The brain is capable of consciously identifying temperatures as either hot or cold, but the precise neural mechanisms that make this possible are still not fully understood. To explore this phenomenon, researchers from Waseda University used electroencephalography to observe brain activity in response to hot and cold stimuli. Their findings indicated that while both types of temperature activate the same ten cortical areas, the EEG readings showed differences in various frequency patterns, which ultimately influence behavior. These insights could lead to more objective methods for evaluating thermal comfort.
The brain recognizes hot and cold by generating distinct temporal activity patterns in shared cortical areas, providing insight into how sensory data is processed and interpreted.
When we touch objects that are hot or cold, our body becomes aware of the temperature. Previous studies suggest that the cortex, which is the brain’s outer layer, is essential for these thermal sensations. However, the specific ways in which the cortex differentiates between hot and cold are still unclear. Sensitivity to temperature is subjective and can differ between individuals; one person’s comfortable temperature might feel too warm or too cool to someone else.
In this recent study, led by Professor Kei Nagashima from the Body Temperature and Fluid Laboratory at Waseda University and Dr. Hironori Watanabe with their research team, electroencephalography (EEG) was used to chart the brain’s responses to various temperature alterations and to clarify the resulting activity patterns. Twenty participants underwent different temperature treatments on their right index and middle fingers. These treatments included 15 seconds of varying temperatures, followed by a 10-second baseline temperature of 32 ËšC. The study recorded neural responses to two specific temperatures, 40 ËšC and 24 ËšC, using a wearable EEG device. This research was published in Volume 564 of Neuroscience on January 9, 2025.
The data gathered were analyzed to discover varying activity patterns based on region and timing. The results revealed grouped brain activity across ten distinct cortical areas. Importantly, both hot and cold stimuli engaged the same ten brain regions, but the EEG signals differed between the sensations. “The differences in these activity patterns will enable us to distinguish between changes in temperature, leading to different behaviors,” said Nagashima.
The different patterns of activity within these common brain regions may represent the core mechanism enabling the distinction between hot and cold temperatures. Furthermore, it was observed that much of this neural activity was concentrated in the right hemisphere, indicating that it plays a more significant role in processing thermal sensations compared to the left hemisphere.
The findings of this study could pave the way for establishing more objective standards for evaluating thermal comfort. Nagashima emphasized, “Thermal comfort is typically used as a guideline for creating optimal indoor conditions (like air conditioning) by the American Society of Heating, Refrigerating, and Air-Conditioning Engineers. However, it currently depends on individual opinions. We believed it was necessary to approach this assessment in a scientific and objective manner.” Gaining a deeper understanding of how the brain reacts can help reduce health risks associated with the uncertainties of subjective evaluations of thermal comfort.
