Surprise when we sense temperature: Our brain processes heat and cold stimuli in a different place than expected. Because the temperature center is not in the other sensory areas in the somatosensory cortex, but in the posterior insular cortex – a sunken area above the temporal lobes. In this area – the thermal cortex – cold and heat stimuli are also processed in different ways by their own neurons, as researchers report in “Nature”.
Whether it’s the icy wind or the warmth of the sun: we can perceive the temperature of our surroundings through our skin. Two different sensors send nerve signals to the brain, which we can use to detect even small temperature differences. But where these temperature stimuli are processed in the brain has only been partially clarified. Accordingly, cold stimuli seemed to arrive in the somatosensory cortex, but where the heat stimuli end up remained unclear.
Unexpected reaction in the insular cortex
Mikkel Vestergaard and his colleagues from the Max Delbrück Center for Molecular Medicine in Berlin have now solved this puzzle. In order to clarify the question of whether there is a thermal cortex in the brain and where it might be located, they looked at mice. To do this, they exposed the animals’ front paws to rising or falling temperatures of between 10 and 42 degrees. Using various imaging methods, the researchers analyzed which part of the brain reacted to the changes in skin temperature.
The result: “Surprisingly, it turned out that the somatosensory cortex reacts to cold but not to heat,” report Vestergaard and his colleagues. Instead, the neurons lit up in a different brain region: the posterior insular cortex. This brain region lies in the fold above the temporal lobe and has long been associated with the processing of some sensory stimuli, including the subjective perception of pain or linguistic-acoustic thought processes.
Thermal cortex reflects body regions
It has now been shown that temperature perception is also located in the posterior insular cortex. This was confirmed when Vestergaard and his team temporarily switched off this brain area in some of their mice. “In these cases, the mice no longer felt the temperature stimulus,” reports senior author James Poulet. Only when their insular cortex was able to react normally again did the mice feel heat or cold again.