[Abstract Title]. - Society for Neuroscience

NIMH (MH61460)
AHFMR
NSERC
Title: Learning parameters mitigate retrograde amnesia after hippocampal damage
Authors: *H. LEHMANN 1 , F. T. SPARKS 2 , S. C. SPANSWICK 2 , R. J. SUTHERLAND 2 ;
1 Dept Psychol, Trent Univ., Peterborough, ON, Canada; 2 Neurosci., Univ. Lethbridge,
Lethbridge, AB, Canada
Abstract: Damage to the hippocampus (HPC) causes retrograde, but not anterograde, amnesia
for several types of memories. With similar learning parameters, HPC damage impairs memories
that were acquired before damage, but does not impair the ability to establish new memories.
Thus, neural systems outside the HPC are capable of acquiring and storing memories, but
normally the HPC competes with and prevents these systems from fully doing so. We examined,
in contextual fear conditioning and object recognition, whether repeated learning sessions would
engage the other systems and mitigate the effects of post-training HPC damage. In the contextual
fear-conditioning task, rats were given 1 or 11 fear conditioning sessions, which were matched
for number of shocks and amount of time in the context. One week after the initial learning
session, the rats received sham or neurotoxic-induced damage to the entire hippocampus.
Following recovery, rats were returned to the context for a retention test during which the
amount of behavioural freezing was measured as an index of memory. The rats were also tested
in a novel context to determine whether the freezing was specific to the learning context. In the
object recognition task, rats received either 10 or 30 learning sessions. Approximately 45 days
after the first learning session, rats received sham or complete HPC damage. Results indicate
that, in the contextual fear conditioning task, sham rats, regardless of the number of learning
sessions, expressed robust freezing in the context that was paired with shock and very little
freezing in the novel context. Rats with HPC damage that previously received a single learning
session expressed minimal and significantly less freezing than their respective control group. In
contrast, rats with HPC damage that received repeated conditioning sessions expressed high
levels of freezing and did not significantly differ from rats in their respective control group.
Moreover, this freezing was specific to the conditioning context because the same rats did not
freeze in the novel context. In the object recognition task, sham rats remembered which of two
objects they had previously encountered, regardless of the number of learning sessions they
received. However, only the HPC rats that received 30 learning sessions showed intact object
recognition memory. Combined, these findings demonstrate that changing learning parameters
can create a memory that is independent of the HPC.
Disclosures: H. Lehmann , None; F.T. Sparks, None; S.C. Spanswick, None; R.J.
Sutherland, None.