Hoorcolleges CNS
Hoorcollege 1
Introduction & EEG methods
History of neuroscience
• Gall: suggested that surface of the head depends on mental skills (phrenology). Measure
enlargement or indentations of the skull.
• Brodmann: was the first one to map the cortex based on cell types.
• More detailed maps followed later.
Brain anatomy
•
• Every neuron has an output, transfer, modulator and input.
• Neurons tend to reproduce after birth. Connections do alter. Each cell type has its own
function:
• What if cells are damaged?
o Stroke
o Tumors of infections (or insects)
o Neural degeneration (bijv. Alzheimer)
o Trauma
o Epilepsy and lesions
o Genetic manifestations
,Methods for measuring brain activity:
1. Actions potentials or local field potentials → electrophysiology
2. Electromagnetic fields at scalp → EEG / MEG
3. Manipulating neural activity → TMS / tDCS
4. Blood oxygenation → fMRI / PET / fNIRS
Temporal (x) and spatial (y) resolution:
EEG (electroencephalography)
• Electrodes on the scalp measuring electricity differences in the brain
• It measures voltage differences across the scalp. When a neuron becomes active, there is more
electricity difference to be measured.
• Reflects post-synaptic potentials (PSP): difference in voltage along axons. Both inhibitory and
excitatory PSP
• Reflects local field potential → not single action potentials but a summation of many neurons.
• You need:
o Mass activity (many neurons with the same alignment)
o synchronized activity (not individual actions potentials)
o close to the scalp (scalp and skull is not a good conductor → smears out the signal)
o No noise sources ( Electronic devices → Artefacts in the data)
• 32-64 electrodes are enough for P100, N200, P3 etc. 128 electrodes is enough for localization.
• Advantages:
o Good temporal resolution
o ERP (event related potentials) can be measured
o Most sensitive to activity in gyri (cortical peaks)
• Spatial resolution is okay
• Relatively cheap, measures more neurons
• Disadvantages: skull blocks information.
• EEG waves
, Gamma: being super alert.
•
Note: always a mixture of multitude of waves. Some can be more dominant, depending on
arousal level.
• Theta/beta ratio: lower ratio = more arousal, higher ratio = less arousal.
• ADHD: patients are super tired, but become hyperactive. Less cortical arousal. It can be treated
by giving a stimulant to raise arousal.
• Frequency reflects a different arousal state
• ERP: many events-related potentials averaged.
Magnetoencephalography (MEG)
• Similar measure as EEG, but better localization (less distortations by skull) and measures
activity mainly originating from sulci
• Very expensive.
, Hoorcollege 2
(f)MRI and visual perception
(f)MRI
• Relies on interactions of a magnetic field with tissue of the body. Measures (magnetic)
properties of tissue.
• Records from many point in space, allowing reconstruction of an image
• fMRI also records at many points in time.
• Types of MRI
1. Structural/anatomical MRI (3D beeld)
2. Diffusion-weighted imaging (DWI)
3. Functional MRI (fMRI) → 4D beeld van structural MRI
• Neuroimaging and fMRI:
o High spatial resolution
o Straightforward analysis / interpretation
o Safe and non-invasive
o Easy access (every hospital has an MRI)
But also negative sides:
o Indirect measure of neural activity
o Low signal to noise ratios
o Awkward environment
o Poor temporal resolution
Hoorcollege 1
Introduction & EEG methods
History of neuroscience
• Gall: suggested that surface of the head depends on mental skills (phrenology). Measure
enlargement or indentations of the skull.
• Brodmann: was the first one to map the cortex based on cell types.
• More detailed maps followed later.
Brain anatomy
•
• Every neuron has an output, transfer, modulator and input.
• Neurons tend to reproduce after birth. Connections do alter. Each cell type has its own
function:
• What if cells are damaged?
o Stroke
o Tumors of infections (or insects)
o Neural degeneration (bijv. Alzheimer)
o Trauma
o Epilepsy and lesions
o Genetic manifestations
,Methods for measuring brain activity:
1. Actions potentials or local field potentials → electrophysiology
2. Electromagnetic fields at scalp → EEG / MEG
3. Manipulating neural activity → TMS / tDCS
4. Blood oxygenation → fMRI / PET / fNIRS
Temporal (x) and spatial (y) resolution:
EEG (electroencephalography)
• Electrodes on the scalp measuring electricity differences in the brain
• It measures voltage differences across the scalp. When a neuron becomes active, there is more
electricity difference to be measured.
• Reflects post-synaptic potentials (PSP): difference in voltage along axons. Both inhibitory and
excitatory PSP
• Reflects local field potential → not single action potentials but a summation of many neurons.
• You need:
o Mass activity (many neurons with the same alignment)
o synchronized activity (not individual actions potentials)
o close to the scalp (scalp and skull is not a good conductor → smears out the signal)
o No noise sources ( Electronic devices → Artefacts in the data)
• 32-64 electrodes are enough for P100, N200, P3 etc. 128 electrodes is enough for localization.
• Advantages:
o Good temporal resolution
o ERP (event related potentials) can be measured
o Most sensitive to activity in gyri (cortical peaks)
• Spatial resolution is okay
• Relatively cheap, measures more neurons
• Disadvantages: skull blocks information.
• EEG waves
, Gamma: being super alert.
•
Note: always a mixture of multitude of waves. Some can be more dominant, depending on
arousal level.
• Theta/beta ratio: lower ratio = more arousal, higher ratio = less arousal.
• ADHD: patients are super tired, but become hyperactive. Less cortical arousal. It can be treated
by giving a stimulant to raise arousal.
• Frequency reflects a different arousal state
• ERP: many events-related potentials averaged.
Magnetoencephalography (MEG)
• Similar measure as EEG, but better localization (less distortations by skull) and measures
activity mainly originating from sulci
• Very expensive.
, Hoorcollege 2
(f)MRI and visual perception
(f)MRI
• Relies on interactions of a magnetic field with tissue of the body. Measures (magnetic)
properties of tissue.
• Records from many point in space, allowing reconstruction of an image
• fMRI also records at many points in time.
• Types of MRI
1. Structural/anatomical MRI (3D beeld)
2. Diffusion-weighted imaging (DWI)
3. Functional MRI (fMRI) → 4D beeld van structural MRI
• Neuroimaging and fMRI:
o High spatial resolution
o Straightforward analysis / interpretation
o Safe and non-invasive
o Easy access (every hospital has an MRI)
But also negative sides:
o Indirect measure of neural activity
o Low signal to noise ratios
o Awkward environment
o Poor temporal resolution
