Cognitive Neuroscience The Brain Story

Download Cognitive Neuroscience The Brain Story

Post on 04-Dec-2014

338 views

Category:

Documents

3 download

Embed Size (px)

DESCRIPTION

 

TRANSCRIPT

<ul><li><p>Cognitive NeuroscienceThe Brain StorybyVaia Lestou</p></li><li><p>A brief History of Cognitive NeuroscienceAncient humans although they wondered extensively about the nature of human feelings, memories, attention, communication, motion and many other cognitive functions, they had one big problem.</p><p>Problem:They did not have the ability to systematically explore the mind through experimentation.</p></li><li><p>A brief History of Cognitive Neuroscience</p><p>But if you can observe, manipulate &amp; measure then you can start to determine how the brain gets its job done Debrck (1986) Mind From Matter?</p><p>If you want to understand how a biological system works then a laboratory is needed and experiments are essential.</p></li><li><p>A brief History of Cognitive NeuroscienceEnigma of whether the brain works in concert or parts of the brain work independently is still the focus of contemporary researchface area specialised only for faces?or objects as well? </p></li><li><p>A brief History of Cognitive NeuroscienceFranz Joseph Gall &amp; J.G. Spurzheim claimed that the brain was organised into 35 specific functionsfounders of phrenology in the early 19th centuryFunctions ranged from language and colour perception to hope and self-esteemIf a person used one of the faculties more than the others the brain representation area grew (bump in the skull idea!)</p></li><li><p>A brief History of Cognitive NeuroscienceGall and colleagues believed that by studying carefully the skull of a person you could go a long way in describing the personality of the person inside the skullAnatomical Personology</p></li><li><p>A brief History of Cognitive NeuroscienceP.J.M. Flourens (1794-1867) challenged Galls localisation views bird experimentsAccording to Flourens(1824) :All sensations, all perceptions and all volitions occupy the same seat in these (cerebral) organs. The faculty of sensation, percept and volition is then essentially one faculty.</p></li><li><p>A brief History of Cognitive NeuroscienceIn France Paul Broca treated a man who had suffered from strokethe patient could understand language but could not speakthe patients left frontal lobe was damagedBrocas area3D MRI of human brain with Broca's area highlighted in red</p></li><li><p>A brief History of Cognitive NeuroscienceThe German Neuroloist Carl Wernicke in 1876 reported a stroke victim who could talk freely but what he said made little sensePatient could not understand spoken or written languageWernickes area3D MRI of human brain with Wernicke's area highlighted in blue</p></li><li><p>A brief History of Cognitive NeuroscienceThe most famous of all physiologists was Brodmann who analysed the cellular organisation of the cortex and characterised fifty two distinct regionsIt was soon discovered that the cytoarchitectonically described brain areas represent distinct brain regions</p></li><li><p>A brief History of Cognitive NeuroscienceThe revolution in our understanding of the nervous system was brought by Camillo Golgi (Italy) and Ramon y Cajal (Spain) Golgi developed a stain that impregnated individual neuronsCajal found that neurons are discrete entities He was also the first to suggest that neurons transmit electrical information in only one directions from the dendrites to the axonal tip</p></li><li><p>A brief History of Cognitive NeuroscienceIn the 20th century physiologist and neurologists continued the debate over the holistic processing or the functional localisation conflict in the field.</p><p>And while the medical profession pioneered most of the studies of how the brain worked, psychologists began to claim that they could measure behaviours and indeed study the mind. </p></li><li><p>A brief History of Cognitive NeuroscienceThe term Cognitive Neuroscience was first coined in a taxi in the 70s and by that time a new mission was clearly requiredneuroscientists were discovering how the cerebral cortex was organised and functioned in response to simple stimulispecific mechanisms were described, such as those relating to visual perception by Hubel &amp; Wieselmodels were build to describe how single cells interact to produce perceptsand psychologists started to abandon the ideas of learning and associationism and believed that the behaviours they were interested in had biological origin and instantiation. </p></li><li><p>Mission Statement of Cognitive Neuroscience:</p><p>How the brain actually does enable the mind</p></li><li><p>Anatomy of the BrainBrain = Cerebral CortexHas two symmetrical HemispheresEach hemisphere consists of large sheets of layered neuronsThe human cortex is highly folded to pack more cortical surface into the skull. The surface area of the average human cerebral cortex is about 2200 to 2400cm2The infolding of the cortical sheets are the sulci and the crowns of the folded tissue are called the gyri</p></li><li><p>Anatomy of the BrainThe cortex has a high density of cell bodies, the grey matter The underlying region is composed primarily by axons of neurons and is known as the white matter, they connect the