Cognitive Neuroscience Intro Themes cognitive psychology has been
Cognitive & Neuroscience Intro • Themes – cognitive psychology has been guided by an information processing approach to theorizing – this approach attempts to characterize how information is processed from its initial input until its response – this approach continues to be used
Cognitive & Neuroscience Intro • Primary measures – Reaction time (RT) ämeasure the elapsed time from the onset of a stimulus until there is a response to the stimulus ägeneral goal of measuring RT is to make inferences about underlying cognitive processes (which are assumed to take time)
Cognitive & Neuroscience Intro • Primary measures – Accuracy äthis measure assesses the accuracy of an individual’s performance äNote: accuracy can be broadly (or narrowly) defined äe. g. , verbatim versus gist recall
Cognitive & Neuroscience Intro • Analogies – channel capacity äearly uses: attention/Broadbent ämore recent uses: controlled processing – computer analogy äserial sequential processing of information
Atkinson-Shiffrin Model (Atkinson & Shiffrin, 1968)
Cognitive & Neuroscience Intro • General early assumptions – sequential stages of processing – stages are independent – stages are non-overlapping
Cognitive & Neuroscience Intro • New conceptualizations – parallel processing äe. g. , typing – hierarchical organization äe. g. , typing a word äe. g. , grasping an object (prepare index finger thumb apperture as you move arm toward object) – context effects äsemantic priming
Cognitive & Neuroscience Intro • Cognitive neuroscience intro – neuron is the basic building block of the brain äcell that is specialized for receiving and transmitting a neural impulse äNote: there is enormous variability in the structure of neurons
Cognitive & Neuroscience Intro • Development of neurons and glial cells – germinal (or stem) cells of an embryo give rise to two types of nervous system cells: neuroblasts and spongioblasts (blast is an immature cell) – neuroblasts develop into neurons – spongioblasts develop into glial cells äglial cells provide support to neurons
Cognitive & Neuroscience Intro • Cognitive neuroscience intro – Major structures of a neuron äinput end: dendrites, which accumulate neural stimulation into the neuron itself äcell body or soma: regulates the biological activity of the neuron äaxon: a long tube-like structure used to transmit information äaxon terminals or terminal arborizations: output end of the neuron, where neural impulses end
An illustration of the various structures of the neuron. The lower diagram illustrates a sensory-motor reflex arc
Cognitive & Neuroscience Intro • Basic elements of nervous system – how a simple reflex works (e. g. , jerking hand away from a hot stove) äreceptor cells in hand react to physical stimulus and that triggers a pattern of firing down a sequence of sensory neurons ätracts of sensory neurons pass message along into the spinal cord where it is routed to brain and back into motor neurons äHowever, at the synapse the message can route directly to the motor neurons
Cognitive & Neuroscience Intro • Basic elements of nervous system – motor neurons in spinal cord transmit message back to arm muscles – these terminate at effector cells, which connect directly to muscle fibres and cause the muscles to pull arm away from hot stove – brain route: message is routed up spinal cord to brain (CNS) änote: central nervous system = spinal cord + brain
Cognitive & Neuroscience Intro • Basic elements of nervous system – synapse: region where the axon terminals of one neuron and dendrites of another neuron come together – synapses are small gaps between neurons äany single neuron synapses on a large number of other neurons: called divergence (a typical neuron synapses on from 100 -15, 000 other neurons) äalso any single neuron is the destination of many neurons (called convergence)
Cognitive & Neuroscience Intro • Basic elements of nervous system – information is transmitted across a synapse chemically by means of a neurotransmitter – a neurotransmitter is released from small buttons or sacs in the axon terminals, which then fit into receptor sites on the dendrites of the next neuron – two types of neurons: inhibitory and excitatory – inhibitory neurons decrease the likelihood of the next neuron from firing; excitatory neurons have the opposite effect
