2 A brief History of Cognitive Neuroscience Ancient 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.Problem:They did not have the ability to systematically explore the mind through experimentation.
3 A brief History of Cognitive Neuroscience But if you can observe, manipulate & measure then you can start to determine how the brain gets its job doneDebrück (1986) ‘Mind From Matter?’If you want to understand how a biological system works then a laboratory is needed and experiments are essential.
4 A brief History of Cognitive Neuroscience Enigma of whether the brain works in concert or parts of the brain work independently is still the focus of contemporary researchface areaspecialised only for faces?or objects as well?
5 A brief History of Cognitive Neuroscience Franz Joseph Gall & 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!)
6 A brief History of Cognitive Neuroscience Gall 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
7 A brief History of Cognitive Neuroscience P.J.M. Flourens ( ) challenged Gall’s localisation viewsbird 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.’
8 A brief History of Cognitive Neuroscience In France Paul Broca treated a man who had suffered from strokethe patient could understand language but could not speakthe patient’s left frontal lobe was damagedBroca’s area3D MRI of human brain with Broca's area highlighted in red
9 A brief History of Cognitive Neuroscience The 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 languageWernicke’s area3D MRI of human brain with Wernicke's area highlighted in blue
10 A brief History of Cognitive Neuroscience The 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
12 A brief History of Cognitive Neuroscience The 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 entitiesHe was also the first to suggest that neurons transmit electrical information in only one directions from the dendrites to the axonal tip
14 A brief History of Cognitive Neuroscience In the 20th century physiologist and neurologists continued the debate over the holistic processing or the functional localisation conflict in the field.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.
15 A brief History of Cognitive Neuroscience The 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 & 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.
16 Mission Statement of Cognitive Neuroscience: ‘How the brain actually does enable the mind’
17 Anatomy of the Brain Brain = Cerebral Cortex Has 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
18 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
19 Anatomy of the Brain Cerebral Hemispheres have four main subdivisions FrontalParietalTemporalOccipital
20 The methods of Cognitive Neuroscience 1. Neuroanatomy2. Neurophysiology3. Neurology4. Functional Neurosurgery5. Cognitive Psychology6. Computer Modelling7. Converging Methods
21 1. Neuroanatomy Studies the nervous system’s 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
22 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
23 1. NeuroanatomyInterested in describing the structure of different neuronsNeurons are heterogeneous, varying in shape and size
24 2. Neurophysiology Structure is closely tied to function We 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
25 A. Electrical Stimulation Early insights to cortical organisation were made by directly stimulating the cortex of awake humans undergoing neurosurgeryPioneers, Penfield & 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
26 B. Single-Cell Recording The 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 animal’s 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
27 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.
29 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)tumoursdegenerative and infectious diseases (MS, Huntington’s Disease)traumaFunctional Neurosurgery (lobectomy)
30 Phineas Gage Case Most famous patient who survived severe brain damage He was a railway construction worker who got injured by an accidental explosionSevere personality change after the accident
31 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
33 5. Computer Modelling Models 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
34 7. Converging Methods Cognitive Deficits Following Brain Damage Single and Double DissociationsGroups versus individualsImaging the Healthy Brain
35 Single and Double Dissociations Single dissociationTwo groups differ on one critical behavioral taskOne 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 lesionThis, in turn, suggests that the brain region that is lesioned probably was responsible for some aspect of the behavior being studiedHowever, this connection is not guaranteed to be the case
36 Single and Double Dissociations Problems with interpreting a single dissociation:The task measuring the behaviour may not be sensitive to the true underlying behaviour that is disruptedThe 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 measureThe behavioural change, though apparently narrow in scope, may be part of a broader behavioural change that we haven't yet identifiedThe lesioned brain area may also affect other brain areas responsible for producing this and related behaviours
37 Single and Double Dissociations Two groups differ, in different ways, on two different behavioral tasksUsually, the two groups each have different types of brain lesionsFor example, one patient with Broca's area damaged and another patient with Wernicke's area damagedThe first patient shows difficulty producing speech, while speech comprehension is apparently normalThe second patient shows difficulty comprehending speech, while speech production is apparently normalWe conclude, fairly confidently, that Broca's area is responsible for speech production while Wernicke's area is responsible for speech comprehension
38 Single and Double Dissociations Double 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 lesionThe 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