neurons of the cerebral cortex to other locations in the brain</p></li><li><p>Anatomy of the BrainCerebral Hemispheres have four main subdivisionsFrontalParietal Temporal Occipital</p></li><li><p>The methods of Cognitive Neuroscience1. Neuroanatomy2. Neurophysiology3. Neurology4. Functional Neurosurgery5. Cognitive Psychology6. Computer Modelling7. Converging Methods</p></li><li><p>1. NeuroanatomyStudies the nervous systems structure Describes how the parts are connectedDescriptions can be made at many levelsFor the neuroanatomist investigations occur at two levels:gross neuroanatomy: general structures and connectionsfine neuroanatomy: main task is to desribe componenents of individual neuronsHistology is the study of tissue structure through dissection, and is essential for neuroanatomists to know</p></li><li><p>1. NeuroanatomyPrimary concern of neuroanatomy is the pattern of connectivity in the nervous system that allows information to get from one site to anotherproblem made difficult by:fact that neurons are not wired together in a simple fashionoften innervated with many neuronsSolution: Refinement of New Stainsstains for cell bodiesstains for axonshave the characteristic that they are absorbed from specific chemicals and therefore colour specific targets</p></li><li><p>1. NeuroanatomyInterested in describing the structure of different neuronsNeurons are heterogeneous, varying in shape and size</p></li><li><p>2. NeurophysiologyStructure is closely tied to functionWe cannot understand brain function from neuroanatomy aloneNeural function depends on electrochemical processes and numerous techniques exist to measure and manipulate neuron activitySome record cell activity in passive or active conditions and other manipulate activity by electrical stimulation or chemical inductiona. Electrical Stimulationb. Single Cell Recordingc. Lesions</p></li><li><p>A. Electrical StimulationEarly insights to cortical organisation were made by directly stimulating the cortex of awake humans undergoing neurosurgeryPioneers, Penfield &amp; jaspers (1954) explored the effect of small electrical currents applied to the cortical surfaceStimulation of the motor cortex: movementStimulation of the somatosensory area: somatic sensation</p></li><li><p>B. Single-Cell RecordingThe most important technological advance in neurophysiology has been the development of methods to record directly the activity of single neurons in laboratory animals.An thin electrode is inserted into an animals brain (brain does not hurt!)The primary goal of single cell recording experiments is to determine experimental manipulations that produce a consistent change in the response rate of a single neuron</p></li><li><p>C. LesionsNeurophysiologists have studied how behaviour is altered by selectively removing one or more of brain components.Logic: if a brain structure contributes to a task then removing that structure should impair performance in that task.Human cannot be subjected to such procedures, so human neuropsychology requires patients with naturally occuring lesions.</p></li><li><p>MRI scan of a normal and lesioned brain</p></li><li><p>3. NeurologyHuman pathology has provided key insights to the relation between the brain and behaviourPostmortem studies by early neurologists such as Broca and Wernicke were instrumental in linking the left hemisphere with language functionsBy selecting patients with a single neurological impairment, we can best link brain structures to specific cognitive functions. Sometimes patients have diffused damage and then conclusions are harder to draw.Structural imaging of neurological damage (CT) helps define the damage (advanced method of x-ray studies)Causes of Neurological Disordersvascular disorders (ie strokes)tumours degenerative and infectious diseases (MS, Huntingtons Disease) traumaFunctional Neurosurgery (lobectomy)</p></li><li><p>Phineas Gage CaseMost famous patient who survived severe brain damageHe was a railway construction worker who got injured by an accidental explosionSevere personality change after the accident</p></li><li><p>4. Cognitive PsychologyCognitive Psychology assumes that our perceptions, thoughts and actions depend on internal transformations or computationsMental Representation and Transformationsinformation processing depends on internal representationball rolls down a hill -pictorial representation better than one that encompasses the laws of physicsmental representations undergo transformationsimagine two letters presented in a screen one vertical the other one rotated in order to decide if they are the same or different you transform them to be into the same positionConstrains on Information Processingexploring the limitation in task performanceStroop task </p></li><li><p>5. Computer ModellingModels are explicit they can be analysed in detail, the way the computer represents the process must be completely specifiedRepresentation in Computer Modelsmodels differ greatly in their representations (ie. symbolic of object recognition would have units that represent visual features such as corners)Models lead to Testable PredictionsLimitations with computer modelsradically simplified and limited in their scopesome of their requirements come in contrast with what we know