Cognitive & Neuroscience Intro • Structure of Nervous System – Nervous system consists of two major parts: central nervous system (CNS) and peripheral nervous system (PNS) – PNS consists of: skeletal nervous system and autonomic nervous system – Skeletal system controls striated (i. e. , striped) muscles, which are under voluntary control, and play an important role in motor cognition and simulation
Cognitive & Neuroscience Intro • Structure of Nervous System – autonomic nervous system governs smooth muscles and some glands – Smooth muscles, found in heart, blood vessels, stomach lining, and intestines, are not usually under voluntary control
Cognitive & Neuroscience Intro • Structure of Nervous System – autonomic nervous system plays a key role in emotion and affects memory functioning – Autonomic nervous system is divided into sympathetic and parasympathetic nervous system
Cognitive & Neuroscience Intro • Structure of Nervous System – sympathetic nervous system prepares animal to respond more vigorously in an emergency (flightor-fight response). Some changes: – Increasing heart rate (and delivering more oxygen and nutrients to organs) – Increasing breathing rate (and providing more oxygen) – Dilating pupils (increasing sensitivity to light) – Reducing digestive function
Cognitive & Neuroscience Intro • Structure of Nervous System – parasympathetic nervous system counters sympathetic nervous system and dampens the organism’s responses
Cognitive & Neuroscience Intro • Cerebral cortex (Overview) – Brain should be thought of as a collection of components that work together – It consists of two halves, which are called the left and right cerebral hemispheres – Hemispheres are connected by a massive collection of nerve fibres called the corpus callosum, as well as several smaller connections
Cognitive & Neuroscience Intro • Cerebral cortex (Overview) – Beneath the skull is a membrane covering the brain called the meninges – Beneath that is a network of blood vessels clinging to the surface of the brain – The surface of the brain contains most of the cell bodies of the neurons, which have a gray colour, hence the term gray matter
Cognitive & Neuroscience Intro – Cerebral cortex äcortex: consists of 4 -6 layers of cells (or gray matter) äthe term cortex (bark) refers to any outer layer of cells äconventionally the terms cortex and neocortex are used interchangeably äthe cortex is wrinkled in order to increase its area (think of crumpled paper)
Cognitive & Neuroscience Intro • Cerebral cortex – Clefts (indentations) in the brain are called fissures if they extend deeply into brain or sulci if they are shallower – A ridge in the cortex is called a gyrus
Gyri and sulci. Lateral (A) and medial (B) views of the gyri. Lateral (C) and medial (D) views of the sulci
Cognitive & Neuroscience Intro • Subcortical structures – Beneath the cortex are found subcortical structures and at the centre of the brain are a series of cavities, called ventricles – Ventricles are filled with the same fluid that is found in the spinal cord
Cognitive & Neuroscience Intro • hemispheres and lobes – cortex consists of two hemispheres separated by the medial longitudinal fissure – each hemisphere is divided into four lobes äfrontal lobe (behind forehead) ätemporal lobe (underneath temples) äoccipital lobe äparietal lobe
The location of the frontal, parietal, occipital, and temporal lobes of the brain
Cognitive & Neuroscience Intro • Lobes – The cognitive activities are not assigned specifically to one of the lobes and the lobes are involved in several cognitive activities – A rough guide – occipital lobes ä – processes visual input from eyes and from memory (visual imagery, some) ä Within the occipital lobe specific different regions process different aspects of vision (e. g. , motion, color, shape) ä if occipital lobes are damaged blindness results
Cognitive & Neuroscience Intro • Lobes – temporal lobes ä Involved in several functions ä Retention of visual memory ä Matching visual input to visual memory ä Process input from the ears ä Posterior region of the left temporal lobe (Wernicke’s area is crucial for comprehending language ä Anterior regions of temporal lobes are crucial for processing new memories, deriving meaning, and processing emotion
Cognitive & Neuroscience Intro • Lobes – Parietal lobes äInvolved in several functions äIts most anterior gyrus, the somatosensory cortex (area S 1), represents sensations on different parts of your body with left S 1 representing right side of body and vice versa for right S 1 äParietal lobes are also involved in representing space and your relationship to it, and in representing tool knowledge
