Interaction of Time Scales in Forced Rhythmic Networks of Neurons

Trustees Of Boston University, Boston

Investigators

Abstract

It is now well accepted that cognitive functions are supported by activity dispersed throughout the brain, and that signals are passed among participating regions of the brain. Indeed, there is an active direction of study, known as connectomics, that seeks to find such connections on multiple spatial scales. It is not sufficient, however, to find what regions are connected. Rather it is important to determine how and in what directions regions are connected. How are signals conveyed and acted upon as part of a neural computational process? To understand such neural computations, it is necessary to understand how input patterns of signals in space and time are processed at the target network. This is a huge scientific program in which mathematics and modeling can play a central role in guiding experiments. The aim of this research is to produce a body of work that is representative of the general issues that are encountered in adding input that has timing structure to networks exhibiting rhythmic structure. From such a body of examples, a goal of this project is to search for general principles about networks of neurons with external input. Such forced networks are far more complex than the well-studied phenomena of simple forced oscillators. This project will support two graduate students and will be carried out within the context of the Cognitive Rhythms Collaborative, a NSF-supported group of more than two dozen labs (mostly) in the Boston area working on brain dynamics and cognition. The CRC is designed to facilitate collaborations among its many groups, with special attention to the graduate students and postdocs of these groups. This project is concerned with the effects of input signals with multiple time scales on target networks of neurons that also have multiple time scales. From the huge number of examples of these phenomena manifest in the nervous system, this research is focused on two of particular biological importance. The first is the interaction of gamma and theta rhythms, mainly in hippocampal networks, with inputs from other parts of the hippocampus and neocortex also carrying such temporal patterns. The second concerns a rhythm that has been experimentally and computationally investigated in a region of parietal cortex in vitro; parietal cortices are known to be hubs of connections, with inputs from many other areas. The particular rhythm in question arises as an after-effect of stimulation, and has been shown computationally to change the network response to later tonic excitation. This research will improve understanding of the effect on a network displaying this rhythm of input with more complex spectral properties, such as inputs from other brain regions. The networks involved have both excitatory and inhibitory cells, sometimes with more than one kind of inhibitory cell producing multiple time scales in the target network.