Complete EEG Guide Part 2

The Complete Electroencephalography Guide [Part 2]

In Part 1 of the EEG guide, we answered seven of the most common electroencephalography questions.

Here, we answer five more.

This time we will focus on what EEG waves mean: what an abnormal EEG looks like, whether EEG can show past seizures, and which EEG patterns are associated with problem-solving and intelligence.

Let’s jump right in.

Who invented EEG?

EEG waves were first recorded by German psychiatrist Hans Berger in 1924. Berger’s first recordings were of a 17-year-old boy who was undergoing neurosurgery.

Berger used a galvanometer for this, which he applied to the boy’s head. The galvanometer scribbled down the electrical currents coming from the boy’s brain during the surgery.

You can still read about these discoveries in Berger’s original paper: Über das Elektrenkephalogramm des Menschen (“On the human electroencephalogram”; Berger, 1929) – however, it is in German!

Hans Berger
Here is Hans Berger (1873-1941), inventor of electroencephalography (EEG).

Berger started studying the brain because he was interested in psychic phenomena, particularly telepathy (İnce et al., 2021). Years earlier his sister purportedly sensed that Berger was injured, even though she was miles away.

Unfortunately for Berger, his investigations into telepathy didn’t go well. Fortunately for us, his interest in the brain led to the discovery of EEG, which is now a gold standard in brain research.

Although Hans Berger is well attributed to EEG, Richard Cantor (1842–1926) deserves an honourable mention. He produced the groundwork for Berger’s discoveries! 

When is EEG abnormal?

To understand when an EEG recording is abnormal, we must first understand when it is normal. And as we learnt in Part 1 of the EEG guide, understanding when EEG is normal is tricky.

Interested in EEG?

For instance, although seeing a lot of delta waves (those are slower brain waves) in an aroused adult is abnormal, you would hope to see them in a drowsy adult.

However, there are several EEG patterns that can signal trouble no matter what the circumstance. Here are three examples:

Triphasic waves

So-called triphasic waves are abnormal EEG waveforms that are associated with physically damaged brains.

Triphasic EEG waves were first reported by John Foley et al. (1950). They consist of three phases: a short negative deflection followed by a large positive wave and a slow return to negativity.

These kind of brain patterns tend to occur in frontal and central regions of the brain and can occur in children (Zhang et al., 2022).


Another well-known abnormal EEG pattern is called spike-and-wave. Spike-and-wave patterns tend to occur during epileptic seizures (Destexhe, 1998).

They are repeated, symmetrical spikes that occur across the brain (rather than locally), usually more than twice a second. During absence seizures, when the individual loses awareness of their surroundings, spike-and-wave patterns form as neurons across the brain fire in synchrony (Snead, 1995).

These types of waveforms were first mentioned by Jasper and Kershman (1941) and are now hallmarks of seizure detection.

You may come across the term ictal and interictal electroencephalographic discharges when reading seizure research. Here you can read ictal and interictal as during and between seizures respectively.

Electrocerebral inactivity

A more obvious abnormality is called electrocerebral inactivity (ECI). As its name suggests, ECIs are indicative of brain death. They occur when no electrical currents can be found in the brain above 2 microvolts (Szurhaj, 2015).

eeg pattern
During electrocerebral inactivity there is no activity in the EEG plot. All these lines would be as good as flat.

Can EEG detect past seizures?

If EEG is an excellent method for detecting seizures as they happen, can they detect previous seizures? Or must the doctor simply wait for a seizure to happen?

The short answer is that EEG cannot detect past seizures with any certainty.  

More than 40% of those suffering from epilepsy display “normal” EEG recordings between seizures (Panayiotopoulos, 2005), and in many cases once a seizure stops the brain reverts to normal behaviour immediately (Kaibara & Blume, 1988).

All this means that if a doctor suspects someone has experienced a seizure, they might adopt ambulatory EEG, which can be worn at home and during sleep. In this way, they can record brain activity for long periods of time and increase the chances of recording a seizure if it happens again.

Which EEG pattern is associated with problem-solving?

Surprisingly enough, EEG can detect changes in brain behavior when someone is solving complex problems.

For example, researchers in China presented individuals with difficult scientific problems and found that the higher the mental workload, the more theta (slow) brain waves synchronized in the frontal brain region (Zhu et al., 2021).

Other researchers suggest that alpha activity is associated with creativity (Fink et al., 2009) and the suppression of irrelevant information (Klimesch et al., 2007).

A deeper dive into the psychology of problem solving, however, reveals a more complex picture. This is because there are different ways to solve a problem.

Cognitive Insight

One important style of problem solving involves “cognitive insight”. Here, an individual will struggle with a complex problem before suddenly realising the solution.

This phenomenon has been broken down into four sequential steps (Sandkühler & Bhattacharya, 2008). Specifically:

  1. Engage with a mental impasse
  2. Restructure the problem
  3. Deepen your understanding
  4. Solve the problem in a sudden, “Aha!” moment

Each of these steps involves multiple areas of the brain and is correlated with several EEG patterns.

aha moment
One type of problem solving involves cognitive insight – you may recognise the “Aha!” moment

For instance, researchers found gamma (high frequency) responses in areas of the brain associated with attention during steps 1 and 4. It is thought that these patterns represent the brain focussing on specific problem representations (incorrectly in step 1 and correctly in step 4).

