Brain-Bases of Behaviour PDF

THE BIOLOGICAL BASES OF BEHAVIOUR U04 | PSYC100 KRISTINA TCHALOVA MCGILL UNIVERSITY | F2024 1 WHAT MAKES YOU ‘YOU’? 2 NEURONS o Neuron = cell of the nervous system specialized for sending and receiving neural messages § ~100 billion neur...

THE BIOLOGICAL BASES OF BEHAVIOUR U04 | PSYC100 KRISTINA TCHALOVA MCGILL UNIVERSITY | F2024 1 WHAT MAKES YOU ‘YOU’? 2 NEURONS o Neuron = cell of the nervous system specialized for sending and receiving neural messages § ~100 billion neurons in the brain making over 100 trillion connections! o Sensory neurons carry messages from the sensory organs (e.g., eyes, tongue, skin) to spinal cord and brain o Motor neurons carry messages from the brain and spinal cord to muscles and glands o Interneurons within the the brain and spinal cord collect, integrate, & retrieve messages from various sources 3 STRUCTURE OF NEURONS o Dendrites: receives chemical messages from other neurons o Cell body/soma: collects neural impulses, contains the nucleus, sustains cell functions o Axon: transports electrical impulses to other neurons via the terminal branches o Axon terminals/terminal branches: convert electrical signals into chemical messages for other neurons o Myelin sheath: fatty layer that insulates the axons & speeds up transmission of electrical signals 4 GLIAL CELLS o Glia = nervous system cells that perform variety of critical support functions § Provide structural support & scaffolding for neurons § Clean up debris § Form blood-brain barrier § Facilitating neurons between neurons and pruning unneeded connections § Nutrient supply § Insulation (myelin sheath) 5 THE ACTION POTENTIAL o Neurons “talk” to each other by firing off electrical impulses called action potentials o Action potentials generated at the junction between the axon and cell body o Travel down the length of the axon to its terminal, where they signal release of chemical messages to neighbouring cells 6 CELL MEMBRANE o Cell membrane = thin fatty “skin” enclosing the neuron § Separation between the intracellular fluid inside the neuron and extracellular fluid outside the neuron § Intracellular and extracellular fluids contains various electrically charged particles (ions)—sodium (Na+), chloride (Cl-), potassium (K+), calcium (Ca2+) § Cell membrane is selectively permeable, allowing for passage of certain ions and not others 7 BEFORE AN ACTION POTENTIAL o At rest, more negatively charged particles inside cell relative to outside o Resting potential = electrical charge across the membrane (~70 millivolts) § Neuron cannot fire action potential in this state 8  BEGINNING DEPOLARIZATION o When neuron sufficiently stimulated by other neurons, opening of ion channels in the cell membrane at end of axon adjacent to soma o Ion channels allow positively charged sodium ions (Na+) to enter o Electrical charge across membrane begins to reverse (depolarization) 9 ACTION POTENTIAL o Voltage threshold = critical level to which a neuron’s membrane potential must be depolarized to initiate action potential (~55 mV) o Once threshold is passed, voltage-gated ion channels open allowing positively charged sodium (Na+) ions to flood in § At peak of action potential, interior of cell more positively charged than outside o All-or-nothing response 10 REPOLARIZATION o As depolarization occurs, channels that were letting sodium (Na+) pass through close, but potassium (K+) channels remain open à flow out of the cell causes repolarization o Temporary dip below resting potential § During the refractory period it is very hard to get the neuron to fire again 11 PROPAGATION OF THE ACTION POTENTIAL o Action potential moves like a wave along axon § Action potential à depolarization of adjacent area, opening of sodium channels § Myelination speeds up this process, allowing signal to “jump” o Refractory period ensures that action potential is propagated forward 12 COMMUNICATING ACROSS THE SYNAPTIC CLEFT o Synaptic cleft = gap separating neurons Postsynaptic Neuron o To traverse synapse, electrical signal has to be converted to a Presynaptic Neuron chemical one § Presynaptic neuron sends Synaptic Cleft chemical messengers