million axons and is fast - Lies below the longitudinal fissure - In the 1960s all forebrain commissures were sectioned: commissurotomy - From the 1970s onwards only the corpus callosum was sectioned: callosotomy - Done in two stages usually anterior and if unsuccessful followed by the posterior - Successful in controlling epilepsy. Reduced in frequency with better control through drugs and the understanding of the psychological effects - Split brain patients seem quite neurotypical. Everyday evidence of a split mind is rare but sometimes occurs with ‘alien hand’ hand takes on a life of its own - One hand will do its own thing and perform oppositely to what is desired to do with the opposite hand. Opening a draw with the right hand but pushing it closed with left - Hand behaves in a manner that is autonomous and coordinated but they cannot control - Psychological effects of the split brain are best shown by experiment rather than being evident in everyday life - Disconnection syndrome best addressed through vision since the visual fields are split cleanly through the vertical meridian. Left visual field (LVF) projects to the right brain - Right visual field (RVF) projects to the left brain - Left hemisphere function in the split brain; cannot name objects or words presented in the left visual field. Can't name objects held in left hand - But can understand words in the left visual field (demonstrated by pointing) - Suggests the right brain can understand but cannot speak - Ball isolated in the right hemisphere. Speech in left hemisphere cannot name the ball - Right hemisphere can ‘tell’ the left hemisphere what it sees by looking at an example in the room so the left hemisphere can then name it. Coding with hands or tongues (cheating) - In some people corpus callosum does not develop naturally split brain: callosal agenesis - Sometimes accompanied by Probst's bundles which are remnants of the corpus callosum that failed to cross the midline. Often have other neurological problems but are neurotypical - Enlarged anterior commissure to allow the two hemisphere to communicate - Less evidence of disconnection in callosal agenesis. Objects and words are usually easily named in either visual field. Interhemispheric transmission time (slightly slower) - Other areas take over called neural plasticity. Some evidence in surgical cases if early surgery Brain Lecture 32 - Electroencephalography (EEG), structural and functional magnetic resonance imaging (f/MRI) and research on Alzheimer’s dementia on the brain - Neuroimaging goal is the study of the structure and function of the nervous system in vivo (while alive) and relatively non invasively. Usage in clinical and research - Used in fields such as medicine, psychology, neuroscience and engineering - EEG is a cap placed on the scalp and electrodes are measuring cortical activity on the brain's surface to monitor and record activities. EEG electrodes act as a conductor - Application: wet or gel based. First human EEG was measured by Hans Berger 1929 - Brain electrical activity is measured very small in microvolts 1/1,000,000 volts. Summated electrical activity measured from pyramidal cells (close to the surface of the brain) - Very quick recordings of the brain done in milliseconds. Excellent temporal resolution (time info or in real time) but poor spatial resolution (not deep). Relatively inexpensive - More electrodes give a more accurate better signal - Noise artefacts can interfere with the signal such as phones leading to large pulses or near a vein or artery or moving and clenching - Faraday booth attenuates noise to improve brain signal, quiet and controlled - Raw EEG clinically useful as distinct brain states show characteristic EEG signal - Raw EEG clinically useful in determining the focus of epileptic seizure - Oscillations (brain waves) have different characteristics and bands (alpha and beta) based on the number of hertz or frequency - Time locked event-related potential (ERPs): everything is locked to a stimulus, activating the brain and take the average ERP to analyse waypoints - First potentials earlier in time are related to attention and later are higher cognitive processes - Structural MRI studies relate to brain anatomy and fMRI relate to brain function such as changes in blood flow in the brain. MRI is sensitive to jewellery and magnets - High spatial resolution in MRI clear image of brain in fine detail, even corital parts - Depends on time, more time better image and number of voxels (pixels) and magnetic field strength based on tesla's (higher = better resolution) - MRI can differentiate between brain tissues, white and grey matter, CSF, skull and meninges - Identify abnormalities in the brain: atrophy, lesions, tumours, leaks, blood clots & bruising - Safe than CT (quicker and cheaper), with no radiation and is non invasive - T2 scan picks up water and edema in the brain (swelling) and tumours - White matter hyperintensities are seen with FLAIR, ignores the normal liquid structure - Diffusion weighted scan can pick up water abnormalities, blood clots and swollen cells or anything that restricts