## 1 Introduction  
While their ability to stimulate gut bacteria and prebiotic activity has been known for some time, it is becoming increasingly evident that oligosaccharides (OS) act through unknown mechanisms to stimulate brain development. Oligofractose (OF), also known as fructooligosaccharide (FOS), is an OS of vegetable origin, commonly found in foods such as asparagus, artichoke, onion, and wheat [1]. Oligofractose is non-digestible and readily fermentable by _Bifidobacterium_ spp. and _Bacteroides_ spp., but not by potentially pathogenic bacteria such as _Escherichia coli_ and _Clostridium perfingens_[2]. Infants consuming formula containing OF display increased fecal bifidobacteria and bacteroides, decreased fecal _Escherichia coli_ and enterococci, and increased stool frequency [3, 4]. Consumptionof OF has also been shown to alter the expression of brain-derived neurotrophic factor (BDNF) and \(N\)-methyl-D-aspartate (NMDA) receptor subunits in the rodent brain [5] and improve cognitive function in a rodent model of [PERSON]'s disease [6; 7]. Human milk contains a heterogenous group of OS that have demonstrated benefits for immune and intestinal function and are hypothesized to promote brain development [8; 9]. The concentration and diversity of these human milk oligosaccharides (HMO) is unmatched by other mammals [10], and these OS are specific to milk as opposed to non-milk OS such as OF. This has significant implications for infants consuming bovine milk-based infant formulas, as bovine milk contains up to a hundred times fewer and less diverse OS [9]. Infants consuming formula containing HMO such as 2\({}^{\prime}\)-fucosyllactose (2\({}^{\prime}\)-FL) and Lacto-\(N\)-neotetarose report fewer incidences of respiratory illness [11]. Evidence from rodent studies suggests that HMO such as sialyllactose and 2\({}^{\prime}\)-FL may improve response to stress [12] and learning and memory [13; 14], respectively. Both sialyllactose and 2\({}^{\prime}\)-FL contain monosaccharides (i.e., sialic acid and fucose, respectively) that are known glycoconjugates in the brain [15; 16]. Whether sialyllactose and 2\({}^{\prime}\)-FL impact the brain in large part due to their sialic acid or fucose content is unclear. sialic acid, alone or as part of a ganglioside, is known to promote cognition [17; 18; 19]. Similarly, fucose has been shown to accrete in glycoproteins after a passive avoidance task in chicks [16], and impairing fucosylation in the rat hippocampus impairs retention during discrimination tasks [20]. Yet, [PERSON] et al. demonstrated that intact 2\({}^{\prime}\)-FL, and not fucose, promotes hippocampal long-term potentiation [14]. Alluding to the probability that intact OS and not their active monosaccharide components are required for promoting cognition is the evidence that OS such as OF, galactooligosaccharideside (GOS), and chitosan oligosaccharideside have been shown to benefit cognition in various animal models and species [7; 21; 22; 23]. This is significant as some formulas contain OF or GOS [24], yet these OS are not found in human milk. Whether HMO provide a cognitive benefit greater than that of non-human milk OS is an important question as infants relying on formula as their sole source of nutrition are typically not provided the level and diversity of HMO that are present in human milk. We chose to use the neonatal pig as an animal model due to fact that similarities with the human regarding gastrointestinal physiology [25], brain development [26], and strengths and limitations of comparisons to the human microbiome are well described [27; 28; 29]. As the majority of studies assessing the efficacy of OS to promote brain development have been conducted in rodent models, this study evaluated whether such effects can be replicated in an animal model closer to humans. As previously mentioned, it is unclear whether HMO provide a cognitive benefit in addition to formula already containing non-HMO OS.