Nineteen male albino rats were trained to perform a memory task ("win-stay; delayed matching to sample") in a radial eight-arm maze. On Trial 1, animals were required to locate food present in only one maze arm and, after a 1-min delay, learned to return directly to the single baited arm on Trial 2. Animals were also trained on a five-trial version, in which three additional trials with interposed 1-min delays were used. Following training, animals were implanted with a single chronic electrode using electrophysiological guidance. In this way, electrodes could be placed directly into the granule cell layer of the dentate gyrus. Thirty seconds of granule cell stimulation administered during the delay period between Trials 3 and 4 of the memory task produced a severe, but reversible, disruption of Trial 4 performance similar to the "working memory" deficits observed after hippocampal lesions.
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