Sheep are a good model to study social recognition memory — they form a strong family bond with their offspring shortly after parturition and strongly reject other newborn lambs. Olfactory cues are crucial for this form of memory, particularly during the early stages, but auditory and visual stimuli are also relevant later on. How is the different sensory information processed and integrated? A recent paper begins to address this issue by looking for transcriptional changes that might be associated with recognition memory in sheep.

The authors focused their efforts on brain-derived neurotrophic factor (BDNF), as this molecule seems to participate in plastic processes that might underlie memory formation. They looked for BDNF mRNA 4.5 hours post partum. At this time, an olfactory memory is already expressed, but the consolidation of the recognition memory is still ongoing. The authors saw that, in addition to structures of the olfactory processing system, BDNF mRNA was found in regions of the temporal, entorhinal, anterior cingulate and frontal cortices, as well as in the hippocampus and the diagonal band of Broca. As these structures have been implicated in attentional processes and visual recognition in some species, the authors speculate that the increase in BDNF mRNA levels reflects the reorganization of neural circuits in these regions at the time of memory formation. Although it is early to draw any definitive conclusions, these results point to several brain regions that we now need to probe in search of the mechanisms that underlie social recognition memory.