1. Early view: O'Keefe and Nadel's (1978)
    1. hippocampus mediates cognitive map (the establishment of an organized neural representation of the physical environment)
    2. Evidence
      1. Rats with hippocampal system damage are severely impaired in many form of spatial exploration and learning, e.g. water maze task
      2. Hippocampus place cells
  2. 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
    1. Many new findings demonstrated deficits in various types of nonspatial learning following hippocampal damage.
  3. Experiments using olfactory cues that exploit rats' natural foraging strategies (Figure 2-42)
    1. animals were trained with stimuli that consisted of distinct odors added to the sand under which was buried a reward.
    2. Initially, the rats learned a set of odor paired associates
    3. Then they learned a second set of paired associates, and each of these associations involved one of the odors used in the previous set
    4. Then, the rats were given a probe test to determine whether the learned representations support two forms flexible memory expression.
      1. 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?
      2. 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?
    5. Both intact rats and rats with hippocampal damage learned paired associates rapidly
    6. Intact rats showed strong transitivity across the sets, while rats with hippocampal damage showed no evidence of transitivity
    7. Intact rats showed their associations were indeed symmetrical, but rats with hippocampal damage showed no evidence of symmetry
  4. 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 change.
    1. 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 Fig. 2-43
    2. 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
      1. Random search
      2. direct search
  5. Hippocampal representations encode any relationship among cues as well as relationships between stimuli and behavioral responses to those stimuli.