In humans, the sense of touch is closely linked with hand movements. An open question in neuroscience is how the brain combines touch signals (sensory) with hand movements (motor) to create a unified tactile perception of an object. Because of difficulties in studying how the human brain combines these cues, researchers study rats, which use ~60 whiskers to tactually explore the environment. The whisker system is an excellent model to investigate how neurons represent and unify touch and movement, but neuroscientists currently struggle to stimulate the whiskers in a way that imitates the signals obtained during natural exploratory behavior. In this proposal, the investigators will characterize naturalistic patterns of tactile input that the rat's brain evolved to process, and will develop new mathematical tools to describe the environmental features that the rat experiences. The proposed work is scientifically important for two reasons. First, because rodents are the most commonly used animals in neuroscience, these experiments will aid researchers studying many parts of the brain involved with touch and movement. Second, these new mathematical tools will help quantify the sense of touch across species, including humans. The proposed work will have significant broader impacts on science and mathematics education and public outreach. Undergraduate students will contribute to the work, and the investigators will lead Northwestern's Robotics Club to explore engineering applications of whisker-based tactile sensing. The investigators will also continue outreach efforts through the Society of Hispanic Professional Engineers, the Society of Women Engineers, and Chicago's Museum of Science and Industry.
In the fields of vision and audition, the receptive fields of central neurons are tuned to the statistics of the "natural scenes,- to those properties of the stimuli that the animal is likely to encounter in its natural environment. In the field of somatosensation it is challenging to quantify the natural tactile scene, in part because somatosensory signals are tightly linked to the animal's movements. The proposed work aims to begin to quantify the natural tactile scene for the rat vibrissal system by combining careful behavioral monitoring and simulations of rat head and whisker movements. The project has two major goals. The first is to characterize the statistics of the environments that the rat naturally inhabits. In Bayesian terms, this statistical distribution is called the "prior," because it describes the environment's geometrical features, unbiased by the tactile sampling choices of the animal. The second is to quantify the statistics of the environment sampled by the rat, given its choices of head motions and whisk cycle. In Bayesian terms, this statistical distribution is called the "posterior," because it incorporates the bias of the rat when preferentially sampling the tactile scene. This work is one of the first attempts to quantify the statistics of active touch, and it aims to make specific predictions for the receptive field properties that enable spatiotemporal integration. Equally important, this work will develop an appropriate mathematical framework for characterizing the geometry of natural scenes, an essential step towards describing active somatosensation using information theoretic measures.
