Brain waves chart: what they are and how they work

Silvi Cadri
Dottoressa in Neuroscienze e Riabilitazione Neuropsicologica
4 minutes
Brain waves: the organization of electrical activity in the brain.
Table of contents

    The study of the electrophysiological mechanisms of our brain is indispensable in neuroscience and neurorehabilitation.

    This is because electrical activity constitutes the core of brain functioning and one of our brain’s most interesting phenomena depends on it: brain waves.

    How do brain waves work?

    Brain organization is determined by incessant bioelectric processes because the brain, thanks to its many connections, constantly generates electrical activity that travels from one neuron to another and carries information with it.

    The electrical impulses, as they synchronize, produce fluctuations of electricity that give rise to temporally oscillating patterns of electrical activity, referred to as brain waves or rhythms.

    In fact, by this term, we refer to the rhythmic and repetitive electrical activity of nervous tissue that, by oscillating, enables the brain to generate its temporal structure. 

    Their functional role seems to be linked to brain processes such as, for example, attentional and perceptual processes. Indeed, the waves change what we are seeing, thinking, or doing, thus underpinning our cognition and behavior.

    How are these waves recorded?

    To date, one of the preferred tools for studying these waves is the Electroencephalogram (EEG), a recording method that is relatively simple in its operation, painless and non-invasive.

    The first EEG studies on humans can be traced back to the psychiatrist Hans Berger (1929), who identified different waveforms of signals in EEG tracings depending on the recording position on the scalp, both in healthy subjects and those with neurological pathologies.

    The EEG makes it possible to analyze the relationship between the brain’s electrical signal and sleep-related aspects, for example, or to identify precise alterations that may indicate the presence of a pathology, such as epilepsy.

    The acquisition of the electrical signal is carried out using electrodes placed on the scalp which, by recording the cortical electrical activity, allows continuous measurement of electro-cortical rhythms.

    The unit of measurement of brain oscillations is the Hertz (Hz), which is the frequency of a periodic phenomenon equivalent to 1 period per second.

    In particular, we refer to rhythms that differ in aspects such as frequency, defined as the number of cycles per second, measured in Hertz, and amplitude, measured in MicroVolts (mV).

    Indeed, different types of events induce changes in the frequency spectrum of the signal of the EEG tracing, so different types of waves can be recorded that change according to brain activity. 

    For example, if we are involved in cognitive activities that require states of extreme activation and concentration, faster waves will be dominant, while if we are in a state of drowsiness, slower waves will be dominant.

    These waves are delineated by their oscillation speed, i.e. by the frequency range within which they vary and on which their functionality depends.

    What are the types of brain waves?

    Brain electricity is conventionally divided into five waves, identified by the Greek letters

    • Alpha.
    • Beta.
    • Delta.
    • Theta.
    • Gamma.

    Alpha waves

    Oscillations in the Alpha wave frequency band are characterized by waves with a frequency between 8 and 12 Hz and an amplitude of normally less than 50 mV.

    They are mostly present in the occipito-parietal regions at the back of the brain and constitute the predominant activity in adults during a relaxed waking state with eyes closed.

    Since the earliest EEG research, Alpha has emerged as the most relevant oscillatory effect and its functional correlation is among the most extensively studied aspects in neuroscience.

    Primarily, numerous studies affirm that the frequency and amplitude of alpha oscillatory activity are parameters related to visual processing; moreover, these appear to significantly affect the information sampling rate and reactivity of the visual system.

    Beta waves

    Beta waves, with a smaller amplitude and a frequency range of 12 to 30 Hz, are more evident in the frontal areas and at the level of other regions during intense mental activity such as talking or reading.

    Therefore, they are associated with physiological activation (arousal), attention, analytical thinking, complex task-solving and other intellectual processes.

    Delta waves and Theta waves

    Delta waves (0.5-4 Hz) and Theta waves (4-8Hz), recorded frontally and centrally, are normally observed when in a drowsy state and the early stages of sleep, while if present during the waking state they may be indicative of brain dysfunction.

    Gamma waves

    Finally, Gamma waves (30-50Hz) are very fast waves and, because of their small amplitude, are not easy to record.

    Identified more recently than the other waves, they are less well known to date and emerge mainly during moments of deep concentration and peak performance, whether physical or mental, as well as during mystical and transcendental experiences.

    In conclusion, research has identified brain waves as an increasingly valuable resource for understanding brain mechanisms, both in healthy brains and in those affected by the disease.

    Therefore, their in-depth study may represent a new frontier in neuroscientific and neurorehabilitation study and intervention approaches.


    1. Adrian, E. D., & Matthews, B. H. (1934). The Berger rhythm: potential changes from the occipital lobes in man. Brain, 57(4), 355-385.
    2. Bear, M. F., Connors, B. W., & Paradiso, M. A. (2007). Neuroscienze. Esplorando il cervello. Con CD-ROM. Elsevier srl
    3. Berger, H. (1929). Über das elektroenkephalogramm des menschen. Archiv für psychiatrie und nervenkrankheiten, 87(1), 527-570.
    4. Buzsaki, G. (2006). Rhythms of the Brain. Oxford University Press.
    5. Buzsáki, G., & Draguhn, A. (2004). Neuronal oscillations in cortical networks. Science, 304(5679), 1926-1929.
    6. Buzsáki, G., & Watson, B. O. (2012). Brain rhythms and neural syntax: implications for efficient coding of cognitive content and neuropsychiatric disease. Dialogues in clinical neuroscience, 14(4), 345.
    7. Kandel, E., Schwartz, J., Steven, T. M., Siegelbaum, A., & Hudspeth, A. J. (2014). Principi di neuroscienze (IV). Milano: Casa Editrice Ambrosiana.
    8. Lopes da Silva, F. H., & Storm van Leeuwen, W. (1978). The cortical alpha rhythm in dog: the depth and surface profile of phase (pp. 319-333). New York: Raven Press.
    9. Lopes da Silva F. (1991). Neural mechanisms underlying brain waves: from neural membranes to networks. Electroencephalography and clinical neurophysiology, 79(2), 81–93.
    10. Niedermeyer, E., Nierdermeyer, E., & Da Silvan, F. L. (1999). The normal EEG of the waking adult. Electroencephalography.
    Silvi Cadri
    Dottoressa in Neuroscienze e Riabilitazione Neuropsicologica
    Creative Commons Attribution Non Commercial No derivatives

    You are free to reproduce this article but you must cite:, title and link.

    You may not use the material for commercial purposes or modify the article to create derivative works.

    Read the full Creative Commons license terms at this page.

    Share Share this article:
    Facebook LinkedIn Telegram Twitter WhatsApp