Cognitive Methods & Techniques Flashcards
The 7 Ideal Properties of the Perfect Neuroscience Technique
High spatial resolution, high temporal resolution, large spacial coverage, taps into cognitive processes, is non-invasive, provides information about the brain, and can be used on the healthy human population.
The 3 Cognitive Methods
Eye-tracking, Computer-Modeling, and Behavioral Responses (psychophysics)
The 4 Intervention Methods
Stimulation/feedback, Surgical lesions (only in animals), Genetic Manipulations (only in animals), and Transcranial Magnetic Stimulation (TMS)
•Goal: Establish causal role
–Correlation techniques (e.g. imaging) = “This
region is associated with this task”
–Causation techniques = “If we alter this region,
does that alter performance on the task?”
What 3 things can we measure with Behavioral Techniques?
Reaction Time, Accuracy, Pattern of Errors
How can we use RT to study mental processing?
Mental chronometry is the use of response time in perceptual-motor tasks to infer the content, duration, and temporal sequencing of cognitive operations. Mental chronometry is one of the core paradigms of experimental and cognitive psychology, and has found application in various disciplines including cognitive psychophysiology, cognitive neuroscience, and behavioral neuroscience to elucidate mechanisms underlying cognitive processing.
Mental chronometry is studied using the measurements of reaction time (RT). Reaction time is the elapsed time between the presentation of a sensory stimulus and the subsequent behavioral response.
In psychometric psychology, RT it is considered to be an index of speed of processing. That is, it indicates how fast the thinker can execute the mental operations needed by the task at hand. Speed of processing is considered an index of processing efficiency. The behavioral response is typically a button press but can also be an eye movement, a vocal response, or some other observable behavior.
Behavioral Techniques: Chronometrics
?… The capitalized and lower-case consonants and vowels game. RT & Mental Processing.
Tasks are composed of set of mental operations; each step takes time.
Physical identity~Phonetic identity~Category
Steps: Encode, Compare, Decide, Respond.
Behavioral Techniques: Stroop Task
?…. the words BLUE flashed in green writing causes a delayed response when subjects are told to say the color. This is because seeing the word blue prompts us to say blue, not green.
Stimuli activate 2 representations:
–Physical color of text (task relevant)
–Color concept / meaning (irrelevant to task)
We are worse at task when word and color are mismatched= Interference
Conceptual representation is automatically activated.
Behavioral Techniques: Uses of Eye-Tracking
Where are they looking?
–How frequently do they make saccades?
–Do they return to previously fixated locations?
–Fixation monitoring (if you don’t want them to
wander)
–Gaze-dependent stimulus presentation
What 4 things can Behavioral Techniques tell us?
~How much Time does it take to perform different
tasks?
~Is there Interference?
~What is Memory Capacity under different Conditions?
~How Many different things can people pay Attention to?
Saccade
A saccade is a fast movement of an eye, head or other part of the body or of a device. A rapid movement of the eye between fixation points.
Goals of Computer Modeling
- Can we program a computer to do this cognitive task?
- Can we program it to do it in a biologically plausible way?
- Can we get it to mimic how the brain actually does it?
- Can we use it to make testable prediction?
Simulation of Computer Modeling
Idea: Computer as metaphor for brain (or mind)
–Computers represent and transform info
–Good model for studying human cognition
Simulation (imitation of behavior):
– Artificial intelligence: mimic behavior & cognitive processes supporting behavior
– Give computer input; must perform internal operations to create a behavior. How well does behavior of model match real behavior?
–Create different models for different theories of cognition. Which perform best?
Pros/Cons of Computer Modeling
• Pros:
– Can simulate complex behaviors
(using neuronlike units too).
–Can vary in level of explanation (Systems level, Molecular level, etc.)
–Can ‘lesion’ network and even retrain it! (testable predictions).
•Cons:
–Oversimplification of nervous system
–Not really biological
–Small in scale, narrow
Neuropsychology
Think Brain-damage Patients, Neurological damage, Cognitive deficits, Broca and Wernicke, “Nature’s experiments,” etc.
•Link cognitive processes to neural structures.