called neurotransmitters 13 C OMMUNIC AT ING AC R OS S T HE S YNAPT IC C LE FT o Arrival of the action potential triggers release of neurotransmitters stored in the axon terminal o Neurotransmitters cross gap & bind to receptors on the postsynaptic neuron § Receptor = channel in membrane of a neuron that binds neurotransmitters 14 COMMUNICATING ACROSS THE SYNAPTIC CLEFT o Receptors bind neurotransmitters in ”lock-and- key” fashion 15 TIDYING UP THE SYNAPSE o Neurotransmitter gets removed from the synapse in order to terminate the chemical message § Diffusion = neurotransmitters drift out of synapse § Degradation = neurotransmitters are broken down in the synapse § Reuptake = neurotransmitters are reabsorbed into the presynaptic terminal branches 16 EXCITATION & INHIBITION o Interaction between neurotransmitters and receptors produces excitation or inhibition by opening of select ion channels o Excitation = receiving neuron slightly depolarized § Moves it closer towards voltage threshold and increases likelihood of initiation of action potential o Inhibition = receiving neuron slightly hyperpolarized § Moves it further from threshold & reduces likelihood of action potential § E.g., coordination between muscle contraction (excitatory inputs) and muscle relaxation (inhibitory inputs) required for coordination § Tetanus bacteria destroys inhibitory inputs leading to lockjaw 17 TYPES OF NEUROTRANSMITTERS o Major classes of neurotransmitters § Amino acids § GABA § Acetylcholine § Monoamines § Norepinephrine, serotonin, dopamine § Neuropeptides § Endorphins 18 GABA o Most common inhibitory neurotransmitter o Downregulation of stress, anxiety, fear § Many sedative drugs act by targeting GABA receptors § Alcohol also promotes activity at GABA receptors 19 ACETYLCHOLINE o Can trigger both excitatory and inhibitory signals o Commonly found in neuromuscular junction § Drugs that interfere with ACh (e.g., curare) used as a bioweapon, result in paralysis and death o Also plays key role in autonomic nervous system, which carries commands from brain to glands & organs, regulates cardiac activitiy o Brain circuits involved in learning and memory § Low levels associated with dementia of Alzheimer’s disease 20 NOREPINEPHRINE o Important for “fight or flight response” o Contributes to arousal & vigilance o In excess, can contribute to high blood pressure, anxiety 21 SEROTONIN o Contributes to regulation of sleep, appetite, mood, and aggression o Thought to play in depression, although precise mechanism still debated 22 DOPAMINE o Involved in movement, planning, and aspects of reward o Most addictive drugs stimulate increased activity in dopaminergic circuits o Excess levels associated with schizophrenia, low levels with Parkinson’s disease 23 ENDORPHINS o “Endogenous morphine” o Promote feelings of pleasure and reduce pain o The OPRM1 gene we discussed earlier codes for the opioid receptor where endorphins bind 24 PSYCHOACTIVE DRUGS o Psychoactive drugs = chemical substances that alter a person’s thoughts, feelings, or behaviors by influencing the activity of neurotransmitters in the nervous system o Includes prescription medications like anti-depressants and drugs like cocaine, heroin, LSD, etc. o Other commonplace examples: caffeine, nicotine and alcohol 25 AGONISTS & ANTAGONISTS o Agonist = enhances action of a neurotransmitter § By increasing release, blocking its reuptake, or mimicking neurotransmitter & activating its postsynaptic receptor o Antagonist = inhibits actions of a neurotransmitter § By blocking release, destroying neurotransmitter in synapse, or mimicking neurotransmitter & binding to a postsynaptic receptor to block neurotransmitter 26 MODEL OF OPIOID ADDICTION o Opioid drugs (e.g., heroin) hijack & eventually overpower reward function of endogenous opioids o Repeated use causes changes to receptor structure § E.g., decrease in # of receptors, decreased sensitivity of receptors o Contributes to emergence of tolerance to drug & loss of sensitivity for naturally occurring rewards o Locus of control for drug-seeking behaviour shifts from positive reinforcement (taking drug to feel good) to negative reinforcement (taking drug to alleviate negative feelings/withdrawal) 27 NERVOUS SYSTEM o Nervous system = complex network of nerves (bundles of neurons) that controls & regulates all bodily functions o Subdivisions: § Central nervous system: § Brain § Spinal cord § Peripheral nervous system = nerves connecting brain to the rest of your body 28 PERIPHERAL NERVOUS SYSTEM o Somatic nervous system § Carries commands for voluntary movement from CNS to muscles § Brings sensory input to CNS o Autonomic nervous system = carries involuntary commands to organs, blood vessels, & glands § Operates outside your conscious control § Further subdivided into sympathetic and parasympathetic branches 29 SYMPATHETIC NERVOUS SYSTEM o Prepares body for situations requiring expenditure of energy (fight-or-flight response) o Pupil dilation, increased breathing, heart rate, & blood flow to muscles o Redirects energy from non-essential processes (e.g., digestion) 30 PARASYMPATHETIC NERVOUS SYSTEM o Controls gland & organs during calm periods, returns body to resting state (rest-and-digest) o Nutrient storage, repair, growth 31 32 ENDOCRINE SYSTEM o Endocrine system = network of glands (hormone-secreting organs) that work together with CNS and PNS o Hormone = blood-borne chemical messengers § Slower than CNS neurotransmitters § Travel over greater distances o Involved in regulating arousal, metabolism, growth, & sex 33 ADRENAL HORMONES o Adrenal glands located on top of kidneys o SNS activates adrenal glands during stressful/threatening events à release of adrenaline and cortisol § Boost energy, increased heart rate, blood pressure, blood sugar levels § Cortisol has slower onset but longer lasting efects 34 PITUITARY GLAND o The ‘master gland’ § Directs other glands § Regulates hunger, sexual arousal, growth, sleep (via pineal gland), navigation of social world 35 OXYTOCIN o Hormone released into bloodstream by pituitary gland o Involved in parturition (stimulates uterine contractions during birth) § Artificial forms of oxytocin used to induce labour o Promotes lactation o Thought to play role in social bonding 36 A TALE OF TWO VOLES o Prairie voles typically form pair bonds after mating, exhibit biparental care o Montane voles: live in isolation, no evidence of pair bonding Insel & Young, 2001; Insel & Shapiro, 1992 37 A TALE OF TWO VOLES o Prairie voles : high density of oxytocin receptors in reward related areas of the brain o Montane voles: few receptors in these areas o Oxytocin receptor antagonist blocks partner preference formation following mating in the prairie vole § Although does not affect frequency of mating Insel & Young, 2001; Insel & Shapiro, 1992 38 Normal circumstances (no drug) 39  Normal circumstances (no drug) Reward related regions Unrelated brain region with oxytocin receptor (control) density prairie > montane Prairie voles given oxytocin receptor antagonist Different substance/ not oxytocin 40 (control) WHAT ABOUT HUMANS? o First study to examine social effects of oxytocin in humans found that intranasal oxytocin increases trust during economic trust game § Player 1 gets some money & decides how much to send to Player 2 § Amount sent is multiplied § Player 2 receives multiplied amount & decides how much to send back o Subsequent flurry of research found number of prosocial effects--e.g., § Generosity & cooperation § Emotion recognition & empathy § More positive communication behaviours during couple conflict discussions 41 42 NOT SO FAST! o Effects of oxytocin agonism in humans are not always consistent § Some studies found no effects, very small effects, or even negative/antisocial effects! § E.g., oxytocin actually decreases trust towards out-group members and in those with very high levels of dispositional distrust o Effects of oxytocin may depend on interpersonal & intrapersonal context § One hypothesis: may make social information more salient, but subsequent behaviour will depend on the filters through which you interpret the social information 43 THE CENTRAL NERVOUS SYSTEM 44 SPINAL CORD o Major bundle of nerves connecting brain to rest of the body o Spinal reflexes are initiated by spinal cord without involvement