Cognitive

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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

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Cognitive Neuroscience Intro

• Primary measures
• Reaction time (RT)
• measure the elapsed time from the onset of a
  stimulus until there is a response to the
  stimulus
• general goal of measuring RT is to make
  inferences about underlying cognitive processes
  (which are assumed to take time)

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Cognitive Neuroscience Intro

• Primary measures
• Accuracy
• this measure assesses the accuracy of an
  individuals performance
• Note accuracy can be broadly (or narrowly)
  defined
• e.g., verbatim versus gist recall

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Cognitive Neuroscience Intro

• Analogies
• channel capacity
• early uses attention/Broadbent
• more recent uses controlled processing
• computer analogy
• serial sequential processing of information

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Atkinson-Shiffrin Model
(Atkinson Shiffrin, 1968)
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Cognitive Neuroscience Intro

• General early assumptions
• sequential stages of processing
• stages are independent
• stages are non-overlapping

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Cognitive Neuroscience Intro

• New conceptualizations
• parallel processing
• e.g., typing
• hierarchical organization
• e.g., typing a word
• e.g., grasping an object (prepare index finger
  thumb apperture as you move arm toward object)
• context effects
• semantic priming

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Cognitive Neuroscience Intro

• Cognitive neuroscience intro
• neuron is the basic building block of the brain
• cell that is specialized for receiving and
  transmitting a neural impulse
• Note there is enormous variability in the
  structure of neurons

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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
• glial cells provide support to neurons

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Cognitive Neuroscience Intro

• Cognitive neuroscience intro
• Major structures of a neuron
• input end dendrites, which accumulate neural
  stimulation into the neuron itself
• cell body or soma regulates the biological
  activity of the neuron
• axon a long tube-like structure used to transmit
  information
• axon terminals or terminal arborizationsoutput
  end of the neuron, where neural impulses end

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An illustration of the various structures of the
neuron. The lower diagram illustrates a
sensory-motor reflex arc
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Cognitive Neuroscience Intro

• Basic elements of nervous system
• how a simple reflex works (e.g., jerking hand
  away from a hot stove)
• receptor cells in hand react to physical stimulus
  and that triggers a pattern of firing down a
  sequence of sensory neurons
• tracts of sensory neurons pass message along into
  the spinal cord where it is routed to brain and
  back into motor neurons
• However, at the synapse the message can route
  directly to the motor neurons

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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)
• note central nervous system spinal cord
  brain

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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
• any single neuron synapses on a large number of
  other neurons called divergence (a typical
  neuron synapses on from 100-15,000 other neurons)
• also any single neuron is the destination of many
  neurons (called convergence)

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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

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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

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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

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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

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Cognitive Neuroscience Intro

• Structure of Nervous System
• sympathetic nervous system prepares animal to
  respond more vigorously in an emergency
  (flight-or-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

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Cognitive Neuroscience Intro

• Structure of Nervous System
• parasympathetic nervous system counters
  sympathetic nervous system and dampens the
  organisms responses

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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

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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

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Cognitive Neuroscience Intro

• Cerebral cortex
• cortex consists of 4-6 layers of cells (or gray
  matter)
• the term cortex (bark) refers to any outer layer
  of cells
• conventionally the terms cortex and neocortex are
  used interchangeably
• the cortex is wrinkled in order to increase its
  area (think of crumpled paper)

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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

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Gyri and sulci. Lateral (A) and medial (B) views
of the gyri. Lateral (C) and medial (D) views of
the sulci
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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

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Cognitive Neuroscience Intro

• hemispheres and lobes
• cortex consists of two hemispheres separated by
  the medial longitudinal fissure
• each hemisphere is divided into four lobes
• frontal lobe (behind forehead)
• temporal lobe (underneath temples)
• occipital lobe
• parietal lobe

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The location of the frontal, parietal, occipital,
and temporal lobes of the brain
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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
• processes visual input from eyes and from
  memory (visual imagery, some)
• Within the occipital lobe specific different
  regions process different aspects of vision
  (e.g., motion, color, shape)
• if occipital lobes are damaged blindness results

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Cognitive Neuroscience Intro

• Lobes
• temporal lobes
• Involved in several functions
• Retention of visual memory
• Matching visual input to visual memory
• Process input from the ears
• Posterior region of the left temporal lobe
  (Wernickes area is crucial for comprehending
  language
• Anterior regions of temporal lobes are crucial
  for processing new memories, deriving meaning,
  and processing emotion

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Cognitive Neuroscience Intro

• Lobes
• Parietal lobes
• Involved in several functions
• Its most anterior gyrus, the somatosensory cortex
  (area S1), represents sensations on different
  parts of your body with left S1 representing
  right side of body and vice versa for right S1
• Parietal lobes are also involved in representing
  space and your relationship to it, and in
  representing tool knowledge

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Cognitive Neuroscience Intro

