EEG, NCV, ECoG,

1. GURUGRAM
UNIVERSITY
M.Sc Neuroscience

2. METHOD OF INVESTIGATING:
ELECTROPHYSIOLOGICAL
PROCEDURES
SACHIN M.SC NEUROSCIENCES

4. ELECTROENCEPHALOGRAPHY(EEG)
 EEG stands for Electroencephalography
 It's record the electrical activity of brain
 During an EEG test, small electrodes like cup or disc type are placed on the
scalp•
 They pick up the brain's Electrical signals and send them to a machine called
Electroencephalogram.
 It records the signals as wavy lines on to a computer screen or paper in order
of microvolt.
 EEG waves frequency range = 0.1 to 100
amplitude = 2 to 200 micro volt.

5. HISTORY
 In 1929, a German psychiatrist Hans Berger invented a machine that
could broad patterns of brain electrical activity.
 It is called Electroencephalograph which monitor the electrical
activity of the brain by means of recording electrodes at the surface
of the scalp.

6. PHYSIOLOGY BASIS OF EEG
 EEG is the summation of excitatory and inhibitory post synaptic potentials

8. PROCEDURE
 A standard non-invasive EEG takes about 1 hour.
 The patient will be positioned on a padded bed or table, or in comfortable
chair.
 To measure the electrical activity in various part of the brain, a nurse or EEG
technician will attach16 to 20 electrodes According to 10-20 international
system) to the scalp.
 The brain generates electrical impulses that these electrodes will pick up.
Then a temporary glue will be used to attach them to the skin, no gain will be
involved.

9. Electrode placement

10. Application
 Epilepsy
 Seizure
 Brain death testing
 Various brain Cancer, sleep disorders (insomnia, OSA, narcolepsy).
 Dementia
 Stroke
 Head injury

11. Normal EEG

12. Advantages
 Non – invasive and harmless
 Lower costs
 Portable
 High temporal resolution
Disadvantages
 High noise ratio
 Not very exact measuring
 Often takes a long time to connect
a subject to EEG

13. What is stereoelectroencephalography
(SEEG)?
 Stereoelectroencephalography (SEEG) is a minimally invasive surgical procedure
that is used to identify areas of the brain where epileptic seizures originate.
 A SEEG can find seizure sites deep in the brain that a regular
electroencephalography (EEG) test may not reach. It covers both sides
(hemispheres) of the brain.
 Intracerebral electrodes are placed within the desired brain areas to record the
electrical activity during epileptic seizures, thus contributing to define with
accuracy the boundaries of the "epileptogenic zone", i.e.
 the area of brain generating the seizures which should be eventually surgically
resected to achieve freedom from epileptic seizures.
 Potential risks of the procedure, accounting for less than 1% of cases, include
brain hemorrhage and infection, which can lead to permanent neurological
impairment or death.

14. WHY SEEG
 To improve outcomes To help those patients who
are not candidates for SDG(subdural grid):-
1.DRE( Drug resistance epilepsy)
2.Bilateral lesions Deep lesions (insula,
cingulate)
3.MRI-negative cases (in particular fronto-
parietal and frontotemporal)

16. Normal SEEG Abnormal SEEG

17. LESSONS LEARNED
 Our series shows that resective surgery leads to
continuous seizure freedom in a group of patients with
complex and severe pharmaco-resistant epilepsy following
SEEG evaluation.
 In addition, up to 58% of patients achieved seizure
freedom at last follow up.
 Our results suggest that SEEG is as effective in patients
with frontal and temporal lobe epilepsy with or without
MRI identified lesions.

18. EVENT- RELATED POTENTIALS (ERPs)
1.EEG is continuous electrical activity recorded from the
scalp.
2. An Event Related Potentials (ERP) is the averaged
electrical activity time locked to a stimulus, e.g., click
or flash.
3. ERPs can be auditory, visual, or somatosensory.
Evoked Potentials are a subset of ERPs, e.g., AEP, VEP
and SEP.
4. EEG/ERPs are easy to record, non-invasive and
relatively inexpensive.

