Summary neural networks- neuroscientific methods

Neuroscientific aspects: neural networks: neurosc. methods
GOALS
 Deficits of neural recruitment underlying common neurological conditions;
 Insight into the compensatory neural networks in relation to acute and chronic disease evolution;
 Insight into the neural basis of motor learning, control and concepts of rehabilitation as applied to
hemiplegia and Parkinson’s disease
 Evidence on non-invasive neurostimulation as potential rehab tool
 Interpreting recent and relevant literature on neural networks
 Translate knowledge to the neurorehabilitation field;
 Critical and scientific attitude to concepts of neurorehabilitation.

INTRODUCTION
 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
- Motor control, motor learning
- Cognition
- Memory
- ...
 Clinical research
- Neural processes underlying ageing
- Neural basis of diseases (stroke, Parkinson, eplipsy, neurodevelopmental disorders..)
- Neural evaluation of disease progression
- Neural evaluation of interventions/ treatments
- …

OVERVIEW OF METHODS
 Magnetic Resonance Imaging (MRI)
 Diffusion Tensor Imaging (DTI)
 Functional Near-infrared Spectroscopy (FNIRS)
 Electro-EncephaloGraphy (EEG)
 Transcranial Magnetic Stimulation (TMS)
=> Equipment
=> Neurophysiological basis
=> Examples of Applications

 Figuur
- Concept voor & nadelen technologie beoordelen
- Temporele (tijd) & spatiale resolutie

MAGNETIC RESONANCE IMAGING – MRI
WHAT ISN’T FMRI

 fMRI is not bumpology
- Claims that bumps on the skull reflected exaggerated functions/traits
 Specifieke bulten in hersenen gerelateerd aan specifieke functies
- It lacked any mechanism underlying its claims.
- It used anecdotal, rather than scientific, evidence.
- Nevertheless, its central idea persisted:
 Localization of Function fMRI is not mind-reading
 fMRI is not invasive
- Positron Emission Tomography (PET)
- Intracranial Stimulation/Recording
- With fMRI nothing is injected!



Nala Melis Pagina 1

, Neuroscientific aspects: neural networks: neurosc. methods
WHAT IS (F)MRI
 3 different modalities
- MRI = brain anatomy
- Functional MRI – fMRI = brain activity
- fc MRI = functional connectivity




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 (+)
- have a spin (they turn around)
because they turn around, they have a small, but measurable magnetic field
door spin= magnetisch veld= interactive met scanner

 Protons are mostly found in water and fat tissue
 In a single molecule of water, H2O there are 10 protons (1 from each hydrogen and 8 from oxygen)
 E.g. a water cube of 2 x 2 x 5 mm contains
- 6 * 1015 protons
- 6.000.000.000.000.000




 In everyday life, the protons in our body are in balance, randomly oriented, but in balance
- Not one specific direction per proton
 Inside MRI scanner, which is one giant magnet, protons align to magnetic field (B0). Either in parallel (same
direction) or anti-parallel (opposite direction)
- Some in parallel or anti-parallel
 Meeste in parallel alligneren= zelfde richting

 majority of atoms aligns in parallel, allowing to define NET
magnetisation of protons in direction of B0
 happens if you are positioned in scanner magnetic field = ALWAYS
on.

 Proton is in ‘excitation state’ head coil “on”
 Emission of a radio frequency pulse by the head coil, induces a flip of the NET magnetisation
(instead of aligning to the Z-axis, the protons now align in the X-Y field)

 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 ‘relaxation state’, protons emit radio frequency themselves, and this signal is measured.
 Proton emits radio frequency during ‘relaxation state’
(the head coil, both emits and measures radio frequencies)




Nala Melis Pagina 2

, Neuroscientific aspects: neural networks: neurosc. methods
 T1-relaxation= gemeten worden
- time it takes for a proton to relax to 63% of it’s initial state (along the z-
axis) is called T1
- KEY PART: the velocity from the proton aligning back to its initial
position is different for different types of tissue ‘relax’ the same way!
 Not all tissue relax in the same way
 Protons in fat (e.g. white matter), relax way 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)

- Vb afbeelding
 Ventrikels= donkerder= ↓ RF
 White matter= lichter= ↑R


Coronal slice Transverse slice Sagittal slice




MRI – EXAMPLE OF APPLICATION

 Clinical: Localization of brain lesions
 Pre-surgical mapping (e.g. epilepsy)
 Prediction of disease progression

 Long term motor function after neonatal stroke: Lesion localization above all
 Prediction of disease progression – example of CP
 Children tested at age 7
 Some developed CP others didn’t
 Lesions are more wide-spread in CP group, compared to group without CP symptoms
 Example studie
 Voorspellen ontwikkeling CP ivm. Andere die niet CP ontwikkelen
 CP ontwikkelen groep= uitgesprokenere leasies
 Afbeelding L
 Unilateral CP
 Afbeelding R
 Zonder CP




Nala Melis Pagina 3