RODENT HIPPOCAMPUS IS NOT JUST FOR 'SPACE'
- Early view: O'Keefe and Nadel's (1978)
- hippocampus mediates cognitive map (the establishment of an organized neural representation of
the physical environment)
- Rats with hippocampal system damage are severely impaired in many form of spatial
exploration and learning, e.g. water maze task
- Hippocampus place cells
- Much research has confirmed that the hippocampus is critical to spatial learning and memory, but recent
studies have indicated limitations to its role in spatial processing
- Many new findings demonstrated deficits in various types of nonspatial learning following
- Experiments using olfactory cues that exploit rats' natural foraging strategies (Figure 2-42)
- animals were trained with stimuli that consisted of distinct odors added to the sand under which was
buried a reward.
- Initially, the rats learned a set of odor paired associates
- Then they learned a second set of paired associates, and each of these associations involved one of
the odors used in the previous set
- Then, the rats were given a probe test to determine whether the learned representations support two
forms flexible memory expression.
- Transitivity: measurement of ability to infer an association between two odors that shared a
common associate, e.g. if A-->B and B -->C then A --> C?
- Symmetry: measurement of ability to recognize associated odors when they were presented
in the reverse of their training order, e.g. if B--> C then C --> B?
- Both intact rats and rats with hippocampal damage learned paired associates rapidly
- Intact rats showed strong transitivity across the sets, while rats with hippocampal damage showed
no evidence of transitivity
- Intact rats showed their associations were indeed symmetrical, but rats with hippocampal damage
showed no evidence of symmetry
- A variety of recording studies have shown in rats hippocampal cells fire in association with conjunctions
or combinations of multiple visual, auditory, and olfactory stimuli. The same hippocampal cells that have
spatial firing properties in some tasks also have other nonspatial firing correlated when the task demands
- A cell that fired when the rat was in a specific location as the animal performed a spatial task also
fired during odor exploration when the animal was performing an olfactory discrimination task. See
- The spatial firing patterns changed dramatically when the behavioral requirements of the task were
altered, even though all the spatial cues were held constant. See Fig. 2-44
- Random search
- direct search
- Hippocampal representations encode any relationship among cues as well as relationships between stimuli
and behavioral responses to those stimuli.
- Eichenbaum, H. B. et al (1996). Is rodent hippocampus just for 'space'? Current Opinion in Neurobiology,
6, 187-195. This journal is in Thode Library (Periodicals, 2nd floor)
- Eichenbaum, H., Schoenbaum, G., Young, B., & Bunsey, M. (1996). Functional organization of the
hippocampal memory system. Proceedings of the National Academy of Science (U.S.A.), 93,
13500-13507. (This article is in courseware)