39 Groups versus individuals Individual case studiesStudy one individual carefully with a known brain deficitIf there is a specific behavioural deficit (after careful testing), it can be correlated with the known brain deficitAnd 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 regionWe are, of course, concerned that one individual case study may not reflect a larger populationIf you are familiar with statistical analysis, you should know that one research subject (N=1) is not very useful in statistical analysesWe 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)
40 Groups versus individuals Group studiesIn this approach, we compare groups of people with similar brain deficits and determine if they show a consistent pattern of behavioural deficitsThis minimizes the chance that individual differences are masking the results of brain damageThe bottom row shows the proportion of overlap for a given brain regionSo we would be fairly confident that the areas of highest overlap were most likely involved in producing the behavioral deficitComparing across brains is not trivial, however, because of individual variationTo accomplish this, individual brains are matched to a "standard" brainThe common technique is to use the Talairach brain--the brain of a French womanAfter matching certain landmark features, the image of a brain is distorted until it matches the Talairach brainThen all the brains are compared from this common, standard brain image
41 Imaging the Healthy Brain Transcranial 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 deactivatedA strong electrical signal is sent to a region of the scalpWe don't exactly know how this works, but it seems to disrupt neural functionSo for a very brief period of time, the behaviours associated with the focus of the TMS should be impairedThere is some control over the location of the "lesion," but the precision is limitedThe device that administers the electrical pulse is fairly largeIt is usually held in place manually, lacking much precision
42 Imaging the Healthy Brain Scalp recordingsElectroencephalogram (EEG)Passively measure electrical activity from neurons that reaches the scalpPlace electrodes on the scalp to record electrical activityHook the electrodes to an amplifier to boost the signal (very little neurally generated electricity will reach the scalp)Have a representation of global neural activityVery useful for determining sleep patterns
44 Imaging the Healthy Brain Event-related potential (ERP)The development of ERPs is when the EEG became useful as an experimental toolThe procedure involves time-locking an EEG recording to the onset of a particular stimulus or behaviourOne EEG reading is very noisy; i.e. the electrical signal is very chaotic and variableBut if we measure EEG multiple events of the same type, all time- locked to the onset of the event, and average them together, a smooth pattern arises
45 Imaging the Healthy Brain Magnetoencephalogram (MEG)The methodology of MEG is very similar to the methodology for ERPThe sensors for MEG are actually measuring magnetic fields produced by neurons, not electrical signalsThe inverse problem still exists for MEG, but because there is less distortion of the magnetic signal than there is for the electrical signal, the solutions end up being more accurate, on the wholeHowever, this technique is extremely expensive ($1 million for a reasonably good set-up)
46 Imaging the Healthy Brain Positron-emission tomography (PET)Methodology:Water labelled with radioactive oxygen, is injected into a subjectBrain cells require oxygen (and glucose) for energyThe radioactive oxygen is unstable enough that protons break off and collide with electrons in the brainThese collisions are measured by a PET scannerWith this technique, we do not directly measure neural activityIt is assumed that the higher concentration of radioactive isotopes reflects higher neural activityThe more active a neuron is, the more energy it should need to replenish and the more likely the radioactive oxygen will enter into that brain region
47 Imaging the Healthy Brain We use the subtraction method to determine relative levels of neural activityPET scans are taken separately for two experimental conditionsThe two conditions are identical except for one feature--the behavior being studiedThen one PET images are subtracted from the other, so the resulting difference should reflect the defining featureSo if Task 1 required Processes A, B and C, and Task 2 required Processes A, B, C and D, the difference between the PET images for Tasks 1 and 2 should reflect the activity unique to Process DOne consideration when using PET as an experimental technique is that it takes minutes for the radioactive isotope to get flushed out of the brainSo each experimental condition takes that long, meaning it is impossible to compare too many conditions in one PET experiment
49 Imaging the Healthy Brain Functional magnetic resonance imaging (fMRI)The BOLD responseBOLD stands for Blood Oxygen Level DependentWhat is measured is dependent on the levels of oxygen in the blood for any local region of the brainWhen oxygen is used by cells, the result is the blood becomes more deoxygenatedDeoxygenated hemoglobin is more ferromagnetic (the iron in the blood is more prominent), which is what the MRI scanner can measureBasically, fMRI measures the ratio of deoxygenated to oxygenated hemoglobin
50 Imaging the Healthy Brain Subtraction method is one technique also used with fMRIPresent variations of a task that each differ in one respectThese differences may be different levels of a single cognitive dimension (e.g., different amounts of visual information presented) or they could be completely different cognitive functionsContrast the fMRI signal from these conditions with each other and with the signal from a control condition, when the extra cognitive function was not present (but everything else was)These subtractive differences are reported as correlating with changes in behaviorMany different variations are possible with fMRI, unlike PET, because it is not necessary to wait minutes between conditionsWe can use alternating epochs of a fixed length of time doing each variation of the task
53 Concluding RemarksAdvances in science are often fueled by technological developmentsThe maturation of cognitive neuroscience as a scientific field provides a tremendous impetus for the development of new methodsThe questions we ask are constrained by the methods available but new research tools are promoted by the questions we ask.