Targeted Path Scanning: An Emerging Method for Recording Fast Changing Network Dynamics across Large Distances

Attention is being increasingly focused on the dynamical behavior of large networks of neurons and astrocytes and the changes in these dynamics that occur during the progression of diseases like epilepsy. Recording from large numbers of identified cell types has been traditionally difficult, but the advent of fluorescent indicators capable of detecting changes in the internal calcium levels of cells has led to the ability to visually record the activity of large numbers of cells. However, for most imaging techniques the temporal resolution is sharply limited by the time it takes lasers to traverse the typical raster scan. As network dynamics can evolve quite rapidly, this is a serious limitation. The present paper describes the Targeted Path Scan technique, which dramatically increases the scanning frequency by allowing the user selection of trajectories through cells of interest. TPS is discussed in the context of a study of altered network dynamics in a common rat model of epilepsy. In this study, traveling waves of calcium transients that were frequently encountered in astrocytes imaged in brain slices obtained from control rats were dramatically reduced in astrocytes imaged in brain slices obtained from rats that had experienced status epilepticus. The speed of these traveling waves would have made them impossible to identify using traditional scanning techniques.