Head-mounted approaches for targeting single-cells in freely moving animals

Neural network processing is usually studied using the spike times of many extracellularly recorded neurons. Elucidating the cellular-synaptic mechanisms underlying these firing patterns requires identifying and controlling single cells and assessing their inputs. Single cell glass electrode techniques (intracellular, patch and juxtacellular) are well suited to filling this gap, in terms of physiology, cell identity and behavior. However, they are typically limited to in vitro and immobilized in vivo experiments, primarily due to the necessity for mechanical stability and steep learning curves. Several approaches have been recently developed to extend these technologies to freely moving animals. Here we summarize the advantages and results for different methods of single neuron glass recordings in vivo. We further review three approaches used to date for single cell recording in freely moving animals: static anchor systems, manual mechanic drives and motorized drives. Finally, we highlight new technologies capable of expanding the utility of single neuron recording in freely moving animals.