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Lecture 6

Lecture 6 - Neuroscience 2.docx

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McMaster University
Joe Kim

Lecture 6: Neuroscience 2 Module Notes: • Ventral = toward the front • Dorsal = toward the back • Lateral = toward the outside • Medial = toward the middle • Rostral = toward top • Caudal = toward bottom o Lesion Studies • Neuroscientists often interested in case studies of accidental brain injury, linking anatomy with associated cognitive & behavioral deficits • Phineas Gage (1848) worked railway construction  terrible accident: 3 foot iron rod completely through left cheekbone and top of skull • Gage survived & recovered almost entirely (some loss of vision & facial disfigurement) • Aonce upbeat, caring person, he became prone to selfish, erratic, unreliable • Supports the view that brain has specialized structures for complex behaviors - *Unlike this case study, most human brain lesions are not isolated to a specific structure within the brain - This makes it more difficult to assign impaired function to specific brain areas - This problem can be overcome: study specific brain lesions in animal models - Researcher destroys/inactivates a brain region  observes behaviour - Accuracy of results/understanding of lesion depends on precision of lesion - Varieties of behaviour can be affected by one lesion (*complex brain) o Stimulation • Alternative to lesioning • Electrically stimulate area of the brain and observe result on behaviour to build an anotomical map related to function • Used by Canadian neurologist Penfield • Penfield revolutionized techniques in brain surgery • Perfected “Montreal Procedure” to treat patients w/ extreme epileptic seizures • Had to be sure critical areas of brain were left intact • Brain = no pain receptors  patient could be under local anesthetic & fully conscious, “working with Penfield” to probe the exposed brain to locate and remove scarred tissues that caused seizures • He used thin wire w/ small electric charge to stimulate cortex  causes individual neurons to fire • Allowed him to accurately map perceptual processes & behaviours to brain • This revealed precise functions for unmapped regions of brain o Single Cell Recording • Also uses electrodes  record ongoing electrical brain activity • Small electrode inserted into nervous tissue small animal model • Tip held just outside cell body of individual neuron • Neural activity recorded while animal performs task/ reacts to stimulus • Firing pattern reveals specific neuron’s function role • Reveals info on only a limitted part of brain o Structural Neuroimaging • Reveals info on large-scale structure and function • First structural imaging technique: neural tomography (or CT) • During CT scan, series of X ray slices or brain taken, then pieced together  produce quick, inexpensive pic. of brain • Often helpful to diagnose brain injuries • Limitation of CT: low resolution = difficult to analyze fine brain anatomy • Now more commonly use MRI (magnetic resonance imaging) • Gives more detailed images • Powerful magnetic fields generated, aligning H atoms in brain • While H+ atoms aligned, MRI localizes tissues precisely throughout the brain o Functional Neuroimaging • Cognitive neuroscientists can use functional image technique: PET scan (possitron emission tomography) – subtractive method • Shows how brain function relates to cognitive tasks (language & memory) • Radioactive tracer of glucose or oxygen injected into bloodstream - radioactive molecules travel to brain, then used in metabolic processes  allows them to be detected by PET scan • More active brain areas use more metabolic resources, so image of brain’s activity can be created • Disadvantage of PET: requires radioactive tracer to be injected (invasive) • fMRI (functional magnetic resonance image) often preferred  can produce relatively clear image of brain activity without radioactive tracer • Subtractive method • fMRI : measures amount of blood O2 dependent signal, uses many of same principles as MRI • Able to measure relative use of O2 throughout brain • Uses same basic function as PET scan (more active areas of brain require more metabolic resources) • Limitations: provides only rough image of brain activation • Oxygen use by brain often spikes few seconds later than spikes of activity in brain (few seconds = long time in terms of brain function) • fMRI = not best method if interested in precise timing of brain activation • EEG (electroencephalogram): electrical activity of brain recorded through scalp • Wear cap of highly sensitive electrodes • Provides only rough image of brain’s overall activity from populations of neurons, but with “clever modifications” can be more informative • Event-related potential (ERP) experiment: specific stimulus presented to subject repeatedly while EEG recording • EEG normally produce noisy waves, the stimulus can have small, consistent effect on readout • By averaging EEG signal across many trials, noise can be balanced out • What remains = characteristic signal • ERP signals can be hard to interpret , but there are number of reliable signals reported in literature that serve as markers for diff. neural processes • Ie) N170 Wave: corresponds to face processing • When combined w/ behavioral measure, EEG & ERP signals = informative markers with precise temporal resolution, on the order of milliseconds Brain Regions: o Hindbrain • All info in and out of brain travels through cranial nerves or spinal cord • These connect to hindbrain at base of brain • Hindbrain contains: medulla, pons, reticular formation, cerebellum • Evolutionarily ^ structures are oldest parts of brain (found in nearly all vertebrate species) • Primarily involved in regulation