Tang Wei: Electroencephalogram introductory strategy, collect it now!

In the face of EEG sometimes it is inevitable to feel helpless, and the undulating waveform is confusing

1.

Electroencephalogram (EEG) is a figure obtained by magnifying the spontaneous biopotential of the brain from the scalp by a sophisticated electronic instrument, and the spontaneous, rhythmic electrical activity

There are many types of EEG, mainly including: conventional EEG, dynamic EEG, video EEG, stereotactic EEG and so on

Second, the basic principle of EEG

Electroencephalogram according to the electrode placed in the skull or outside the skull, can be divided into scalp electrode electroencephalogram, intracranial electrode electrode electroencephalogram, this guide mainly introduces the scalp electrode electrode electrocephalogram

EEG is the same as electrocardiogram, electromyography of the use of instruments to record electrical activity, scalp electrode electroencephalogram is from the scalp to magnify the spontaneous electrical activity of the brain to record and obtain a graphic

EEG signals go through amplifiers (because EEG signals are very weak, mV or uV level, and have to decay the skull and scalp, so they need to be magnified millions of times before they can be displayed), filters (to reduce interference) and finally form the pattern

The transverse axis of the EEG

The EEG graphics we usually see are not similar to the ECG, in fact, the EEG and the ECG principle are similar

The ECG between the two longitudinal lines (1mm) represents 0.

EEG is the same reason, generally used paper or recording speed is (paper speed corresponds to the horizontal axis) 30mm / s, that is to say, 30mm = 1s, and the sensitivity of the EEG (vertical axis) is uv / mm, generally used is 10 uv / mm, that is to say, 1mm = 10 uv

There will be a ruler in the lower right corner of the EEG (similar to the scale bar on the map) that tells you how long the horizontal axis is 1s and how long the vertical axis is 1uv

How are the electrodes placed?

The placement of electrodes in the scalp electrode electrodes is routinely carried out using the International 10-20 system, consisting of 19 recording electrodes and 2 reference electrodes

From the root of the nose 10% backwards is FPz (frontal pole midline), from FPz backwards every 20% of the electrode position, followed by Fz (frontal line), Cz (central centerline), Pz (top midline) and Oz (occipital midline), Oz and occipital outer tuberosity spacing of 10%.

The amphora anterior concave line is 10% away from the anterior concave of the left ear at the position of the T3 (left middle temporomal) electrode, and then every 20% to the right is placed, C3 (left center), Cz, C4 (right center) and T4 (right middle temporom), and T4 is 10%

10% from FPz to the left is FP1 (left frontal pole), and one electrode is placed every 20% from FP1 backwards, followed by F7 (left anterior temporom), T3 (left median temporom), T5 (left posterior temporomy) and O1 (left occipital), of which T3 is the intersection of this line and the anterior concave line of both ears, and O1 is 10% from Oz; The right temporal correspondence is FP2 (right anterotemporal pole), F8 (right anterior temporom), T4 (right mediatal temporom), T6 (right posterior temporal), O2 (right occipital)

Third, how to combine the leads of the EEG?

Commonly used lead combinations are ear pole reference leads, average reference leads, and bipolar reference leads

(1) Otopole reference lead: The ear pole reference lead adopts the left and right lobes as the G2 end, which are marked as A1 and A2
respectively.

(2) Average reference lead: Each recording electrode of the scalp is connected in series with a resistor, and then paralleled, after this treatment, the potential of each point of the scalp is weakened and averaged, and the potential is close to zero, as the average reference electrode (abbreviated as AV).

Fp1, F3, Fp2, F4.
.
.
As the G1 terminal, the average reference electrode (AV) is the G2 terminal, which forms Fp1-AV, F3-AV.
.
.
Fp2-AV、F3-AV.
.
.
.
.
.
The average reference lead of each lead combination forms an EEG
of the lead.

(3) Bipolar lead: Bipolar lead is an EEG formed by using the two recording electrodes as G1 and G2 terminals
respectively.

4.
What does the EEG look at?

(1) Frequency: The concept of frequency can be understood by everyone, in the EEG refers to the number of times
the same brain wave is repeated within 1s.
For example, in the following figure, assuming that there is 1s between the two vertical lines, we count how many waves (8) there are in the middle of the two vertical lines, and the frequency is how much (8Hz).

