Samenvatting
Samenvatting Neural networks - deel 1
Vak Neurological Aspects, deel 1 van Neural Networks, gegeven door Prof. Alaerts (KUL). Deel 2 (gegeven door Prof. Gilat) is ook beschikbaar.
[Meer zien]Voorbeeld 4 van de 51 pagina's
Voorbeeld 4 van de 51 pagina's
In winkelwagen
Voorbeeld van de inhoud
NEUROLOGICAL ASPECTS:NEURAL NETWORKS AND
REORGANIZATION
Academiejaar 2023-2024 – 2MARE
H1. NEUROSCIENTIFIC METHODS
H2. THE POTENTIAL OF NON-INVASIVE BRAIN
STIMULATION IN NEUROREHABILITATION
H3. AGEING AND NEUROPLASTICITY
H4. NEUROREHABILITATION AFTER STROKE
PART PROF. KAAT ALAERTS
, PART KAAT ALAERTS
Neurological aspects: neural networks
and reorganization
CHAPTER 1: NEUROSCIENTIFIC METHODS
• Measuring ‘brain activity’ at the systems level (not single-cell)
• Non-invasive (not ‘inside’ the brain, but at the level of the scull)
• Fundamental research
o Motor control, motor learning
o Cognition
o Memory
o ...
• Clinical research
o Neural processes underlying ageing
o Neural basis of diseases (stroke, Parkinson, epilepsy, neurodevelopmental disorders)
o Neural evaluation of disease progression
o Neural evaluation of interventions/ treatments
Look for each technique at equipment, neurophysiological basis and examples of applications
Important concept to evaluate the advantages and disadvantages of different techniques
Temporal and spatial resolution
o Some better for temporal: what is happening in time regarding brain activity?
o TEMPORAL = when in time
o SPATIAL = where in the brain
1/ MAGNETIC RESONANCE IMAGING (MRI)
What isn’t fMRI?
➢ fMRI is not bumpology (claims that bumps on the skull reflected exaggerated functions/traits)
➢ fMRI is not mind-reading
➢ fMRI is not invasive (the skull remains closed)
What is fMRI: a relative, safe, non-invasive technique
1
, PART KAAT ALAERTS
1.1 Equipment
- Giant magnet
- Head coil (helps with high-quality images)
MRI = brain anatomy
fMRI = functional MRI = brain activity
fcMRI = functional connectivity
First MRI-scan around 1950, first functional MRI-scan developed way later (around 1990)
1.2 Biological basis of MRI
• Measures brain anatomy
• Former name: (Nuclear) Magnetic Resonance Imaging → nothing to do with ‘radioactivity’, but
with the magnetic properties of protons, in the nuclei of atoms
Protons:
- Have a mass, are positive (+) and have a spin (they turn around)
- Because protons turn around, they have a small, but measurable magnetic field
- In everyday life, the protons in our body are in balance, randomly oriented, but in balance
- Inside the MRI scanner, which is one giant magnet, the protons align to the magnetic field (B0).
Either in parallel (same direction) or anti-parallel (opposite direction)
- Most protons will align parallel in MRI-scan
- The majority of atoms aligns in parallel, allowing to define the NET magnetization of protons
in the direction of B0
- This is what happens if you’re positioned in the scanner. And this magnetic field is ALWAYS on.
- Emission of a radio frequency pulse by the head coil, induces a flip of the NET magnetization
(instead of aligning to the Z- axis, the protons now align in the X-Y field)
- Proton is in excitation state
- Head coils will emit a radiofrequency: magnetic field of protons will shift (excitation
state) → follow the Y-axis
- However, protons don’t like being in this ‘high-energy’ excitation state’, and from the moment
the radio frequency pulse is turned off, it will ‘relax’ to its initial position (i.e., align back to the
Z-axis of the B0 field).
