A floating microwire technique for multichannel chronic neural recording and stimulation in the awake freely moving rat.

We describe a cheap, and relatively simple, method for the construction and implantation of bundles of six fully-floating 25 microm microwire electrodes in the rat central nervous system (CNS). Wires are stiffened for implantation by temporarily attaching them to a micropipette guide with sucrose which subsequently dissolves in the brain. The associated headpiece connector mates with a plug-in FET which gives high quality recordings, free of movement artefacts, even when used with 3 m of unscreened cable. Different electrode configurations are easily selected and sufficient space is available on the headpiece to accommodate injection guide cannulae. The electrode performance was evaluated in 42 implanted rats where the system was used successfully for long term recording of superior colliculus (SC) deep layer neurons and behavioural responses evoked by electrical stimulation of the same wires. We obtained neural recordings on 81% of the 252 implanted wires, with 79% of these providing good, reliably discriminable, single unit responses following post-operative recovery. During a five-week testing period on a subsample of the 42 'best' electrodes (one per animal), we found the same sensory or motor response 1 week after initial testing in 91% wires, 67% after 2 weeks and 24% after 5 weeks. Using waveform templating techniques we were able to show that 62% of the electrodes still working at 5 weeks were reliably recording the same cell.