The ventral hippocampus is necessary for expressing a spatial memory
Brain Struct Funct. 2011-06-12; 217(1): 93-106
DOI: 10.1007/s00429-011-0332-y
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Loureiro M(1), Lecourtier L, Engeln M, Lopez J, Cosquer B, Geiger K, Kelche C, Cassel JC, Pereira de Vasconcelos A.
Author information:
(1)Laboratoire d’Imagerie et de Neurosciences Cognitives, UMR 7237, Université de
Strasbourg, CNRS, IFR 37 des Neurosciences, GDR CNRS 2905 Neuromem, 12 rue
Goethe, 67000 Strasbourg, France.
Current views posit the dorsal hippocampus (DHipp) as contributing to spatial
memory processes. Conversely, the ventral hippocampus (VHipp) modulates stress,
emotions and affects. Arguments supporting this segregation include differences
in (i) connectivity: the DHipp is connected with the entorhinal cortex which
receives visuospatial neocortical inputs; the VHipp is connected with both the
amygdala and hypothalamus, (ii) electrophysiological characteristics: there is a
larger proportion of place cells in the DHipp than in the VHipp, and an
increasing dorsoventral gradient in the size of place fields, suggesting less
refined spatial coding in the VHipp, and (iii) consequences of lesions: spatial
memory is altered after DHipp lesions, less dramatically, sometimes not, after
VHipp lesions. Using reversible inactivation, we report in rats, that lidocaine
infusions into the DHipp or VHipp right before a probe trial impair retrieval
performance in a water-maze task. This impairment was found at two
post-acquisition delays compatible with recent memory (1 and 5 days).
Pre-training blockade of the VHipp did not prevent task acquisition and drug-free
retrieval, on the contrary to pre-training blockade of DHipp, which altered
performance in a subsequent drug-free probe trial. Complementary experiments
excluded possible locomotor, sensorimotor, motivational or anxiety-related biases
from data interpretation. Our conclusion is that a spatial memory can be acquired
with the DHipp, less efficiently with the VHipp, and that the retrieval of such a
memory and/or the expression of its representation engages the dorsoventral axis
of the hippocampus when the task has been learnt with an entirely functional
hippocampus.