We describe the diverse steps to implant chronic silicon probes and to record place cells in mice that are running head-fixed on a cue-enriched treadmill apparatus.
An important requisite for understanding brain function is the identification of behavior and cell activity correlates. Silicon probes are advanced electrodes for large-scale electrophysiological recording of neuronal activity, but the procedures for their chronic implantation are still underdeveloped. The activity of hippocampal place cells is known to correlate with an animal's position in the environment, but the underlying mechanisms are still unclear. To investigate place cells, here we describe a set of techniques which range from the fabrication of devices for chronic silicon probe implants to the monitoring of place field activity in a cue-enriched treadmill apparatus. A micro-drive and a hat are built by fitting and fastening together 3D-printed plastic parts. A silicon probe is mounted on the micro-drive, cleaned, and coated with dye. A first surgery is performed to fix the hat on the skull of a mouse. Small landmarks are fabricated and attached to the belt of a treadmill. The mouse is trained to run head-fixed on the treadmill. A second surgery is performed to implant the silicon probe in the hippocampus, following which broadband electrophysiological signals are recorded. Finally, the silicon probe is recovered and cleaned for reuse. The analysis of place cell activity in the treadmill reveals a diversity of place field mechanisms, outlining the benefit of the approach.
Silicon probes present several advantages for electrophysiological recordings, including the fact that they are designed with sharp profiles minimizing tissue damage and that they present a precise layout of densely packed recording sites1,2,3,4. They are used to study various systems in different species, including humans3,5,6, with diverse approaches1,7. Yet, their recurrent use is still relatively limited because of their cost, fragility, and the fact that convenient methods for chronic experiments are lacking8. Recent advances in 3D printing technology have made possible the custom designing of devices such as micro-drives and head-plates to allow an easier handling of these delicate electrodes. In a first step, we will describe how to build and use a set of tools that we have developed for the implantation of chronic silicon probes14.
While place cells are typically studied using freely-moving animals running in mazes, recently they were also investigated in virtual environments15 and in treadmill apparatii9 (Figure 1A). These experimental methods offer the advantage that animals can be head-restrained, making the use of 2-photon microscope15, patch-clamp16, and optrode9,10,11 techniques easier, in addition to providing enhanced control on animal behavior and environmental cues12. In a second step, we will present the procedures for training mice and recording place cell activity in a treadmill apparatus.
Chronic recording of neuronal activity is critical for understanding neural processes such as hippocampal place fields. Our approach to perform chronic silicon probe implantantation distinguishes itself from other methods7,18,19,20 by the fact that it is relatively simple to recover the electrode package at the end of the experiment. While place cells are typically studied in freely-moving cond…
The authors have nothing to disclose.
This work was supported by the Korea Institute of Science and Technology Institutional Program (Projects No. 2E26190 and 2E26170) and the Human Frontier Science Program (RGY0089/2012).
Silicon Probe | Neuronexus | Buzsabi32 | Recording electrode |
Recording system | Intantech | RHD2132/RHD2000 | |
3D printer | Asiga | Pico Plus 27 | High resolution printer for micro-drive |
3D printer | Stratasys | Mojo | Lower resolution printer for hat components |
Stereotaxic apparatus | Kopf | Model 963 | |
Binocular microscope | Leica | M60 | |
Treadmill apparatus | We build them |