Ch 2 Flashcards
research methods in cognitive neuroscience can be divided into 2 methods
a. Perturbational methods
b. Monitoring methods
Perturbational methods
change the workings in the brain, then measures cognition = shows causal relationship
monitoring methods
measures brain activity = showing correlational relationship between behaviour and brain activity
manipulates cognitive process, then measures the brain
Perturbational methods
a. brain lesions
b. pharmacological perturbations
c. intracranial brain stimulation
d. extracranial brain stimulation
PM: brain lesions
observing the effect of damage to the brain resulting from stroke, tumor, trauma
Can be natural or directed (in animals)
Major limitation for natural
- not under control
- lesion isn’t focal
- no 2 patients are the same, therefore can’t generalise
solution is to group patients together and look at the overlap
Disadvantages for directed
- ethical issues
- diaschisis
Natural brain lesions: advantages/ disadvantages
Advantages: naturally occurring,
Disadvantages:
- no control
- no temporal resolution
- damage is not focal (it impacts many areas of the brain)
- complex effects of recovery
- difficult to generalise as no 2 patients are the same
solution: use fMRI to look at the overlap of multiple patients with similar lesions
Directed brain lesions in animals
Advantages:
- control
- temporal resolution
Disadvantages
- difficulty in training animals to perform a particular task
- ethical reasons
- animals are different from humans
- Diaschisis: the brain is very interconnected, therefore damage to one area may affect another due to the lack of input for example
Diaschisis
damage to one area may cause damage to another due the brain’s interconnectedness
= decrease activity in surviving neurons after damage to other neurons
PM: pharmacological perturbations
involves interfering with neurotransmitters and their signalling
2 methods:
Method I: measuring the effects of chronic drug on cognition
Method II: controlled pharmacological experimentation
Disadvantages:
- very unspecific (drugs affect the whole brain)
solution: drugs can be injected directly to an area of an animal’s brain
Agonist drugs
drugs that activate receptors, identical to neurotransmitters (such as nicotine for acéthylcoline)
Antagonist drugs
drugs that bind and block receptors ex: antipsychotic drugs
PM: Intracranial Brain Stimulation
electrical stimulation works to perturb the brain with chronically implanted electrodes
— > mostly done in animals but also in patients with severe Parkinson’s disease
Wilder Penfield mapped the somatosensory and motor cortex with this method
Advantages: we can map brain regions, it is very specific
Disadvantages: invasive method, limited to animals
recently developed technique: optogenetics
Somatotropic organisation
adjacent body parts have adjacent cortical representations proportional to sensitivity of the body part
Optogenetics
only in animals, a virus with genetic material to make light-gated ion channels is injected into a targeted brain area
light-gated ion channels: channels that open or close in response to light. when a laser is targeted at the ‘infected’ area, this causes an influx of ions, which can inhibit or excite neurons
advantages: very specific, high temporal resolution
disadvantage: expensive, can only be done with animals
Extracranial brain stimulation
2 methods:
a. TMS: Transcranial Magnetic Stimulation
b. TES: Transcranial Electrical Stimulation or tDCS
TMS
a strong magnetic field creates a changing electric field in the underlying brain areas, which can activate neurons
2 types:
a. single pulse TMS: pulse is delivered at each trial, when a stimulus is presented
b. repetitive TMS: series of pulses that change underlying brain areas for a longer period of time
Advantages: non-invade, high temporal resolution
Disadvantages: limited to outer cortex, non-specific areas of the brain are affect: LOW SPATIAL RESOLUTION, can cause seizures
TES (or tDCS)
A constant but weak electrical current directly on the scalp to either increase or decrease excitability
used to treat depression
Anodal (positive) stimulation: increases excitability of the stimulated area
Cathodal stimulation: decreases excitability of the stimulated area
Advantages; higher temporal resolution
Disadvantages: low spatial resolution, can’t target deep areas, pulses cause unpleasant scalp and head muscle contractions, can cause seizures
Monitoring methods