of vital body functions • Medulla: - Most caudal part of hindbrain - Lies directly above spinal cord - Looks like extension of spinal cord - Plays imp. role in vital functions (breathing, HR, digestion, reflexes) • Pons: - Small structure rostral to medulla - Relays info about movement from cerebral hemispheres to cerebellum - Contains number of nuclei that’re generally part of reticular formation - Posesses some auditory info - Involved in some aspects of emotional processing • Ascending Reticular Formation: - AKAreticular activating system (RAS) - Primarily involved in arousal & motivation - May be part of large network responsible for conscious experience - Plays role in circadian rhythms - Damage to RAS leads to devastting losses in brain function - In extreme cases leads to permanent coma • Descending Reticular Formation: - Involved in posture, equilibrium & motor movement • Cerebellum: - Translates to “little brain” - Resembles miniature version of entire brain - Maestro of the orchestra (coordinates all movement **) - Motor commands pass through cerebellum as they signal muscle contracitons - During production of movement, sensory signals return to cerebellum allowing immediate correction of movement - Damage to cerebellum = jerky, exaggerated movements or overshooting/missing targets completely o Midbrain • Relatively small region between hindbrain & forebrain • Midbrain contains 2 major subdivisions: tectum & tegmentum • Within these 2 regions = number of structures involved in variety of functions: perception, arousal, motor control • Tectum: - Located in dorsal portion of midrain - Controls 2 primary structures: superior & inferior colliculi - These structures involved in perception and action - Superior Colliculus: eye movements & visual reflexes - Inferior Colliculus: auditory integration • Tegmentum: - Contains nuvlei of reticular formation, the red nucleus & substantia nigra - Red Nucleus: - One of most important structures in vertebrates w/ less complex brains, needed for regulation & production of eye movement - In humans with advanced forebrain structures, red nucleus plays lesser role in production of movement and serves primarily as relay station for information from higher motor areas to and from cerebellum & spinal cord - In still developing brain of young infants, motor behaviors may be controlled by red nucleus - Substantia Nigra: - Imp, highly interconnected region of midbrain - Projections into variety of forebrain regions - Involved in motor planning, learning, reward seeking - Contains neurons that produce neurotransmitter dopamine, which is released in high [] during variety of rewarding behaviors - Artificial rewards such as drugs of abuse act to increase dopamine in synaptic cleft to unnatural levels (contributes to addictive properties) - Damage to dopaminergic neurons in substantia nigra leads to reduced levels of dopamine - ^ Directly implicated in motor tremors characteristic of Parkinson’s disease o Forebrain • Contains structures involved in complex functions: emotion, memory, perception, thought • Largest region of brain • Examine in 2 sections: subcortical structures of limbic system, then cortex itself & the sheet of neurons lying on outside of brain 1. Limbic System: • Hypothalamus: - Controls several integrative functions: directing stress responses, regulates energy metabolism by influencing feeding, digestion & metabolic rate, regulating production through hormonal control of mating, pregnancy & lactation - Summarized: 4F’s  fight, flight, feeding Reproduction (fucking) - Exhibits these roles thru a) neurons capable of producing variety of hormones & b) connectionsbetween pituitary gland and key subcortical structures that lie below surface of cortex - Pituitary Gland: - Size of garbanzo bean, lies inferior to hypothalamus - Regulates & releases many vital hormones  often called master gland - Contains 2 subregions: anterior & posterior pituitary - Anterior pituitary: receives signals from brian (usually via hypothalamus), releases stimulating hormones  regulate other important endocrine glands like thyroid, testes, ovaries & adrenas - Posterior Pituitary: extension of hypothalamus & only releases 2 hormones called oxytocin and vasopressin - Oxytocin involved in basic physiological functions (lactation and uterine cotnractions) in women & can play role in bonding, love and trust - Vasopressin = vital blood hormone: interacts with kidneys to regulate thirst & glucose levels • Thalamus: - Large structure near centre of brain - Often called “relay station” to cerebral cortex - Axons from every sensory modality (except olfaction) synapse in thalamus, which processes and relays info selectively to cerebral cortex - Output from cerebellum & limbic system first relay through thalamus on way to cortex • Amygdala: - 2 symmetrical almond-shaped structures located below surface of each temporal lobe - Receive sensory info from thalamus, contain nuclei which plays role in decoding emotions- particularly stimuli that may be threatening - During intense emotions, amygdala = very active - When nuclei of amygdala are damaged, animals often show deficits in classical conditioning of fear responses - Amygdala functions = implicated in disorders like post-traumatic stress • Hippocampus: - Horseshoe shaped structure, in temporal lobe - Involved in memory formation - Activity here related to ability to hold short-term memories, may be involved in process of transferring short-term memories to long-term - Connected to amygdala (may be reason why strong emotions triggered by particular memories) - Plays vital role in ability to navigate through world - May contain a “spatial map” of world around - One of few regions of
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