introduction Flashcards
EEG/ ERP method type, invasiveness and brain property
recording, non invasive, electrical
single cell (and multi-unit) recordings method type, invasiveness, brain property
recording, invasive, electrical
TMS method type, invasiveness and brain property
stimulation, non invasive, electromagnetic
MEG method type, invasiveness and brain property
recording, non-invasive, electromagnetic
PET method type, invasiveness and brain property
recording, invasive, hemodynamic
fMRI method type, invasiveness and brain property
Recording, non-invasive, hemodynamic
single cell recording
Very small electrode implanted into axon
(intracellular) or outside axon membrane
(extracellular)
Records neural activity from population of
neurons
single unit recording
Electrodes, consisting of thin
wires, are implanted into
specific areas of the brain.
Recordings of brain cell
activities are made by
measuring the electrical
potential of nearby neurons
that are in close proximity to
the electrode
what is EEG?
Electroencephalography (EEG) is the measurement of the electrical activity of the brain by
recording from electrodes placed on the scalp
what are resulting traces of an EEG called, what do they represent?
The resulting traces are known as an
electroencephalogram (EEG) and represent an electrical signal from a large number of
neurons
what do EEG signals represent?
the change in the potential difference between two electrodes placed on the scalp
in time
how can EEG be combined to form a ERP
The EEG obtained on several trials can be averaged together time locked to the stimulus to form an
event-related potential (ERP)
how do we record ERP
ERPs can be recorded from the
human scalp and extracted from
the ongoing
electroencephalogram EEG by
means of filtering and signal
averaging.
what are ERPs
ERPs (event related potentials) are voltage fluctuations that are associated in time with particular event
(visual, auditory, olfactory stimuli)
what are different ERP peaks associated with?
Different ERP peaks associated with different aspects of face processing
what is the N170 relatively specialised for?
specialized for faces,
recorded from right PSTS (posterior superior temporal sulcus)
affected by perceptual changes to image
perceptual coding of the face
wat is P300 associated with?
famous and familiar faces
N250
face recognition (identity processing)
unaffected by view changes, affected by familiarity
P400-600
person recognition (faces and names)
affected by both faces and names
ERPs change from healthy controls to Alzheimer’s patients
A markedly reduced P300 is seen for demented patients at each electrode site
What is an MEG
Magnetoencephalography (MEG) is an imaging technique used to measure the magnetic
fields produced by electrical activity in the brain via extremely sensitive devices known as
SQUIDs
commonly used in both research and clinical settings
MEG spatial and temporal resolution
excellent for both
MRI
magnetic resonance imaging
uses differential magnetic properties of types of tissue and of blood to produce images of the brain
structural imaging
different types of tissue (skull, gray matter, white matter, CSF fluid) have
different physical properties – used to create STATIC maps (CT and structural MRI)
functional imaging
temporary changes in brain physiology associated with cognitive
processing (PET & fMRI)
PET
positron emission tomography
* Measures local blood flow (rCBF)
* Radioactive tracer injected into blood stream
* Tracer takes up to 30 seconds to peak
* When the material undergoes radioactive decay, a positron is emitted, which can be
picked up be the detector
* Areas of high radioactivity are associated with brain activity, based on blood volume
fMRI
Directly measures the concentration of deoxyhemoglobin in the blood
This is called the BOLD response (Blood Oxygen Level Dependent contrast)
what is change in BOLD response over time called?
Hemodynamic response function
when does the hemodynamic response function peak? what does this limit?
peaks in 6-8 seconds
this limits the temporal resolution of fMRI
what do we study with fMRI?
correlation between brain activity and stimulus timings
what can fMRI maps be used to produce?
activation maps showing which parts of the brain are involved in a particular mental
process
what does fMRI measure activity in?
in voxels — or volume pixels the smallest distinguishable box- shaped part in 3D image
what does one need to do in order to functional specialisation (infer a brain region is active)?
compare RELATIVE
differences in brain activity between two or more conditions
This involves selecting a baseline or comparison condition
when is a brain region active?
