Robust, highly customizable, and economical multi-channel electrode for chronic multi-unit recording in behaving animals.

Multi-unit recording has been one of the most widely used techniques to investigate the correlation between multiple neuronal activities and behavior. However, a common problem of currently used multi-channel electrodes is their physical weakness. In this study, we developed a novel multi-channel electrode with sufficient physical strength to penetrate a thickened dura mater. This electrode consists of low-cost materials and is easily fabricated, and it enables recording without removing dura mater, thereby reducing the risk of inflammation, infection, or brain herniation. The low-cost multi-channel electrode developed in this study would be a useful tool for chronic recording in behaving animals.

Neck collar for restraining head and body movements in rats for behavioral task performance and simultaneous neural activity recording.

BACKGROUND: Head fixation has been one of the major methods in behavioral neurophysiology because it allows precision in stimulus application and behavioral assessment. Most neural recordings in awake monkeys have been obtained under head fixation, which is nowadays also being used in awake rodents. However, head fixation devices in rats often become unstable within several months, which increases risks for inflammation, infection, and necrosis of the bone and surrounding tissue. NEW METHOD: In this study we developed a novel non-invasive "neck collar system" for restraining the head and body movements of behaving rats. RESULTS: The attachment of the neck collar for 2-3 months did not affect the animals' health and welfare. Rats under neck-collar fixation could learn a behavioral task (standard delayed licking task) with the same efficiency as those under standard head fixation. They could also learn a more complicated task (delayed pro/anti-licking task) under neck-collar fixation and afterwards transfer their learning to the task under standard head fixation. Furthermore, we were able to record single-unit activity in rats under neck-collar fixation during the performance of the standard delayed licking task. COMPARISON WITH EXISTING METHOD(S): This system consists of economical materials and is easily constructed, and it enables head-restraint without surgery, thus eliminating the risk of inflammation or infection. CONCLUSIONS: We consider the neck-collar fixation developed in this study would be useful for restraining the head of a behaving rodent.

Discrete coding of stimulus value, reward expectation, and reward prediction error in the dorsal striatum.

To investigate how the striatum integrates sensory information with reward information for behavioral guidance, we recorded single-unit activity in the dorsal striatum of head-fixed rats participating in a probabilistic Pavlovian conditioning task with auditory conditioned stimuli (CSs) in which reward probability was fixed for each CS but parametrically varied across CSs. We found that the activity of many neurons was linearly correlated with the reward probability indicated by the CSs. The recorded neurons could be classified according to their firing patterns into functional subtypes coding reward probability in different forms such as stimulus value, reward expectation, and reward prediction error. These results suggest that several functional subgroups of dorsal striatal neurons represent different kinds of information formed through extensive prior exposure to CS-reward contingencies.