Computational Neuroscience: The Relationship between Individual Neurons and Population Network Activities

Announced on Jul 18, 2012 (UHN Research News on intranet) and part of UHN online publication - Net Results EXPRESS (NRx) July 2012.

The hippocampus is the region of the brain responsible for processing a number of important functions, including memory formation and storage. Hippocampus activity is controlled in part by inhibitory cells and the networks they comprise. The individual inhibitory cells fire at high frequencies but collectively produce activities at significantly slower rhythms—termed slow population activities (SPAs). While the underlying mechanisms that help to coordinate this network are poorly understood, TWRI Senior Scientist Dr. Frances Skinner and her former doctoral student, Ernest Ho, have recently shed new light on the coordination of neuron activity in the hippocampus.

Drs. Ho, Skinner and their collaborators used a multifaceted approach consisting of computer simulations, mathematical analyses, experimental analyses and validation to show that low frequency SPAs are due to both the existence of particular properties of inhibitory cells and network interactions. Specifically, when excitatory and inhibitory network interactions are balanced, the network can transition from one state to another, allowing SPAs to emerge as part of the inhibitory response. This switching ability occurs if the fast-spiking inhibitory cells have a steep change in firing rate activity and are supported by the network interactions in this regime during hippocampus activation.

Using interneuron recordings from mice and rat models, a plot of frequency versus current produced results that were consistent with the model predictions. “This is the first study to have uncovered the precise conditions in a physiological context that promote network multistability,” explains Dr. Skinner. “The fundamental understanding achieved will contribute to hippocampal function and dysfunction understanding from network perspectives, as well as give insight into underlying mechanisms in other brain regions.”

Inhibitory networks of fast-spiking interneurons generate slow population activities due to excitatory fluctuations and network multistability. Ho ECY, Struber M, Bartos M, Zhang L, Skinner FK. Journal of Neuroscience. 2012 July 17.

This work was supported by the Natural Sciences and Engineering Research Council of Canada and the SciNet HPC Consortium.