- During this ‘relaxation state’, the protons emit radio frequency themselves, and this signal is
measured. (The head coil, both emits and measures radio frequencies)
- Proton emits radio frequency during relaxation state
- Protons want to align with the Z-axis → when the radiofrequency is turned off, they
return to the Z-axis
- While doing this, they will emit radiofrequency itself → MRI can measure the different
relaxation times in the different tissue
2
, PART KAAT ALAERTS
The time it takes for a proton to relax to 63% of its initial state (along the z-axis) is called T1
T1 = relaxation time
• Not all tissues ‘relax’ the same way!
• Protons in fat (e.g., white matter), relax much faster, than protons
in liquid (e.g., cerebrospinal fluid)
• By measuring the relaxation in different tissues, contrasts can be
visualized!
• In so-called ‘T1-weighted’ images, liquid is dark (less energy emitted), and fat is bright (more
energy emitted) → dark matter needs less energy at T1 compared to white matter (grey matter
is in between)
1.2.1 Examples of application
➢ Clinical: Localization of brain lesions
➢ Used in pre-surgical mapping (e.g., epilepsy) and prediction of disease progression
1.3 Functional MRI (fMRI)
Uses MRI to indirectly measure brain activity
Same principle as MRI: contrasts in brain images based on measurement of magnetic relaxation
→ Here however, it is not about protons, but about hemoglobin in the blood...
1.3.1 Biological basis of fMRI
• Brain region active => increased O2 metabolism => increased blood flow
• fMRI measures the Blood Oxygen Level Dependent (BOLD) signal
o Oxyhemoglobin = diamagnetic (same as tissue)
o Deoxyhemoglobin = paramagnetic (weak magnetic) → interacts with the signal of MRI
• fMRI always measures a change in BOLD-response
o You always need a baseline to see how BOLD has changed
o During baseline situation, the BOLD-signal goes back down again
LEFT-LEFT = brain at rest
Basic metabolism (good balance between oxy and de-oxy Hb in bloodstream, normal usage of
oxygen by the neuronal cells, normal glucoses dosage as energy resource)
LEFT-RIGHT = activation of the neuron
→ Neurons will require an increased metabolism of glucoses and oxygen
Initially in bloodstream will be higher amount of de-oxy compared to oxy
→ This gives a reduced BOLD-signal
RIGHT = this triggers a haemodynamic respons rendering an increased transport of oxy to this region
of activation
Rendering in a lowering of the ratio de-oxy/oxy → rendering in an increase of BOLD-signals
3
Voordelen van het kopen van samenvattingen bij Stuvia op een rij:
√ Verzekerd van kwaliteit door reviews
Stuvia-klanten hebben meer dan 700.000 samenvattingen beoordeeld. Zo weet je zeker dat je de beste documenten koopt!
Snel en makkelijk kopen
Je betaalt supersnel en eenmalig met iDeal, Bancontact of creditcard voor de samenvatting. Zonder lidmaatschap.
Focus op de essentie
Samenvattingen worden geschreven voor en door anderen. Daarom zijn de samenvattingen altijd betrouwbaar en actueel. Zo kom je snel tot de kern!
Veelgestelde vragen
Wat krijg ik als ik dit document koop?
Je krijgt een PDF, die direct beschikbaar is na je aankoop. Het gekochte document is altijd, overal en oneindig toegankelijk via je profiel.
Tevredenheidsgarantie: hoe werkt dat?
Onze tevredenheidsgarantie zorgt ervoor dat je altijd een studiedocument vindt dat goed bij je past. Je vult een formulier in en onze klantenservice regelt de rest.
Van wie koop ik deze samenvatting?
Stuvia is een marktplaats, je koop dit document dus niet van ons, maar van verkoper LB2001. Stuvia faciliteert de betaling aan de verkoper.
Zit ik meteen vast aan een abonnement?
Nee, je koopt alleen deze samenvatting voor €10,49. Je zit daarna nergens aan vast.
Is Stuvia te vertrouwen?
4,6 sterren op Google & Trustpilot (+1000 reviews)
Afgelopen 30 dagen zijn er 67096 samenvattingen verkocht
Opgericht in 2010, al 14 jaar dé plek om samenvattingen te kopen