of the brain § E.g., response to painful stimulus § Pain receptors in skin detect potentially harmful stimulus § Electrical signals from pain receptors carried by sensory neurons to spinal cord § Interneurons within spinal cord process signal and relay it motor neuron § Motor neurons send command to muscles to react 45 BRAINSTEM o Lowest region of the brain, sits on top of spinal cord o Where spinal nerves & most cranial nerves connect o Regulates vital functions; damage to this area is often lethal o Contains the midbrain, pons, and medulla 46 47 MEDULLA Heart rate, blood pressure, reflexes like coughing and swallowing 48 MEDULLA Heart rate, blood pressure, reflexes like coughing and swallowing PONS Breathing Balance & coordination Relays sensations (hearing, taste) to higher levels of the 49 brain (pons = bridge) MEDULLA Heart rate, blood pressure, reflexes like coughing and swallowing RETICULAR PONS FORMATION Breathing Arousal (not the Balance & coordination sexy kind), Relays sensations (hearing, attention, taste) to higher levels of the wakefulness brain (pons = bridge) 50  MIDBRAIN Orientation towards salient stimuli (tegmentum) Movement (substantia nigra) Motivation & reward (ventral tegmental area) Downregulation of pain MEDULLA (periaqueductal grey) Heart rate, blood pressure, reflexes like coughing and swallowing RETICULAR PONS FORMATION Breathing Arousal (not the Balance & coordination sexy kind), Relays sensations (hearing, attention, taste) to higher levels of the wakefulness brain (pons = bridge) 51 CEREBELLUM Coordination, balance, precise movements & accurate timing 52 LIMBIC SYSTEM o Includes § Hypothalamus § Thalamus § Amygdala § Hippocampus § Basal ganglia o Known as the ‘emotional brain’, but plays a number of other important roles as well 53 HYPOTHALAMUS ‘Interface’ between brain & body Homeostatic regulation: temperature, thirst, hunger, biological rhythms Motivation, reward seeking Fight-or-flight response Directs the autonomic nervous system & endocrine system 54  THALAMUS ‘Relay station’ for all sensory signals (except smell) Alertness & consciousness 55 AMYGDALA Processing emotional significance of sensory information Responds both to positive and negative stimuli Works with hippocampus to create vivid memories Damage can lead to psychic blindness = normal vision, but visual stimuli lose their emotional significance 56 CAPGRAS SYNDROME o Rare psychiatric disorder where a person believes that someone close to them has been replaced by an impostor o Neuroscientist Vilayanur Ramachandran explains his theory of how disconnection between brain areas responsible for facial recognition and the amygdala, which is responsible for processing the emotional significance of stimuli, may give rise to this condition o https://www.ted.com/talks/vs_ramachandran_3_clues_to_understanding_your_brain?s ubtitle=en 57 HIPPOCAMPUS Memory Spatial navigation Mental time-travel 58 BASAL GANGLIA Planning , executing, & controlling voluntary movement Suppression of unwanted movement (substantia nigra) Reward and pleasure (nucleus accumbens) 59 60 CEREBRAL CORTEX o Outermost and largest part of the human brain o Divided into left and right hemispheres connected by large bundle of nerve fibers (corpus callosum) o Further divided into five lobes § Frontal § Parietal § Occipital § Temporal § ( + insular lobe) 61 FRONTAL LOBE o Movement and planning § Contains the primary motor cortex (a “map” of the body’s muscles) o The rest consists of the prefrontal cortex: § Responsible for executive function (self-regulation & control of behaviour): planning, judgment, decision-making § Conscious experience of emotions 62  “ His contractors, who regarded him as the most efficient and capable foreman in their employ previous to his injury, considered the change in his mind so marked that they could not give him his place again 63 FRONTAL LOBOTOMIES o Surgical procedure disconnecting prefrontal area from the rest of the brain § Used as treatment for severe mental disorders in 1940s-1950s o Led to apathy/emotional blunting, inability to plan & organize behaviour, impulsive, antisocial beahviour 64 PARIETAL LOBE o Contains the