Summary
A bioRxiv preprint reports that a scalp EEG signal associated with awareness of touch corresponds to activity recorded inside the brain. The study connects the N140/SAN with an insulo-opercular signal that follows high-frequency activity after stimulation.
Researchers using simultaneous high-density scalp EEG and intracranial EEG recordings report a link between a scalp signal associated with awareness of touch and activity recorded inside the brain. The bioRxiv preprint identifies the scalp signal, called the N140 or somatosensory awareness negativity (SAN), with an insulo-opercular local field potential that follows a response of high-frequency brain activity to stimulation.
Connecting scalp and intracranial signals
Scalp electroencephalography (EEG) records electrical activity through electrodes on the head. Intracranial EEG records activity from electrodes placed inside the skull, allowing researchers to measure signals close to brain tissue. The authors used both methods at the same time to investigate whether previously reported scalp and intracranial correlates of touch awareness were related.
The N140 is a negative deflection in scalp EEG that peaks 120–200 milliseconds after a stimulus. It has been proposed as a marker of tactile awareness, but the neuronal activity underlying it has been uncertain. Intracranial recordings have, in turn, identified broadband high-frequency activity (BHA)—activity spanning 50–150 Hz—in the insulo-opercular region after stimulation. The preprint describes this BHA response as following an initial, brief activation mainly localised to primary somatosensory cortices.
The authors report that the N140/SAN corresponds to an insulo-opercular local field potential that follows the BHA response. A local field potential reflects electrical activity from a nearby population of neurons. Linking it to the scalp signal gives a proposed neural origin for the N140/SAN and connects measurements made with non-invasive and intracranial methods.
What the link means
The result offers a way to relate a signal measurable at the scalp to activity recorded from a specific brain region. That connection may help researchers interpret scalp EEG studies of touch awareness in relation to intracranial measurements. The findings concern neural correlates of awareness; the N140/SAN is described as a proposed marker, not as a definitive standalone measure of conscious perception.
The report is a bioRxiv preprint. Its abstract does not state the number of participants or provide detailed methods, so the scale of the study and how broadly the correspondence applies cannot be assessed from the information presented there.