13.15 o14.2 m elbohouty
DESCRIPTION
Research 16: M ElbohoutyTRANSCRIPT
![Page 1: 13.15 o14.2 m elbohouty](https://reader035.vdocuments.mx/reader035/viewer/2022062418/5550b6afb4c905ff618b4ba9/html5/thumbnails/1.jpg)
Measuring Electrical Conductivity of Brain Tissue
By:Maher Elbohouty
Supervisors:Dr Marcus Wilson
AProf Alistair Steyn-Ross
12 April 2023
![Page 2: 13.15 o14.2 m elbohouty](https://reader035.vdocuments.mx/reader035/viewer/2022062418/5550b6afb4c905ff618b4ba9/html5/thumbnails/2.jpg)
Has anyone measured the conductivity ? • Gabril et al.* (2009) in his review shown that the
conductivity of brain tissue depends on many parameters as:
• The animal and the part of the brain investigated
• The stimulus frequency
• The direction of measurements
• He found that it ranges from:0.01 to 0.47 S/m* Phys. Med. Biol. 54 (2009) 4863–4878
• Logothetis et al.** (2007) said that: “ Our results show that impedance is independent of frequency, is homogeneous and tangentially isotropic within gray matter, and can be theoretically predicted assuming a pure-resistive conductor ”.
** Neuron 55, 809–823, September 6, 2007
12 April 2023© THE UNIVERSITY OF WAIKATO 2
![Page 3: 13.15 o14.2 m elbohouty](https://reader035.vdocuments.mx/reader035/viewer/2022062418/5550b6afb4c905ff618b4ba9/html5/thumbnails/3.jpg)
…slicing…
Brain removal…
12 April 2023© THE UNIVERSITY OF WAIKATO 3
![Page 4: 13.15 o14.2 m elbohouty](https://reader035.vdocuments.mx/reader035/viewer/2022062418/5550b6afb4c905ff618b4ba9/html5/thumbnails/4.jpg)
Three methods:
1. One dimension
12 April 2023© THE UNIVERSITY OF WAIKATO 4
2. Two dimensions
3. Three dimensions
![Page 5: 13.15 o14.2 m elbohouty](https://reader035.vdocuments.mx/reader035/viewer/2022062418/5550b6afb4c905ff618b4ba9/html5/thumbnails/5.jpg)
1. Modified syringe and two stainless steel plate electrodes (Flat Electrodes):
12 April 2023© THE UNIVERSITY OF WAIKATO 5
![Page 6: 13.15 o14.2 m elbohouty](https://reader035.vdocuments.mx/reader035/viewer/2022062418/5550b6afb4c905ff618b4ba9/html5/thumbnails/6.jpg)
Taking the sample ..
12 April 2023© THE UNIVERSITY OF WAIKATO 6
![Page 7: 13.15 o14.2 m elbohouty](https://reader035.vdocuments.mx/reader035/viewer/2022062418/5550b6afb4c905ff618b4ba9/html5/thumbnails/7.jpg)
The resistivity of brain slices at 10 kHz
12 April 2023© THE UNIVERSITY OF WAIKATO 7
The Syringe (V3) digital calliper (DIGMATIC- Mitutoyo Corporation, Model CD-6”) and LCR meter (Agilent E4980A)
![Page 8: 13.15 o14.2 m elbohouty](https://reader035.vdocuments.mx/reader035/viewer/2022062418/5550b6afb4c905ff618b4ba9/html5/thumbnails/8.jpg)
Defining equation in 1D
12 April 2023© THE UNIVERSITY OF WAIKATO 8
𝐑𝐀𝝆𝒂 = 𝒅 𝟏𝑨𝒔𝑨ቀ𝝆𝒂𝝆𝒔−𝟏ቁ+𝟏 − 𝟏൩+ 𝒙
Where:
R: measured resistance
A: electrode area.