primary somatosensory cortex (a ”map” of the body’s skin surface) enabling us to process touch o Helps pay attention to and locate objects, navigate our surroundings 65 OCCIPITAL LOBE o Vision o Contains the primary visual cortex which is necessary for sight § Interprets input from eyes by responding to basic information about image (e.g., shading, edges, colour) o Links to temporal and parietal lobes allow you to recognize objects and process their movement 66 TEMPORAL LOBE o Contains the primary auditory cortex o Allows you to hear and understand language o Allows you to recognize objects and people o Contains the primary olfactory cortex 67 INSULAR LOBE o Allows us to perceive our inner world o Perceives state of internal organs § Racing heart, pain o Includes the primary taste cortex § Damage à loss of conscious experience of taste § Stimulation produces sensation of taste 68 PRIMARY SENSORY AREAS o First cortical areas to receive signals from their associated sensory nerves § Parietal lobe: somatosensory area § Occipital lobe: visual area § Temporal lobe: auditory & olfactory areas § Insular lobe: primary taste area 69 ASSOCIATION CORTEX o Association cortex integrates incoming information from sensory areas with existing knowledge to produce meaningful experience of the world § E.g., recognizing complex visual objects or sounds o Multisensory integration o Association = connection § Bridge between sensation & action, language, abstract thought 70 ORGANIZATION OF PRIMARY SOMATOSENSORY & MOTOR AREAS o Primary somatosensory and motor areas are organized topographically § Brain areas “map” onto specific parts of the body § Body parts that are physically close are represented in adjacent areas of cortex § Amount of cortex space corresponds to amount of fine control or sensory discrimination required 71 72 THE SYMMETRICAL BRAIN o Nearly every structure of the brain exists in duplicate § Right and left portion of cerebellum, thalamus, amygdala, etc. o Cerebral cortex is also divided in half by deep fissure à left & right hemisphere o How do the left and right hemispheres communicate? 73 CORPUS CALLOSUM o Bridge of fibres that connecting the two cerebral hemispheres o Helps the two hemispheres “talk” to each other (interhemispheric transfer) 74 DIFFERENT VIEW 75 CONTRALATERAL ORGANIZATION o When it comes to primary sensory and motor functions, the two hemispheres are quite similar § Both hemispheres involved in receiving sensory information from your body, and sending motor commands to your muscles o BUT each hemisphere does this for the OPPOSITE side of the body 76 LATERALIZATION o Some functions of the brain are located on either the right or the left side o Best characterized distinctions between the two hemispheres: § Areas in the left hemisphere are specialized for language § Analogous area in right hemisphere specialized for nonverbal, visuospatial processing of information o Evidence from strokes § Left hemisphere damage: deficits using & understanding language § Right hemisphere: deficits recognizing faces, reading maps, drawing geometric shapes 77 SPLIT BRAIN PROCEDURE o Severing of the corpus callosum o Performed in cases of severe epilepsy to limit extent of seizures o Disrupts interhemispheric transfer o Revealed that in special conditions, when information is provided to only one hemisphere, split-brain patients behave as if they have two separate minds 78 SPLIT BRAIN PROCEDURE o With split brain patients, possible to § Send visual information to just one hemisphere by presenting the stimulus in only the opposite half of the visual field § Send tactile (touch) information about an object to just one hemisphere by having a participant feel the object with the opposite hand § Test the knowledge of each hemisphere by having the participant respond with the hand opposite to that hemisphere 79 EXAMPLE o If we present a picture of an object (e.g., an apple) to the right visual field of a patient, they will be able to describe it (because language is controlled by the left hemisphere) o But if we present the picture to the left visual field, the patient will no longer be identify it verbally § But they