•Logic: “If a behavior depends on processing
within a certain brain structure, then damage
to this structure should disrupt the behavior.”
Neuropsychology: 5 Types of Acquired Brain
•Vascular disorder strokes (or
cerebro-vascular accident; CVA), aneurysm.
–Blood flow disrupted, brain cells die
•Tumors
– Abnormal cells destroy or displace healthy cells.
•Degenerative & Infectious disorders – Alzheimer’s,
Parkinson’s, Huntington’s, MS, AIDS dementia,
Korsakoff’s
- Traumatic head injuries – most common in under 40 year-old males
- Neurosurgery – severe epilepsy (HM, split-brain)
Caveat
a warning or proviso of specific stipulations, conditions, or limitations.
synonyms: warning, caution, admonition.
Caveats & Considerations, Pros & Cons of Neuropsychology:
–Necessary vs Sufficient
–Plasticity / Reorganization
–Diffuse vs Focal Lesions
–Need proper controls (Control tasks, Control populations, etc.)
–Pro: Powerful test of whether a brain region is
critically involved and necessary for behavior
–Pro: Testable predictions for other techniques
–Con: No control over location, size, extent
–Con: Small sample sizes
–Con: Individual differences (pre-existing conditions and the nature of brain damage)
Control Tasks & Populations:
Single vs. Double Dissociations
?….. double is better, tripole dissociation is best
refers to a logical progression of scientific assumptions in localizing functional areas in the brain. For example, if symptom A appears with lesions in brain str ucture X, but not with those in Y, and symptom B appears with lesions of Y, but not of X, then those specific areas of the brain each have a specific function.
In brain damage, when function A is present and function B is absent in one person, and function A is absent and function B is present in another. Presence of a double dissociation means that the two functions involve different mechanisms and operate independently of one another.
Moreover, Double dissociation is the finding that some individuals usually brain damaged perform normally on task A and poorly on task B, whereas others show the opposite pattern.
Neurophysiology
Think Animal Research.
Research with animals: –Why? More invasive, more control = be_er experiments –Considerations: •Good model for humans? •Ethical concerns –Recording vs Lesioning
Neurophysiology: Single-cell Recording
Singlecell recording:
•Invasive (direct recording from brain)
•Thin electrode inserted into cortex
•Measure electrical activity from nearby neurons
–Extracellular (more common): action potentials (“spikes”)
–Intracellular (very difficult): graded membrane potentials
•Single-cell recording: “firing rate”
•Baseline activity: Neurons are constantly active
–Measure changes to experimental manipulation
–What increases or decreases firing rate?
•Awake behavior vs anesthetized
•Find a neuron: Does it respond to
visual stimuli?
•Characterize its response properties
–Neurons have preferences and receptive fields.
What’s involved in Single-cell recording?
–Train monkey to do task (can’t just give instructions) –MRI scan to localize recording site –Surgery –Recording sessions –Train on new task –Recording sessions –Etc
Baseline Activity of Neurons
The baseline activity of neurons in the cerebellar nuclei, studied during exposure to external factors, can be used as a measure of changes in cell activity.
Receptive Field
Location in space for which neuron is responsive.
Pros & Cons of Single-cell Recording
•Pros:
–Excellent spatial AND temporal resolution (“gold
standard”)
•Cons: –Poor spatial coverage –Is single neuron(s) representative of whole region? –Not humans –Not causal
Types of Functional Neuroimaging
–Scalp EEG / ERPs
–Intracranial electrodes (ECoG)
–FMRI
–MEG, PET, DTI, NIRS
Electrical & Magnetic Types of Functional Neuroimaging
- EEG = Electroencephalography = electrodes on scalp
- ERP = event-related potential = a type of EEG analysis
- ECoG=ElectrocorEcography= intracranial electrodes (invasive)
- MEG =magnetoencephalography= magnetic detectors on scalp
Metabolic Types of Functional Neuroimaging
- fMRI = functional magnetic resonance imaging = blood flow changes (type of MRI)
- DTI = diffusion tensor imaging = white matter pathways (type of MRI)
- NIRS = nearinfrared spectroscopy = optical imaging of blood flow changes through scalp (typically infants)
- PET = positron emission tomography = distribution of radioactive tracer
Functional Imaging:
Electrical & Magnetic Signals
•Neural activity = electrical changes
–An electrode inside brain can record action
potentials (single-cell recording)
–But that’s really invasive…
–Solution 1: If large populations of neurons are
active together, electrical (or magnetic) changes
large enough to be measured on the scalp!
