In animals, a Western style diet–high in saturated fat and added sugar–causes impairments in hippocampal-dependent learning and memory (HDLM) and perception of internal bodily state (interoception). In humans, while there is correlational support for a link between Western-style diet, HDLM, and interoception, there is as yet no causal data. Here, healthy individuals were randomly assigned to consume either a breakfast high in saturated fat and added sugar (Experimental condition) or a healthier breakfast (Control condition), over four consecutive days. Tests of HDLM, interoception and biological measures were administered before and after breakfast on the days one and four, and participants completed food diaries before and during the study. At the end of the study, the Experimental condition showed significant reductions in HDLM and reduced interoceptive sensitivity to hunger and fullness, relative to the Control condition. The Experimental condition also showed a markedly different blood glucose and triglyceride responses to their breakfast, relative to Controls, with larger changes in blood glucose across breakfast being associated with greater reductions in HDLM. The Experimental condition compensated for their energy-dense breakfast by reducing carbohydrate intake, while saturated fat intake remained consistently higher than Controls. This is the first experimental study in humans to demonstrate that a Western-style diet impacts HDLM following a relatively short exposure–just as in animals. The link between diet-induced HDLM changes and blood glucose suggests one pathway by which diet impacts HDLM in humans.

Animal data indicate that greater intake of fats and sugars prevalent in a Western diet impairs hippocampal memory and tests of behavioral inhibition known to be related to hippocampal function (e.g., feature negative discrimination tasks). It has been argued that such high-fat high-sugar diets (HFS) impair the hippocampus, which then becomes less sensitive to modulation by physiological state. Thus retrieval of motivationally salient memories (e.g., when seeing or smelling food) occurs irrespective of state. Here we examine whether evidence of similar effects can be observed in humans using a correlational design. Healthy human participants (N = 94), who varied in their habitual consumption of a HFS diet, completed the verbal paired-associate (VPA) test, a known hippocampal-dependent process, as well as liking and wanting ratings of palatable snack foods, assessed both when hungry and when sated. Greater intake of a HFS diet was significantly associated with a slower VPA learning rate, as predicted. Importantly, for those who regularly consumed a HFS diet, though reductions in liking and wanting occurred between hungry and sated states, the reduction in wanting was far smaller relative to liking. The latter effect was strongly related to VPA learning rate, suggestive of hippocampal mediation. In agreement with the animal literature, human participants with a greater intake of a HFS diet show deficits in hippocampal-dependent learning and memory, and their desire to consume palatable food is less affected by physiological state-a process we suggest that is also hippocampal related. (PsycINFO Database Record

Human and animal olfactory perception is shaped both by functional demands and by various environmental constraints seemingly peculiar to chemical stimuli. These demands and constraints may have generated a sensory system that is cognitively distinct from the major senses. In this article we identify these various functional demands and constraints, and examine whether they can be used to account for olfaction’s unique cognitive features on a case-by-case basis. We then use this as grounds to argue that specific conscious processes do have functional value, a finding that naturally emerges when a comparative approach to consciousness across the senses is adopted. More generally, we conclude that certain peculiar features of olfactory cognition may owe more to limited neocortical processing resources, than they do to the challenges faced by perceiving chemical stimuli.

Background/Objectives: Television viewing has been linked with increased weight and obesity, likely through decreased physical activity associated with sitting and viewing television, as well as increased intake of food, likely through reduced awareness of eating and intake behaviours. This review sought to determine the effects of television viewing on energy intake relative to the absence of television. Methods: We adhered to the PRISMA guidelines and pre-registered this review in PROSPERO (CRD42023493092). The PICOS strategy included children, adolescents and adults of all ages (P), exposed to television viewing only during meals (I) compared to no television and no other distractors (C), with the outcome as energy intake or consumption (O) for both within-subject and between-subject randomised controlled trial (RCT) designs (S). Results: Robust-variance meta-analyses of k = 57 effect sizes from 23 studies showed no overall effect, noting high heterogeneity. When analyses were limited to television alone with k = 29 effect sizes from 23 studies, we revealed a small significant effect of television viewing on intake (g = 0.13, 95% CI [0.03–0.24]) compared to no television. Moderation analysis showed that television viewing strongly increased intake at the next meal (g = 0.30, 95% CI [0.03–0.57]) but not immediate intake (g = 0.10, 95% CI [−0.01–0.21]). Conclusions: This review showed that television viewing increases food intake, especially at the next meal. This effect was evident across both children and adults. This review highlights how television viewing impacts intake and offers potential avenues for intervention based on our findings.