Our sense of touch tells us whether an object is wet or dry, rough or smooth, hard or soft. At the same time, the brain is able to recognize that a freshly filled coffee cup feels both smooth and warm. Yet how does the brain process temperature and touch simultaneously?
The brain is our body’s most complex organ. In humans, the nerves alone make up a total length of five million kilometers. Although researchers already know a certain amount about numerous structures, many of the processes that take place in the central nervous system are not yet understood. James Poulet from the Max Delbrück Center for Molecular Medicine (MDC) in Berlin is currently investigating how a single uniform perception arises from two different stimuli.
For his work, the British neurobiologist chose to focus on “temperature” and “touch”. “We take our ability to perceive these sensory impressions simultaneously completely for granted, but we don’t know much about how they are processed and combined,” says Poulet. Just recently, he received a “Consolidator Grant” from the European Research Council (ERC) for this research project. The 41-year-old MDC scientist is now using mice as a model to track the various sequences that occur from the skin’s reception of the stimulus to the processing of the stimulus in the brain.
Poulet aims to solve the mystery of combined perception in a project comprising three phases. The first phase involves find out which neural circuits process thermal and tactile stimuli. For this, he is locating the responsible “nerve cell networks” and depicting them in a kind of map with the intention of finding out which regions of the brain respond to each sensation and which neurons are involved.
Mice are about as sensitive to temperature differences as humans
The second phase involves tracking the perception process in action. For this, Poulet and his team are training mice to touch a lever with their front paws as soon as they perceive a sensation of cold when touching an object. “Mice are especially sensitive to temperature differences,” explains the neuroscientist. “They can recognize temperature differences of just half a degree, which is roughly the temperature sensitivity of a human.” The researchers are observing which nerve cells in the cerebral cortex combine the thermal and haptic signals when the mice signalize a change in temperature.
Finally, Poulet wants to research whether this perception can be changed. For this, he will be linking light-sensitive proteins to certain cells in the brain using a so-called optogenetic process. The proteins act as a kind of switch that can be used to activate or deactivate perception processes. “This special method allows us to change the activity of marked brain cells with the help of light. This gives us whole new insights and allows us to experience the processing of sensory perceptions live,” explains Poulet.
These research findings could help distinguish healthy connecting processes in the brain from deviant ones. In the long term, this information could help improve our understanding of neurodegenerative diseases in which the brain’s perception processes are disordered.
Poulet has already received two awards from the ERC for his fundamental research. In 2010, he received a “starting grant” for up-and-coming scientists. The researcher used these funds to investigate changes in brain activity in waking states, for example the various patterns observed when paying attention. “The cortex region was at the forefront of my research even then. I want to understand how the brain works,” says Poulet.
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Authors: Sophie Rau and Kristine August