How the Brain Masters Complexity Without Descending Into Chaos

Researchers reveal that neurons exhibiting “mixed selectivity” enable our brains to handle multiple computations simultaneously, providing the flexibility needed for complex cognitive tasks.

Many neurons exhibit “mixed selectivity,” meaning they can integrate multiple inputs and participate in multiple computations. Mechanisms such as oscillations and neuromodulators recruit their participation and tune them to focus on the relevant information.

Every day our brains strive to optimize a trade-off: With lots of things happening around us even as we also harbor many internal drives and memories, somehow our thoughts must be flexible yet focused enough to guide everything we have to do. In a new paper published in the journal Neuron, a team of neuroscientists describes how the brain achieves the cognitive capacity to incorporate all the information that’s relevant without becoming overwhelmed by what’s not.

The Role of Mixed Selectivity

The authors argue that the flexibility arises from a key property observed in many neurons: “mixed selectivity.” While many neuroscientists used to think each cell had just one dedicated function, more recent evidence has shown that many neurons can instead participate in a variety of computational ensembles, each working in parallel. In other words, when a rabbit considers nibbling on some lettuce in a garden, a single neuron might be involved in not only assessing how hungry it feels but also whether it can hear a hawk overhead or smell a coyote in the trees and how far away the lettuce is.

The brain does not multitask, said paper co-author Earl K. Miller, Picower Professor in The Picower Institute for Learning and Memory at DOI: 10.1016/j.neuron.2024.04.017