We use in vivo electrophysiology in acute or chronic applications. Acute preparations involve using silicone probes in head-fixed mice, and allow for a high yield of isolated single units (neurons) during optogenetic tagging and manipulation experiments. In chronic preparations, electrode assemblies are implanted permanently, and changes in neuronal activity or in vivo functional connectivity can be tracked over longer time periods (weeks to months).
In both cases, a microelectrode array is inserted into a specific brain region, where it can record voltage changes. During an action potential, electric current flowing across the plasma membrane can be measured as a change in voltage potential. Each microelectrode will record a signal that is the summed voltage change from activity of multiple neurons and processes. The signal is first filtered to isolate spike activity from the lower frequency local field potential (LFP). Spikes are then detected, and identifying features (i.e. amplitude, waveform characteristics) are used to cluster spikes and determine which spikes come from which neuron, a process known as spike sorting.
In the Creed Lab, we combine optogenetic manipulations with in vivo electrophysiology to record from genetically-identified neurons within the basal ganglia as animals perform behavioral tasks. We also use the technique to assess connectivity between brain regions. This approach lets us ask how neural activity and network dynamics change over the course of pain chronification or drug withdrawal, and whether our neuromodulation interventions affect neural circuit function during behaviors.