Human Neurophysiology 2020
VU Amsterdam
,Lecture 1
You will be able to explain:
- The difference between stimulus difference (exogenous) and spontaneous (endogenous)
brain activity.
- Mind wandering
What is cognitive neuroscience?
- Combined study of mind and brain revolutionized by neuroimaging techniques.
- Allows exploring the biology of conscious experience, unconscious processes, the disordered
mind.
- Aims to improve also diagnosis and treatment of brain disorders and increasingly inspires
artificial intelligence (cognitive computing)
PET: positron emission tomography imaging:
- Radioactive material accumulates in brain areas that are metabolically active.
- Decay of FDG (material) gives off a neutron and a positron, positron hits an electron and
annihilates into 2 gamma rays, which are detected.
- Slow temporal resolution enough decay is there after longer time (10-20s)
- Different brain parts are metabolically active at their own standard level, on activities some
parts get more active, this relies on substraction of measurements.
fMRI has replaced PET:
- No radioactive material and better resolutions
- fMRI = BOLD respons (blood-oxygenation-level-dependent signal)
- With neuronal activity, the brain consumes more energy, it gets that from the oxygentated
hemoglobin. Increase of oxygenated hemoglobin in a brain area is called the hemodynamic
response. Exygenated and deoxygenated hemoglobin have different magnetic properties,
imaged with fMRI
- It is a delayed imaging of brain activity as activity will take place and secondary bloodflow
happens which is detected.
95% of the brain shows task-related activity
Baseline problem:
- Two states of the brain get analysed and subtracted to find differences
- Brain at rest is not doing nothing at resting stated
- Task induced decreased correspond to areas with high resting-state metabolism
- Default mode network: punt, midden en zijkant of brain is always active, but not during
tasks. All three areas create the same BOLD signals during rest, synchronized
- By finding synchronized areas on hemodynamics, we can find intrinsically correlated regions
- Little evidence for functional role of default mode network
- Theory of mind: mind wandering is often on some-one you know, putting yourself in the shoe
of another seems to activate the default mode network, as well as envisioning the future, so
no distinct function.
Why is mind wandering important?
- Smartphone allowed new tools for cognitive research
- Wandering mind is unhappy mind, 47% of the people were mindwandering
ARSQ: sleeping questionnaire
- Less compfort when discontinuity of the mind
,Lecture 2: EEG and ERP
Learning objectives: You can explain:
- The relation between neuronal activity and EEG signals.
- The possibilities and limitations for interpreting the amplitude or scalp distribution of EEG
fields.
- The units and typical magnitudes of EEG parameters.
- What is “spatial and temporal resolution”
…and why the resolutions are as they are.
- The usefulness of EEG measurements by way of examples.
Why EEG?
- To look into functional significance of mass-neuronal activity
- Inexpensive and safe brain-computer interface (BCI)
- Fundamental knowledge, free-will and consciousness research
- Brain disorders: 35% of healthcare costs, but only 50% of all brain disorders is treated
- Real-time feedback on your brain activity: possible treatment using brain plasticity
- EEG is behind on other physiological measurements: we have no proper analysis tools on
brain data (when are values critical etc)
Advantages of EEG
- Direct reflection of activity
- High temporal resolution (~1ms) = no delay
- PLAATJE: where has activity taken place can be
determined with an accuracy of 1cm
- One fMRI reading generates multiple oscillations
with distinct functions, it gives information on a
block of brain
- Increasingly portable: EEG devices
- Non-invasible
- Available
- Inexpensive
Exam: Know what the abbreviations stand for, the The time-space trade-off: some techniques provide
difference between structural and functional methods, high temporal resolution of brain activity, while
whether a method is electrical or metabolic, and the
others provide higher spatial resolution.
approximate spatial and temporal resolution.
Why do you think the temporal resolution for fMRI has
such a broad range? (Is it actually 0.1 or is it ~8 seconds ...???)
What is “resolution”?
• Ability of a technique to separate two events in space (spatial resolution) or time (temporal
resolution).
• Or accuracy of localizing an events in space (spatial resolution) or time (temporal resolution).
Abbreviations:
- EEG = Electroencephalography
- fMRI = functional magnetic resonance imaging, detects blood flow related to neuronal
activity
- PET = Positron emission tomography
- MEG = Magnetoencephalography
How is it measured?
, - High concentration of sodium (Na) on the outside of the cell, when a neurotransmitter
reaches it sodium ions will flow into the cell. A positive charge is in the cell and charge
separation happens when Na moves without delay. Na/K pumps pump it into extracellular
space. The electricity field of the charge separation will move through your head (decays
with distance). Electrodes on head measure the difference between them.
- High temporal resolution
EEG: recording of electrical activity
- Neurons are like small batteries: the concentration of ions such as sodium is not the same on
the inside and outside of the cell.
- Thus, when a neurotransmitter causes the opening of a transmembrane ion channel, a
current of ions will flow from the outside to the inside of the cell =>
- That causes a transient potential difference around the neuron, and because the head is full
of water, which conducts electric fields, electric potentials are propagated to the outside of
the head.
- These potentials are not the same on different places of the head, because the field decays
with distance to the electric-dipole source
- Thus, by measuring the potential difference with electrodes having good electrical contact
with the skalp, we can measure brain activity entirely non-invasively!
- Only, because of each neuron producing a very small electric dipole (i.e., separation of
positive and negative charge), many neurons (thousands…) need to be active, which can
happen either because of some stimulus/task event, or spontaneously as we will later treat
in greater detail…
Electric dipoles in cortex produce electric potentials on the scalp:
- Resting membrane potential is negative (~ -70 mV).
- EPSCs (excitatory postsynaptic current) give rise to current sinks (e.g., Na+ flows into the cell)
and sources (conservation of current). Current moves form high to low potentials,
perpendicularly to electric field potential lines.
Transiently an unequal distribution of
positive and negative charges in the
extra-cellular space,
This is an electric dipole,
And its electric field propagates
(instantaneously) through the head
(conducting medium) all the way to
the scalp.
The EEG is a measurement of electric
potential differences between
electrodes in electrical contact with
the scalp and a reference electrode
Standard electrode locations:
- Critical standard: 10-20 system: n = 20 channels
- The lettering of electrodes refers to the main underlying anatomical lobes (frontal, central,
temporal, parietal, occipital)
- Not possible to measure absolute potential: EEG is the electrode potential at a given lead
relative to a reference (e.g. the average across electrodes)
EEG system at CNCR:
- Cz is reference electrode during measurements. It has 128/256 channels
Reference electrode:
