Electrophysiological recording and optogenetic control of neuronal activity in behaving animals have been integral to the elucidation of how neurons and circuits modulate network activity in the encoding and causation of behavior. However, most current electrophysiological methods require substantial economical investments and prior expertise. Further, the inclusion of optogenetics with electrophysiological recordings in freely moving animals adds complexity to the experimental design. Expansion of the technological repertoire across laboratories, research institutes, and countries, demands open access to high-quality devices that can be built with little prior expertise from easily accessible parts of low cost. We here present an affordable, truly easy-to-assemble micro-drive for electrophysiology in combination with optogenetics in freely moving rodents. The DMCdrive is particularly suited for reliable recordings of neurons and network activities over the course of weeks, and simplify optical tagging and manipulation of neurons in the recorded brain region. The highly functional and practical drive design has been optimized for accurate tetrode movement in brain tissue, and remarkably reduced build time. We provide a complete overview of the drive design, its assembly and use, and proof-of-principle demonstration of recordings paired with cell-type-specific optogenetic manipulations in the prefrontal cortex (PFC) of freely moving transgenic mice and rats. Tetrode-containing micro-drives have long been an important technique for recordings of extracellular neuronal signals in behaving mice 1 and rats 2. More recently developed techniques, such as neuronal population calcium imaging 3 and high-density silicon probes 4 are superior to micro-drive arrays in respect to the number of neurons that can be recorded simultaneously. Despite this, there is still a range of application areas where micro-drive arrays are the method of choice, particularly for chronic recordings of action potential and local field potential (LFP) activity in freely moving rodents, including in conjunction with optogenetics. We here present a lowcost, easy to assemble micro-drive for tetrode recordings in conjunction with optogenetics (the DMCdrive). The strategy for the design has been to construct a user-friendly low size-low weight drive that reliably provides a) single-unit recordings over time b) persistent precise and predictable movement of all tetrodes c) efficient opto-tagging and optical manipulation of neurons. The drive consists of a few lab-made parts, printed using a standard 3D printer, a custom-made electronic interface board (EIB), and parts available off-the-shelf, and the easy-to-assemble design makes the drive particularly suitable for researchers with no or little experience of drive building. The production cost of the 3D printed material is ~ 1$, and the total cost for one drive ~ 40$ (six 3D-printed parts, an EIB with an 18-pin Omnetics connector, eight screws and a screw nut).

Electrophysiological recording and optogenetic control of neuronal activity in behaving animals have been integral to the elucidation of how neurons and circuits modulate network activity in the encoding and causation of behavior. However, most current electrophysiological methods require substantial economical investments and prior expertise. Further, the inclusion of optogenetics with electrophysiological recordings in freely moving animals remains a general challenge. Expansion of the technological repertoire across laboratories, research institutes, and countries, demands open access to high-quality devices that can be built with little or no prior expertise from easily accessible parts of low cost. We here present a very affordable, truly easy-to-assemble micro-drive for electrophysiology in combination with optogenetics in freely moving mice and rats. The DMCdrive is particularly suited for reliable long-term recordings of neurons and network activities, and simplify optical tagging and manipulation of neurons in the recorded brain region. The highly functional and practical drive design has been optimized for accurate tetrode movement in brain tissue, and remarkably reduced build time. We provide a complete overview of the drive design, its assembly and use, and proof-of-principle demonstration of long-term recordings paired with cell-type-specific optogenetic manipulations in the prefrontal cortex (PFC) of freely moving transgenic mice and rats.

This commentary centers on the novel findings by Shepard et al. (2016) published in eNeuro. The authors interrogated tonotopic map dynamics in auditory cortex (ACtx) by employing a natural sound-learning paradigm, where mothers learn the importance of pup ultrasonic vocalizations (USVs), allowing Shepard et al. to probe the role of map area expansion for auditory learning. They demonstrate that auditory learning in this paradigm does not rely on map expansion but is facilitated by increased inhibition of neurons tuned to low-frequency sounds. Here, we discuss the findings in light of the emerging enthusiasm for cortical inhibitory interneurons for circuit function and hypothesize how a particular interneuron type might be causally involved for the intriguing results obtained by Shepard et al.