Cognitive & Neuroscience Intro • Lobes – Frontal lobes ä Involved in several functions ä Managing sequences of behaviors or mental activities ä Major role in producing speech—Broca’s area of left hemisphere ä Controlling movements– area M 1 (most posterior gyrus of frontal lobes (also called motor strip); this area is immediately adjacent to S 1 ä Left M 1 controls movements by right part of body and vice versa ä Frontal lobes also involved in memory retrieval, in planning and reasoning, and in some emotions
Cognitive & Neuroscience Intro • Projection maps – constructed by tracing axons from sensory systems into the brain, and by tracing axons from the neocortex into the motor systems of the brain stem and spinal cord
Cognitive & Neuroscience Intro • Projection maps ädark areas in figure are primary projection areas. These areas receive input from the sensory systems or project to the spinal motor systems älightly shaded areas receive projections (input) from the primary projection areas and are called secondary projection areas äunshaded areas are called higher-order association or tertiary areas
Cognitive & Neuroscience Intro • Topography of the neocortex – primary projection areas ävisual system--occipital lobes äauditory system -- temporal lobes äsomatosensory system -- parietal lobes ämotor system -- frontal lobes
A projection map
Subcortical structures
Cognitive & Neuroscience Intro • Subcortical areas äthalamus consists of several nuclei; all sensory systems except for smell have relays here on their way to cortex; also different cortical regions communicate with each other via thalamus
Cognitive & Neuroscience Intro • Thalamus (fyi) – consists of two symmetric nuclei at base of cerebral hemispheres superior to hypothalamus – each hemisphere contains half of the thalamus – thalamus receives ascending input (sensory information) and descending input from cerebral hemispheres, particularly from those cortical regions to which it projects – all sensory systems except for smell have relays here on their way to cortex
Cognitive & Neuroscience Intro • Thalamus – can be thought of as a complex relay station for sensory and motor systems except for olfaction (smell) – thalamus is thought to play an important role in the classification, integration of information, before sending it to the cortex for further processing
Cognitive & Neuroscience Intro • Thalamus – Thalamus also plays an important role in selective attention – Pulvinar nucleus (a nucleus refers to a cluster of cells) is involved in focusing attention
Cognitive & Neuroscience Intro – Hippocampus located at the anterior end of the temporal lobes; it plays a central role in entering new information into memory although it is not where memories are stored; it governs processes that allow memories to be stored
Cognitive & Neuroscience Intro – Amygdala (named, from Greek, because of its almond shape) plays an important role in the appreciation of emotion in others and in the expression of our own emotion (esp. fear) – The amygdala can modulate the functioning of the hippocampus; this helps you store vivid memories of highly emotional information – The amygdala and hippocampus along with other structures are part of the limbic system, which used to be thought to regulate emotion
Model of the human limbic system and its major structures
Cognitive & Neuroscience Intro • Basal ganglia – collection of nuclei lying beneath the anterior regions of the neocortex äinclude the putamen (shell), the globus pallidus (pale globe), the caudate nucleus (tailed nucleus), and the amygdala (almond). [Note: striatum = putamen + caudate; globus pallidus = pallidum] äcaudate nucleus receives projections from all parts of the neocortex and then projects through the putamen and globus pallidus to the thalamus, and then to the motor areas of the cortex
Cognitive & Neuroscience Intro • Basal ganglia äbasal ganglia also has reciprocal connections to the substantia nigra (black area) äthis projection provides dopamine to the basal ganglia; when dopamine is lost a motor disorder called Parkinson’s disease results
Cognitive & Neuroscience Intro • Basal ganglia – functions of basal ganglia äinvolved in motor function--including postural changes, sequencing of movements into a smoothly executed response, and habit learning äHabit learning (e. g. , development of routinized activities such as coming to this lecture hall)
