Lecture 3: Methods in cognitive neuroscience Flashcards
Key idea in cognitive psychology
we use mental representations that undergo internal transformations
independent variable
the different conditions
dependent variable
relevant measurement that is used
The word superiority effect
shows that we do not need to identify all the letters of a word before we recognize the word.
we activate both the representation of the individual letters and the word in parallel
The stroop test
the simultaneous activation of multiple representations is not always beneficial.
Damaged brain is caused by? (5)
vasular disorders: disruptions in blood-flow
tumors
degenerative and infectious disorders (parkinson, alzheimers)
traumatic brain injury: damage to cell bodies, white matter, vascular systems.
epilepsy
Main idea of studying the damaged brain?
brain injury disrupts/eliminates the processing ability of the affected brain structure
Patient A: damage to the left inferior frontal cortex (Broca’s area)
can understand language but cannot produce fluent language (non-fluent aphasia)
understanding and production of language seem to be a separate processes and production is related to Broca’s area.
Single dissociation
Single dissociation
when an impairment affects one cognitive function but leaves the other intact, indicating some level of functional independence
Patient B: Damage to the left superior temporal gyrus (Wernicke’s area)
can produce fluent (but nonsensical) language but cannot understand language.
understanding and producing language are separate processes and take place in different brain areas.
double dissociation
double dissociation
involves two different functions that are each impaired in one individual while remaining intact in another
Diaschisis
a decline of cognitive function because of a brain leasion could also indicate that other brain areas dont receive input anymore and might not function properly anymore. Diaschisis is decreased activity in surviving neurons after damage to other neurons.
Corpus callosotomy
split brain patient
Methods to perturb neural function
1. pharmacological interventions
interfering with neurotransmitters changes signalling.
Agonists/antagonists
Disadvantage: very unspecific. administering a drug affects the whole brain.
Agonists
Drugs that work like the real neurotransmitter
example: bromocriptine, a drug that binds to dopamine receptors and activates them as dopamine does.
Antagonists
A drug that blocks neurotransmitters
example: haloperidol, binds to dopamine receptors and blocks them. prevents real dopamine to bind with receptors.
Methods to perturb neural function
2. Genetic manipulations
used in animal research
knock-out animal: animal with specific genes manipulated vs. wild type: normal animal.
Methods to perturb neural function
3. invasive stimulation methods
mostly animal research, but also in patients undergoing neurosurgery (epilepsy)
Deep brain stimulation: parkinsons disease.
Methods to perturb neural function
3. invasive stimulation methods
Optogenetics
a biological technique that allows the control of neurons using light
light gated ion channels: channels that open or close in response to light.
Methods to perturb neural function
4. non-invasive stimulation methods
Tanscranial magnetic stimulation (TMS)
Tanscranial magnetic stimulation (TMS): strong current is sent through coil and produces a strong magnetic field. this field induces a changing electrical field in the underlying brain area and causes neural activity (motor activity)
Single pulse TMS: during the experiment a TMS pulse is delivered on each trial (when a stimilus is presented)
Repetitive TMS: before the start of the experiment, a train of pulses is delivered that changes the underlying brain area for longer duration
Effect of TMS
Effect of TMS depends on the strenght of the pulse. a strong pulse causes temporary lesions, weaker pulses can sometimes facilitate activation
disadvantage of TMS
Spatial resolution is small: a pulse affects a relatively large brain area.
only target superficial brain regions, not possible to target structures deeper in the brain
a pulse contracts scalp and head muscles and could be annoying to the patient.
stimulation might trigger epileptic seizure.
Methods to perturb neural function
4. non-invasive stimulation methods
Transcranial direct current stimulation (tDCS) & Transcranial alternating current stimulation (tACS)
in tDCS and tACS a small electical current is applied directly to the scalp. effects last for an extended period and is used in research and to treat clinical problems (depression)
could not be strong enough to have any effect on the brain at all
Structural analysis of the brain:
Computerized Tomography CT or CAT scan
first method. based on Xray. currently only used in medical imaging
Structural analysis of the brain:
Magnetic Resonance imaging (MRI)
uses magnetic properties of atoms. most pervasive atom in the brain is hydrogen.
structural image of the brain at high spatial resolution.
image of the structural connectivity of the brain (diffusion tentsor imaging DTI) measuring the density and flow of water molecules in axons.
