Neurons - Normalesup.org

Sensing and monitoring neuronal
activity through magnetic fields
Vincent Trauchessec
Service de Physique de l’Etat Condensé, CEA Saclay
PhD advisor : Myriam Pannetier-Lecoeur
June 17th
1
Outline
Neurophysiology
•
•
•
Introduction
The nervous system
Neuronal communication
Measurement techniques
Neurophysiology
Magnetrodes
Experiments
Conclusion
2
Outline
Neurophysiology
•
•
•
The nervous system
Neuronal communication
Measurement techniques
Magnetrodes
•
•
•
Introduction
GMR sensors
Microfabrication
Characterization
Neurophysiology
Magnetrodes
Experiments
Conclusion
3
Outline
Neurophysiology
•
•
•
The nervous system
Neuronal communication
Measurement techniques
Magnetrodes
•
•
•
GMR sensors
Microfabrication
Characterization
Experiments
•
•
Introduction
Action Potential in skeletal
muscle (in vitro)
Evoked Response Field in
cat’s visual cortex (in vivo)
Neurophysiology
Magnetrodes
Experiments
Conclusion
4
Outline
Neurophysiology
•
•
•
The nervous system
Neuronal communication
Measurement techniques
Magnetrodes
•
•
•
GMR sensors
Microfabrication
Characterization
Experiments
•
•
Introduction
Action Potential in skeletal
muscle (in vitro)
Evoked Response Field in
cat’s visual cortex (in vivo)
Neurophysiology
Magnetrodes
Experiments
Conclusion
5
Outline
Neurophysiology
•
•
•
The nervous system
Neuronal communication
Measurement techniques
Magnetrodes
•
•
•
GMR sensors
Microfabrication
Characterization
Experiments
•
•
Introduction
Action Potential in skeletal
muscle (in vitro)
Evoked Response Field in
cat’s visual cortex (in vivo)
Neurophysiology
Magnetrodes
Experiments
Conclusion
6
The Nervous System
• First arose 600 million years ago in our wormlike ancestors
• Always the same fondamental structure :
wiki.org
• Depends on the symmetry of the species : radiata vs. bilateria
P. Vernier
• Very precise topography of the N.S for bilaterian animals (great majority)
Introduction
Neurophysiology
Magnetrodes
Experiments
Conclusion
7
The Nervous System
• In vertebrates, NS is divided in two main parts :
 Central Nervous System (CNS)
 Peripheral Nervous System (PNS)
aviva.co.uk
Introduction
Neurophysiology
Magnetrodes
Experiments
Conclusion
8
The Nervous System
• In vertebrates, NS is divided in two main parts :
 Central Nervous System (CNS)
 Peripheral Nervous System (PNS)
aviva.co.uk
• Composed of two types of cells :
 Neurons : treatment and transmission
of information
 Glial cells : energetic support and
protection of neurons
• Brain => 2% of body weight but 20%
of its global energy
Magistretti, Science (2009)
Introduction
Neurophysiology
• « We use only 10% of our capacity »
Magnetrodes
Experiments
Conclusion
9
The Nervous System
• In vertebrates, NS is divided in two main parts :
 Central Nervous System (CNS)
 Peripheral Nervous System (PNS)
aviva.co.uk
• Composed of two types of cells :
 Neurons : treatment and transmission
of information
 Glial cells : energetic support and
protection of neurons
• Brain => 2% of body weight but 20%
of its global energy
Magistretti, Science (2009)
Introduction
Neurophysiology
• « We use only 10% of our capacity »
Magnetrodes
Experiments
Conclusion
10
Neuronal communication
Pre-synaptic neuron
(axon terminal)
Synapse
Post-synaptic neuron
(dendrite)
Other neurons
Extracellular
currents
Transmembrane
currents
Post-Synaptic Potential (PSP)
Action Potential (AP)
10 mV
100 mV
1 ms
10 ms
• Main signaling unit of the
nervous system
• Fast transient depolarization of
the cell membrane
Introduction
Neurophysiology
Magnetrodes
Experiments
• Slow
• Excitatory or inhibitory
Conclusion
11
Neuronal communication
Pre-synaptic neuron
(axon terminal)
Synapse
Post-synaptic neuron
(dendrite)
Other neurons
Extracellular
currents
Magnetic field
Transmembrane
currents
Post-Synaptic Potential (PSP)
Action Potential (AP)
10 mV
100 mV
10 ms
1 ms
• Main signaling unit of the
nervous system
• Fast transient depolarization of
the cell membrane
Introduction
Neurophysiology
Magnetrodes
Experiments
• Slow
• Excitatory or inhibitory
Conclusion
12
Measurement techniques
Scale
Electric (scalar)
Magnetic (vectorial)
ElectroEncephaloGraphy (EEG)
MagnetoEncephaloGraphy (MEG)
Range : µV
Range : f T
Brain
supraconductivite.fr
digitaltrends.com
Electrophysiology
Magnetophysiology
Range : mV
Range : pT-nT
Cells
Introduction
Neurophysiology
Magnetrodes
Experiments
Conclusion
13
Outline
Neurophysiology
•
•
•
The nervous system
