Neurons communicate by both slow chemical and fast electrical signaling. The membranes of neurons are excitable, and the coordinated voltage fluctuation through the neuronal membrane is a fundamental function. By collectively changing their membrane potentials in a synchronous manner neurons can generate large electrical fields in their extraneuronal milieu. This project asks whether these collectively generated electrical fields can influence the activity of individual neurons. The proposed work impacts the understanding of how individual nerve cells are influenced by their electrical environment. Since neurons are not surrounded by a constant extracellular potential, it is critical to understand the effect of an inhomogeneous local field on a neuron's excitability. These inferred field effects could be relevant in any excitable, neuronal tissue.
Current understanding of the dynamics of the membrane potential in individual neurons and in small networks is based on the theories of linear and nonlinear electrical phenomena. A key assumption is that the extracellular potential does not vary significantly in space and its effect on the membrane potential along neuronal processes can be neglected. However, spatial inhomogeneities in the local electrical field at the sub-millimeter scale, challenge the assumption. Experimentally observed fluctuations in the local field potential can be as large as 1 to 3 mV and are large enough to potentially shift spike timing. Thus local electrical fields might entrain synchronization among the embedded neurons, both under normal and pathological conditions. Given the physics of hippocampal and neocortical tissue, such effects might therefore play an important role in information processing in health and disease.
The experimental part of this proposal will be carried out at Rutgers University, while the modeling will be done at Caltech. The broader impact of the proposal is to promote training of minority and female undergraduate students via a summer intern program. Also, the project has a strong interdisciplinary nature through the blend of experimental and computational components in the research. Understanding the effects of spatially varying external potential is also important for public safety. People are increasingly surrounded by devices that emit low- and high-frequency electro-magnetic fields. Devices such as electric power distribution systems, cell phones, and wireless WiFi nodes can create electrical fields with the potential to modify nerve funciton. There is also risk from the growing use of deep-brain, transcranial magnetic stimulators and other neuroprosthetic devices. These devices introduce external current sources into the nervous system, demanding a better understanding of the induced extracellular voltages on neuronal activity.