–Solution 2: If someone is already having brain
surgery, electrodes placed for medical purposes
can be shared for research (ECoG).
Electroencephalography (EEG)
Electrodes on scalp record electrical signals
Ways to analyze Electroencephalography (EEG)
–Look at different patterns / brain states –Look at frequency of oscillations –Timelock data to event and look at magnitude/latency of response (ERP)
Event-Related Potentials (ERP)
ERP’s are EEG’s aligned to stimulus onset & average
- ERP is a type of EEG analysis
- Activity related to sensory, motor, cognitive events
- Superb temporal resolution
Pros & Cons of ERP’s & EEG’s
•Important strength: temporal resolution
•Important weakness: spatial localization
•Electrical current conducted through brain, skull, scalp
–Poor spatial resolution (32128 electrodes)
–Challenges in localizing source
ERP’s & EEG’s: The Inverse Problem
The objective of an inverse problem is to find the best model describing the explicit relationship between the observed data, and the model parameters. It is mathematically impossible to reconstruct a unique intracranial current source for a given EEG signal, as some currents produce potentials that cancel each other out. This is referred to as the inverse problem.
The “inverse problem” is comparable to reconstructing an object from its shadow: only some features (the shape) are uniquely determined, others have to be deduced on the ground of additional information. However, by imposing reasonable modelling constraints or by focussing on rough features of the activity distribution, useful inferences about the activity of interest can be made.
Magnetoencephalography (MEG)
•Neural activity produces magnetic field changes that can be measured as well
–Same great temporal resolution as EEG/ERP
–More accurate spatial localization
•Magnetic fields not distorted by brain/skull/scalp
•Better solution to inverse problem
•Still not ideal
Electrocorticography (ECoG)
Intracranial EEG (electrodes placed directly in/on
brain)
–Patients with severe epilepsy: if drugs don’t work,
may try to surgically remove epileptic focus
•Brain surgery is a big deal (think H.M.)
•Need to precisely localize epileptic focus before surgery to minimize extent
•Surgeons will place electrodes directly on brain (surface & depth) to localize seizure activity
•Patients in hospital for days/weeks waiting for seizures to occur
• Can invite them to participate in cognitive experiments while electrodes are implanted
Most famous ECoG finding
the “Jennifer Aniston” cell
Pros & Cons of Electrocorticography (ECoG)
•Advantages:
–Excellent temporal AND spatial resolution
–Recording directly from brain
•Disadvantages: –Extremely invasive –No experimental control over where electrodes are placed (up to surgeons) –Recording from damaged tissue?
Functional Imaging: Metabolic Signals
•Detect changes in blood flow in brain while subjects perform cognitive tasks •Indirect neural measure •Brain area active ~increased blood flow ~more oxygen/glucose
–Can measure changes in blood flow (PET)
–Or changes in oxygenated blood concentration
(fMRI,NIRS)
Positron Emission Tomography (PET)
•Measures local variation in cerebral blood flow (CBF)
•Need to inject radioactive tracer (typically 15O)
–Inject while subject performs task
–PET scanner detects radiation
–More blood flow = more radiation
•Mostly replaced by fMRI
Functional Magnetic Resonance Imaging (fMRI)
MRI studies brain anatomy. Functional MRI (fMRI) studies brain function.
How does MRI work?
MRI machine applies powerful magnetic field
–How powerful? 60,000 times stronger than Earth’s magnetic field.
•Protons become oriented parallel to field
•Radio frequency (RF) pulse perturbs them
•MRI measures how long it takes protons to return
(by detecting energy released)
–Different types of tissue have different properties
How does fMRI work?