water movement - Susceptibility weighted scans can pick up abnormalities in the blood such as microbleeds - MRI machine: powerful magnets that are reverberating of protons. Normal state protons are aligned in different directions and inside the machine the radiofrequency pulse manipulates protons to align the protons in one way. RF pulse turns off to flip the protons and energy is released to create the image. More energy released from some structure vs others depending on how oxygenated or deoxygenated the blood is or the water content - MRS can measure the brain volume, white matter tracts, gyrification (brain folds) and lateralisation, left vs right hemisphere of the brain - Different cohorts and groups of interests such as ageing, development or clinical groups - Study example: London taxi drivers. Number of years driving was increased posterior hippocampal volume due to memory of the map of London - fMRI: changes in blood flow related to behaviour cognition. Indirect measure of brain activity with small changes in cerebral blood flow. Series of images collected over time (seconds) - Higher neuronal activity requires more oxygenated blood to engage in that activity - Exchange of deoxygenated and oxygenated blood - Depending on the hemodynamic response function (HRF). Takes the average of neural activity being followed by blood flow in a predictable manner. - Active brain regions = more blood changes but poor temporal resolution compared to EEG - See the brain activity which is tired (neural correlates) to cognitive task (memory) - Time locked events, similar yo EEG ERP research  - However, fMRI needs to account for poor temporal resolution. Localise brain activity to the brain region with good spatial resolution - Intrinsic activity: resting state fMRI, resting brain still an active brain (mind wandering) - Intrinsic functional organisation of the brain. Networks for different parts of the brain - Default mode network when at rest - Better spatial resolution but poorer temporal resolution compared to EEG - Suggest to artefacts such as motion distortion - contraindications, with possible adverse factors such as pacemakers, implants, tattoos, claustrophobia and very loud. Very expensive Perception 33 - Three broad categories of sense: mechanical senses (touch and hearing), chemical senses (smell and taste) and electromagnetic senses (sight and visible light) - Mechanical senses only inform you about what is touching your body, chemical understanding of toxins and rewarding food but electromagnetic senses are much broader - Mechanical senses: involve detecting physical movement on or in the body - Touch is sensed by mechanoreceptors in the skin, different nerve endings to detect different things. Meissner's corpuscles are responsive to light brief pressure - Merkel’s disk is a response to light sustained pressure. Light touch for longer amount of time - Free nerve endings detect high temperatures and pain - Krause’s end bulb senses low temperature - Pacinian corpuscle detects deep sustained pressure such as standing on the floor - Nerve endings wrapped around hair follicle sense hair movement - The first stage of perception is transduction: the process of converting physical energy or stimuli into neural impulses in the nervous system - Vast majority of senses go through the spine to the brain (somatosensory cortex) - Mechanoreceptors transduce physical touch into nerve impulses which travel from the peripheral to the central nervous system - Perception of touch is based on which receptors fire and how somatosensory cortex interprets the signal but these signals are not always correct - For example szechuan pepper causes a vibrational false alarm in mouth Meissner receptors, firing away at 50Hz a second to the brain - Touch: mechanical pressure/motion on the body surface. There are several types of mechanoreceptors in the skin to detect special kinds of touch. Mechanical deformation/vibration/pressure on mechanoreceptors causes them to send an action potential which travels along nerves to the spine and brain - Where does the brain process? Involuntary reflexes via the spinal cord only. All other touch is via nuclei in the medulla, midbrain and thalamus, then somatosensory cortex - Sounds: pressure waves in the air (mechanical vibration and movement on a surface) - Frequency (pitch) and amplitude (loudness or size of the oscillation) can differ between sound waves in repeating oscillations. Complex apparatus can amplify subtle sound vibrations - Help us localise. Vibrating air enters the auditory canal and hits the back of the ear drum which vibrates in time to the vibrations in the air which is amplified through delicate bones called ossicles which convey the vibrations from eardrum to cochlea - Cochlea is the registering of the sound. The mid ear is amplification - Inside the cochlea: sound waves are transduced into nerve impulses. Inside there is a thick but flexible basilar membrane and when sound reaches it, it causes a wave of displacement along  the basilar membrane and depending on the loudness and frequency has a different pattern of displacement. Loud