Another finding is that more intelligent and creative people require less mental activity to solve problems. Brain regions cooperate more for creative and intelligent individuals (Jaušovec, 2000).

That’s right! Certain EEG patterns can correlate with intelligence.

Will EEG show brain damage?

Yes, EEG can show brain damage. In fact, EEG was one of the first diagnostic tools doctors had to diagnose abnormal brain activity following traumatic brain injury (Glaser & Sjaardem, 1944).

For chronic brain deficits that are the result of traumatic brain injury, EEG can be the only evidence a doctor has that something is wrong (Duff, 2004).

Immediately after a mild traumatic brain injury, the brain produces signals that resemble an epileptic seizure. This is soon replaced by 1-2 minutes of suppressed activity and, with it, a slowing of the EEG patterns (Ianof & Anghinah, 2017).

EEG waves tend to look normal within ten minutes to an hour after brain injury, however it can take weeks to months before the brain fully recovers. Commonly, EEG will record a 1 – 2 Hz increase in the brain’s alpha frequency for around three months.

In general, brain damage causes an increase in slow wave activity, and a decrease in fast wave activity.

In some cases, it can take just 15 minutes after a concussion for EEG signals to look healthy again (Dow et al., 1944).

Still have more questions about EEG? Look out for part three of our complete EEG guide coming soon!


Berger, H. Über das Elektrenkephalogramm des Menschen. Archiv f. Psychiatrie 87, 527–570 (1929).  

Destexhe A. (1998). Spike-and-wave oscillations based on the properties of GABAB receptors. The Journal of Neuroscience: The Official Journal of the Society for Neuroscience, 18(21), 9099–9111.

Dow, R. S., Ulett, G., & Raaf, J. (1944). Electroencephalographic studies immediately following head injury. American Journal of Psychiatry, 101(2), 174-183.

Duff J. (2004). The usefulness of quantitative EEG (QEEG) and neurotherapy in the assessment and treatment of post-concussion syndrome. Clinical EEG and neuroscience, 35(4), 198–209.

Fink, A., Grabner, R. H., Benedek, M., Reishofer, G., Hauswirth, V., Fally, M., Neuper, C., Ebner, F., & Neubauer, A. C. (2009). The creative brain: investigation of brain activity during creative problem solving by means of EEG and FMRI. Human brain mapping, 30(3), 734–748.

Foley, J. M., Watson, C. W., & Adams, R. D. (1950). Significance of the electroencephalographic changes in hepatic coma. Transactions of the American Neurological Association, 51, 161–165.

Glaser, M. A., & Sjaardem, H. (1944). Value of the electroencephalogram in craniocerebral injuries. The Journal of Nervous and Mental Disease, 99(4), 433.

Ianof, J. N., & Anghinah, R. (2017). Traumatic brain injury: An EEG point of view. Dementia & neuropsychologia, 11(1), 3–5.

İnce, R., Adanır, S.S. & Sevmez, F. (2021). The inventor of electroencephalography (EEG): Hans Berger (1873–1941). Childs Nerv Syst 37, 2723–2724.

Jasper, H., & Kershman, J. (1941). Electroencephalographic classification of the epilepsies. Archives of Neurology & Psychiatry, 45(6), 903-943.

Jaušovec, N. (2000). Differences in cognitive processes between gifted, intelligent, creative, and average individuals while solving complex problems: An EEG study. Intelligence, 28(3), 213–237.

Kaibara, M., & Blume, W. T. (1988). The postictal electroencephalogram. Electroencephalography and clinical neurophysiology, 70(2), 99–104.

Klimesch, W., Sauseng, P., & Hanslmayr, S. (2007). EEG alpha oscillations: the inhibition-timing hypothesis. Brain research reviews, 53(1), 63–88.

Panayiotopoulos, C. P. (2005). The Epilepsies: Seizures, Syndromes and Management. Bladon Medical Publishing.

Sandkühler, S., & Bhattacharya, J. (2008). Deconstructing insight: EEG correlates of insightful problem solving. PloS one, 3(1), e1459.

Snead O. C., 3rd (1995). Basic mechanisms of generalized absence seizures. Annals of neurology, 37(2), 146–157.

Szurhaj, W., Lamblin, M. D., Kaminska, A., Sediri, H., & Société de Neurophysiologie Clinique de Langue Française (2015). EEG guidelines in the diagnosis of brain death. Neurophysiologie clinique = Clinical neurophysiology, 45(1), 97–104.

Zhang K, Xu S, Zhou Y and Su T (2022) Case Report: Triphasic Waves in a 9-Year-Old Girl With Anti-NMDAR Encephalitis. Front. Neurol. 13:819209.  

Zhu, Y., Wang, Q. & Zhang, L. (2021). Study of EEG characteristics while solving scientific problems with different mental effort. Sci Rep 11, 23783