Relation between the basal ganglia and the cortex. Arrows indicate theoretical projections of the various areas into basal ganglia structures
Cognitive & Neuroscience Intro • Brainstem – Includes the pons and medulla and reticular formation – regulates many movements of animals – responds to sensory features of the environment – regulates eating, sleeping, drinking, body temperature
The three divisions of the brain
Cognitive & Neuroscience Intro • Topography of the neocortex – The remaining functional neuroanatomy slides, about 6, contain additional useful, reference information – You will not be tested on this material
Medial view through the center of the brain showing structures of the brainstem
Cognitive & Neuroscience Intro • Topography of the neocortex – cytoarchitectonic maps äconstructed by examining the neurons in the neocortex to identify regions that have unique organization äthe best known of these is called Brodmann’s map shown in Figure 3. 9
Brodmann’s areas of the cortex
Cognitive & Neuroscience Intro
Cognitive & Neuroscience Intro
The First “Brain Imaging Experiment” … and probably the cheapest one too! Angelo Mosso Italian physiologist (1846 -1910) E = mc 2 ? ? ? “[In Mosso’s experiments] the subject to be observed lay on a delicately balanced table which could tip downward either at the head or at the foot if the weight of either end were increased. The moment emotional or intellectual activity began in the subject, down went the balance at the head-end, in consequence of the redistribution of blood in his system. ” -- William James, Principles of Psychology (1890) Courtesy: J. Culham, Robarts Research Institute
Brain imaging and cognition • Brain imaging techniques – early 1970 s x-ray computed tomagraphy or x-ray CT technique developed – when highly focused x-rays are passed through the body, the beam is affected in predictable ways by the relative density of the tissue – by passing a beam through the body at many different angles it becomes possible to reconstruct an image of the body
Brain imaging and cognition • Brain imaging techniques – this technique led to the development of Positron Emission Tomography (PET) – PET identifies anatomical correlates of cognitive processes – PET detects changes in blood flow in the brain while task being performed; it does not measure neural activity directly
Brain imaging and cognition • PET – PET uses radioisotopes that have positrons that emit gamma radiation when they collide with electrons – Gamma rays detected by sensors outside of the head – Sensors locate brain region where collision occurred
Brain imaging and cognition • PET (how it works) – subject is injected with positron-emitting radioactive isotope oxygen-15 (half-life about 2 minutes) – radioactive water accumulates in brain in proportion to the local blood flow – More active brain get more blood – the greater the blood flow the more radiation counts recorded by PET
Brain imaging and cognition • PET (experimental strategy) – Paired image subtraction ärecord image of subject while she is performing an experimental task ärecord image of subject while she is performing a control task ä(e. g. , dots in motion - stationary dots) ädifference tells us what brain regions are associated with representation of motion
Brain imaging and cognition • PET (experimental strategy) – to eliminate noise or random variation, the differenced images are averaged across subjects – the slide on the following page illustrates the strategy ärow 1 -- experimental - control = difference ärow 2 -- individualized difference images ärow 3 -- mean difference image
Brain imaging and cognition • Disadvantages of PET – Invasive – Poor temporal resolution – Expensive; few PET scanners exist because of expense
Brain imaging and cognition • What is MRI and f. MRI – MRI measures brain structure – Important to study brain structure when it is suspected there is neurological change to brain (e. g. , stroke, dementia) – f. MRI is designed to reveal short-term physiological changes associated with the active functioning of the brain; it can also reveal patterns of brain activation associated with these changes
MRI vs. f. MRI studies brain anatomy. Courtesy: J. Culham, Robarts Research Institute Functional MRI (f. MRI) studies brain function.