As: brain slice area
a: ACSF resistivity
s: slice resistivity
x: electrode separation
d: slice thickness
Slice ACSF
s a
RA/a (m)
x (m)
![Page 9: 13.15 o14.2 m elbohouty](https://reader035.vdocuments.mx/reader035/viewer/2022062418/5550b6afb4c905ff618b4ba9/html5/thumbnails/9.jpg)
Measurement of resistance (R) against different separation of electrodes (x)
12 April 2023© THE UNIVERSITY OF WAIKATO 9
-0.01
0
0.01
0.02
0.03
0.04
0.05
0.06
-0.01 0 0.01 0.02 0.03 0.04 0.05 0.06
RA
/a
(m)
x (m)
ACSF only
ACSF with real slice
![Page 10: 13.15 o14.2 m elbohouty](https://reader035.vdocuments.mx/reader035/viewer/2022062418/5550b6afb4c905ff618b4ba9/html5/thumbnails/10.jpg)
The measured conductivity is affected by the uncertainty of y-intercept and….
12 April 2023© THE UNIVERSITY OF WAIKATO 10
• Slice surface area (As) and ACSF resistivity (a) was studied• 0.0 - 0.7 S/m
y-intercept electrodes surface area (A)
![Page 11: 13.15 o14.2 m elbohouty](https://reader035.vdocuments.mx/reader035/viewer/2022062418/5550b6afb4c905ff618b4ba9/html5/thumbnails/11.jpg)
The measured conductivity is affected by the uncertainty of ...
12 April 2023© THE UNIVERSITY OF WAIKATO 11
ACSF resistivity (a) electrodes surface area (A)
• Also slice surface area (As) was studied• 0.5 – 0.7 S/m
![Page 12: 13.15 o14.2 m elbohouty](https://reader035.vdocuments.mx/reader035/viewer/2022062418/5550b6afb4c905ff618b4ba9/html5/thumbnails/12.jpg)
Next Step ..• More accurate measurements using...
12 April 2023© THE UNIVERSITY OF WAIKATO 12
Advantages:• Electrodes will be used as a cutters so the brain slice area will
equal the surface area of the electrodes • Ag/AgCl electrodes are more efficient with measurements • The random and systematic error in the electrodes separation will
be minimizedDisadvantages:• The brain slice folding• The tube leakage of ACSF and many other limitations
![Page 13: 13.15 o14.2 m elbohouty](https://reader035.vdocuments.mx/reader035/viewer/2022062418/5550b6afb4c905ff618b4ba9/html5/thumbnails/13.jpg)
2. 2D Electrical conductivity by4 Cylindrical electrodes
12 April 2023© THE UNIVERSITY OF WAIKATO 13
![Page 14: 13.15 o14.2 m elbohouty](https://reader035.vdocuments.mx/reader035/viewer/2022062418/5550b6afb4c905ff618b4ba9/html5/thumbnails/14.jpg)
12 April 2023© THE UNIVERSITY OF WAIKATO 14
4 Tiny Cylindrical electrodes:
• The difference is 1 %
![Page 15: 13.15 o14.2 m elbohouty](https://reader035.vdocuments.mx/reader035/viewer/2022062418/5550b6afb4c905ff618b4ba9/html5/thumbnails/15.jpg)
Defining equation in 2D
12 April 2023© THE UNIVERSITY OF WAIKATO 15
Where:
: is the fluid conductivity
I: the measured current.
D: the depth of the fluid
: the voltage
r1: distance between Iin and V2.
r2: distance between Iout and V2.
r3: distance between Iin and V1.
r4: distance between Iout and V1.
For the ACSF we expect the relationship:
![Page 16: 13.15 o14.2 m elbohouty](https://reader035.vdocuments.mx/reader035/viewer/2022062418/5550b6afb4c905ff618b4ba9/html5/thumbnails/16.jpg)
12 April 2023© THE UNIVERSITY OF WAIKATO
b
d
where:
z = effective measured impedance of the tissue
b = separation between the two voltmeter electrodes
d = separation between the inward and the outward current electrodes
3. 3D Electrical Conductivity
16
![Page 17: 13.15 o14.2 m elbohouty](https://reader035.vdocuments.mx/reader035/viewer/2022062418/5550b6afb4c905ff618b4ba9/html5/thumbnails/17.jpg)
Multielectrode Array
We place the brain slice on a commercially available multielectrode array (MEA) consisting of 60 three-dimensional platinum electrodes.
