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Brain & Cognition 3: Cognitive Neuropsychology summary
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Brain & Cognition 3: Cognitive Neuropsychology summary of all the lectures and required book chapters
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Cognitive NeuropsychologyWeek 1
Chapter 3 - Methods of Cognitive Neuroscience
3.1 Cognitive Psychology and Behavioral Methods
• Cognitive psychology: mental activity as an information-processing problem
• Basic assumption that we don’t directly perceive & act
• Internal processing = acquisition, storage, use of info (underlying observable behavior)
• Cognitive approach:
(1) Processing depends on mental
representations
(2) Representations undergo internal
transformations
Mental Representations
• Letter-Matching task by Posner
• Posner’s results show that we derive multiple
representations of stimuli
• Physical aspects
• Letters identity
• Response latencies re ect degrees of
processing required
Internal Transformations
• Mental representations undergo internal transformations (smell of garlic makes you think of your
grandmas house)
• Memory may alter how we perceive something
• Sternbeg’s task (Memory comparison task): participant sees set of letters to memorize —>
then sees single letter and must decide whether this letter was part of the memorized set
• Postulated four stages: Encoding,
Comparing, Deciding, Responding
• If comparison process parallel =>
reaction time independent of number
of items
• If comparison process serial =>
reaction time slows Dows
• Results supported serial hypothesis
• Word superiority e ect: participants
brie y see stimulus then deiced which of
two target letters they saw, participants
most accurate when stimulus is a word
Constraints on Info processing
• Stroop e ect shows multiplicity of
mental representations (activate at least two separable representations)
• Representations linked closely to vocal response system (little e ect when response produced
manually, e.g. pressing a button)
Take home message
• Cognitive psychology focuses on understanding how the brain represents and manipulates
objects or ideas
• Fundamental goals of cognitive psychology include identify- ing the mental operations that are
required to perform cognitive tasks and exploring the limitations in task performance
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, 3.2 Studying the Damaged Brain
Vascular Disorders
• Issues with supply of oxygen and glucose
• Brain uses 20% of all oxygen we breath
• Cerebral vascular accidents (strokes): sudden disruption of the
blood ow to the brain
• Ischemia = inadequate blood supply
• Sudden drop in blood pressure (shock or bleeding) prevents
blood from reaching brain
• Sudden rise in blood pressure may prevent blood from
reaching brain and cause aneurysm (rupture)
• Location & extend of disruption determine consequences
• If infarct is cortical, initial symptoms may be striking or subtle
• Severity of initial symptoms can predict chronic problems
Tumors
• Most brain tumors originate in glial cells (white matter)
• Benign: do not recur vs. Malignant: distributed over several areas and/or recur
Degenerative and infectious disorders
• Huntington’s or Parkinson’s: in basal ganglia (by MRI scans)
• Alzheimer’s: atrophy of cerebral cortex
• HIV virus causes —> immunode ciency (AIDS) in subcortical regions —> di use lesions of
white matter & destroying axonal bers —> dementia
• Herpes simplex virus: destroys neurons in cortisol and limbic structures
Traumatic brain Injury
• Damage may be at the site of blow or at distant locations (reactive forces)
• Edema (swelling) —> increases in cranial pressure —> reducing perfusion —> ischemia &
secondary lesions
• Axons are particularly vulnerable to mechanical forces (di use axonal injury - DAI)
• DAI may be main pathology involved with TBI even without focal lesions
Epilepsy
• Abnormally patterned activity
• Seizure, transient loss of consciousness
• EEG used
Studying Brain-Behavior Relationships Following Neural Disruption
• Lesion studies: assumption that brain injury is eliminative - brain injury disturbs or eliminates
processing ability of a ected structures
• Surgical interventions: unique opportunity to investigate link between brain and behavior
(epilepsy -> tissue removal)
• Lesions may alter function of neural regions connected to it but may also result in development
of compensatory processes
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, Take Home Message
• Researchers study patients with neurological disorders or brain lesions to examine structure–
function relation- ships. Double dissociations are better evidence than single dissociations that
damage to a particular brain region may result in a selective de cit of a cognitive operation
• Traumatic brain injuries are the most common cause of brain lesions. Even when the injuries are
mild, they can have chronic neurodegenerative consequences
• Impairments in a particular cognitive process do not mean that the damaged part of the brain
“performs” that pro- cess. Brain lesions can disrupt processing in intact brain structures or
disrupt brain networks on a larger scale
3.3 Methods to perturb Neural Function
Pharmacology
• Psychoactive drugs: ca ein, alcohol, cocaine, pharmaceutical drugs
• Pharmacological studies: administration of agonist drugs (similar structure to a
neurotransmitter) or antagonist drugs (bind to receptors and block neurotransmission)
• E.g. E ect of dopamine on decision making when potential monetary reward or loss
