Electroencephalography | EEG

The recording and study of electrical activity of the brain is Electroencephalography. To record the signals, the electrodes (needle electrodes) are attached on the skull of the patient. Neural depolarization occurs in brain due to stimuli from five senses and thought process. Brain waves are the summations of this neural depolarization. The voltage level on the brain surface is around 10mV. Due to propagation of signals, voltage value may range between 1 to 100µV. EEG electrodes are used to pick up these signals. During EEG, measurement electrodes are placed around frontal, temporal and occipital lobes of brain.

Evoked Potential of the Brain

When brain responds to external stimuli like light, sound, etc. they develop a potential called Evoked Potential. The various sense organs detect the evoked potential and change the electrical activity of the brain.

Anatomy of the Brain

Human brain has four lobes namely cerebrum, cerebellum, medulla oblongata and spinal cord. In our body functions like breathing, heart rate and kidney functions depends on medulla. The interconnecting area is Pons. They are responsible for face expressions and auditory system. Cerebellum is required for a person to maintain the stability and balance. Thalamus has the region for visual and auditory system. The area named Hypothalamus is responsible for emotions in our brain. Another important part of cerebrum is cerebral cortex. It has billions of neurons in it. The cerebrum has four lobes named as Frontal, Parietal, Temporal and Occipital. Frontal lobe is responsible for human intelligence. Parietal for eye movement and control. Temporal is for hearing and to store process in long-term memory. Finally, occipital is for vision of the human system.

Analysis of EEG Waveforms

The continuous electrical activity of the brain is recorded from the outer surface of the brain. The excitation level of the brain decides the intensity and pattern of this electrical activity. This results in functions like reticular activating system, which makes us to wake from sleep. In the recorded electrical potentials, we find some variations, which are Brain Waves. We have four major type of brain waves given as Alpha, Beta, Theta and Delta waves. At most, of the instance, our brain waves will be irregular and does not have regular pattern.

Alpha Wave

  • 8 – 13 Hz.
  • Alpha waves occur in the occipital region of a person. It occurs when he is awake and stays in quiet state. When he sleeps, it disappears. The wave has an amplitude of 20 – 200µV.

Beta Wave

  • 13 – 30 Hz.
  • Beta wave arises from the parietal and frontal regions of cerebrum. It can be either beta I or beta II waves. Mental activity of a person like tension, results in excited beta waves.

Theta Wave

  • 4 – 8 Hz.
  • Theta wave arises from the parietal and temporal regions of cerebrum. It occurs commonly in children. In adults, it occurs when they are depressed and frustrated.

Delta Wave

  • 0.5 – 4 Hz.
  • Delta wave occurs during deep sleep in premature babies for every 2 to 3 seconds. They occur in cortex of the brain.

analysis of ecg waveforms

About Vidya Muthukrishnan

Ms M.Vidya has been teaching professionally for the past 5 years, and is currently employed as an Assistant Professor in the Department of Instrumentation and Control Engineering at the Sri Krishna College of Technology. She has completed her B.Tech Electronics and Instrumentation from SASTRA University and M.Tech in Biomedical Engineering from VIT University Vellore.

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