## 4 Discussion
It is therefore surprising to observe in the OF + 2'-FL group a trend toward a reduction in relative hippocampi volume (\(0.05\leq p<0.1\)) concurrent with increased performance in the novel object recognition with a long delay (48 h). Here, the absolute volumes of the hippocampi were similar between groups. However, the relative decrease in volume in the OF + 2'-FL group may suggest a shift in the process of synaptogenesis and/or myelination. Conversely, given the stability between groups in absolute volume, it is possible that the reduction in relative volume of the hippocampi is an artifact of more significant growth in other brain regions. Of the genes affected by diet in the present study, it appeared that pigs fed OF displayed opposite effects of those fed OF + 2'-FL, and this is evident in the pattern shown in Figure 6B. Overall, pigs fed OF demonstrated greater hippocampal downregulation as compared to controls than pigs fed OF + 2'-FL. Specifically, pigs fed OF displayed reduced gene expression of _DRD3_, _GABBR1_, _HDAC5/8_, _NCAMI_, and _CHRM2_ relative to controls. Pigs fed OF + 2'-FL displayed increases in all of the previous genes except for _HDAC8_ and _CHRM2_. Although the magnitude of expression was similar for _CHRM2_, a gene known to be related to cognition in humans [51], the downregulation of _HDAC5_ was greater for pigs fed OF than those fed OF + 2'-FL. Such a pattern may be related to the apparent difference in behavior observed in the NOR task, but it remains difficult to reconcile the differential effects of OF and OF + 2'-FL on gene expression given their apparent benefit to recognition memory. Our results share some overlap with previous work examining GOS and FOS on cognition and gene expression. Oral gavage with 3 g/kg FOS or 4 g/kg GOS for 5 weeks has been shown to differentially alter BDNF, NMDAR, and plasma D-serine in adult male rats [5]. BDNF and the glutamatergic NMDA receptor NR1 were greater in the hippocampus of those fed FOS, whereas NR1 was greater in the frontal cortex and NR2 greater in the hippocampus of those fed GOS. Interestingly, we did not see an increase in mRNA expression of _BDNF_, any of the glutamate ionotropic receptor NMDA type subunits (_GRIN1_, _GRIN2A/B/C/D_), or \(\alpha\)-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) type subunits (_GRIA1-4_). We noted similar departures from rodent work in a previous study [21], and these differences may be accounted for by a myriad of differences such as outcome (protein or mRNA expression), animal model (pig or rodent), and the relative difference in development over the course of a four week period between pigs and rodents. We assessed the relationship between the genes affected by diet and behavioral outcomes. Of the affected genes, _CHRM2_, _GABBR1_, and _HDAC5_ were inversely correlated with the recognition index after a 1 h delay. While significant relationships were observed overall, these appeared to be driven by specific dietary groups. The relationship between the recognition index and _CHRM2_ was strongest in the OF + 2'-FL group, whereas the relationship between _HDAC5_ and the recognition index was driven by the CON and OF + 2'-FL group. All dietary groups showed an inverse relationship between _GABBR1_ and the recognition index, and linear regression revealed the strongest and most significant relationship between these two outcomes. None of the affected genes were related to the recognition index after a 48 h delay, suggesting a different mechanism for the behavioral demonstration of recognition memory after intermediate and long delays, and that these mechanisms are sensitive and differentially altered by oligosaccharides supplementation. The idea that some genes are differentially expressed in context of time or familiarity/novelty of a stimuli is not new [52; 53]. However, the possibility that dietary oligosaccharides may differentially alter such processes is novel.