Limits of Information Transmission in Primary Motor Cortex

Many people consider the brain to be the ultimate computer. Much like computers, the brain receives input information from the environment via various sensory receptors. The brain then processes that input information, formulates goals, and transmits information to create output movements that seek to achieve those goals. Again similar to computers, the brain has limits in its ability to transmit information. These limits can be studied using information theory, the branch of applied mathematics that gave rise to modern day computing. Although many researchers have studied the limits of the nervous system in transmitting input sensory information, little effort has been applied towards linking information in neural populations to movement. In this work, we created a novel method for estimating information transmitted by neural populations during a movement task using a limited number of trials per stimulus condition. Using this method, we found that the information transmitted by the population increased up to a limit, as the information required to be encoded by the task increased. We found that this limit was a function of the size of the population. Larger populations could transmit greater amounts of information. However, this relationship also appeared to reach a limit. Lastly, we found that the limit of information transmission is greater in a three-dimensional task compared to a two-dimensional task. We also studied neural activity during a brain-computer interface where the task dimensionality changed. We found that neurons changed their tuning to identical targets depending on whether they were encountered in the 2D or the 3D context. We present evidence that the observed changes are a motor system analogue to the phenomenon of dynamic range adaptation, which has been observed throughout various sensory systems. The neurons in the population adapted their tuning models to better utilize their limited range of firing rates to transmit information about desired output movement. Overall, this work opens up opportunities for future research investigating the role of motor cortex in transmitting contextually-encoded information