(2) Volatility

The amplitude is also easy to understand, the amplitude of the brain wave is the vertical height of the brain wave peak to the trough, reflecting the potential difference between the two electrodes
.

In an EEG with a sensitivity of 10 μV/mm, if the vertical height of a brain wave is 7 mm, its amplitude is 70 μV
.

In EEG, according to the height of the amplitude can be divided into several levels, for adult EEG:

• < 25μV is called low amplitude;

• 25-75μV is called medium amplitude;

• 75-150μV is called high amplitude;

• > 150μV is called a very high amplitude
.

(3) Phase: polarity of spike wave and spike wave: the peak recorded down becomes a normal phase spike wave and a positive phase sharp wave, respectively; The upward crest becomes a negative phase spike wave and a negative phase sharp wave
, respectively.

(4) Regulation: Regulation refers to the regularity and stability
of the basic frequency of brain waves.

The frequency in the same part is stable, the difference can not be more than 1 time / s, if more than 2 times / sec is regarded as the adjustment difference
.

The left and right parts of the same place should not be more than 0.
5 times / s, if more than 1 time / sec is regarded as the adjustment difference
.

(5) Amplitude modulation: refers to the law
of amplitude change.
Normal high and low, change every 3-5 seconds, such as spindle shape is good, no change and amplitude is uneven, loss of regularity, for poor
amplitude modulation.

5.
Electroencephalogram during the adult waking period

(1) α wave rhythm

α rhythm is the 8-13Hz rhythm that appears in the back of the head in the waking state, most people 9-10Hz, the amplitude is 10-100μV, the basic rhythm of normal people, generally the highest
amplitude in the occipital area.
It is easy to appear with closed eyes and a relaxed state, and the sides are roughly symmetrical
.
It is the most important index for analyzing the background activity of EEG, and is closely related
to the state of brain function and development.

Waves that are faster than α wave are called fast waves; A wave that is slower than α wave is called a slow wave
.

In the same examiner, the α inhibition that occurs in the open state

(2) β activities

β activity refers to fast-wave activity with a frequency greater than 13-25Hz, which is the main component of normal adult sober EEG, widely distributed, with a amplitude of 5-20 μV and no more than 50 μV
.
Not affected by the struggle to close the eyes
.
The activities of the frontal, temporal and central β are the most obvious
.
β waves are the main manifestation of electrical activity in the cerebral cortex when it is in a state of tension and agitation
.

Many sedative-hypnotic drugs (e.
g.
, barbiturates, benzodiazepines, chloral hydrate, etc.
) can increase the amplitude of β activity, thus making the amount of β activity obvious
.

(3) The θ wave frequency is 4-7Hz, the amplitude is 20-40μV, which is found in the apical region and the frontotemporal region, and the normal person does not exceed 10%-15%.

Generally not rhythmic
.
During light sleep α wave disappears, and the theta wave appears on both sides of the
forehead first.

Fulminant theta rhythm on both sides – deep subcortical lesions
.

The often focal theta rhythm is abnormal
.

In early childhood, EEG frequencies are slower than in adults, and theta waves
are generally often seen.

EEG shows extensive and moderately abnormal EEG, with total conduction dominated by
θ waves.

(4) δ waves: the frequency is below 4Hz, the amplitude is 10-200μV, and normal adults will hardly have δ waves in the awake state, but δ waves can appear in the sleep state, and the EEG frequency in infancy is slower than that of young children, and δ waves
can often be seen.

Frequent focal δ waves, regardless of age, are abnormal—cortical lesions
.

Bilateral fulminant δ rhythm – subcortical lesions
.

It is generally believed that slow waves (theta waves or δ waves) of high amplitude may be the main manifestation
of electrical activity when the cerebral cortex is in a suppressed state.

The theta wave or δ wave is a slow wave and is found during normal sleep in
infants to children and adults.
Localized slow waves are seen in localized EPI, brain tumors, brain abscesses, and softening foci
of cerebral infarction.

Diffuse slow waves are seen in infection, poisoning, hypoglycemia, intracranial hypertension, and various comas
.

Low volatility of slow activity – inhibition deepens
.

For example (sporadic Creutzfeldt-Jakob disease)

Patient, female, 62 years old, housewife
.
Due to "mental behavior abnormalities for 3 months, aggravated by 20d" on September 2, 2010 in the hospital
.
In early June 2010, the patient appeared taciturn without obvious triggers, often sitting alone in a daze, with insomnia, and did not seek medical attention
.