f. MRI Setup Courtesy: J. Culham, Robarts Research Institute
Brain imaging and cognition • MRI (overview) – MRI uses strong magnetic fields to create images of biological tissue – many atoms in the presence of a magnetic field behave like little bar magnets or compasses – that is, they line up in a particular orientation – when a radio wave is applied to this aligned sample, the sample emits detectable radio signals characteristic of the chemical environment
Brain imaging and cognition • f. MRI – To map brain function it is necessary to create images that distinguish between active and inactive brain regions – Called functional contrast – This is done by measuring the metabolic consequences of neuronal activity
Brain imaging and cognition • f. MRI – (BOLD) contrast is a sensitive MRI marker of neuronal activity – How BOLD works – Red blood cells contain hemoglobin, which carries oxygen in blood stream
Brain imaging and cognition • f. MRI – How BOLD works – BOLD signal measures the ratio of oxygenated to deoxygenated blood – When brain functions it draws in more red blood cells than it needs; by detecting extra oxygenated blood cells BOLD signal detects brain activity
Brain imaging and cognition • Parameters of neuroimaging data – Spatial resolution – Refers to the ability to distinguish between different locations within an image – In 2 -dimensional pictures, a pixel refers to the smallest picture element that can be resolved. – In a satellite photo of a large region a picture element might represent hundreds of metres, whereas a zoom picture of a region might represent 1 metre
Brain imaging and cognition • Parameters of neuroimaging data – Spatial resolution – In MR images, 3 -dimensional samples of the brain are obtained and the smallest resolvable 3 D element is called a voxel; in MRI, voxels are often 1 to 2 mm, in each dimension, whereas in f. MRI, voxels are 3 to 5 mm on each side
Brain imaging and cognition • Parameters of neuroimaging data – Temporal resolution – Factors affecting temporal resolution include: – 1. the rate at which an imaging technique obtains its images (sampling rate) – 2. the sluggishness of the physiological process being measured; in f. MRI BOLD measures blood oxygenation, a relatively slow process
Brain imaging and cognition • Advantages of f. MRI vs PET – f. MRI less expensive – Less invasive – Same participant can be retested numerous times in several condition; important because each brain slightly different
Brain imaging and cognition • Advantages of f. MRI vs PET – f. MRI has better spatial and can have better temporal resolution
Brain imaging and cognition • f. MRI event-related experimental design – BOLD signal is measured in response to a single event (e. g. , presentation of a single stimulus) – Repeating this event several times produces a clear signal by averaging across the event
Brain imaging and cognition • f. MRI event-related experimental design – Example. – Participants presented moving dots or stationary dots over several trials – BOLD signal measures moving dots compared to stationary dots – Results demonstrated several regions in the visual cortex were more active when dots were moving relative to stationary
Brain Imaging: Anatomy CAT Photography PET MRI Courtesy: J. Culham, Robarts Research Institute Source: modified from Posner & Raichle, Images of Mind
Brain imaging and cognition • Disadvantages of f. MRI – Poor temporal resolution – Machines are: – Expensive – Noisy – Tube narrow, which some people find upsetting
Brain imaging and cognition • PET and f. MRI are correlational methods – That is, they correlate areas of brain activation that accompany information processing when performing a task – Correlation does not necessarily imply causation – Brain regions that are activated may not necessarily play a functional role in performing the task – Hence these methods only suggest which brain regions may process information when performing a task
Brain imaging and cognition • PET and f. MRI are correlational methods – Data from PET and f. MRI can be used to compare 2 (or more) tasks to determine whether the same or different brain regions are activated – If different brain regions are activated, this suggests that these tasks are carried out by different processes – If the same brain regions are activated, this provides evidence to support the claim that similar processes are involved in performing the 2 tasks
