The hippocampus plays a critical role at encoding discontiguous events for subsequent declarative memory expression in mice
Hippocampus. 2007-01-01; 17(4): 264-270
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1. Hippocampus. 2007;17(4):264-70.
The hippocampus plays a critical role at encoding discontiguous events for
subsequent declarative memory expression in mice.
Mingaud F(1), Le Moine C, Etchamendy N, Mormède C, Jaffard R, Marighetto A.
(1)CNRS UMR 5106 Neurosciences Cognitives, Université Bordeaux 1 Avenue des
Facultés, Talence, France.
The hypothesis that hippocampal activity at encoding is causally related to
subsequent declarative memory expression is tested in the mouse, by using
lidocaine inactivation of the hippocampus in combination with c-fos neuroimaging
analysis. We employed a two-stage radial maze paradigm of spatial discrimination,
which was previously shown to dissociate between declarative and nondeclarative
expression of memory related to the same acquired material. In Stage 1
(encoding), mice learnt the constant location of food among a set of six arms
(three baited, three unbaited) by being submitted repeatedly to discontiguous
experiences with each arm separately (« go/no-go » discrimination). In Stage 2
(test-session), they are challenged with novel presentations of the arms, which
are either combined into pairs of opposite valence (« two-choice » discrimination),
or opened all six together (« six-choice » discrimination). Previous experiments
have demonstrated that the « two-choice » situation is a critical test for
declarative memory while « six-choice » discrimination may rely on procedural
memory. We observed that (i) hippocampal activity measured by c-fos mRNA
expression was increased by « go/no-go » learning, and this activation was blocked
by pre-training local infusions of lidocaine; (ii) when performed just before
each session of Stage 1, such inactivation spared the acquisition of « go/no-go »
discrimination but produced, subsequently, a selective deficit in the
« two-choice » test (not in the « six-choice » test). This study indicates that the
hippocampus is « spontaneously » engaged in encoding processes necessary for
long-term storage of discontiguous experiences under a form enabling flexible
declarative memory expression.
PMID: 17265459 [Indexed for MEDLINE]