Methods to measure neural activity:
Single cell neurphysiology in animals
A visual stimulus is presented in the receptive field of the neuron that we are recording.
Invasive neurophysiology in humans
Electrocorticography (EGoG)
a grid of electrodes is placed directly on the cortex. neural activity often shows oscillatory activity: these oscillations can have different frequencies and amplitudes (power)
Non-invasive electrical recordings
Electroencephalography EEG
electrical recordings outside the skull
cap with electrodes is placed on the subjects head.
electrodes register changes in electrical potentials.
Non-invasive electrical recordings
Electroencephalography EEG
oscillations
power of different frequency bands. EEG data can be decomposed in sum of weighted sine waves.
example: during stage 1 of sleep, the power of the theta band is high (oscillations between 4 and 7 Hz). during slow-wave sleep (stage 3), the delta band (between 1 and 4 Hz) is very high
Non-invasive electrical recordings
Electroencephalography EEG
Event related potentials (ERP)
small voltage differences in an ongoing EEG triggered by sensory and cognitive events
Disadvantages of EEG
EEG tells you something about the electrical potential at the level of the electrodes but not about the electrical potentials at the brain level.
inverse problem: the pattern observed at the sensors can be caused by an infinite number of different brain regions
low spatial resolution: low conductance of CSF, meninges, skull and scalp blurs the electrical signal before it reaches the electrodes
for similar reasons EEG cannot detect any activity from deep brain structures. electrical signal decayed before it reaches the electrodes.
Non-invasive electrical recordings
Magnetoencephalography (MEG)
an electrical current produces a magnetic field orthogonal to the electical field
in contrast to EEG, MEG is sensitive to neurons that are parallel to the skull (Sulci neurons)
MEG advantage over EEG
a magnetic field is not obstructed by the skull. more possible to obtain signals from deep brain structures
better spatial resolution compared to EEG
MEG disadvantage
much more expensive and patients are restricted.
Hemodynamic response
when a brain area is active, the blood flow to that region, increases to supply that area with more energy (oxygen, glucose)
Non-invasive electrical recordings
Positron emission tomography (PET)
a radioactive substance (tracer) is injected into the bloodstream of subjects.
The tracer becomes distributed in the brain
an active brain area consumes more oxygen, so the tracer will be more present in active brain areas.
because the tracer is radioactive, a series of events will cause it to emit radioactive beams that can be detected by specialized detectors.
Disadvantage PET
scary to subjects: radioactivity & needles.
Very expensive
slow procress: uptake in blood, transport to brain
Blocked design
many trials from one condition are presented in block
brain activity in one block is compared to another block, with trials from another condition
PET trace had to decay between blocks, this takes long
Non-invasive electrical recordings
Functional magnetic resonance imaging (fMRI)
blood with oxygen (oxyheamoglobin) has different magnetic properties than blood without oxygen (deoxyhaemoglobin)
active brain areas use more oxygen. this results in a local increase in oxyheamoglobin. these small changes in the magnetic properties of the bloof (BOLD signals) are detected by the FMRI Scanner
Event related designs
change conditions on a trial by trial level. this makes experimental designs possible. many more research questions can be investigated
example: how does the previous trial affects the cognitive processing of the current trial
Magnetic resonance spectroscopy
information about the chemical composition of tissue.
example: measure the concentration of neurotransmittors in different brain areas.
disadvantage FMRI
relatively low temporal resolution compaired to EEG
brains of different participants need to be normalized to a common space (standardized template of the brain). analyses of this type of data requires a lot of preprocessingm meaning that the raw data you acuire from scanning a participants need to go through several steps before you can use them
Connectivity maps
evidence for correlations between brain areas and cognitive functions. how the brain is connected
feels like modern day phrenology
brain regions do not work in isolation but as a complex interconnected network
computational neuroscience
simulate cognitive processes in a computer model
neural networks: makes predictions, what if we lesion a specific part of the model?
converging methods
convergence vs. complementary
integrating different methods
use a method to generate hypotheses to test with different methods
convergence: study a theoretical concept with different paradigms. a hypothesis is tested with different experimental designs that all give the same results, provides a very strong empirical evidence.
complementarity: different methods provide different sorts of information. some have high temporal resolution some have high spatial resolution.
