As we go about our daily lives, we are constantly bombarded by a steady stream of sensory information. Take a typical morning routine for example- roused from sleep by a shrill alarm, the strong aroma of freshly brewed coffee, and the brake lights and traffic horns of rush hour. In the course of a single day, we experience thousands of different cues across all senses.
Despite the numerous chaotic cues we encounter, our brains do a remarkable job assembling and processing them; allowing us to make sense of the world around us. This processing can take shape in very noticeable ways, such as our vision and hearing, but also occurs more subtly and unexpectedly. For instance, when learning a new movement, our brain is constantly keeping track of the sensory cues around us. This sensory snapshot helps to instruct and guide motor learning so that when we encounter the same context again, we’ll be more likely to perform the movement in a better way.
Though there is a wealth knowledge supporting the idea that sensory cues benefit motor learning, the precise brain circuitry and mechanisms tying these two together has been debated in recent years. Shedding new light on this topic, a recently published paper in Neuron from the lab of Dr. Jason Christie, Research Group Leader at the Max Planck Florida Institute for Neuroscience (MPFI), has revealed that a special input pathway into the cerebellum seems to hold the key to coding sensory information.
The cerebellum is a unique structure within the brain that plays a critically important role in motor coordination and learning that improves movements. By receiving many inputs from various regions of the brain, the cerebellum integrates and sends refined information out through a single neuron type called a Purkinje cell. One significant input to the Purkinje cells, are long-range projections called climbing fibers.
Sensory enhancement is encoded in the presynaptic activity level of Climbing Fibers. Comparison of the sensory enhancement of calcium event amplitudes in Climbing Fibers compared to observations in Purkinje cells, measured in separate experiments. The change in Purkinje cell response size closely parallels that of Climbing Fibers across modalities.
“Climbing fibers are very well-known and extensively studied in the field.” describes Dr. Michael Gaffield, Research Fellow in the Christie Lab and first author of the publication. “These fibers form long-range connections with the cerebellum and are thought to deliver instructive motor signals and relay sensory information. But in the past few years it’s been suggested that local circuits within the cerebellum, such as parallel fibers or molecular layer interneurons, may also play a part in coding of sensory information.”
To investigate, the team used two-photon calcium imaging to monitor the activity of Purkinje cells within the cerebellum of mice while presenting various sensory stimuli (auditory, visual and somatosensory). They then isolated and assessed changes in Purkinje cell activity that directly corresponded to the timing of each individual stimulus and climbing fiber input.