brain signal seminar

1. Stress Effects in the Brain During
Transcranial Magnetic Stimulation
Abas Sabouni, Mahsa Khamechi and Marc Honrath,
14th May 2019
Presented by
Nafiz Ishtiaque Ahmed
UOU- University of Ulsan.
Computational
Neural
Engineering Lab.

2. Introduction
• Brain mechanisms are still not unknown to us.
• Transcranial Magnetic Stimulation (TMS), widely used to unveiled
those mechanism through investigating signal conduction.
• In clinical settings TMS is used to investigate the potential for
treatments like,
▫ Posttraumatic stress disorder,
▫ Stem cell proliferation,
▫ Stroke recovery,
▫ Depression
• However; 5%-25% participants
undergoing TMS reports mild
tension headaches.
• The mechanism of TMS is not
fully understood. Fig 1 : Stoke rehabilitation

3. TMS
• TMS generates electrical currents within the brain through
noninvasive magnetic fields
▫ Short-term current is applied to the coil to create a magnetic field
▫ Time-varying magnetic field creates an electric field
▫ This electric field generates eddy (spherical) current in brain
▫ This made affected areas neurons to fire off action potential
▫ Repetitive magnetic pulse cause hyperpolarize
Fig 1 : TMS
Fig 2: Action Potential

4. TMS
• Repetitive TMS causes long-lasting effects.
• Lorentz force (Electromagnetic force) that is created by electric and
magnetic fields is suspected for the headaches
• Brain tissue may damage by intracranial pressure making mild
cranial inflammation.
• Here 3D MRI is used to made numerical head model of a healthy
patient to investigate the TMS effects of white matter (WM)and gray
matter (GM) of the brain.
• In previous study, human head model was not and did not
investigated stress on WM and GM.

5. TMS
• Magnetic field
▫ 𝑓 = 𝑝 𝐸 + 𝐽 ∗ 𝐵
𝑓- force density, ρ - charge density, J - current
density,
E - electric field, B - magnetic flux density
• Electromagnetic field distribution was
stimulated in brain during MRI.
• Also it measures the thermal effects in the
human brain during TMS.
• Numerical head model of a healthy patient
developed by Computer Simulation
Technology
• Head model has the
▫ skin/scalp,
▫ bone/skull,
▫ cerebrospinal fluid (CSF),
▫ GM,
▫ WM layer of brain tissue.
Fig 1 : head model generated from whole-head MRI.
(a) 3D with circular magnetic coil.
(b) segmented head model (WM, GM, CSF, skull, and
scalp) (c) Sagittal plane. (d) Transverse plane

6. Force of Constant Current
• Calculating The Force at Each Layer With Constant Current
• CST presented the force in three components in three vectors.
▫ DC component, AC component and Imaginary AC component.
▫ Vector Fx , Fy , and Fz ; represents the magnitude of
the forces in x, y, and z
• Lorentz force
▫ 𝐹𝑜𝑟𝑐𝑒 (𝑁) = 𝐹𝑥2 + 𝐹𝑦2 + 𝐹𝑧2
• DC and AC real components are
at the same magnitude
• Imaginary AC component is at
extremely small portion
Fig 1: Force created by single-turn coil with 100 kA
current at each tissue layer at different direction.

7. Lorentz Force vs current & magnitude
• The coil current was initially set to 10 A and increased to 100 A, 1, 10, and 100
kA, frequency stayed constant at 3.35 Hz
• Direct correlation between the current present in the coil and the force that
develops in the tissue layers.
• Direct correlation among the magnetic field in the tissue layer and the force
that develops
Fig 1: Total Lorentz force versus
amplitude of current (linear relation)
Fig 2: Total Lorentz force versus magnetic flux
density(non-linear relation)

8. Lorentz Force vs magnitude
• Relationship between the force and the electric field is linear
• Charge velocity and the magnetic field made non-linear relationship among
the magnetic field and the force .
Table 1: Maximum force in each layer
with 1 T magnetic flux density
Table 1: Maximum force in each layer
with B magnetic flux density

9. Calculation of stress
• GM tolerates approximately 5% shear and tensile deformation and no
compressive strain at 19.56 N/m2 stress
• WM creates 57.63 N/m2 stress around 10% shear deformation, 3.0%
compressive deformation, and 5.2% tensile deformation
Table 1: Calculation of stress and percent deformation
for the force from 1 T magnetic flux density

10. Conclusion
• During the TMS, a small force generated within the cranial tissue
layers in different layers of brain tissues.
• Force increases as the magnetic field increases.
• Within each tissue layer B-filed strength and force were found.
• In GM force of 3.02 N creates 5% shear and tensile deformation and
almost no compressive strain .
• In WM, a force of 2.88 N provides 10% shear deformation, 3.0%
compressive deformation, and 5.2% tensile deformation.
• Valuable information about the safety of the TMS device