a. Direct electrophysiological recordings
b. EEG
c. MEG
d. PET
e. fMRI
Direct Electrophysiological Recordings (Single Cell Recordings)
electrical recordings directly in the brain
a. intracellular: recordings in the cells, single neurons are penetrated with an electrode tip, provides insights on how neurons behave while the brain carries out a function
b. extracellular: monitoring electrical activity of neurons near the tip of the electrode, provides info on how groups of neurons behave
Peristimulus time histogram
Tuning curves
Advantages: HIGH TEMPORAL AND HIGH SPATIAL RESOLUTION, control, specific
Disadvantages: very invasive, cannot identify networks
Peristimulus time histogram
compilation of spikes = when a neuron has an action potential from all trials when a stimulus is presented. This illustrates how responsive a neuron is to the stimulus
Tuning curve
measuring the response time of a neuron when a stimulus is varied, for example orientation
If a neuron is tunes to a specific orientation, it will fire the most for that type of stimulus
EEG
measures electrical recordings outside the skull
a cap with 28-128 electrodes is placed on a participant’s scalp and can measure changes in electrical potential
Advantages: temporal resolution, non-invasive, rapid
Disadvantages:
- inverse problem: patterns observed could have been cause by something else
- low spatial resolution
- not sensitive to deep brain structure or sulci
How and what do we measure with EEG
HOW: LFP: local field potential is produced when many neurons at the same location have similar changes in potential
If LFP strong enough, EEG will pick it up
WHAT:
- summed dendritic field potentials
- extracellular return current
- electrical fields in gyri
= electrical potential at the level of electrodes, not the brain
IT DOES NOT MEASURE:
- individual action potentials
- intracellular current
- electrical fields in sulci (cause must be perpendicular to the electrodes
- activity in deep bain structures
How is the information extracted with EEG
a. Oscilllations
h. ERPs : even related potentials: voltage differences that are triggered by something
—> epoch: EEG data is ‘cut’ in portions, then averaged so the most frequent signal of a certain time remains
- topographic maps show the spatial-temporal patterns of ERPs, we can observe how activity at the electrodes dynamically change over time and space
MEG: magnetoencephalography
an electrical current produces a circular magnetic field
it detects ERFs : event-related magnetic-field responses over space and time
Advantages:
- no obstruction from skull, non-invasive, can reach deep brain structure, sensitive to sulci, HIGHER SPATIAL RESOLUTION than EEG
Disadvantages: more expensive than EEG, restricts movement, inverse problem
PET: positron Emission Tomography
a tracer = radioactive substance, is injected into the blood
since active brain areas require more oxygen and therefore more blood = detection of active brain areas
related to metabolic activity: activity related to the supply of energy
Disadvantages:
- scary; very expensive, slow process: uptake in blood, transport to brain, time required to get a clear signal, blocked design only
fMRI: functional magnetic Resonance Imaging
Oxyhemoglobin vs deoxyhemoglobine
active brain areas require more oxygen, resulting in a local increase of oxyhémoglobine
an fMRI scanner can detect active brain areas by picking up BOLD signals (Blood Oxygenation Level Dependant signals)
uses event-related design : switching between 2 conditions can be done without the need to wait 10 minutes as in PET
fmri adaptation: helps the understanding of brain areas by making use of repetitive suppression
advantages: HIGH SPATIAL RESOLUTION
- better temporal resolution than PET
- even-related design, non invasive
Disadvantages
- expensive
MR scanner
used for DTI: diffusion tensor imaging -, which reveals white matter tracts of the brain (such as axons)
Analysing activation patterns in a brain area in fMRI
most fMRI research is concerned with the activation of different bran areas in response to a manipulated variable
researchers use multivoxel pattern analysis for this: machine learning techniques are used to make sense of activation patterns in brain areas
or principal and independent component analysis: where data is being decomposed to find brain areas that behave similarity
- structural equation modelling: incorporates anatomical connections
- dynamic causal modelling: incorporates functional connections
