For a long time, scientists have believed neutrons to be responsible for generating thoughts, actions, and perceptions by emitting electrical pulses called spikes or action potentials. The problem is, that under that theory, neurons must always be firing at some kind of spontaneity.





As described by Dr. Joe Z. Tsien, Georgia Research Alliance Eminent Scholar in Cognitive and Systems Neurobiology and corresponding author of the study, the firing of neurons can be compared to that of how an ocean appears to be still, but never really is. One thing that has been noted by many scientists is that there is often variation in how the same neuron responds to the exact same stimulus. Getting to the bottom of why that happens is what neuroscientists call “cracking the neural code.”

From Tsien and colleagues’ study, they found that it’s the silent spaces between firing and entering an atypical state when all the magic happens. These periods of time are known as interspike intervals and as theorized by Tsien, neurons having atypical intervals simultaneously are part of a group that’s responsible for generating actions, thoughts, and perceptions. “These cells belong to the same group, an assembly,” says Tsien. “It’s a very general finding of how neuron activity codes information.”





The team has identified a total of 15 different cell assembly groups in the hippocampus and cortex of the brain that comes together to regulate things such as sleep cycles and how you act when experiencing new things. For example, as part of the study, the team had mice engaging in a game where a light was shined on a wall and every time the mouse poked a hole in the spot where the light was, it received a treat. If the task wasn’t completed on time or the mouse poked the wrong hole, it received nothing.

“To identify the cell cliques that help the mouse be successful, you have to find out what each neuron’s interspike intervals look like when they are out of their normal range of occurrence,” explains Tsien. “Among all the cells you record, you then identify the ones that move into that different state – called a surprisal state – at the same time. That is when these cells start to act as a clique. That is when the neural cliques are coming together to encode a train of thought or a set of actions.” He then adds: “If it’s what happens usually, that means it does not carry much information, it’s like a ground state.”





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