The effects of sleep on neurons in isolated cerebral cortex

Slabs of cat parietal cortex with some 2 mm of underlying white matter were surgically isolated from the rest of the nervous system, without interference with the superficial blood supply. Wire micro-recording electrodes were inserted into the isolated cortex; bone, muscle and skin wounds were repaired and the animal allowed to recover from anaesthesia. The adequacy of surgical isolation was examined histologically 8-12 weeks after operation. Only one of the six preparations reported here showed surviving neural connections with the rest of the brain. Soon after operation, spontaneous bursts of neural activity appeared within the isolated area. These became more frequent until neural dis­charge was continuous but irregular. Our records were made from this time onwards. The interval distributions obtained from neurons within the isolated area did not differ significantly from log-normal curves. When the unrestrained animal fell asleep, there was no significant alteration in the modal interval or geometric standard deviation of interval distributions recorded from cells in isolated cortex. The interval distributions of neurons in isolated cerebral cortex resembled those of neurons in the intact cortex of an alarmed animal. It is concluded that the reduction of modal interval that is shown by neurons in intact cortex when an animal falls asleep is probably due to the neural influence of infracortical structures.

Technique for Monitoring Cardiac Function without Handling or Restraining the Animal

The method presented in this paper allows the long-term recording of HR in an unrestrained animal, housed in the actual experimental cage, with permanently attached recording leads. Using this technique, it is possible to employ automated apparatus and programming equipment and to experiment with more than one animal at a time in a research area which has not been characterized by such procedures. Techniques for the construction of rat-proof leads, a terminal to which the leads are attached, a commutator, and the surgical procedure for implanting the terminal, were described.