Memory researchers were stumped for many years by the apparent lack of learning deficits in animal models of human patients with medial-temporal lobe lesions. Only after recognizing the difference between declarative and non-declarative memory and the different ways in which tasks can be learned did the research data start to make sense. Developing a declarative memory task for non-human primates was one of the key steps in understanding the role of the medial temporal lobes in long-term memory formation.