about living organismsrestricted to narrow problemsmodelling often also occurs in isolation to current theories</p></li><li><p>7. Converging MethodsCognitive Deficits Following Brain DamageSingle and Double DissociationsGroups versus individualsImaging the Healthy Brain</p></li><li><p>Single and Double DissociationsSingle dissociation Two groups differ on one critical behavioral task One group has a particular brain lesion, the other doesn't (the other group is usually a control group who is considered healthy and without any known brain abnormality) We then tentatively conclude that the difference on the behavioral task is due to the brain lesion This, in turn, suggests that the brain region that is lesioned probably was responsible for some aspect of the behavior being studied However, this connection is not guaranteed to be the case </p></li><li><p>Single and Double DissociationsProblems with interpreting a single dissociation: The task measuring the behaviour may not be sensitive to the true underlying behaviour that is disrupted The task may reflect something similar to, or a derivative of, or part of the real behaviour that brain region is involved in, but it may not be a completely accurate measure The behavioural change, though apparently narrow in scope, may be part of a broader behavioural change that we haven't yet identified The lesioned brain area may also affect other brain areas responsible for producing this and related behaviours </p></li><li><p>Single and Double DissociationsDouble dissociation Two groups differ, in different ways, on two different behavioral tasks Usually, the two groups each have different types of brain lesions For example, one patient with Broca's area damaged and another patient with Wernicke's area damaged The first patient shows difficulty producing speech, while speech comprehension is apparently normal The second patient shows difficulty comprehending speech, while speech production is apparently normal We conclude, fairly confidently, that Broca's area is responsible for speech production while Wernicke's area is responsible for speech comprehension </p></li><li><p>Single and Double DissociationsDouble dissociations are more powerful than single dissociations because we can isolate fairly specific behaviours that change with one type of lesion but don't change with a different type of lesion </p><p>The problems with the task (how sensitive it is to the actual behavioural change) are still a concern, but we are more confident with conclusions about brain localization when there are double dissociations </p></li><li><p>Groups versus individualsIndividual case studies Study one individual carefully with a known brain deficit If there is a specific behavioural deficit (after careful testing), it can be correlated with the known brain deficit And if two case studies are compared, each with different lesions, and double dissociations are found, we have strong confirmation for the link between behavior and brain region We are, of course, concerned that one individual case study may not reflect a larger population If you are familiar with statistical analysis, you should know that one research subject (N=1) is not very useful in statistical analyses We cannot know for sure that the behavioural deviations from normality are due to the brain deficit and not just because this person was different (with or without the brain deficit) </p></li><li><p>Groups versus individualsGroup studies In this approach, we compare groups of people with similar brain deficits and determine if they show a consistent pattern of behavioural deficits This minimizes the chance that individual differences are masking the results of brain damage The bottom row shows the proportion of overlap for a given brain region So we would be fairly confident that the areas of highest overlap were most likely involved in producing the behavioral deficit Comparing across brains is not trivial, however, because of individual variation To accomplish this, individual brains are matched to a "standard" brain The common technique is to use the Talairach brain--the brain of a French woman After matching certain landmark features, the image of a brain is distorted until it matches the Talairach brain Then all the brains are compared from this common, standard brain image </p></li><li><p>Imaging the Healthy BrainTranscranial magnetic stimulation (TMS) The goal of this technique is to intentionally induce a temporary "lesion" As far as we know, the brain is not damaged in any way, but a region is temporarily deactivated A strong electrical signal is sent to a region of the scalp We don't exactly know how this works, but it seems to disrupt neural function So for a very brief period of time, the behaviours associated with the focus of the TMS should be impaired There is some control over the location of the "lesion," but the precision is limited The device that administers the electrical pulse is fairly large It is usually held in place manually, lacking much precision </p></li><li><p>Imaging the Healthy BrainScalp recordings Electroencephalogram (EEG) Passively measure electrical activity from neurons that reaches the scalp Place electrodes on the scalp to record electrical activity...</p></li></ul>