MagnetoenCephaloGraphy (MEG) is a technique for mapping brain activity by recording magnetic fields produced by electrical currents occurring naturally in the brain, using very sensitive magnetometers.

1. Seminar On The Topic:
“MagnetoEncephaloGraphy”
In this Presentation of mine; I’ll introduce you regarding-
 M.E.G.- Overview.
 Origin of the Signal.
 Entire Setup of the Process.
 S.Q.U.I.D.S.
 JosephSon Junctions.
 Detecting Brain Activity.
 Magnetic Shielding.
 Benefits of Employing this Technology.
 Future Scope of M.E.G. Technology.

2. Just An Overiew….. What Actually It Is…??
MagnetoenCephaloGraphy (MEG)
is a technique for mapping brain
activity by recording magnetic
fields produced by electrical
currents occurring naturally in
the brain, using very
sensitive magnetometers.
 M.E.G. Signals were first
measured using a copper
induction coil as the detector.

3. V
Skull
CSF
Tissue
MEG
EEG
B
- Non-Invasive Measurement.
- Direct Measurement.
Scalp
Recording
Surface
Current
Flow.
Orientation
of Magnetic
Field.
Origin of the signal

4. Actual Phenomenon:
 Currents in Neurons create very tiny Magnetic
Fields.
 MEG uses SQUIDs to detect these Magnetic
Fields.
 Magnetic Signals from the brain are only a few
fT in strength.
 Needs a Magnetically Shielded Room.

5. Entire Setup of the Process

6. S.Q.U.I.D.S….
 Superconducting Quantum
Interference Devices.
 Superconducting material is
niobium or lead alloy with
Gold/Indium.
 Cooled to low temperature
with either liquid He (4K) or N
(77K).
 Manufactured at NIST in
Boulder.
 Noise levels about
3fT*Hz(-1/2).

7. Axial Gradiometer
Recording Surface
Neuronal Source
Capturing The Signal:
 For a gradiometer of this type, a
signal from cortex looks different
between the two coils because of
the distance between the two coils.
 A signal from far away, however,
will look similar in size to the two
coils.
 This gradiometer principle can help
further with the challenging
problem of measuring small source
that exist in an electro-magnetic
environment with many large
source (subways,
elevators,computers, etc.).

8. Josephson Junctions
 Two superconductors separated by a thin insulating
barrier:
 A small current will tunnel across the barrier:
 The constant current Ic depends on temperature and
magnetic field.
 SQUIDS measure fractions of the phase difference in
terms of the flux quantum h/2e.

9. Detecting Brain Activity
 50,000 neurons need to fire to generate a
Readable signal.
 Neurons near the outside of the brain generate
the strongest signals.

10. Magnetic Shielding
 Rooms for MEGs have walls made of Aluminum and
MU-metal (a type of nickel-iron alloy with extremely
high magnetic permeability).
 Aluminum shields from high frequency Noise.
 MU-metal shields from low frequency noise.

11. Let The Pictures
Speak:

13. Sensor layout: recording from 160 channels
Response peak at 98ms after onset of an auditory stimulus,
in the left and right temporal lobes.

14. What is the benefit of using MEG?
EEG
MEG
-As high temporal resolution as EEG …
… but much easier and quicker to set up (kids, patients)
-Magnetic fields are not differentially attenuated ….
…. easier to get a reasonable estimate of source over time.
- Sensitivity to within-subjects effects.

15.  MEGs are used in research to measure the
time course of brain activity.
 MEGs can detect Epilepsy, as well as detect
areas of the brain that are most important to
avoid during surgery.
 Does not depend on head geometry like EEG.
 Magnetic fields decay faster over distance
than electric fields.
Few Other Notable PointS-

16. MEG is a technique that allows you to
(i) record brain activity directly, with
excellent temporal resolution (ms)
(ii) design within-subjects experiments and
evaluate single-subject data
(iii) test models of cognitive processes and
evaluate how these models map on to the brain.
SummmariSation:

17. THANK YOU ALL..
Presented By:
Anuj Malik.
Roll No. MT-2112607
[E.E.E.] M.Tech.
FOR YOURS PRECIOUS
TIME....
Any
Query