Recording brain activity

RECORDING BRAIN ACTIVITY

1. RECORDING BRAIN ACTIVITY - ASHISH BUDHWAR

2. RECORDING ELECTRICAL ACTIVITY OF THE BRAIN The brain emits various electrical signals through the neurons. These electrical signals can be useful in the study of the functioning of the brain and its relation with the behavior of organisms. Recording of electrical signals from the brain can be obtained from the scalp by ELECTROENCEPHALOGRAPHY

3. ELECTROENCEPHALOGRAPHY It was first discovered by German psychiatrist Hans Berger in 1924. In this process, the ELECTROENCEPHALOGRAM (the measure of the electrical activity of the brain) of the human brain is recorded via a device called ELECTROENCEPHALOGRAPH. The E.E.G measures voltage fluctuations resulting from ionic current within the neurons of the brain. The fluctuations in the recording can signify different conditions in the brain and the behavior including normal activities, disease or disorder.

4. MECHANISM OF E.E.G The brain’s electrical charge is maintained by billions of neurons. Neurons are electrically charged by membrane protein that pumps ions across their membranes. Ions of similar charges repel each other. When many ions are released from many neurons at the same time, they push other ions which push further ions thus creating a wave. When this wave of ions reaches the electrodes on the scalp, a voltmeter detects the difference of voltage between the electrodes. An E.E.G is a recording of these voltages over time.

5. E.E.G The scalp EEG signal reflects the sum of electrical events throughout the head. These events include action potentials and postsynaptic potentials as well as electrical signals from the skin, muscles, blood, and eyes. The utility of EEG as a research and diagnostic tool rests on the fact that some EEG wave forms are associated with particular states of consciousness or particular types of cerebral pathology (e.g., epilepsy). For example, high-amplitude waves are associated with relaxed wakefulness.

6. ELECTROENCEPHALOGRAM

7. EVENT RELATED POTENTIALS ERPs are the EEG waves accompanying some psychological activity in the background. By this method, the functioning of the brain while the psychological activity is ongoing can be ascertained. One common method of ERP is the SENSORY EVOKED POTENTIAL.

8. SENSORY EVOKED POTENTIAL It is a method of ERP in which a momentary stimulus is presented to the subject and the following change in the cortical electrical activity of the brain recorded via EEG is studied. The cortical EEG that follows the sensory stimulus has 2 component, the response to the stimulus (signal) and the ongoing background EEG activity (noise). The signal is the part of interest for researchers.

9. PROBLEMS FACED IN S.E.P The problem arises in the sensory evoked as the noise of the background EEG is often so high that the signal (response) to the stimulus gets masked. It can a like detecting a whisper in a rock concert. To reduce the noise of the background, the method of signal averaging is used. In this, first the subject’s response to a meaningful stimulus is recorded for say 1000 times. Then the computer identifies the millivolt value at each starting point then at the 1 st millisecond, then at 2 nd millisecond and so on and finds their mean and the random background EEG is cancelled out.

10. ANALYSIS OF AEPs The analysis of average evoked potentials (AEPs) focuses on the various waves in the averaged signal. Each wave is characterized by its direction, positive or negative, and by its latency.