Human insula divides into four regions, with the front one steering the others

Folded deep inside the brain, the insular cortex has long been tied to pain, emotion and cognition. Yet how its subregions divide the labour, and which of them drives which, has remained poorly understood. A study of 87 neurosurgical participants, published in Nature, reports that the human insula is built from four functionally distinct regions. The one at its front exerts a strong, direct influence over the others while receiving only weaker, indirect signals in return. The authors argue that this lopsided arrangement offers an electrophysiological route through which thinking could shape how pain and other bodily sensations are felt.

Working out cause and effect in the living human brain is difficult, because knowing that two areas are active together does not reveal which one is influencing the other. To get closer to that question, the team drew on people undergoing neurosurgery who had electrodes placed inside the skull. Through these electrodes the researchers applied electrical stimulation directly to brain tissue, recorded electrical activity while participants carried out tasks, and mapped the connections between sites. All of this was placed within a cytoarchitectonic atlas of the insula, a map that divides the region according to differences in the arrangement and structure of its cells.

The combined data, the authors report, point to four regions with distinct roles. A dorsal-posterior region, towards the top and back, encodes pain-related (nociceptive), temperature and touch signals. It does so somatotopically, meaning that different parts of the body are represented in an orderly map. A ventral-posterior region, lower down at the back, integrates bodily information across several body parts at once. A mid-anterior region is associated with visceral sensations, those arising from the internal organs, and with anxiety states. The fourth, anterior-polar region at the very front was largely silent when stimulated directly. It nonetheless showed robust activity during salience detection, the process of registering that something is important, and during changes of action mode.

That front region is the centrepiece of the study. According to the abstract, it has strong connections with the prefrontal cortex, including the anterior cingulate cortex, and it exerts a strong and direct influence over the other insular regions. Influence in the opposite direction is weaker and indirect. The authors interpret this as an electrophysiological pathway for the cognitive modulation of pain and bodily perception. In other words, it is a route by which higher mental processes might alter how sensations from the body are experienced.

Taken together, the authors say, the findings tie the insula's cellular architecture to a directed and asymmetric pattern of electrical interaction. They describe the consequences for how cognition shapes pain and interoception, the sense of the body's internal state, as mechanistic implications rather than demonstrated effects. How this pathway operates in everyday experiences of pain and bodily feeling is therefore left for further work. The evidence also comes from neurosurgical participants, the setting in which such direct recordings from inside the brain are possible.