Global brain states and local cortical processing

The cerebral cortex—the outermost, wrinkled layer of the brain—is involved in many cognitive processes, including sensory processing, decision-making, and movement. It’s generally thought that these tasks are carried by so-called “local” circuitry, which is composed of networks of nearby neurons. However, the brain also experiences what are called “global states,” such as attention, arousal, or motivation. These global states can affect the processing carried out by local circuits. Exactly how global states influence local circuitry, however, remains a mystery. We plan to investigate these fundamental interactions between local computations and global brain states. Global brain states are characterized by slow oscillations of neuronal activity across the entire cortex—what are commonly referred to as brainwaves. When the brain needs to perform a certain task, however, it carries it out using local circuitry. We hypothesize that when local circuitry is in use to perform a task, the cortex stops oscillating near that local region. To test this hypothesis, we plan to use imaging techniques to visualize global patterns of brain activity while a mouse transitions from one global brain state to another—in this case, the global brain state will be changed by having the mouse engage in a visually demanding task followed by passive viewing. But how do changes in global brain states affect processing in local networks of neurons? One hypothesis is that global brain states affect the responsiveness of neurons. For example, during the visually demanding task, the global brain state may increase the responsiveness of certain neurons related to visual processing. To test this hypothesis, we plan to visualize the activity of local groups of neurons and compare their responsiveness as the mouse transitions from a visually demanding task to passive viewing. Finally, to understand exactly how this brain-state modulation of local processing is carried out in individual neurons, we plan to visualize the responses of one neuron at a time. The hypothesis is that one part of the neuron—termed the apical dendrites—carries information about global brain state to the neuron’s main processing center, termed its soma. Our research will reveal how global patterns of activity affect processing of local circuitry, shedding light on a common motif in neuronal computation.

Matteo Carandini, University College London

Kenneth Harris, University College London