Transitivity, flexibility, conjunctive representations, and the hippocampus. I. An empirical analysis.
After training on a set of four ordered, simultaneous, odor discrimination problems (A+B-, B+C-, C+D-, D+E), intact rats display transitivity: When tested on the novel combination BD, they choose B. Rats with damage to the hippocampus, however, do not show transitivity (Dusek and Eichenbaum, 1997. Proc Natl Acad Sci U S A 94:7109-7114). These results have been interpreted as support for the idea that the hippocampus is a relational memory storage system that enables the subject to make comparisons among representations of the individual problems and choose based on inferential logic. We provide evidence for a simpler explanation. Specifically, subjects make their choices based on the absolute excitatory value of the individual stimuli. This value determines the ability of that stimulus to attract a response. This conclusion emerged because after training on a five-problem set (A+B-, B+C-, C+D-, D+E-, E+F-) rats preferred B when tested with BE, but not when tested with BD. The implication of these results for how to conceptualize the role of the hippocampus in transitive-like phenomena is discussed.
Department of Psychology, University of Colorado, Boulder, Colorado 80309, USA.
Michael
M
Van Elzakker
Randall C
RC
O'Reilly
Jerry W
JW
Rudy
D000818:Animals; D001522:Behavior, Animal / Q000502:physiology; D003071:Cognition / Q000502:physiology*; D003463:Cues; D003714:Denervation; D004193:Discrimination Learning / Q000502:physiology*; D006624:Hippocampus / Q000293:injuries / Q000473:pathology / Q000503:physiopathology*; D007859:Learning Disabilities / Q000473:pathology / Q000503:physiopathology*; D008569:Memory Disorders / Q000473:pathology / Q000503:physiopathology*; D008959:Models, Neurological; D009483:Neuropsychological Tests; D051381:Rats; D020318:Rats, Long-Evans; D012903:Smell / Q000502:physiology