if it shows a greater response in one condition relative to another
cognitive subtraction
activity in a control task is subtracted from the activity in an experimental task
DTI
Diffusion tensor imaging
An imaging method that uses a modified MRI scanner to reveal bundles of axons in the living brain
We can visualize connections in the brain
Measures white matter organization based on limited diffusion of water molecules in axons
fNIS
Functional Near-Infrared Spectroscopy
Measures the same BOLD response as fMRI but in a completely different way
‘Light’ in infrared range passes through skull and scalp but is scattered differently by oxy- v. deoxyhemoglobin
Portable and more tolerant of head movement but can’t image deep structures
what is the only method that gives us high resolution in both place and time
intercranial recording, when we record directly from inside the human brain when people are undergoing neurosurgery
intracranial electroencephalography (iEEG) or ECoG
electrodes are placed to locate the seizure and map function (for neurosurgery purposes)
recording straight from the cortical surface, approximately from tens of thousands of neurons
ECoG in humans
recorded extracellular activity from 1177 cells in human medial frontal and temporal
cortices while patients executed or observed hand grasping actions and facial emotional
expressions (control condition)
Neurons in supplementary motor area SMA, and hippocampus responded to both
observation and execution of actions
TMS
a means of disrupting normal brain activity by introducing neural noise - ‘virtual lesion)
Michael Faraday (1791-1867)
Faradays coil- principle of electromagnetic induction
what happens when you apply a TMS pulse at any cortical node (area) of the network?
TMS will interfere with the relevant neural signal:
-efficiency of the neural signal will be degraded
-observe change in behaviour (RT change- it will take us longer to read)
advantages of TMS
interference/virtual lesion technique.
transient and reversible
control location of stimulation
establishes a causal link of different brain areas and a behavioural task
what does degree of language lateralisation determine
susceptibility to unilateral brain lesions
language
Language considered a function of the left side of the brain
in exceptional cases – right side of the brain
Functional imaging studies: graded
continuum of language lateralization
Transcranial Doppler Sonography (TCD) -
functional lateralization
how does TES work?
uses low level (1-2 mA) currents applied via scalp electrodes to specific brain regions
what are 3 different protocols for TES?
transcranial direct current stimulation- tDCS
Transcranial alternating current stimulation- tACS
transcranial random noise stimulation- tRNS
current generator (TES)
battery delivers constant current of up to 2mA, with 2 sponge electrodes in saline solution (20-35cm2). The stimulation is less focal, and very safe
what happens when tDCS is applied in sessions of repeated stimulations
can lead to changes in neuronal excitability that outlast the stimulation itself. These aftereffects are the heart of tDCS protocols for clinical application
what does TES show promising results in
in therapy: migraines, dementia, stroke, Parkinson’s disease, neglect,
depression, schizophrenia, OCD, eating disorders….
TES protocols : tDCS
1) Anodal: facilitation effects
2) cathodal: inhibition effects
3) sham (CONTROL) - 30 sec stimulation
neurotransmitters and tDCS
anodal stimulation inhibits GABA
cathodal stimulation inhibits glutamate
tACS
Transcranial alternating current stimulation (tACS) uses low level (0.5-2 mA) alternating
currents applied via scalp electrodes to specific brain regions.
The rationale behind tACS is the entrainment (synchronization) of internal brain rhythms
with externally applied oscillating electric fields. The oscillatory fields cause phase-locking
of a large pool of neurons, leading to increases of neural synchronization at the
corresponding frequency
lucid dreamin
an overlap between two states of consciousness — the one that exists in normal dreaming, and the one during wakefulness, which involves higher levels of awareness and control
In lucid dreaming, we transfer elements of waking consciousness into the dream
EEG and lucid dreaming
overlap between two states of consciousness is reflected in brain waves (EEG)
when people have lucid dreams, they show gamma waves in the frontal cortex, an activity pattern that is linked to consciousness but is nearly absent during sleep and normal dreaming
Voss et al., 2014
EEG was measured in 27 participants who were not lucid dreamers, while tACS was applied 2min
2 minutes after participants entered REM phase, tACS was applied for 30sec in the range
of 2Hz-100Hz. The participants were then immediately woken up to report their dreams
(LuCID scale)
The LuCiD scale consists of 28 statements, each followed by a 6-point rating scale
(0 strongly disagree - 5 strongly agree)
The EEG data showed that the brain’s gamma activity increased during stimulation with
40 Hz, and to a lesser degree during stimulation with 25 Hz
insight
the awareness that one is currently dreaming
dissociation
taking a third person perspective
control
control over the dream plot