12 April 2023© THE UNIVERSITY OF WAIKATO 17
1.6 mm 20 m
![Page 18: 13.15 o14.2 m elbohouty](https://reader035.vdocuments.mx/reader035/viewer/2022062418/5550b6afb4c905ff618b4ba9/html5/thumbnails/18.jpg)
Options of 4 point electrodes:
• Not suitable because: the distances or they are mechanically unstable
• The difference range from 2% up to 25 %
12 April 2023© THE UNIVERSITY OF WAIKATO 18
5 mm
1 mm
2 mm
![Page 19: 13.15 o14.2 m elbohouty](https://reader035.vdocuments.mx/reader035/viewer/2022062418/5550b6afb4c905ff618b4ba9/html5/thumbnails/19.jpg)
Conclusion:
• 1D is the most encouraging.
• The conductivity ranges from 0 to 0.7 S/m which is consistent with Gabril et al. (2009) review.
12 April 2023© THE UNIVERSITY OF WAIKATO 19
![Page 20: 13.15 o14.2 m elbohouty](https://reader035.vdocuments.mx/reader035/viewer/2022062418/5550b6afb4c905ff618b4ba9/html5/thumbnails/20.jpg)
What is the problem?
mouse brain slices
12 April 2023© THE UNIVERSITY OF WAIKATO 20
1 cm
![Page 21: 13.15 o14.2 m elbohouty](https://reader035.vdocuments.mx/reader035/viewer/2022062418/5550b6afb4c905ff618b4ba9/html5/thumbnails/21.jpg)
• Is there a link between seizure activity and electrical conductivity?
• Can we measure changes in electrical conductivity of mouse cortex just before, during and after seizure-like events.
12 April 2023© THE UNIVERSITY OF WAIKATO 21
Further work:
![Page 22: 13.15 o14.2 m elbohouty](https://reader035.vdocuments.mx/reader035/viewer/2022062418/5550b6afb4c905ff618b4ba9/html5/thumbnails/22.jpg)
12 April 2023© THE UNIVERSITY OF WAIKATO 22
Thank you
Thanks to my friends in the University of Waikato Cortical Modelling Group
THE UNIVERSITY OF WAIKATO
INTERNATIONAL DOCTORAL SCHOLARSHIP
![Page 23: 13.15 o14.2 m elbohouty](https://reader035.vdocuments.mx/reader035/viewer/2022062418/5550b6afb4c905ff618b4ba9/html5/thumbnails/23.jpg)
12 April 2023© THE UNIVERSITY OF WAIKATO 23
The importance of conductivity
• Neurons communicate electrically through gap junctionsgap junctions
• Neurons touch
• A conductive channel through their two membranes
• Ions can flow, implying electrical conductivity
• Is this effect measurable?
![Page 24: 13.15 o14.2 m elbohouty](https://reader035.vdocuments.mx/reader035/viewer/2022062418/5550b6afb4c905ff618b4ba9/html5/thumbnails/24.jpg)
12 April 2023© THE UNIVERSITY OF WAIKATO 24
Gap junctions and seizures
• Gap junction blockade increases the frequency and amplitude of seizure events in rat and mouse brain slices
• Voss et al. (2009). Epilepsia, 50(8), 1971 – 1978.
• Voss et al. (2010). European Journal of Pharmacology 643, 58 – 62.
•Our questions:
• Can we measure changes in electrical conductivity due to opening / closing of gap junctions?
• Is there a link between seizure activity and electrical conductivity?
![Page 25: 13.15 o14.2 m elbohouty](https://reader035.vdocuments.mx/reader035/viewer/2022062418/5550b6afb4c905ff618b4ba9/html5/thumbnails/25.jpg)
Modelling:The approximate calculation our equation is supported by more accurate computer modelling of the electric fields between the three-dimensional electrodes using COMSOL Multiphysics. We have used COMSOL Multiphysics to investigate electric field between the array.
12 April 2023© THE UNIVERSITY OF WAIKATO 25
Modeling shows very high current density on the electrodes which make them burning