noise has more displacement - The long cochlea can register different frequencies at different points along the length of it - At the start sense large frequencies - Movements of tiny hairs inside the cochlea trigger nerves to fire (stereocilia) which move about and rub against the inside of the cochlea to trigger nerve cells that they are attracted to fire an action potential to the brain. Hairs are jostled at different areas and frequencies - Hearing only occurs after a hierarchy of processing steps out from the auditory nerve to the brain stem, medulla, thalamus and auditory cortex have made sense of the auditory signals - Hearing: environmental information is sound waves in the air, sensors our bodies have to detect it include a complex apparatus in the inner ear that allows sound waves in the air to produce precise patterns of vibration in the basilar membrane of the cochlea - Senses transduce info from the environment to the nervous system by hair cells in the cochlea detecting patterns of vibration in the basilar membrane and transduce these into action potential in auditory nerves. Nuclei in the medulla, midbrain, thalamus and extensively in the auditory cortex process this information in the brain - Activer hearing = echolocation, our hearing is passive we wait for us to reach us whereas animals such as bat send out a sound and listen how it bounces back from the environment to inform about the spatial layout with greater resolution - Chemical sense involve detecting chemical molecules in water/food/air by taste and smell - The olfactory system: breath in air through nasal cavities and tendrils in the mucus have olfactory receptor cells that bind different odour molecules and transduse them into nerve signals. One end dangles in mucus at the top of the nose and the axon passes through the tiny holes in the skull and connect to neurons in the olfactory bulb - Lose smell in head injury due to shearing axons through the tiny holes of the skull - Taste receptors: different taste receptors cells bind with different molecules in the salvia and transduce them into nerve signals to the gustatory cortex to process taste - Smell is the only sense that does not go via the thalamus and medulla and the midbrain, it goes directly from receptors in the olfactory bulb and olfactory cortex - Smell is detected by receptors cells in the olfactory epithelium and taste is sensed by receptor cells in the tastebuds of the tongue. Hearing is processed in the olfactory cortex directly from the olfactory tract/bulb. Taste is processed in nuclein in the medulla and thalamus the gustatory cortex. Catfish have taste buds all over their bodies - Electromagnetic senses: involve detecting electromagnetic radiation that reaches the body (vision). Sensing a narrow band of radiation emitted from the sun - Humans only sense a small position of the electromagnetic spectrum light - Light bounces off objects in straight lines until it reaches a surface where it is refracted, scattered inside the surface, bounces off or is absorbed - If you can detect the light that arrives at any point, you can reconstruct the objects around you - Passing light through a small hole creates a perfect image of the environment (inverted) - An upside down image of the world is projected onto the inside back of the eyeball. The retina interprets the image. Pupil controls how large hole is for the image - The cornea and lens focus the light coming - The retina is for neural processing. The retina is a very thin translucent layer of cells - The focused light passes easily through the back layer on photoreceptors - Photoreceptors transduce light via chemical reactions into neural activity - Photoreceptors contain proteins that undergo a chemical reaction when struck by light which then triggers a nerve impulse. Different wavelengths have different chemicals  - Cortical processing of vision. Send signals out of the optic nerve to the thalamus in the centre of the brain and to the primary visual cortex at the back of the head - ⅓ cortex is involved in visual processing and input - Different regions are specialised for detecting different things in the images - We sense wavelengths of light 400-700 nm. Bees have shifted less towards red and closer to ultraviolet (300-650nm). Flowers have striking colours in ultraviolet wavelengths - We have 3 types of photoreceptors that sense different wavelengths - Mantis shrimp have 12 types of photoreceptors Perception 34 - Transduction: registering light on the retina → receptive fields in the retina and LGN: combining photoreceptors to encode changes in lightness or colour → primary visual cortex (V1) → ventral and dorsal streams: hierarchical visual processing - The upside down image of the word is projected into the inside back wall of the eyeball (the retina). The cornea, pupil and lens make sure the image is in focus - The retina has multiple layers of neurons and blood vessels. Processing starts in the photoreceptors where light is sensed, neurons with chemicals that react to light - Photoreceptors have two broad types: rods (dark) and cones (reasonable levels