The Hippocampus and Complex, Nonspatial Discrimination: Is Learning Still "Not Possible"?
Leonard E. Jarrard Washington and Lee University
T. L. Davidson Purdue University
Karl Lashley spent a major part of his career attempting to identify the areas of the brain that underlie learning and memory functions ( Beach, Hebb, Morgan, & Nissen, 1960). A basic research strategy used by Lashley was to assess the acquisition and retention of discrimination learning in rats following surgical destruction of parts of the cortex generally thought to be involved in the formation of associations and with memory. After reviewing the evidence obtained from these and other experiments, Lashley suggested that little had been discovered about the localization of learning and memory processes in the brain. Given that the substrates for memory could not be located, Lashley concluded somewhat whimsically, but also with a degree of resignation, that he sometimes felt that "learning just is not possible."
An important development in the study of the neural substrates of learning and memory occurred a few years after Lashley's lament when Scoville and Milner( 1957) reported the case of H.M., the patient who suffered severe anterograde amnesia following bilateral damage to hippocampus and adjacent medial temporal lobe structures. The discovery of H.M.'s impairment attracted attention to the hippocampus as a possible substrate for learning and memory, and led to the generation of a number of animal models of hippocampal function. Based in large part on data used to support such models, the hippocampus has been implicated generally in the processing of information -- both spatial and nonspatial.