Rabbit and monkey visual cortex: more than a year of recording with up to 64 microelectrodes.

In the visual cortex of rabbits and a marmoset monkey, 32 and 64 microwires, respectively, were chronically implanted by an indirect insertion method so that the cortex was penetrated from the white matter. For more than 1 year recordings of action potentials of good quality were obtained at most electrodes. Recording stability was judged by spike shape, spike train autocorrelograms, and spike rates: within recording sessions, stability was essentially perfect. Periods in which the signals of several electrodes were stable could last for several days. A method of in vivo reconstruction of the electrode locations by micro-X-rays and subsequent stereophotogrammetry is presented. The aspect of animal welfare is considered.