Learning associations between places and visual cues without learning to navigate: Neither fornix nor entorhinal cortex is required

Abstract

ABSTRACT:Rats with fornix transection, or with cytotoxic retrohippocampal lesions that removed entorhinal cortex plus ventral subiculum, performed a task that permits incidental learning about either allocentric (Allo) or egocentric (Ego) spatial cues without the need to navigate by them. Rats learned eight visual discriminations among computer-displayed scenes in a Y-maze, using the constant-negative paradigm. Every discrimination problem included two familiar scenes (constants) and many less familiar scenes (variables). On each trial, the rats chose between a constant and a variable scene, with the choice of the variable rewarded. In six problems, the two constant scenes had correlated spatial properties, either Allo (each constant appeared always in the same maze arm) or Ego (each constant always appeared in a fixed direction from the start arm) or both (Allo ؉ Ego). In two No-Cue (NC) problems, the two constants appeared in randomly determined arms and directions. Intact rats learn problems with an added Allo or Ego cue faster than NC problems; this facilitation provides indirect evidence that they learn the associations between scenes and spatial cues, even though that is not required for problem solution. Fornix and retrohippocampal-lesioned groups learned NC problems at a similar rate to sham-operated controls and showed as much facilitation of learning by added spatial cues as did the controls; therefore, both lesion groups must have encoded the spatial cues and have incidentally learned their associations with particular constant scenes. Similar facilitation was seen in subgroups that had short or long prior experience with the apparatus and task. Therefore, neither major hippocampal input-output system is crucial for learning about allocentric or egocentric cues in this paradigm, which does not require rats to control their choices or navigation directly by spatial cues. Hippocampus 2003; 13:445-460.

Fornix Lesions Decouple the Induction of Hippocampal Arc Transcription from Behavior But Not Plasticity

“…Performance on hippocampal-independent tasks such as cue-approach learning remains intact after fornix lesions (Packard et al, 1989;McDonald and White, 1993;Sziklas and Petrides, 2002;Gaffan et al, 2003). The deficits reported here in spatial but not cue-approach learning after fornix lesions are consistent with this previous work.…”

“…Fornix lesions reduce long-term potentiation (LTP) persistence in the dentate gyrus (Buzsaki and Gage, 1989;Nakao et al, 2001), impair hippocampus-dependent spatial learning, but spare hippocampus-independent cue-approach learning (Nilsson et al, 1987;Packard et al, 1989;Sutherland and Rodriguez, 1989;Sziklas and Petrides, 2002;Gaffan et al, 2003). The behavioral correlates of hippocampal neuronal activity are essentially maintained after fornix lesions, such that pyramidal cells reveal place fields (Miller and Best, 1980;Shapiro et al, 1989).…”

Movements of exploration intact in rats with hippocampal lesions

“…For example hippocampal rats do respond to ambient cues, and display both instrumental [10,14,46] and latent [16,48] learning in response to ambient cues. Furthermore, rats with hippocampal lesions do explore novel objects [29,30,37], and respond to changes in the arrangement of those objects [9,28,40].…”

A study on the role of the dorsal striatum and the nucleus accumbens in allocentric and egocentric spatial memory consolidation

“…Behavioral and electrophysiological data suggest that the subject's place of introduction into the environment can induce the preferential use of an egocentric or an allocentric coding system (Whishaw et al 1987;Sharp et al 1990;Moghaddam and Bures 1996;Holdstock et al 2000;De Leonibus et al 2003b;Gaffan et al 2003). Accordingly we found (Experiment 1) that animals subjected to the spatial change from the same position as during habituation (SP-DA group) selectively reacted to the spatial change, exploring far more DO than NDO.…”