19. ERPs can be used in diagnosing: hearing problems, brain-
stem lesions epilepsy, visual system disorders (especially
before birth and in new born)

20. Clinical Instrumentation

21. Clinical Auditory Evoked Potentials (ABR
and AEP)

22. Clinical Visual Evoked Potentials (VEPS)

23. Clinical Somatosensory Evoked
Potentials (SEPs)

24. ELECTROCORTICOGRAPHY (ECOG)
 Electrocorticography (ECOG), or intracranial encephalography (iEEG), is a
type of electrophysiological (electrical properties of biological cells) that uses
electrodes placed directly on the exposed surface of the brain to record
electrical activity from the cerebral cortex.
 In contrast, conventional electroencephalography (EEG) electrodes monitor
this activity from outside the skull.
 ECOG may be performed either in the operating room during surgery (intra-
operative ECOG).Because a craniotomy (a surgical incision into the skull in
which a bone flap is temporarily removed from the skull to access the brain)
is required to implant the electrode grid, ECOG is an invasive procedure.
 •Invasive- tendency to spread very quickly and undesirably or harmfully.

25. ELECTROPHYSIOLOGY BASIS
 ECoG signals are composed of synchronized postsynaptic
potentials (local field potentials), recorded directly from
the exposed surface of the cortex.
 The potentials occur primarily in cortical pyramidal cells,
and thus must be conducted through several layers of the
cerebral cortex, cerebrospinal fluid (CSF), pia mater, and
arachnoid mater before reaching subdural recording
electrodes placed just below the dura mater (outer
cranial membrane).

26. Why we do ECOG?
 To determine the site and borders of epileptogenicity and offers predictive
information about post surgical outcome.

28. Magneto encephalography (MEG)
 MEG signal were first measured by David Cohen in 1968
 Magnetoencephalography (MEG) is a non-invasive
neurophysiological technique that measures the magnetic
fields generated by neuronal activity of the brain using
very sensitive magnetometer.
 The spatial distributions of the magnetic fields are
analyzed to localize the sources of the activity within the
brain, and the locations of the sources are superimposed
on anatomical images, such as MRI, to provide information
about both the structure and function of the brain.

29. PHYSIOLOGY BASIS
 At the cellular level, individual neurons in the brain have electrochemical
properties that result in the flow of electrically charged ions through a cell.
 Electromagnetic fields are generated by the net effect of this slow ionic current
flow.
 While the magnitude of fields associated with an individual neuron is
negligible, the effect of multiple neurons (for example, 50,000 -
100,000)excited together in a specific area generates a measurable magnetic
field outside the head.
 These neuron magnetic signals generated by the brain are extremely small-a
billionth of the strength of the earth's magnetic field.
 Therefore, MEG scanners require superconducting sensors SQUID
 MEG scanners detect magnetic fields produced by the brain electrical activity.

32. MEG INDICATION
 Other noninvasive tests do not adequately localize the epileptogenic zone
 The MRI is normal.
 More refined delineation of the seizure focus
 Multiple or extensive lesions are present
 Guidance for placement of intracranial electrodes is required.

33. MEG ADVANTAGES
 MEG provides timing as well as spatial information about brain activity.
 MEG signals are obtained directly from neuronal electrical activity.
 MEG signals are able to show absolute neuronal activity
 MEG does not make any operational noise
 Adaptable to mapping many functions- sensory, motor-language, memory
cortex

34. INTRAOPERATIVE NEUROPHYSIOLOGY
MONITORING (IONM)
 Intraoperative neurophysiological monitoring (IONM) or intraoperative
neuromonitoring is the use of electrophysiological methods such as
electroencephalography (EEG), electromyography (EMG), and evoked
potentials to monitor the functional integrity of certain neural structures
(e.g., nerves, spinal cord and parts of the brain) during surgery.
 The purpose of IONM is to reduce the risk to the patient of iatrogenic damage
to the nervous system, and/or to provide functional guidance to the surgeon
and anesthesiologist.

36. THANK YOU

37. Question
 What is EEG test used to diagnose?
 Who is discovered EEG test?
 Types of EEG wave?
 Which type potential record in EEG?
 What is event related potentials?
 Indication of ERPs?
 What is different between ECoG and SEEG?
 Who is measured first time MEG signal?
 What is IONM?
 What is different between IONM and ERPs?