Brain activity recording - EEG

 EEG -History

Electroencephalography is the measurement of electrical activity produced by the brain as recorded from the electrodes placed on the scalp. In 1875 Richard Caton from Germany discovered electrical activity of the brain by probing the surface of exposed brains (cerebral hemispheres) of animals such as Rabbits and Monkeys.

              In 1890 Adolf Beck, a Polish physiologist of Poland, Investigated the spontaneous electrical activity of the brains of rabbits and dogs. In 1920 Hans burger an Australian psychiatrist was the first to record EEG tracings from human beings. He discovered waves at 10 HZ

(Alpha waves were the first he isolated in the human EEG) .

              In 1935 Forester and Alteberger first used intra operative EEG. In 1950 Herbert jasper and

Wilder penfield developed ECoG for localisation and surgical treatment of epilepsy.

COMPONENTS OF EEG

1.Electrodes : small metal discs usually made of stainless steel ,tin,gold or silver covered with silver chloride coating. Placed on the scalp in a special position, this position is specified using the international 10/20 system. Each electrode site is labeled with a letter and a number , the letter refers to the area of the brain underlying the electrode. Even numbers denote the right side of the head and odd numbers denote the left side of the head.

2. Amplifier : it is an electronic device that increases the power of a signal. It does this by taking energy from a power supply and controlling the output to match the input signal shape but with a larger Amplitude. Human brain wave activity is too subtle to read unless the signal is amplified. These units are connected Through a USB port and transmit signals to the therapist computer.

3. Filters : The use of filters in recording and displaying EEG data is an indispensable tool in producing interpretable EEG tracings.Without filters, many segments of EEG would be essentially unreadable.The main benefit of filters is that they can appear to clean up the EEG tracing, making it easier to interpret and generally more pleasing to the eye.

4.Writing unit :The final link between the patient and legible EEG tracing is the writer. The writing unit may be replaced by a digital screen in modern EEG devices.

USES OF EEG

● To distinguish epileptic seizures from other types of spells such as Psychogenic nonepileptic seizures syncope ,Subcortical movement disorders and migraine variants.

● To characterize seizures for the purpose of treatment

● to localise the region of brain from which a seizure originates for work up of possible seizure surgery.

● To monitor for nonconvulsive seizures or nonconvulsive status epilepticus.

● To differentiate organic encephalopathy or delirium from primary psychiatric syndromes such as catatonia.

● Monitoring depth of anaesthesia

● As an indirect indicator of cerebral perfusion in carotid endarterectomy.

● To serve as an adjunct test of brain death.

● Determine the level of brain function in people who are in coma .

● Used to investigate other conditions such as head injuries, brain tumors, dementia, hemorrhage.

ADVANTAGES

EEG Has several strong sides as a tool for exploring brain activity; its time resolution is very high. EEG measures the brain’s Electrical activity directly while the other methods record changes in blood flow or metabolic activity indirect markers of brain electrical activity. It can be used simultaneously with FMRI so that high temporal resolution can be recorded at the same time as high spatial resolution data. EEG can be recorded at the same time as in MEG so that data from these complementary high time resolution techniques can be combined.

LIMITATIONS OF EEG

EEG has several limitations. Most important is its poor spatial resolution. EEG is most sensitive to a particular set of postsynaptic potentials. those which are generated in the superficial layers of the cortex on the crests of gyri directly abutting the skull and radial to the skull.Dendrites which are deeper in the cortex inside sulci are in midlane or deep structures or produce currents which are tangential to the skull have far less contribution to the EEG signal.The meninges, cerebrospinal fluid and skull smear the EEG signal obscuring its intracranial source.it is mathematically impossible to reconstruct a unique intracranial current source for a given EEG signal as some currents produse potentials that cancel each other out. This is an inverse problem.

CONCLUSION

Brain activity can be recorded by electroencephalography.it detects the abnormalities in brain waves.sometimes EEG is described as abnormal but does not specify the abnormality or disease.in general EEG is the best method to diagnose a disease and it is better than its alternatives for many reasons, and there are almost no low cost alternatives to EEG. Brain stimulation can be used to treat brain abnormalities such as Parkinson's disease,dystonia and psychiatric conditions.brain lesions are damages to brain cells.it is permanent condition so with medication can reduce the symptoms.through radiation therapy tumors are treated.