Methods Flashcards
perturbation methods
change the brain -> causal relation
monitoring methods
measure the brain -> correlation
limitation van damage to the brain als info over cognition
experimenter heeft geen control:
- damage not focal (single lesion can have a diverse effect)
- not generalizable (not every patient is the same)
wat moet je doen om damage als exp. hogere validiteit te geven
groups of patients en dan kijken naar wat ze allemaal in gemeen hebben qua loss of function
lesions maken in animals als researcher limitations
- animals need time to learn
- animals not as complex behaviour
- ethical
- interpretation problems: diachisis (damage to one neuron leads to decreased activitiy in another neuron); damage to fiber tracts bv heeft een hoop andere gevolgen
wat zijn de 3 perpetuating methods
- lesions
- pharmacological
- brain stimulation
pharmacological perpetuations
interfere with neurotransmitters that influence a certain cogntion.
- chronic drug abusers
- trials met drugs
agonist
activates the same receptors
antagonist
deactivates the receptors
limitation of pharmacological
unspecific
Penfield wat deed hij
intracranial brain stimulation -> somatotopic organization
optogenetics
Genetic material responsible for making ligand-gated ion channels is extracted and inserted in a virus. This virus is injected in a brain area and will infect the targeted neurons. The inserted genetic material will lead to the production of channelrhodopsins in the membranes of the infected neurons. Dit is intracranial brain stimulation
voorbeeld extracranial brain stimulation
TMS
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 neuronal activity ( e.g. motor
activity).
-
Single pulse TMS : during the experiment, a TMS pulse is
delivered on each trial (e.g., when a stimulus 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.
The effect of TMS depends on the strength of the pulse. A strong
pulse causes temporary ‘lesions’; weaker pulses can sometimes
facilitate activation.
TMS + en -
+ great temporal resolution
- bad spatial resolution
- only superficial structures
- contractions in head and neck: hard to mimic for control condition and annoying
- heeeel soms epileptic seizure
Transcranial Electrical Stimulation (TES)
ook wel tDCS (transcranial Direct Current Stimulation).
small electrical current is applied directly
to the scalp. Effects can last for an extended period
and is used in research and to treat clinical
problems (e.g., depression).
maar niet duidelijk of dit ook echt sterk genoeg is.
monitoring methods
direct recordings
EEG
MEG
PET
fMRI
optical brain imaging
single cell recordings
electrical recordings directly in the brain (vooral animal research). laten zien met peristimulus histogram
tuning curves
a neuron is stimulated in different dimensions (bv orientation) en dan kijken hoe hij op verschillende versies reageert.
electroencephalography:
cap, electrical potential recordings outside of the skull
what do we measure with eeg
membrane potentials –> als veel neuronen op hetzelfde moment signalen krijgen (EPSP en IPSP) –> local field potential LFP -> sterke LFPs kunnen gemeten worden.
dus wat meet eeg wel en wat niet (2 dingen)?
niet: actiepotentialen en intracellular, maar wel: combined input to dendrites of neurons, dus extracellular
In welke orientation meet je EEG?
alleen als de electrode perpendicular is to the signal -> dus alleen in gyri.
wat voor 2 dingen kun je uit een EEG signaal halen
- oscillations: different waves with different frequencies (dus de verschillende waves uit de som halen)
- ERPs: event related potentials -> small voltage differences in an ongoing EEG wave, triggered by sensory and cognitive events (dus de verschillen tussen ‘standaard’ gaande wave, wanneer er iets gebeurd)
–> The EEG data is ‘cut’ in portions (called epochs ) and aligned to the onset of the
stimulus presentation. The epochs are averaged and the signal that is most common in all epochs remains.
topographic map
laat zien hoe de activiteit bij de electroden verandert over tijd en space -> per brain region (spatial and temporal patterns of ERPs
3 electrical methods for monitoring
direct recordings, EEG, MEG
limitations EEG
- gaat op level van electrodes, niet op level van brein
- inverse problem: het signaal kan van veel verschillende brain activation combinations komen
- low spatial resolution: door hindernis CSF, skull, hair etc.
- only superficial brain structures
MEG
magnetoencephalography.
- neurons parallel to the skull (EEG = perpendicular)
- electrical current produces magnetic field
- magnetic field geen last van hindernissen zoals skull, dus:
also deeper structures
better spatial resolution than eeg
dus MEG vs EEG
- EEG measures electrical potentials/activity, MEG measures the magnetic field outside of the head
- EEG bad spatial resolution, MEG good
- EEG only superficial, MEG deeper structures
- EEG cheap, MEG expensive
- both EEG and MEG have the inverse problem
limitations MEG
expensive
subjects movements are restricted by the machine
3 methods for monitoring that have to do with metabolism of the brain: energy
PET, fMRI, optical brain imaging
PET
radioactive tracer injected in bloodstream, zo kun je zien waar meer bloed heen gaat. tracer is more present in active brain regions. detectors measure the gamma rays that are created.
limitations PET
scary for participants (needles, radioactive), expensive!, slow process (in bloed opnemen etc)
wat is het enige design dat kan bij PET
blocked design (door langzaam) -> In a blocked design, many trials from one condition
are presented in a block. This allows the integration of activity across time. The brain activity in one block is compared to the activity of another block that has trials
from another condition. In PET, the tracer needs to decay between different
blocks. This takes a long time (about 10 minutes).
fMRI werking
bloed met oxygen has different magnetic properties than blood without oxygen. active brain area -> more oxyhemoglobin -> fMRI meet dit.
verschil PET en fMRI
PET zie je het hele brein areas, bij fMRI zie je een klein gebiedje gekleurd.
fMRI kan je vaker doen omdat het niet radioactieve tracers zijn etc.
fMRI kan je veel sneller switchen tussen condities, hoeft geen blocked design zoals bij PET
event-related designs
change conditions on a trial by trial level.
fMRI is heel duur, maar samen met EEG de meest gebruikte techniek.
oke
2 fMRI methods
- Multivoxel Pattern Analysis : application of machine learning techniques to disentangle
activation patterns. - Principal and Independent Component Analysis : Decompose data to find brain areas that behave similarly.
Structural equation modeling
causality based on anatomical connections
Dynamic causal modeling
causality based on functional connections
structural images of the brain (twee dingen)
- PET laat zien hoeveel receptors er zijn
- diffusion tensor imaging DTI: reveals the white matter tracts
