Electrical activity in the brain contains rhythmic oscillations at different frequencies ranging from 0.01 Hz to 600 Hz. Like musical notes in a symphony, these electrical rhythms are the result of precisely timed, coordinated activity. They are generated by thousands of brain cells of different type arranged as ensembles.

Oscillations with different frequencies have different functions depending on the brain region and behavioural state. In the temporal lobe, oscillations called sharp waves and ripples (SWs) occur during sleep to help consolidate memories. SWs are one of the most synchronized brain rhythms, and understanding these rhythms at the cellular level could help to explain how they contribute to memory function and disorders such as epilepsy.

To investigate the origin and generation of SWs, Brain Function CoE researchers examined networks of brain cells in the temporal lobes of rodents. The research was led by Madhusoothanan Perumal in Pankaj Sah’s group at the Queensland Brain Institute.

Using recordings of the electrical activity in different types of brain cells during SWs, the researchers discovered that SWs are initiated by a rare type of brain cell known as a chandelier neuron. These neurons form extensive connections within local regions of the brain. The recordings showed that chandelier neurons orchestrate other cells and their circuits at precise times to generate SWs.

To understand how oscillations are produced at specific frequencies, the researchers built a computational model of a neural network containing microcircuits controlled by chandelier neurons. Simulations using the model generated SWs. They also revealed that interactions between microcircuits and the distribution of connections between neurons in the network produced the distinctive frequencies of SWs.

Next steps:
The simulations predicted a distinctive role for another type of neuron, basket neurons, in stopping brain networks from becoming epileptic. The researchers plan to investigate the different roles that distinct cell types have in generating brain oscillations.

Reference:
Perumal, M. B., Latimer, B., Xu, L., Stratton, P., Nair, S., & Sah, P. (2021). Microcircuit mechanisms for the generation of sharp-wave ripples in the basolateral amygdala: A role for chandelier interneurons. Cell Reports, 35(6), 109106. doi: 10.1016/j.celrep.2021.109106

This article originally appeared on The Brain Dialogue. Read the original article https://www.cibf.edu.au/brains-orchestra available under CC-BY 4.0