Time and treason to the trisynaptic teachings: theoretical comment on Kesner et Al. (2005)

Early descriptions of the hippocampal formation emphasized the serial nature of its circuitry, a description that suggests even a focal lesion would break a chain of processing and leave the entire region inoperative. Nevertheless, R. P. Kesner, M. R. Hunsaker, and P. E. Gilbert (2005) show that rats with CA1 lesions, but not rats with CA3 lesions, were impaired on a task in which animals were required to make associations between an object and an odor that were separated by a brief (10-s) delay. The present commentary makes 2 points relevant to their findings. First, several lines of evidence suggest that CA1 can operate somewhat independently of CA3 in some instances. Second, it is unclear whether the delay interval acted directly (by requiring a memory for a timeline of events) or indirectly (by outlasting the associative abilities of areas other than CA1) in causing performance to depend on the integrity of CA1.