Summary neural networks- non invasive brain stimulation
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Course
Neural networks
Institution
Katholieke Universiteit Leuven (KU Leuven)
Summary of the non-invasive brain stimulation lesson given by prof. K. alaerts of the neuroscientific aspects course. It is a summary of the powerpoint slides and additional items noted during the lesson. The slides were in English and my own notes are always in Dutch as much as possible. It is the...
Neural networks: non-invasive brain stimulation
INTRODUCTION
Non-invasive brain stimulation (NIBS) techniques increasingly used for modulation of central nervous
system excitability in humans
- (non-invasive: not ‘inside’ the brain, but at the level of the scull)
Fundamental Research: study fundamental aspects of human behavior
- Motor control, motor learning
- Cognition
- Memory
- ...
Clinical Applications: induce neuromodulation facilitating neurorehabilitation
- Stroke
- Parkinson’s disease
- Depression
- Aging
CONTENT
Transcranial Magnetic Stimulation (TMS)
Transcranial direct current stimulation (tDCS)
Evidence for application in stroke
Evidence for application in Parkinson
HISTORY OF NIBS
In 1959, Kolin et al. stimulated the nerves of frogs through alternating magnetic fields for the very first
time.
Later in 1965, Bickford applied magnetic fields to stimulate the human peripheral
nerve.
In 1980, Merton and Morton (1980) electrically stimulated the motor cortex through the scalp using
transcranial electrical stimulation (TES).
- => TES became very useful for many purposes, but it was very painful…
- Stimuleren motor cortex= AP krijgen door stim. Corticospinale tract
Later, in 1985, Barker et al. introduced transcranial magnetic stimulation (TMS) to stimulate the brain…
with no pain.
- also electrical field but with an magnetic field -> not detected by the pain sensors
Nala Melis Pagina 1
, Neural networks: non-invasive brain stimulation
TRANSCRANIAL MAGNETIC STIMULATION – TMS
Non-invasive, focal stimulation of the brain
Equipment
- Condensator
- Coil
Primary electriccurrent in coil
- Induces magnetic field
- When coil is held over the brain
=> Magnetic field induces secondary electric current in underlying brain tissue
- Secondary = opposite direction!
TMS over Primary motor contrex (M1)
- activation of corticospinal tract through stimulation of pyramidal cells in the primary motor cortex
- activation of α- motorneurons at the spinal tract
- measurable activity in the contralateral muscle (using electromyography)
- Motor evoked potential (MEP)
Different types of TMS
- Single-pulse TMS
Measurement of corticospinal excitability (MEPs)
- Repetitive TMS protocols (rTMS)
Used to modify brain plasticity
- Basic mechanisms underlying rTMS-induced plasticity remain poorly understood
Hoe kan TMS gebruikt maken van plasticiteit
- Suggested mechanisms for inducing plasticity
At the level of the synaps
o Induction of long-term potentiation (LTP)
o Induction of long-term depression (LTD)
(Non-synaptic)
o Cellular pathways by TMS
REPETITIVE TMS
Different protocols
- Low-frequency rTMS (less than 1 stimulation/ sec) (< 1 Hz)
=> Inhibitory (decrease excitability through LTD)
o LTD+long term depression
- High-frequency rTMS (more than 5 stimulations/sec) (> 5 Hz)
=> Facilitatory (increase excitability through LTP)
o LTP= long term potentiation
- Continuous theta-burst stimulation (cTBS)
Three pulses at 50 Hz every 200 ms for 20 – 40 seconds
o => Inhibitory (decrease excitability through LTD)
- Intermittent theta-burst stimulation (iTBS)
Three pulses at 50 Hz every 200 ms for 2 seconds given at 10 sec intervals
o => Facilitatory (increase excitability through LTP)
frequency=impact op richting
- Facilitatie
- Inhibatie
Intervallen hebben ook invloed
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, Neural networks: non-invasive brain stimulation
1. FACILITATION – HIGH-FREQUENCY RTMS
Synaptic mechanism
- Magnetic field simultaneously depolarizes the pre- and post-synaptic neurons.
- Induced action potentials in the presynaptic neuron result in the release of glutamate into the
synapse, whereas simultaneous depolarization of the post-synaptic dendrite by the stimulation
activates voltage-gated calcium channels and removes the magnesium block from the NMDA
receptor (receptor for glutamate) (N-methyl-D- aspartate) .
- This “cooperative” activation of the pre- and post-synaptic neurons promotes the accumulation
of AMPA receptors (α-amino-3-hydroxy-5- methyl-4-isoxazolepropionic acid) on the post-synaptic
cell, resulting in an overall strengthening of the synapse and LTP-like effects.
- Of note!
Shown IN VITRO (single-cell culture) of subcortical cells of the hippocampus
Not known whether mechanism is similar for cortical neurons (which are more commonly
stimulated with rTMS at the scalp)
Mechanism demonstrated for LTP Not known whether mechanism is the same for LTD
2. NON-SYNAPIC MECHANISMS FOR INDUCING PLASTICITY
Biochemical : Regulation of gene and protein expression
- Brain-derived neurotrophic factor (BDNF)
Belangrijke factor= trofic factor
=> potent trophic factor implicated in synaptic plasticity, neuronal survival, and regeneration
- Humans with genetic variants of BDNF respond differently to TMS protocols
- Human studies show up-regulation of BDNF in serum samples following high-intensity rTMS
Role of rTMS-induced upregulation of BDNF?
- Promote plasticity
- Induce Neurogenesis
- Neuroprotection
Main mechanisms
details hiervan niet kennen! Wel het volgende:
- Promoting neuroplasticity, neuro survival -> inhibits neuronal cell death
↑ metabolische effecten
- Regulatie gene expression proteins
TRANSCRANIAL DIRECT CURRENT STIMULATION – TDCS
tDCS is a transcranial electrical stimulation (tES) technique that involves the application of a weak direct
electrical current (e.g., 1–2 mA) through two or more electrodes placed on the scalp
Gedetecteerd als kleine tinteling op huid/schedel
- Is niet onaangenaam
- Electrode kunnen eender waar geplaatst worden
Magnetisch veld registreren
- LOW intensity/current!
- TMS: massive synchronized discharge of action potentials
- tDCS: electrical current is too weak to induce action potentials
Modulation of membrane potential of neurons
Steeds I tussen + &-
IN VITRO RODENT BRAIN TISSUE
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