will be able to reach for it with their left hand (although they won’t know why they did that) 80 LET’S TRY IT OUT 81 THE ‘INTERPRETER’ o Can split-brain patients offer a window into the nature of human consciousness? (Gazzaniga, 2000) o The left (language dominant) hemisphere plays unique role in interpreting behaviour and unconsciously produced emotion, making sense of everything we do § E.g., chicken claw + snowy scene experiment 82 BROCA’S AREA o Left frontal lobe o Damage à telegraphic speech § E.g., “I hungry” o Can understand speech 83 WERNICKE’S AREA o Temporal lobe o Damage: fluent but nonsensical speech, difficulty understanding language § E.g., “Nothing the keesereez the, these are davereez and these and this one and these are living. This one’s right in and these are... uh... and that’s nothing, that’s nothing” 84 PHRENOLOGY o Phrenology = 19th century belief that all mental faculties and characteristics are localized in specific brain regions and can be inferred from pattern of indentations on the skull 85 WHAT PHRENOLOGISTS GOT WRONG & RIGHT o Skull does not reflect either internal brain structure or mental traits o Complex behaviours & traits emerge from interaction of multiple brain areas o Some regions of the brain specialized for specific functions o Structural changes do occur with repeated use 86 HOW DO WE STUDY THE BRAIN? Neuropsychology Brain stimulation Methods with good Methods with good methods spatial resolution, temporal resolution, poor temporal poor spatial resolution resolution Examine functional DBS PET EEG alterations following TMS fMRI brain TDCS damage/lesions 87 NEUROPSYCHOLOGY o Study of brain function by examining functional alterations following brain damage o Lesion = abnormal tissue resulting from disease, trauma, or surgical intervention o Some examples we’ve seen so far: § Role of Broca’s area and Wernicke’s area in speech § Phineas Gage § Split brain patients & the contralateral organization of the brain 88 DISSOCIATION o Single dissociation: lesion to brain structure A disrupts function X but not function Y o Double dissociation: lesion to brain structure A disrupts function X but not function Y, and lesion to brain structure B disrupts function Y but not function X (“gold standard” in neuropsychology) § E.g., Broca’s area & Wernicke’s area 89 LIMITATIONS o Naturally occurring brain damage is not specifically localized & may spread over time o Difficulty generalizing from one person’s brain and behaviour to another 90 NON-HUMAN ANIMAL STUDIES o Induce lesions in experimental animals using electric or chemical methods o Allows for the observation of behavioral effects following the lesion o E.g., role of amygdala in emotional processing 91 BRAIN STIMULATION STUDIES o Deep brain stimulation § Stimulating specific parts of the brain with implanted electrodes § Used for treatment of disorders like depression o Transcranial Magnetic Stimulation (TMS) § Exposure to magnetic field to create temporary disruption or enhancement of cortical brain function o Transcranial Direct Current Stimulation (TDCS) § Low levels of direct current delivered via electrodes on the head to stimulate brain function 92 BRAIN STIMULATION STUDIES o Advantages § Causal insights into brain function § Some techniques may have therapeutic potential o Limitations § Limited spatial precision (particularly TMS & TCDS) § Limited depth penetration § More invasive 93 POSITRON EMISSION TOMOGRAPHY o Injection of radioactive tracer (glucose) o The radiotracer is taken up by brain tissues involved during particular task o PET detects radiation emitted by the tracer o Areas with higher concentration of the tracer emit more radiation 94 POSITRON EMISSION TOMOGRAPHY o Can go beyond glucose to study brain’s use of specific neurochemicals o For example: PET studies have revealed that expectation of pain relief can cause reductions in pain (placebo effect) through activation of the endogenous opioid system (Zubieta et al., 2005) 95 FUNCTIONAL MAGNETIC RESONANCE IMAGING (FMRI) o Used to measure brain activity by detecting changes in blood oxygenation § When a part of you brain is active, it needs more oxygen § Blood