Construction of Microdrive Arrays for Chronic Neural Recordings in Awake Behaving Mice

The use of the microelectrode technique for recording extracellular neural signals in vivo has a long and valued tradition in neuroscience ^{1, 2}. The ability to record electrical activity from many brain regions in freely behaving animals is, however, a more recent technology that is becoming increasingly common as the software packages for the acquisition, analysis and discrimination of neural signals becomes more sophisticated and user-friendly ^{3, 4}. The technological advances on the software side have also been accompanied by reductions in the weight and bulk of the implantable devices, which have been scaled down sufficiently for recording in small mammals, such as mice. By using lightweight (mostly plastic) components, researchers are able to construct microdrives that allow for independent positioning of electrodes or tetrodes to target a wide variety of brain regions ^5-7. Even deep brain structures, such as the amygdala ⁶ and the striatum ⁵, can be routinely targeted with the selection of an appropriately long drive screw. These recording techniques allow researchers to obtain high-fidelity neural signals and are in register with the electrical activity of single neurons recorded intracellularly ^{8, 9}. Using these types of microdrives, we have successfully recorded single-units from mice for up to two months after implantation ¹⁰. In addition, the lightweight nature of the devices (approximately 1.5-2.0 g) has resulted in behavioral performance that is comparable to non-implanted mice in many behavioral tasks. In particular, we have demonstrated that implanted mice exhibit normal performance in the novel object recognition task ¹⁰ and the object place task (unpublished data).

The use of microdrives coupled to multiple tetrodes allows researchers to monitor and analyze neural activity at the network level while also recording from multiple single-units within the brain. Recording with these tetrodes has several major advantages for unit identification purposes and enables the high accuracy acquisition and discrimination of multiple single-units ¹¹. We describe how to fabricate and gold-plate tetrode bundles and then subsequently load them into driveable electrode carriers. One type of drive carrier we describe is commercially available and the other is a simple, but easily expandable, drive design that can accommodate multiple carriers and tetrode arrangements without a significant investment of resources.