Abstract
Four monkeys (Macaca mulatta) were trained on a delayed-response test prior to surgery. They were tested either within a few hours following a trephining procedure and for several days thereafter or within a few hours following frontal lobotomy and for 14 days thereafter, and just before sacrificing several weeks later. The effects of lobotomy appeared within 1 1/2 to 6 hours following surgery, and no delayed effects were detected. These effects (called primary) persisted at least for 10 weeks after testing terminated. Additional transient effects disappeared by the 5th to the 13th day.

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