Effect of focality of transcranial currents on neural responses

To elicit localized neural activity, focused electric fields are necessary. In the case of transcranial electric fields, the relationship between the spatial extent of the field and the extent of the resulting neural response is not well understood. To understand this relationship, an ex vivo platform allowing stimulation at a distance was created. By separating the brain slice from the stimulation electrodes, the electric fields reaching the slice are similar to transcranial fields. We compare the resulting spatial extent of neuronal response across various electrode patterns designed to elicit different extents of focused electric fields. Comparing the attained focus of the neural response with the focus of the electric field, we observe that neural responses are more focused than fields, and that improving the focus by 17% improves that of the response by around 50%.