Sight, hearing, smell, taste, touch: We’re all familiar with the five senses that allow us to experience our surroundings. Equally important but much less well known is the sixth sense: “Its job is to collect information from the muscles and joints about our movements, our posture and our position in space, and then pass that on to our central nervous system”, says Dr. Niccolò Zampieri, Head of the Development and Function of Neural Circuits Lab at the Max Delbrück Center in Berlin. “This sense, known as proprioception, is what allows the central nervous system to send the right signals through motor neurons to muscles so that we can perform a specific movement.” This sixth sense--which, unlike the other five, is entirely unconscious--is what stops us from falling over in the dark, and what allows us to raise a cup of coffee to our mouth with our eyes shut in the morning. But that’s not all: “People without proprioception can’t actually perform coordinated movements,” says Dr. Zampieri. He and his team have now published an article in Nature Communications (November 11, 2022), in which they describe the molecular markers of the cells involved in this sixth sense. The findings should help researchers to better understand how proprioceptive sensory neurons (pSN) work. The open-access article is titled “Molecular Identity of Proprioceptor Subtypes Innervating Different Muscle Groups in Mice.”