of light) - Rods are further back in the periphery. Cones are packed wherever you are looking in the centre. Rods have subtle light sensitivity. Rods are at the edge of where you are looking - Rods give lower resolution with almost no colour - Cones act in the fovea (centre of vision), giving high resolution colour vision - Rods only come in one kind and are the most numerous and work best at night and do not allow you to distinguish colours. There are around 12 million per eye - There are three kinds of cone photoreceptors each sensitive to short, medium or long wavelengths of light. They are less numerous with 8 million per eye. The relative activity in different cone types allow you to see colour - Not all of the cone types are present in every individual or have them in equal quantities - Common in men to have low amounts of one or more of cone types or one is missing - Deuteranopia (missing medium cones) in 6% of men respond well to blue and red but cannot distinguish between red and green. Photoreceptors are on the X chromosome - Protanopia (missing long cones) in 2% men and tritanopia (missing short cones) very rare - After sensing light it is transduced into electrical signals in a series of neuron layers inside the retina and neurons have dendrites which get the input, the cell body that incorporates inputs and the axon which travels elsewhere. The final layer of retina cells are called ganglion cell axons (nerve fibres) carries these signals along the inside of the retina to the optic disc (blind spot) passing it around the inside of the eyeball to the brain - The signal is passed through small holes into the brain called the optic disc - The bundles of nerve fibres forms the optic nerve which goes to the brain for more processing - 10 million nerve fibres leaving each eye forming the optic nerve - Blind spots are due to electrical cables leaving the eye to go somewhere. The optic disc = the blind spot (perceptual phenomenon). Optic disc is a hole for cables (optic nerve) to exit - Photoreceptors detect light in the back of the eye so it has to come back out of the eye - Photoreceptors could be protected at the back from any disturbances and have blood supply - Almost all of our vision is really low resolution so we have to move our eyes constantly - Cones are almost always in the centre so we move our eyes (saccades) eye movement - About 3 eye movements or saccades per second, 1 every 300 milliseconds - Use movements for whatever we are looking for at the time to establish information - Encoding the retinal image: combining photoreceptors into receptive fields in the retina. Photoreceptors are combined into centre-surround receptive fields - Light in the excitatory centre increases neuron’s firing rate in the centre of the field - Light in the inhibitory surround increases neurons firing rate on the edge around the centre - Receptive field are the neurons that respond to things - Equal amounts of light in the centre and surround → no response from this neuron within the dark part of the image. If all photoreceptors experience the same amount of light no response - Bright: response in the centre but inhibited in the edge so cancel out - When the image is overlapping the circle, there is not a perfect balance so is more excited than inhibited and sends an action potential - When nothing in the image is changing the neurons do not send a signal to the brain - The purpose of centre-surround receptive field: signal change - Next step in visual processing: combining and stacking simple receptive fields to make more complex ones in the primary visual cortex (V1). In the brain simple RFs are combined to get more complex RFs. Each V1 neuron (in the brain’s primary visual cortex) receives input from multiple retinal ganglion cells (via the LGN in the thalamus) - Each V1 gets information from multiple inputs and each neuron receives input from a line of retinal ganglion cells that have overlapping receptive fields - Light in the excitatory centre increases neurons firing rate - Light in the inhibitory surround decreases neurons firing rate - In the brain simple RFs are combined to get more complex receptive fields → edge detector - Primary visual cortex is full of edge detectors at different locations and orientations arranged in columns. V1: columns of neurons that prefer every orientation of edge at every location in the visual field. These neurons are lawfully organised into a map of the visual field - The rest of the visual system is a hierarchy of functionally specialised cortical areas - Cortical processing of vision (close to ⅓ of cortex is involved in visual processing) - Dorsal processing steps “where” pathway → visually guided action to interact with the world - MT = specialised for motion perception, posterior parietal cortex involved in coordinating reaching and grasping with vision - Ventral processing → what you are looking at recognizing people, scenes and objects - Damage to high level areas can cause complex visual agnosias (deficit of visual knowledge) - Initially V1 detects edges and feeds into these two pathways with specialised functions