Brain imaging and cognition • Limitations of neuroimaging methods – Excitatory and inhibitory activity cannot be distinguished – More activation does not necessarily mean more processing – Same functional areas may be located in slightly different brain areas making averaging across participants difficult – Brain is always active making it difficult to know what processing is going on during ‘baseline’ condition (note: neuroimaging methods usually involve comparison of a treatment to a control condition – Finding of no activity is difficult to interpret—could mean process is active in both conditions, inactive in both conditions or activation is subtle – Different processes appear to be implemented in the same area (e. g. , different neurons in area 17 process colour and shape)
Brain imaging and cognition • Other correlational methods – Other correlational methods are called electroencephalography (EEG); event-related potentials (ERP) – In both of these methods electrodes are placed on the scalp – EEG records fluctuations in electrical activity over time, at different “bands” or sets of frequencies (e. g. , 8 – 12 cycles per second) – ERP uses electrodes to observe fluctuations in activity relative to presentation of a stimulus (e. g. , P 300 is a positive fluctuation that is observed 300 milliseconds after a stimulus – Both ERP and EEG have disadvantages: 1. Both are sensitive to muscle twitches because muscles produce electrical activity when they twitch; 2. spatial resolution poor because electrical activity detected comes from spatially distributed regions
Method Spatial Res EEG Poor (1 inch) ERP Poor (1 inch) PET Good (about Poor 1 cm) Good (about Poor. 5 cm) f. MRI Temporal Res Excellent (ms) Invasiveness Low High Low
Brain imaging and cognition • Causal neural methods – It is also possible to use other methods to establish causal connections between brain activation and behavioral performance – Classic method is the neuropsychological patient study – Logic is straightforward—if a brain region plays a key role in carrying out a task, a patient with damage to that region should be impaired in carrying out that task
Brain imaging and cognition • Causal neural methods – Brain damage can occur for a variety of reasons including: – Stroke or other medical conditions that result in disruption of blood flow to the brain (e. g. , heart attack) – Brain surgery (e. g. , to remove a tumor) – Traumatic brain injury (e. g. , MVA, assault) – Brain-damaging toxins (e. g. , certain drugs including alcohol) – Brain-damaging diseases (e. g. , Alzheimers, Parkinsons)
Brain imaging and cognition • Causal neural methods – Limitations of neuropsychological studies – Brain damage usually affects a large area of neural tissue – It is possible that brain damage results in a change in the functioning of the brain as a whole
Brain imaging and cognition • Causal neural methods – Lesions indicate necessity of region, but not sufficiency; i. e. , other brain regions may also be necessary for function – E. g. , think of a radio that won’t play music; examination of the radio revealed that its speakers were broken; conclusion that speakers are necessary for music to play is correct; however, it does not mean that a radio with undamaged speakers will necessarily play (e. g. , think of a radio with a broken switch)
Brain imaging and cognition • Causal neural methods – Note: a given brain region may have more than one function
Brain imaging and cognition • Causal neural methods – Another causal neural method is Transcranial magnetic stimulation (TMS) – In this method brain processes of a small, circumscribed area of the brain are disrupted (1 cubic cm) – A coil is placed on the participant’s head and a current is run through the coil, which disrupts the neural areas of the brain beneath the coil – 2 versions of TMS – Single pulse TMS delivers a single pulse to specific brain area; repetitive TMS (r. TMS) delivers a series of pulses to specific brain area before a task is performed – If enough pulses are delivered, this has the effect of temporarily disrupting neural processing of specific brain area (like inducing a specific lesion)
Brain imaging and cognition • Causal neural methods – Limitations of r. TMS – Stimulating 1 brain area can affect other areas making it difficult to infer which area is responsible for effects – r. TMS can induce seizures if it is not used according to safety guidelines – r. TMS can be used to investigate only those regions directly below the skull
Brain imaging and cognition • Limitations of neuroscience methods – As this overview shows, each neuroscience method has strengths and weaknesses – This is why neuroscientists rely on evidence from a variety of different methods (converging evidence) to understand which cognitive processes and brain regions perform specific tasks –
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