EEG vs intracortical recording

Also: noninvasive vs invasive BCI, scalp EEG vs implanted electrodes

By neuraspeak editorial · Updated 2026-10-07 · 1 min read

EEG versus intracortical recording describes the main tradeoff in brain-computer interfaces: EEG measures brain activity noninvasively through electrodes on the scalp, while intracortical recording uses electrodes surgically inserted into the cortex to detect the firing of individual neurons, giving far more detailed signals at the cost of brain surgery.

What is the difference in signal quality?

Scalp EEG measures the combined electrical activity of very large numbers of neurons after it passes through the skull, scalp, and fluid, which blur and weaken it. It is good at tracking timing and broad brain states but poor at telling apart activity from nearby patches of cortex. Intracortical microelectrodes, such as the Utah array, sit within the tissue and can pick up spikes from individual neurons or small groups. Between the two sit ECoG, with electrodes on the brain's surface, and endovascular electrodes inside a blood vessel.

How do they compare for communication?

EEG BCIs usually depend on indirect signals, such as the brain's response when a desired letter flashes. The first such speller allowed about 2.3 characters per minute (Farwell and Donchin, 1988), and EEG spellers have improved since, but they remain far slower than implanted systems. Implanted speech neuroprostheses decode attempted speech directly: intracortical systems have reached 62 words per minute (Willett et al., Nature 2023) and about 32 words per minute in self-paced conversation with 97.5% accuracy (Card et al., NEJM 2024).

Why use EEG at all?

EEG needs no surgery, costs less, and can be tried by many people quickly. It has been studied for decades as a communication aid for people with severe paralysis (Wolpaw et al., Clinical Neurophysiology 2002). Intracortical systems involve surgical risk, a skull-mounted or implanted connector in current research devices, and signal quality that declines over years.

Why it matters for speech BCI

For speech decoding, the detail of the signal matters. The record-setting speech neuroprostheses all use implanted electrodes over or in speech motor cortex. Noninvasive approaches remain attractive for safety and access, but they have not shown comparable fluent speech decoding in people with paralysis. Families and investors comparing BCI approaches should weigh invasiveness against the communication speed each approach has actually demonstrated in peer-reviewed studies.

Questions

Can a headset decode my speech?+

Research on decoding speech from EEG continues, but published results have not matched the speed and accuracy of implanted systems in people who cannot speak.

Is ECoG intracortical?+

No. ECoG electrodes rest on the brain's surface without penetrating it. Intracortical electrodes, like the Utah array, are inserted into the cortex.

Sources

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