2 key differences for functional imaging:
•Focus on oxygenated vs deoxygenated blood
– More active brain area = more oxygen flowing through blood
–Oxygenated blood less magnetic = bigger MR signal
–“Blood oxygen level dependent (BOLD)” response
•Measure timecourse
–Take image of brain every 2 sec
–Look at changes in BOLD over time while subjects do cognitive task
BOLD
Blood Oxygen Level Dependent
The 5 fMRI Experiment Stages
- Design
- Preparation
- Data Collection
- Pre-processing
- Analysis
fMRI: Block Design
Run a continuous block of the same condition
same cognitive state for appro. 16-40sec, then find the average across that interval
Event-Related Design
Single trials, MANY repetitions, then average all trials from same condition
•Similar idea as ERP: single events, average
across repetitions
•Can choose “conditions” in advance (e.g., verb vs noun) or after experiment (e.g., remembered vs forgotten)
Example: ball chair desk mug buckeye buckeye ball chair desk mug
VOXEL
Volumetric Pixel
fMRI Pre-processing
–What: series of steps to “clean” data
–Why: data are noisy, subjects move, things
change over time (scanner signal, subject alertness, etc)
–How: motion correction, alignment to common
space, smoothing,
Subtraction Logic
•Brain activation levels must always be considered
relative to another condition
– The absolute level of signal is relatively meaningless on its own
Need at least 2 conditions so can subtract
the difference!
E.g.: What part of the brain processes motion? Compare activity to moving dots > stationary dots
fMRI Analysis: Region of Interest (ROI)
“Is there a significant difference in this region?”
as oppose to the Whole-brain approach.
Pros & Cons of fMRI
•Pros:
–High spatial resolution (better than EEG, worse
than single-neuron recording)
–Simultaneous coverage of whole brain, able to look at multiple regions at once
–Non-invasive
•Cons:
–Poor temporal resolution
–Need lots of data
–Purely correlation
Near Infrared Spectroscopy (NIRS)
•Optical imaging (new technique)
–IR light projected at head, scatters back; detected by sensors
–Active brain areas scatter light more
–High temporal, good spatial, but only “surface” areas
Diffusion Tensor Imaging (DTI)
- Uses MRI to measure diffusion of water through axons
* White matter pathways; connectivity between regions
Transcranial Magnetic Stimulation (TMS)
•“Virtual lesions” •Same logic as neuropsychology / lesion patient studies (“Nature’s experiments”), but: –Noninvasive –Temporary –Focal / precise –Experimental control
Explain TMS
•Magnetic coil placed on skull
–Sends electrical current which induces a magnetic field that passes through skull, altering neural activity.
•How does it work?
–Figure out which brain areas you want to target.
Can pick multiple areas to try for double dissociations. Also want control areas (Vertex=top of head), and/or no TMS control condition.
–Localize areas with MRI / fMRI
–Find corresponding locations on subject’s head
(register head to MRI image)
–Place coil over simulation location
–Apply TMS while subject performs task
–See if behavioral performance is impaired
Uses of Transcranial Magnetic Stimulation (TMS)
•Functional localization/specialization:
–Which brain areas are necessary for this cognitive
task?
–If we interfere with this brain region, what changes in behavior do we see?
•Timing:
–What is the timecourse of processing for this task?
–When does information pass through this region?
•Combination w/ neuroimaging
–E.g., Does repetitive offline TMS lead to changes in fMRI activation/connectivity?
Pros & Cons of TMS
•Pros –Great temporal, good spatial –Causal –Temporary (few seconds for online TMS, 30min1hr for offline TMS)
•Cons
–Can only target superficial areas
–Mechanisms not entirely known
–(temporarily) altering brain activity
Which techniques are causal?
TMS, Neuropsychology brain damage
Which techniques have high temporal resolution?
EEG,ERP, MEG, NIRS, Single-cell Recording, ECoG
Which techniques have high spatial resolution?
fMRI, MRI, Single-cell Recording, ECoG
Which techniques require control tasks?
TMS
Which techniques can be combined (in a single study)?
Single-cell and fMRI
fMRI and TMS
Which techniques tell us whether a brain region is necessary for a cognitive process?
TMS
fMRI Analysis: The Whole-brain Approach
“Where in the brain do I see a significant difference?”
