Anikeeva, P. et al. Nat. Neurosci. advance online publication (4 December 2011).

Studying brain physiology in freely moving rodents is steadily replacing neuroscience practices in which animals are anesthetized or restrained to study their brains. Multi-unit electrode-based neural recording systems can be combined with optical hardware for optogenetic control, but so far these setups have not been small and light enough to be easily carried by behaving mice. Anikeeva et al. attached 16 electrodes (four 'tetrode' units) to an optical fiber shaft and generated a lightweight and compact device, the 'optetrode', that enables delivery of both the light source and recording electrodes together in multiple regions of the animal's brain. The optetrode can be used to perform optical stimulation or inhibition of brain activity and simultaneous multichannel electrophysiological recordings in mice during open-field exploration.