Summary of all lecture slides of Neuroimaging 1 ()
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Course
Neuroimaging I (SOWDGCN02)
Institution
Radboud Universiteit Nijmegen (RU)
This is a summary of all the lecture slides and the additional information the lectures gave.
It is a quite long summary but it is very elaborate and contains all the information required for the exam that where discussed during the lectures.
The paper of the last lecture is also summarized. All ot...
Neuroimaging I
Introduction
The Goal of cognitive neuroscience is
To map the information-processing structure of the human mind onto the physical organization of the brain
AKA: Map information processing to locations in the brain
(History if neuroscience is not important for the exam.)
Cortical localization
Phrenology
Involves the measurement of bumps on the skull to predict mental traits.
Pseudoscience, but it was very popular
Largely based on observations of the skull of extreme cases
Some interesting case studies (on lesions) where done
Broca’s area
First clearly localized function of the brain
Electrical Stimulation of the cortex
Edouard Hitzig & Gustav Theodor Fritsch
o Sketched the localization of the motor cortex of dogs by applying weak currents to the cortex
Daniel Ferrier
o Applied stimuli to various species and cortices to localize function’’
Richard Caton
o Recorded action potentials from the brains of monkeys and rabbits
Hans Berger
o Invented electroencephalography (EEG)
David Cohen (at MIT)
o Performed the first magnetoencephalography (MEG) recordings in a squid
Mental work vs. Cortical work
Hans Berger
o Mental work adds only a small increment to the cortical work which is going on continuously, and not
only in the waking state.
Blood flow related to brain functions
Angelo Mosso
o Developed numerous measurement devices relating to human physiology
Plethysmograph
Measurement of volume pulsation; cerebral pulses
Human Circulation Balance
Measures redistribution of blood during emotional and intellectual tasks
Seymour S. Kety & Carl F. Schmidt
o Demonstrate that blood flow is regionally regulated
, o Developed an instrument to measure CBF (cerebral blood flow) and the metabolic rates of oxygen in
living unanestethetized humans.
Modern blood flow based measurements
Positron Emission Tomography (PET)
o Most biological molecules are made up of hydrogen, carbon, nitrogen and/or oxygen.
o Uses radionuclides (with fixed half-lives) to measure the related metabolism of these molecules
Oxygen utilization is not correlated to blood flow
In an experiment
Increased blood flow, leads to
Higher oxygenation of blood, leads to
Less disturbed signal, leads to
Signal increase, leads to
blobs.
Functional Imaging
Electrophysiological
o EEG
o MEG
o Measures electromagnetic activity in
neurons
Pro: It is fast
Con: Easily distorted, difficult to localize
Hemodynamic
o PET
o fMRI
o Measures indirect blood flow
Pro: Very well localized
Con: slow
,01 – Electrophysiology
1.1 – Demonstrating EEG and MEG
EEG & MEG have great temporal resolution but not so good spatial resolution.
There are techniques with an even better temporal resolution, but they are invasive.
The brain consists of active and passive tissue. The currents pass through these tissues.
Electroencephalography (EEG)
The electrical activity of active neurons produces currents that spread through the head.
On the scalp, voltage differences can be recorded as the EEG.
EEG reflects brain electrical activity with millisecond temporal resolution.
Spontaneous EEG can be helpful in clinical environments.
Electrode cap
The standard placement scheme has been developed in the 1950’s.
It relies on 4 anatomical landmarks (which you can feel)
o Nose (also called Nasion)
o Inion (on the back)
o Preauricular points (on both sides, in front of the ear)
From these landmarks all electrodes are placed on the head.
o 10-20 system is often used.
o Means 10 and 20% spaces between adjacent electrodes.
Source of the EEG Signal
EEG measures post-synaptic potentials
o Action potentials (APs) are very short and biphasic
o Post-synaptic potentials are longer than APs and hare mostly monophasic
Sum of all dendritic synaptic activity
The temporal and special aspects of neurons are important.
o Only synchronously activated neurons give a measurable signal
They have the same direction at the same time
o For all others, the signal gets cancelled out by each other.
o Repolarization causes some currents to flow in the opposite direction.
Repolarization means going negative after
depolarization which means going to zero.
When this happens while other neurons are
polarizing, the signals cancel each other out.
Image:
Left top: Radially symmetric neurons
Left bottom: Randomly oriented neurons
Right top: Asynchronously activated neurons
Right bottom: synchronously activated neurons
, Event-related potentials (ERPs)
We often look at even related activity, so activity following a stimulus
If we present the stimulus many times, we can average the activity, and thus, average out noise
o If we average over 10 trials, the noise will be 10^2 times smaller.
o So noise is reduced by (number of trials)^2.
o When averaging over multiple trails we average after each trial and plot this all.
So the systematic reflection becomes more and more visible.
If you know what you’re looking for, you can already see it without averaging, but the noise is
making it hard to see.
We often present stimuli (trials) with a fixed time + or – a random bit.
o This reduces predictability.
We look at the time before, during and after the stimuli
o Before = baseline
Potential Artifacts
Eye blinks
o Temperature and humidity are regulated to reduce eye blinking
o Vertical Electrooculography (VEOG) recording, which reflex eye blinking, can be used to distinguish trials
with (many) blinks from averaging.
Deflection during blink is negative for VEOG while inflection in the rest
It is measured from above and below the eye.
Measurements are the difference between 2 points
Sometimes blinks can be subtracted from the data (instead of removing the trial) but this depends
on the task.
Eye movements
o Participants are asked to reduce eye movement
o Visual stimuli are presented in the middle of the screen to reduce eye movements
o Participants are asked to keep looking at one point during auditory stimulation
Muscle tension
o Jaw, Neck and face muscles
Reading aloud
ECG, pulse artifacts (Heart signal)
o Normally ECG is recorded separately and subtracted from the signal
o ECG can also function as an indicator of arousal
Loss of electrode contact
Spontaneous Activity: Oscillations in different mental states
When excited
o Mostly Beta (13-30 Hz) and Gamma (30-100 Hz) waves
When relaxed
o Mostly Alpha (8 12 Hz) waves
Slow wave (deep) sleep
o Mostly Delta (< 4 Hz) waves
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