carries oxygen to active areas, which then becomes consumed § Because oxygenated and deoxygenated blood has different magnetic properties, fMRI can use strong magnets to detect changes in blood flow and oxygenation 96 FMRI VS PET o fMRI has better spatial and temporal resolution than PET, although temporal resolution (“when” brain activity happens) is still limited o Less invasive (does not require injection of radioactive substance) o Unlike PET, fMRI cannot reveal changes in neurochemical activities (i.e., which neurotransmitters may be actively involved in a process) § But can combine with other methods-–e.g., drug administration 97 FMRI STUDY EXAMPLE o Participants randomly assigned to receive either naltrexone (opioid receptor antagonist) or inert placebo o During fMRI scan, view pictures of close others and unfamiliar individuals o Naltrexone reduced activation in parts of ventral striatum (reward-related brain region in the basal ganglia) in response picture of close others but not strangers Inagaki et al., 2019 98 INTERPRETING IMAGING DATA o Determine which brain areas are “active” by subtracting amount of activity in each brain region in the control condition from the activity seen those in those brain regions in the experimental condition § Need to think carefully about the control condition § E.g., in Inagaki et al., 2019, strangers matched on gender, race, & age (but not emotional expression) o Neuroimaging data is correlational § Correlation between VS activation and feelings of social connection, but cannot definitively say that VS activation causes feelings of social connection 99 100 ‘WHEN’ BRAIN ACTIVITY HAPPENS o Single-cell recording = measurement of the electrical activity of a single neuron o Studies have identified single neurons that play important roles in specific abilities like recognizing words, faces, and the emotional content of images 101 ELECTROENCEPHALOGRAPHY (EEG) o Recording of electrical waves from many thousands of neurons in the brain, gathered using electrodes placed on the scalp Can be used to diagnose brain states such as sleep or wakefulness 102 EVENT-RELATED POTENTIALS o Synchronized electrical response to a sensory, cognitive, or motor event o Extracted from EEG data o Allows researchers to see how brain responds to specific stimuli or tasks Weinberg, 2022 103 MAGNETOENCEPHALOGRAPHY o The recording of the magnetic fields produced by the brain’s electrical currents § Allows for greater temporal resolution than EEG 104 LIMITATIONS OF EEG & EMG o Good temporal but not spatial resolution § Can tell us “when” but not “where” something happens o Recurring theme: must make trade-offs in research 105 NEURAL PLASTICITY o Neural plasticity = brain’s ability to change and adapt throughout individual’s life § Includes reorganization of neural networks in response to learning, experience, or injury 106  IF YOU USE IT, IT WILL GROW o Rats housed in “enriched” vs. ”deprived” environments: § Thicker cerebral cortices, more synapses per neuron, neurogenesis in hippocampus § New hippocampal neurons contribute to enhanced capacities for learning o Critical periods = specific timeframe during development when brain is particularly receptive to environmental stimuli, allowing for larger changes in neural connections § E.g., visual stimulation in early life required for visual abilities like depth perception & recognizing faces 107 IF YOU USE IT, IT WILL GROW o Extensive spatial learning linked to increased hippocampal size § London cab drivers show enlarged hippocampi relative to controls § Longitudinal studies: hippocampus size increases with training, shrinks after retirement 108 DAMAGE PLASTICITY o Damage plasticity = neural modification/reorganization following injury o Phantom limb syndrome = continuing sensation in limb that has been amputated § Cortical reorganization following amputation: “freed up” space in somatosensory cortex gets taken over by adjacent brain regions o Similar reorganization happens following other sensory deprivation § E.g., in blind individuals, parts of occipital cortex devoted to helping identify sound location or analyzing tactile input (Braille) 109