Review Article DOI: 10.18231/2394-2126.2018.0068 Indian Journal of Clinical Anatomy and Physiology, July-September, 2018;5(3):291-294 291 Cortical generators of normal electroencephalographic waveforms: A literature review Pooja Ojha 1,* , Nitin Pandey 2 , Seema Singh 3 1 Assistant Professor, 2 Associate Professor, 3 Professor, Dept. of Physiology, Era’s Lucknow Medical College, Lucknow, Uttar Pradesh, India *Corresponding Author: Email: drpojha@gmail.com Received: 15 th December, 2017 Accepted: 5 th April, 2018 Abstract Introduction: EEG is a useful, noninvasive, safe technique to study the electrical activity of brain in various physiological and pathological conditions like alertness, sleep, seizure activity. Normal brain rhythms, the electroencephalogram (EEG) represents the electrical activity of brain as recorded through the metal electrodes applied over scalp. An insight to the possible source of EEG, various rhythms and its activation during certain maneuvers can give a better understanding to its applications. Materials and Methods: Number of electronic database, as well as library resources were searched for related references included in published literature till 2017, using following key words ‘cortical’, ‘electroenchephalogram’,’ EEG’,’ EEG Rhythm’,’ EEG wave’, ‘alpha wave’,’ beta wave’,’ theta wave’,’ delta wave’. Those which were related to our subject were included in the review. Results: Of the total number of studies we have finally included 35 studies from search results. These are mentioned in the references. Conclusion: Beta, Alpha, Theta & Delta are produced from various regions of the brain, including cortical & thalamic networks, hippocampus, reticular networks and so on. The rhythm of EEG can be correlated with the level of activation of the brain, with beta wave being produced during alert state and delta wave being produced during deep sleep. Interventions like hyperventilation and photic stimulation can be used to increase the diagnostic yield of EEG. It has been seen that sex-related differences do exist in the degree of lateralization of hemispheric function. Keywords: Electroencephalogram, Brain waves, Cortex, Thalamus, EEG. Introduction The electroencephalogram (EEG) is the record of electrical activity of brain obtained through the metal electrodes applied over scalp with the help of conductive paste. 1 It is the difference in voltage between two different recording locations plotted over time. Electroencephalographic recording is a non- invasive procedure which can be repeated on the patients without any risk. Introduction of EEG to the pool of investigations for brain has been a boon to mankind. It has helped researchers to know a lot about the functioning of brain in health and disease. An insight to the possible source of EEG, various rhythms and its activation during certain manoeuvres can give a better understanding to its possible applications. This work intends to provide a literature review from past and recent times which will throw light upon the foresaid queries. Materials and Methods Number of electronic database, as well as library resources were searched for related references included in published literature till 2017, using following key words ‘cortical’, ‘electroenchephalogram’,’ EEG’,’ EEG Rhythm’,’ EEG wave’, ‘alpha wave’,’ beta wave’,’ theta wave’,’ delta wave’. Manual search was also done to find related references from books and journals. Those studies which were duplicated or had irrelevant content or failed to provide any detail were excluded. 35 studies, which had relevant content to our subject were finally included in the review. Discussion This section is described in four subheadings. First part of article presents the details of origin of EEG, second section has details of classification of brain waves. Followed by EEG during sleep and various interventions in third subheading and lastly variation in EEG with gender. Origin of EEG: It was Caton who, more than a hundred years ago found that there is electrical activity occurring in the brain. 2 In the year 1920, Berger demonstrated that it is possible to record this electrical activity from the surface of the brain with the help of Electroencephalogram (EEG). Only after this EEG became popular as a modality to study the normal and abnormal functioning of brain. 3 The Electroencephalography reached a new stage when in the year 1934, two renowned scientists Adrian and Matthews confirmed the concept of human brain waves in a paper and they were also successful in observing oscillations with a frequency of 10-12 Hz. It was later termed as “alpha rhythm”. 4 Classification of Brain Waves: Electroencephalographic rhythms are defined as regularly recurring waveforms of similar shape and duration. These rhythms have been identified since times when EEG was recorded in humans and animals. It is observed that there is intrinsic firing property in