• Group A receives drug haloperidol (dopamine receptor antagonist)
• Group B receptor agonist L-dopa
• Learning task with two symbols associated with unknown probability of gain/no gain, loss/no
loss, neither —> participant had to choose symbols on each trial
• On gain trials L-dopa group won more money, On loss trials groups don’t di er
=> dopamine has selective e ect on reward-driven learning
• Studies with drug injections in blood stream lack speci city
• Rats depleted of dopamine = unwilling to make e ortful responses that are highly rewarding
• ACC is important for evaluating cost vs. bene t and has two dopamine receptors
• D1: if blocked rats act like couch potatoes
=> critical for e ort-based decision making
• D2: if blocked still pursue high reward
Genetic Manipulations
• Develop genetically altered animals using a knockout procedure
• Manipulate gene(s) so it doesn’t express itself
• At focal level: ‚take out‘ single type of postsynaptic receptor in speci c region
• Mouse strain in which (NMDA) receptors absent in hippocampus -> poor learning
Invasive Stimulation Methods
• Placement of electrodes on or into the brain (direct neural stimulation)
• In humans direct stimulation of cerebral cortex primarily used during surgery (to treat
neurological disorders, e.g. intractable epilepsy)
• Deep Brain stimulation: implant electrode in brain to modulate neural activity
• Parkinsons: continuous stimulation of sub thalamic nucleus of the basal ganglia
(progression of disease itself is not halted)
• Optogenetics: attach speci c piece of DNA to virus & injected in speci c regions
—> virus a ects targeted cells (ChR-2 will construct light sensitive ion channels)
• High speci city and temporal resolution
Noninvasive Stimulation Methods
• Transcranial Magnetic Stimulation (TMS): tightly wrapped wire coil sends electrical current
through coil & generates magnetic eld —> altering electrical activity on cortical surface
• For most areas of cortex TMS has no direct observable e ects
• Online: while patient performs a task vs. O ine: consequences
• Inhibits or enhances neural activity
• Use behavioral consequences (using a ‚virtual lesion1’) to shed light on normal functioning
• e.g. stimulation of visual cortex interferes with ability to identify letter (only if stimulation
immediately after presentation of letter)
• Only activates relatively super cial areas
• Repetitive TMS —> Treatment for unipolar depression
1 transient disruption of cortical activity during task performance
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, • Transcranial direct current stimulation (tDCS): constant, low current to brain via electrodes
placed on the scalp (tingling, itching feeling)
• Neurons under cathode hyper polarized (less likely to re/away from threshold)
• Anodal tDCS = improvements in performance vs. Cathodal = may hinder performance
• Repeated stimulation can prolong e ects
• Transcranial Alternating Current Stimulation (tACS): electrical current oscillates (varies) rather
than staying constant
• Di erent frequencies associated with di erent functions
• Simultaneously applying multiple stimulaters -> manipulates degree of synchronization in
activity of two di erent brain regions
• Can boost performant on WM-task
• Transcranial static magnetic stimulation (tSMS):
• Magnetic eld temporarily alters cortisol function, no skilled operator needed
• Transcranial focused ultrasound (tFUS): able to target deeper structure, increases activity in
sodium & calcium channels (triggers action potentials)
Take-home message
• Brain function can be perturbed by drugs, genetic manipulations, and magnetic or electrical
stimulation. In most cases, these methods allow the same participants to be tested in both “on”
and “o ” states, enabling within-participant comparisons of performance
• Genetic manipulations have played a major role in neuroscience studies using animal models.
Knockout technology enables scientists to explore the consequences of the lack of expression
of a speci c gene in order to determine its role in behavior. Optogenetic methods provide the
experimenter with the ability to control neuronal activity in targeted cells
• Noninvasive stimulation methods perturb neural activity in healthy and neurologically impaired
humans. By varying the stimulation protocols, we can enhance or suppress neural activity in
targeted regions
3.4 Structural Analysis of the Brain
• Density of biological material varies, absorption of X-ray
radiation correlates with tissue density
Visualizing the Gross Anatomy of the Brain
• Computerized tomography (CT & CAT): 1st method fro in vivo
looks, 3D perspective form series of thin sliced 2D images
• Magnetic resonance imaging (MRI): uses magnetic properties
of atoms (hydrogen protons become oriented parallel because
of eld - synchronized rebound detected), clear contrast of grey
& white matter, ventricles
Visualizing Structural Connectivity of the Brain
• Di usion tensor imaging: info about connectivity between
regions, performed with MRI scanner
• Free di usion of water is isotropic (equally in all directions) , especially axons are anisotropic
(directionally dependent)
Take-home message
• Computerized tomography (CT or CAT) and magnetic resonance imaging (MRI) provide 3-D
images of the brain
• The spatial resolution of MRI is superior to CT
• Di usion tensor imaging (DTI), performed with an MRI scanner, measures white matter
pathways in the brain and provides information about anatomical connectivity between regions
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