Neuronal communication
Measurement techniques
Magnetrodes
•
•
•
GMR sensors
Microfabrication
Characterization
Experiments
•
•
Introduction
Action Potential in skeletal
muscle (in vitro)
Evoked Response Field in
cat’s visual cortex (in vivo)
Neurophysiology
Magnetrodes
Experiments
Conclusion
14
Magnetrodes
• Spin Valve structure based on the Giant Magneto-Resistance effect :
Pinned layer « hard magnet »
(PtMn)/(CoFe) and SAF (CoFe)/(Ru)/(CoFe)
Fixed magnetization
Substrate
Silicon
Introduction
Neurophysiology
Magnetrodes
Experiments
Conclusion
15
Magnetrodes
• Spin Valve structure based on the Giant Magneto-Resistance effect :
Spacer
Thin non-magnetic layer (Cu)
Pinned layer « hard magnet »
(PtMn)/(CoFe) and SAF (CoFe)/(Ru)/(CoFe)
Fixed magnetization
Substrate
Silicon
Introduction
Neurophysiology
Magnetrodes
Experiments
Conclusion
16
Magnetrodes
• Spin Valve structure based on the Giant Magneto-Resistance effect :
Free layer « soft magnet »
Free magnetization
Rotates in plane according to an external
magnetic field
Spacer
Thin non-magnetic layer (Cu)
Pinned layer « hard magnet »
(PtMn)/(CoFe) and SAF (CoFe)/(Ru)/(CoFe)
Fixed magnetization
Substrate
Silicon
The resistance depends on the angle between the magnetization of layers
Introduction
Neurophysiology
Magnetrodes
Experiments
Conclusion
17
Magnetrodes
• Spin Valve structure based on the Giant Magneto-Resistance effect :
The resistance depends on the angle between the magnetization of layers
Introduction
Neurophysiology
Magnetrodes
Experiments
Conclusion
18
Magnetrodes
• Spin Valve structure based on the Giant Magneto-Resistance effect :
The resistance depends on the angle between the magnetization of layers
Introduction
Neurophysiology
Magnetrodes
Experiments
Conclusion
19
Outline
Neurophysiology
•
•
•
The nervous system
Neuronal communication
Measurement techniques
Magnetrodes
•
•
•
GMR sensors
Microfabrication
Characterization
Experiments
•
•
Introduction
Action Potential in skeletal
muscle (in vitro)
Evoked Response Field in
cat’s visual cortex (in vivo)
Neurophysiology
Magnetrodes
Experiments
Conclusion
20
Action Potential in skeletal muscle
• Simple mechanism: muscle cells are mono-innervated with a single synapse in
their center
• Skeletal muscle cells are excitable cells and generate AP like neurons
• Nerve stimulation produces synchronous AP in all fibers
• Cables with large diameter => large axial currents expected (few nA => few nT)
• Information: axial currents, not accessible with other techniques
Nerve
Excitatory
synapse
Introduction
Neurophysiology
Magnetrodes
800 fibers
Experiments
Conclusion
21
Action Potential in skeletal muscle
 AP 2-3 ms after stimulation
o Nerve stimulation
o 500 acquisitions
 Signal amplitude = 2 nTpp
 In agreement with modeling (shape and amplitude)
2
1
B (nT)
AP propagation
0
-1
-2
5
10
15
Time (ms)
AP propagation
Magnetic signature of muscular axial currents along fibers induced by AP
Introduction
Neurophysiology
Magnetrodes
Experiments
Conclusion
22
Action Potential in skeletal muscle
Validation of magnetic origin:
Switching-off the feeding current
No AP detection
AP propagation
Orientation selectivity
No AP detection
AP propagation
Pharmacology : Curare injection
(blocks synaptic receptor)
No AP detection
Wash out curare
AP detection
AP propagation
Introduction
Neurophysiology
Magnetrodes
Experiments
Conclusion
23
ERF in cat visual cortex
• Very first in-vivo local magnetic recordings of neuronal activity
• Measurement setup @ Ernst Strungmann Institute for Neurosciences, Frankfurt :
Introduction
Neurophysiology
Magnetrodes
Experiments
Conclusion
24
Conclusions
• GMR sensors open the way to magnetophysiology
• What about local neuronal magnetic stimulation ?
drchugh.com
Introduction
Neurophysiology
Magnetrodes
Experiments
Conclusion
25
Collaborators
Laure Caruso, Josue Trejo-Rosillo, Elodie Paul, Amala Demonti,
Pierre-André Guitard, Gérald Legoff, Gregory Cannies, Claude
Fermon, Myriam Pannetier-Lecoeur
Gilles Ouanounou, Francesca Barbieri, Apostolis Mikroulis,
Thierry Bal, Alain Destexhe, Claude Bédard
Thomas Wunderle, Christopher Lewis, Jianguang Ni,
Pascal Fries
João Valadeiro, Jose Pedro Amaral, Susana Cardoso de Freitas
Paulo Freitas
Joonas Iivanainen, Lauri Parkkonen
Introduction
Neurophysiology
Magnetrodes
Experiments
Conclusion
26
Thank you for your attention !
Introduction
Neurophysiology
Magnetrodes
Experiments
Conclusion
27