Outer brain and inner brain: computational principles and interactions

Loosely speaking, we all have two brains. Our ‘outer brain’ interacts with the surroundings via the senses or translates intentions into movements. Our ‘inner brain’ receives sensory information from the outer brain, integrates it with memories, internal states — such as hunger or arousal — and goals, then sends a plan of action back out to our muscles. Each brain appears to process information distinctly, a phenomenon observed from flies to humans. Even devices using artificial intelligence, such as self-driving cars, have different ways of processing ‘outer’ and ‘inner’ data. That they are different makes intuitive sense. The outer brain has to deal with enormous amounts of data. Our eyes, for example, take in 1 gigabyte per second of raw image information, but we ultimately only use a fraction of that data. The inner brain, on the other hand, processes information at a far lower rate. Humans can speak, play piano or remember things at about 20 bits per second, meaning we can choose among a million possible thoughts per second. This is a lot, but pales in comparison to the information-processing task faced by the outer brain. While the outer brain excels at filtering relevant information, the inner brain excels at integrating information from the senses, our past experience and our internal state to decide and initiate an action. Traditionally, neuroscientists have studied one system or the other — inner or outer. We have assembled a team of five neuroscientists, each an expert in one region of the inner or outer brain, to bridge the gap. By performing related experiments in parallel and leveraging our combined expertise, we can examine how the inner and outer brains communicate with each other. We will explore whether the systems really use different processing strategies or if there are alternative explanations that do not require this dichotomy. Our work will investigate these questions in mice and humans and build computer models to test different theories. With a collaborative approach, we will determine the principles underlying the different brain systems, providing insight into human behavior and potentially enhancing artificial intelligence.