• Lobes
• Frontal lobes
• Involved in several functions
• Managing sequences of behaviors or mental
  activities
• Major role in producing speechBrocas area of
  left hemisphere
• Controlling movements area M1 (most posterior
  gyrus of frontal lobes (also called motor strip)
  this area is immediately adjacent to S1
• Left M1 controls movements by right part of body
  and vice versa
• Frontal lobes also involved in memory retrieval,
  in planning and reasoning, and in some emotions

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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

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Cognitive Neuroscience Intro

• Projection maps
• dark areas in figure are primary projection
  areas. These areas receive input from the sensory
  systems or project to the spinal motor systems
• lightly shaded areas receive projections (input)
  from the primary projection areas and are called
  secondary projection areas
• unshaded areas are called higher-order
  association or tertiary areas

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Cognitive Neuroscience Intro

• Topography of the neocortex
• primary projection areas
• visual system--occipital lobes
• auditory system -- temporal lobes
• somatosensory system -- parietal lobes
• motor system -- frontal lobes

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A projection map
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Subcortical structures
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Cognitive Neuroscience Intro

• Subcortical areas
• thalamus 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

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Cognitive Neuroscience Intro

• Thalamus
• 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

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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

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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

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Cognitive Neuroscience Intro

• hypothalamus composed of small nuclei involved
  in feeding, sexual behaviour, sleeping,
  temperature regulation, blood pressure, heart
  rate, etc.
• Some of these functions are accomplished by
  hormones (chemicals that affect various organs)
• 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

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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

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Model of the human limbic system and its major
structures
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Cognitive Neuroscience Intro

• Basal ganglia
• collection of nuclei lying beneath the anterior
  regions of the neocortex
• include the putamen (shell), the globus pallidus
  (pale globe), the caudate nucleus (tailed
  nucleus), and the amygdala (almond). Note
  striatum putamen caudate globus pallidus
  pallidum
• caudate 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

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Cognitive Neuroscience Intro

• Basal ganglia
• basal ganglia also has reciprocal connections to
  the substantia nigra (black area)
• this projection provides dopamine to the basal
  ganglia when dopamine is lost a motor disorder
  called Parkinsons disease results

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Cognitive Neuroscience Intro

• Basal ganglia
• functions of basal ganglia
• involved in motor function--including postural
  changes, sequencing of movements into a smoothly
  executed response, and habit learning
• Habit learning (e.g., development of routinized
  activities such as coming to this lecture hall)

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Relation between the basal ganglia and the
cortex. Arrows indicate theoretical projections
of the various areas into basal ganglia structures
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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

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The three divisions of the brain
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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

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Medial view through the center of the brain
showing structures of the brainstem
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Cognitive Neuroscience Intro

• Topography of the neocortex
• cytoarchitectonic maps
• constructed by examining the neurons in the
  neocortex to identify regions that have unique
  organization
• the best known of these is called Brodmanns map
  shown in Figure 3.9

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Brodmanns areas of the cortex
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Cognitive Neuroscience Intro
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Cognitive Neuroscience Intro
58
The First Brain Imaging Experiment
and probably the cheapest one too!
Angelo Mosso Italian physiologist (1846-1910)
In Mossos 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
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Brain imaging and cognition

• Brain imaging techniques
• early 1970s 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 (using
  sophisticated math techniques) to re-construct an
  image of the body

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Brain imaging and cognition

• Brain imaging techniques
• this technique led to the development of Positron
  Emission Tomography (PET)
• PET also built on a technique known as
  autoradiography

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Brain imaging and cognition

• autoradiography
• radioactive labeled compound is injected into
  organism
• experiment is performed
• organ is removed and sectioned
• individual slices are placed on film which is
  sensitive to radioactivity

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Brain imaging and cognition

• PET
• PET also uses radioisotopes but does not require
  organs to be removed
• PET uses radioisotopes that have positrons that
  emit gamma radiation that can be detected by
  sensors outside of the head

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Brain imaging and cognition

• PET (how it works)
• a PET camera is a set of radiation detectors that
  circle the subjects head
• 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
• the greater the blood flow the more radiation
  counts recorded by PET

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Brain imaging and cognition

• PET (experimental strategy)
• Paired image subtraction
• record image of subject while she is performing
  an experimental task
• record image of subject while she is performing a
  control task
• (e.g., dots in motion - stationary dots)
• difference tells us what brain regions are
  associated with representation of motion

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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
• row 1-- experimental - control difference
• row 2 -- individualized difference images
• row 3 -- mean difference image

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Brain imaging and cognition

• Disadvantages of PET
• Invasive
• Poor temporal resolution
• Expensive

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Brain imaging and cognition

• What is MRI and fMRI
• MRI uses strong magnetic fields to create images
  of biological tissue
• The strength of the magnetic field created by an
  MRI scanner is measured in Tesla
• MRI scanners are typically 1.5 3.0 Tesla
  (earths magnetic field is 0.00005 Tesla
• Refs Smith and Kosslyn (2007) Huettal, Song,
  McCarthy (2008) functional magnetic resonance
  imaging