In mid-August, he had obvious memory loss, often forgot his family name, and was first treated at the local county people's hospital, and the cranial MRI showed lacunar cerebral infarction, and there was no abnormality in the EEG, and there was no improvement
after treatment (specific drug name and dosage unknown).

August 22 after going out did not see home, the family called the police to find it, after not recognizing the family, there are hands groping in sleep, diagnosed in the local hospital as "cerebral infarction, vascular dementia", given ginkgo biloba extract injection, citicoline and other drugs treatment is ineffective, so come to our hospital for treatment, outpatient treatment with "dementia to be checked"
.
There was no fever, no headache and dizziness, no nausea, vomiting or limb twitching during the course of the
disease.

MRI of the patient's skull showed bilateral cerebral cortex, insula cortex, caudal nucleus, crustal nucleus T2 weighted image, Flair, DWI high signal, typical "lace" sign of the DWI sequence cerebral cortex, slightly lower signal and equal signal of T-weighted image, A:T2WI sequence, B:Flair sequence, C:DWI sequence, D:T1WI sequence
.

On September 3, the conventional EEG showed that each brain region had a short to long-range θ rhythm of 4 to 6 Hz, 20 to 70 μV and a high amplitude δ rhythm, with more on the right side, in which there were scattered to short-range voltage α activity and low voltage β waves, showing periodic three-phase waves, indicating moderate to severe abnormal EEG
.

Past history: history of denial of hypertension, diabetes, no history of smoking and drinking, history of denial of trauma and surgery, no history of
blood transfusion.
There is nothing special
about family history.

Physical examination for admission: body temperature 36.
5 ° C, pulse 70 times / min, breathing 20 times / min, blood pressure 150 / 80 mm Hg
.

Neurological examination: clear consciousness, indifferent expression, less speech
.
Memory, orientation, computing power loss, "100-7=?" Can't answer
.
The double pupils are isocircular and have a diameter of about 3 mm, and the light response is sensitive
.
Limb muscle strength level V, normal
muscle tone.
Bilateral tendon reflexes are symmetrical and normal
.
Pathological reflexes are not precipitated
.
Masonic exercise, sensory examination is not cooperative
.
Meningeal irritation signs are negative
.

CSF examination after admission: pressure 150mmH2O (1mmH2O = 0.
0098kPa), protein 0.
52g/L (normal 0.
15~0.
45g/L), sugar 5.
1mmol/L (normal 2.
2~3.
9mmol/L), chloride 123mmol/L (normal 119~129 mmol/L), immunoglobulin A5.
83mg/L (normal 0.
00-5.
00mg/L), immunoglobulin G, M are in the normal range, acid staining, ink staining negative, no malignant tumor cells
.
Negative serum antibody to HIV and treponemal antibody to Syphilis
.

Dementia syndrome is diagnosed after admission, Creutzfeldt-Jakob disease (CJD) is possible
.
The treatment of drugs such as Piracetam and Citicoline, and hyperbaric oxygen therapy at the same time, the effect is poor, and there is gradually silence, ignoring others' speeches, going to the toilet, dressing, eating, etc.
need family assistance
.

On 10 September, the patient developed an episodic convulsion of the extremities lasting a few seconds to minutes, 5 to 10 seizures per day, considering seizures, treatment with phenobarbital sodium and diazepam, and intermittent seizures
.

The ambulatory EEG examination on September 13 showed that there were θ rhythms and δ activities in various brain regions, with scattered low-voltage α waves and β waves, and paroxysmal sharp slow waves and spinous slow waves
.

The patient was automatically discharged from the hospital
on 16 September.
Telephone follow-up after discharge: After discharge, he went to the 307th Hospital of the People's Liberation Army and the Xuanwu Hospital of Capital Medical University, and was diagnosed with CJD (whether the family of the patient did the relevant examination was unclear), and then gave up treatment and went home
.
The patient died
on 20 October 2010 after frequent convulsions and urinary incontinence outside the hospital.

The above strategy mainly explains the introductory knowledge of EEG interpretation, and how to interpret abnormal EEG is to be explained
next time.
I hope that everyone will continue to make steady progress
on the foundation of mastering the basic knowledge.