Editing Brain (section)

=== Electrical activity ===
[[File:Spike-waves.png|thumb|right|alt=Graph showing 16 voltage traces going across the page from left to right, each showing a different signal. At the middle of the page all of the traces abruptly begin to show sharp jerky spikes, which continue to the end of the plot.|Brain electrical activity recorded from a human patient during an [[Epilepsy|epileptic seizure]]]]

As a side effect of the electrochemical processes used by neurons for signaling, brain tissue generates electric fields when it is active. When large numbers of neurons show synchronized activity, the electric fields that they generate can be large enough to detect outside the skull, using [[electroencephalography]] (EEG)<ref name = "Niedermeyer">{{cite book |last1=Speckmann |first1=E-J |last2=Elger |first2=CE |chapter=Introduction to the neurophysiological basis of the EEG and DC potentials |veditors=Niedermeyer E, Lopes da Silva FH |title=Electroencephalography: Basic Principles, Clinical Applications, and Related Fields |publisher=Lippincott Williams & Wilkins |year=2004 |isbn=978-0-7817-5126-1 |pages=17–31}}</ref> or [[magnetoencephalography]] (MEG). EEG recordings, along with recordings made from electrodes implanted inside the brains of animals such as rats, show that the brain of a living animal is constantly active, even during sleep.<ref name="Buzsaki">{{cite book|last=Buzsáki|first=Gyorgy |title=Rhythms of the Brain|publisher=Oxford University Press|year=2006|isbn=9780199828234}}</ref> Each part of the brain shows a mixture of rhythmic and nonrhythmic activity, which may vary according to behavioral state. In mammals, the cerebral cortex tends to show large slow [[delta wave]]s during sleep, faster [[alpha wave]]s when the animal is awake but inattentive, and chaotic-looking irregular activity when the animal is actively engaged in a task, called [[Beta wave|beta]] and [[gamma wave]]s. During an [[epilepsy|epileptic seizure]], the brain's inhibitory control mechanisms fail to function and electrical activity rises to pathological levels, producing EEG traces that show large wave and spike patterns not seen in a healthy brain. Relating these population-level patterns to the computational functions of individual neurons is a major focus of current research in [[neurophysiology]].<ref name=Buzsaki/>