An electrode needle with 14 recording contacts will target the insula traversing through the frontal lobe. While the first couple of electrodes capture insular activity, the other contacts along the electrode needle will provide unique recordings from structures such as the claustrum. The EEG discussed here is sometimes called “quantitative EEG” and is used for basic research on brain electrical activity during cognitive or affective processing. The EEG signal recorded from the scalp is composed of multiple sine waves cycling at different frequencies.
It is one of the few mobile techniques available and offers millisecond-range temporal resolution, which is not possible with CT, PET, or MRI. Another milestone will be the development of new computational systems that will increase the power of current clinical recording systems that cannot process more than several hundred channels simultaneously. Large channel counts will have major implications for every downstream component, including connectors, routing, amplification, signal processing, and storage. Multiplexing the signals will be required to get all the signals in a single or few wires.
Electroencephalography, or EEG, is a non-invasive technique used to measure brain activity by recording electrical signals produced by the brain. While EEG is a valuable tool in neurology and research, there are disadvantages associated with this method.
In other research, it is useful in investigating various cognitive functions, such as memory or attention; it is also used in language and clinical research; for example, studies that investigate EEG patterns in individuals with aphasia. A clear advantage of working with the iEEG signal is the access to data with exceedingly high signal-to-noise ratio (SNR). For instance, local energy consumption increase owing to a typical task-related response in fMRI is as little as 1%44.
Interference from External Factors
Implanted electrodes can not only record signals from a specific population of neurons but also deliver electrical pulses to that population. The fact that humans can explain their subjective experience during electrical stimulation of their brain makes the intracranial experiments in humans unique. When stimulation intensity was increased in parietal areas, participants believed they had really performed these movements, although no electromyographic activity was detected55.
If the laterality of seizures is unknown, or if the seizure onset zone is hypothesized to be in the deeper structures of the brain (such as the hippocampus or the insula) the sEEG approach is preferred. In these cases, each patient is often implanted with 5–15 depth electrodes, unilaterally or bilaterally (each consisting of 10–14 recording contacts). These electrodes often target the limbic structures (medial temporal lobes, cingulate, orbitofrontal and insular regions), but since they penetrate the brain from its lateral surface, they also offer recordings from the lateral sites as well (Figure 1). The electroencephalogram (EEG) is a non-invasive neuroimaging test that can detect and record minute changes in electrical activity within the brain. This is recorded using microelectrodes (large, flat electrodes stuck to the skin or scalp).
One major disadvantage of EEG is its susceptibility to interference from external factors such as movement, muscle activity, and environmental noise. These external factors can distort the recorded brain signals, making it difficult to accurately interpret the results.
Difficulty in Locating the Source of Activity
Another disadvantage of EEG is the limited spatial resolution, which makes it challenging to pinpoint the exact source of brain activity. Unlike imaging techniques like fMRI or PET scans, EEG cannot provide detailed information about the specific regions of the brain involved in a particular task or function.
This signal is too crude for understanding a distributed code among many cells within a small region. Understanding the temporal dynamics of neuronal responses in different nodes of a specific brain network is of great importance for generating a neuromechanistic account of human brain function at the systems level. For example, neuroimaging studies have shown that the posterior cingulate cortex (PCC) and angular gyrus (AG) are engaged in autobiographical memory functions and also connected at rest52. However, based on these data, it was almost assumed that a large area of PCC should be connected to a large area of AG. Instead, using the same metrics validated in prior studies 53,54, it was found that the coupling at rest occurred between those discrete populations of neurons in the PCC and AG that were co-activated during the experimental task 34.
Lack of Deep Brain Activity
EEG is primarily sensitive to activity occurring on the surface of the brain, known as cortical activity. This means that deeper brain structures, such as the hippocampus or thalamus, may not be as easily detected or measured using EEG alone. As a result, EEG may not provide a comprehensive view of all brain activity.
Almost 50 years later, in 1924, Hans Berger made the first EEG recording on the human scalp, by using simple radio equipment in order to amplify the electrical activity of the brain, and obtained a written output on paper. He claimed that brain activity that is observed through the use of EEG can change in a consistent, reliable and recognizable fashion when the state of the patient changes, such as going from relaxation to alertness, sleep, lack of oxygen (Bronzino 1995). This breakthrough gave rise for the research of the years to come and the varied applications of EEG use today.
Limited Frequency Range
EEG is limited in its ability to detect high-frequency brain activity, particularly above 100 Hz. This limitation can restrict the types of brain processes that can be effectively studied using EEG, potentially missing out on crucial information related to certain cognitive functions.
Dependence on Electrode Placement
The accuracy and reliability of EEG data can be highly dependent on the placement of electrodes on the scalp. Incorrect electrode positioning can lead to distorted or unreliable results, making it essential for researchers and clinicians to carefully consider electrode placement during EEG recordings.
In conclusion, while EEG is a valuable tool for studying brain activity, it is important to be aware of its limitations and potential disadvantages. Understanding these drawbacks can help researchers and clinicians make informed decisions when choosing the appropriate methods for studying the brain.
