Methods in Cognitive Neuroscience Flashcards
Lecture 1
Cognitive Neuroscience
provides a brain based account of cognitive processes e.g. thinking, perceiving, remembering etc.
how was cognitive neuroscience made possible
by technological advances in studying the brain that are safer than Penfield’s method
what did cognitive psychology provide
experimental paradigms and theoretical framework
Dehaene et al. 2001
compared reaction times with fMRIs
- reaction time faster to second word when it follows the same word (that is previously shown so quick it is not consciously perceived)
- left fusiform cortex has less activation if same word
- processing for word has already happened earlier hence faster and less activation
Methods of Behavioral Neuroscience
advantages and disadvantages of methods in Cognitive Neuroscience - Spatial and Temporal resolution
temporal - the accuracy of measuring when an event is occurring
spatial - the accuracy of measuring where an event is occurring
Single-cell recording
- electrophysiological technique
- spatial resolution at neuron level as measuring directly from neuron
- records electrical activity
how are single cell recordings done
- electrode implanted into axon: intracellular
AND/OR - electrode implanted outside axon membrane: extracellular
- records neural activity from a population of neurons
- normally in animals e.g. monkey
EEG
- measures electrical activity of brain through recording electrodes attached to the scalp
- electrical signal from large number of neurons
- often in humans
what do EEG signals represent
the change in the potential difference between two electrodes placed on the scalp in time
what are ERPs
- event related potentials
- average of EEGs over trials
- voltage fluctuations that are associated in time with particular event e.g. visual stimuli
- tell us about timing
using ERP to study face recognition
- different ERP peaks associated with different aspects of face processing
- N170
- N250
- P400-600
N170
perceptual encoding of the face / recognizing it is a face
- recording from right posterior superior temporal sulcus
P300
famous and familiar faces
N250
identity processing
- affected by familiarity
P400-600
person recognition (faces and names)
- affected by faces and names
ERPs in Alzheimer’s disease
- reduced P300 for dementia patients
- shows how ERPs can be used as biomarkers for diseases
MEG
- magnetoencephalography
- measures magnetic fields produced by electrical activity in the brain via extremely sensitive devices know as SQUIDs
- high temporal and spatial resolution
what does neuronal activity generate
electrical and magnetic field that can be measured invasively (single cell) and non-noninvasively (EEG, MEG)
what do single cell studies tell us
how neurons code information by measuring their response to external stimuli
what can electric field produced by neurons be measured by
EEG
MRI
- magnetic resonance imaging
- uses magnetic properties of tissue and blood to produce images of the brain
Structural imaging
different tissues have different physical properties so can be used to create STATIC maps
- CT and MRI
functional imaging
temporary changes in brain physiology associated with cognitive processing
- PET and fMRI
PET
positron emission tomography
- measures local blood flow (rCBF)
- radioactive tracer injected into blood stream
- tracer peaks after 30s
- when material undergoes radioactive decay, positron emitted is picked up by detector
- high radioactivity = high brain activity based on BLOOD VOLUME
- neurochemical changes
fMRI
- directly measures concentration of deoxyhemoglobin in the blood
- BOLD response (Blood Oxygen Level Dependent contrast)
- hemodynamic response function
- behavioural aspects
- limited temporal
what is the change in BOLD response over time called
hemodynamic response function
- peaks in 6-8s
what do we normally study with fMRI
correlation between brain activity and stimulus timings
- produce activation maps showing which parts are involved in mental processes
how is activity measured in fMRI
- in voxels or volume pixels
(smallest box shaped part in 3D image)
when we say a brain region is active we mean…
it shows a greater response in one condition relative to the other
- normally have a baseline
cognitive subtraction
activity in a control task is subtracted from the activity in an experimental task
(only problem is baseline task may result in different areas of activation)
Disagreements between imaging and lesion studies
- lesion suggests it is more central to the task/ critical
- imaging implies it is used in a given task or not used
- evidence from semantic processing and semantic dementia patient (lose meaning of words and objects etc) who have degeneration of temporal lobes
- imaging: left inferior frontal gyrus
- lesions: left anterior temporal gyrus
- inconsitent data…
Devlin et al.
- compared imaging methods in semantic task
- PET scans, found activation in temporal area
- fMRI may not pick up activation in temporal lobe
- important to keep discovering methods
DTI
diffusion tensor imaging
- modified MRI scanner to show bundles of axons in the living brain
what does DTI measure
- measures white matter organization based on limited diffusion of water molecules in axons
- allows us to visualise connections in the brain
fNIRS
what does it measure
- functional neaer-infrared spectroscopy
- measures the same BOLD responses as fMRI but in a different way
- portable and more tolerant of head movement
- can’t image deep structures
fNIRS
how does it measure
‘light’ in infrared range passes through skull and scalp but is scattered differently by oxy- v. deoxyhemoglobin
iEEG or ECoG
- intracranial electroencephalography
- high resolution in place and time
- record directly from insde the brain in neurosurgery
- used to locate a seizure and map function
where does an iEEG record from
the cortical surface
