'Rhythmic' Firing of Neurons in the Brain Detailed in New Study

by Rajashri on Aug 7 2008 2:24 PM

The reason why groups of neurons in the brain fire up simultaneously in random rhythms for just milliseconds at a time has been identified by a team of neuroscientists from Indiana University and the University of Montreal.

Reporting their work in the Journal of Neuroscience, the researchers say that their findings draw on the variability and creative nature of neurons - no two are exactly the same, providing for a rich and ever-changing repertoire of brain activity.

The group insists that the new findings expand their understanding of brain rhythms, both reoccurring and random, and shed light on the decades-old mystery of how the brain learns temporal patterns.

"Our model is proposing a way that the brain processes temporal information and how this can vary over time," said Jean-Philippe Thivierge, a post-doctorate researcher in IU Bloomington's Department of Psychological and Brain Sciences.

Thivierge and co-author Paul Cisek, an assistant professor at the University of Montreal, say that a better understanding of rhythms in the brain -- how to create them or stop them - may be useful for researchers in studying neural diseases like epilepsy, which involves seizures or uncontrollable rhythms in the brain.

During the study, the researchers created a mathematical model for how hundreds of neurons interact after being stimulated by an electric current.

They propose that the random synchronization, which occurs in large populations of neurons, results from "positive excitatory feedback originating from recurrent connections between the cells."

According to the researchers, the synchronization involves most of the cells in the group but begins with a preferred small group of cells - like "elite" cells - which tend to become active just before all the others do.

When enough cells in the group become active, a threshold, or "point of no return" is reached where all the cells become active and their activity spikes.

The research group has also found how neural activity can spike periodically or rhythmically.

Upon introducing a specific rhythm to the model, they found that the model could learn and repeat the rhythm.

Though scientists have known for about five decades that the brain can do this, they hardly knew anything about the mechanism.

Thivierge said that the mechanism was based on how the neurons come together to motivate each other to fire in a specific, periodic way, following the rhythmic stimuli.

The spontaneous neural activity modelled in the study has been detected in several regions of the brain as well as in other species.

The authors guess that the benefits of such spontaneity come in the brain's ability to be more flexible and responsive to external events, that the random synchronization can prevent the brain from remaining "stuck" in a particular state.

"It seems like when you're in a more flexible brain state, it's easier for you to redirect your attention to new and important things," Thivierge said.