Transitivity, flexibility, conjunctive representations, and the hippocampus. I. An empirical analysis

Hippocampus. 2003;13(3):334-40. doi: 10.1002/hipo.10083.

Abstract

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.

Publication types

  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Animals
  • Behavior, Animal / physiology
  • Cognition / physiology*
  • Cues*
  • Denervation
  • Discrimination Learning / physiology*
  • Hippocampus / injuries
  • Hippocampus / pathology
  • Hippocampus / physiopathology*
  • Learning Disabilities / pathology
  • Learning Disabilities / physiopathology*
  • Memory Disorders / pathology
  • Memory Disorders / physiopathology*
  • Models, Neurological
  • Neuropsychological Tests
  • Rats
  • Rats, Long-Evans
  • Smell / physiology