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Brain imaging and cognition

• What is MRI and fMRI
• To create images the scanner uses a series of
  changing magnetic gradients and oscillating
  electromagnetic fields known as pulse sequences
• These electromagnetic fields result in energy
  being absorbed and then emitted by atomic nuclei
  in the tissue being examined
• The amount of emitted energy depends upon the
  number and type of nuclei present, thus creating
  an image of the tissue being examined

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Brain imaging and cognition

• What is MRI and fMRI
• MRI structures brain structure
• Important to study brain structure when it is
  suspected there is neurological change to brain
  (e.g., stroke, dementia)
• fMRI 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

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MRI vs. fMRI
Functional MRI (fMRI) studies brain function.
MRI studies brain anatomy.
Courtesy J. Culham, Robarts Research Institute
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fMRI Setup
Courtesy J. Culham, Robarts Research Institute
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Brain imaging and cognition

• MRI (overview)
• 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

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Brain imaging and cognition

• fMRI
• functional magnetic resonance imaging
• nuclear magnetic resonance (NMR) image intensity
  reflects the concentration of water in the sample

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Brain imaging and cognition

• fMRI
• 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

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Brain imaging and cognition

• fMRI
• (BOLD) contrast is a sensitive MRI marker of
  neuronal activity
• How BOLD works
• Red blood cells contain hemoglobin
• the iron ion in hemoglobin can have oxygen bound
  to it or stripped off

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Brain imaging and cognition

• fMRI
• How BOLD works
• When brain functions it draws in more red blood
  cells than it needs by detecting extra
  oxygenated blood cells BOLD signal detects brain
  activity

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Brain imaging and cognition

• fMRI
• fMRI contrast is tailored to optimize the signal
  dependence on deoxyhemoglobin concentration
• deoxyhemoglobin is used as a contrast agent
• this so called, blood oxygenation level dependent
  (BOLD) contrast is a sensitive MRI marker of
  neuronal activity
• MRI signal arises from the stimulation of
  transitions of hydrogen atoms in water, placed in
  a large field

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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

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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
  fMRI, voxels are 3 to 5 mm on each side

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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 fMRI BOLD measures blood
  oxygenation, a relatively slow process

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Brain imaging and cognition

• fMRI (Experimental strategy)
• acquire MR images while subjects are presented
  with blocks of stimulation (experimental) for
  about 30 seconds
• have control or baseline activity
• subtract one from the other

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Brain imaging and cognition

• fMRI
• echo-planar imaging (EPI)
• this technique commonly used to obtain images
• multi-slice EPI is acquired by first exciting an
  nuclear magnetic resonance (NMR) signal from a
  thin-slice of the head, using a shaped RF pulse
  in the presence of a rapidly switched magnetic
  field gradient
• this generates a series of echoes of the NMR
  signal that can then be used to construct a
  2-dimensional image of the slice

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Brain imaging and cognition

• fMRI
• echo-planar imaging
• volume data are built up by repeating the process
  of image acquisition at different slice positions
  (40 slices commonly used to cover the brain)
• TR refers to the time between repeated
  acquisitions of the same slice
• a common set of parameters is 100 ms per slice x
  50 slices 5 seconds (TR 5 seconds)
• a parameter, TE, is defined as the time needed to
  generate half of the echoes for a single slice

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Brain Imaging Anatomy
CAT
Photography
PET
MRI
Source modified from Posner Raichle, Images of
Mind
Courtesy J. Culham, Robarts Research Institute
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Brain imaging and cognition

• Disadvantages of fMRI
• Poor temporal resolution
• Machines are
• Expensive
• Noisy
• Tube narrow, which some people find upsetting

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Brain imaging and cognition

• PET and fMRI 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

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Brain imaging and cognition

• PET and fMRI are correlational methods
• Data from PET and fMRI 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

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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
  interpretcould 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)

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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., P300 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

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Method Spatial Res Temporal Res Invasive-ness
EEG Poor (1 inch) Excellent (ms) Low
ERP Poor (1 inch) Excellent (ms) Low
PET Good (about 1cm) Poor High
fMRI Good (about .5 cm) Poor Low
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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 straightforwardif 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

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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)

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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

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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 wont 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)

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Brain imaging and cognition

• Causal neural methods
• Note a given brain region may have more than one
  function

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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 participants 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 (rTMS)
  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)

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Brain imaging and cognition

• Causal neural methods
• Limitations of rTMS
• Stimulating 1 brain area can affect other areas
  making it difficult to infer which area is
  responsible for effects
• rTMS can induce seizures if it is not used
  according to safety guidelines
• rTMS can be used to investigate only those
  regions directly below the skull

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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