Cognitive control of meal onset and meal size: Role of dorsal hippocampal-dependent episodic memory

Hippocampus Oxytocin Signaling Promotes Prosocial Eating in Rats

BACKGROUND

Oxytocin (OT) is a hypothalamic neuropeptide involved in diverse physiological and behavioral functions, including social-based behavior and food intake control. The extent to which OT's role in regulating these 2 fundamental behaviors is interconnected is unknown, which is a critical gap in knowledge given that social factors have a strong influence on eating behavior in mammals. Here, we focus on OT signaling in the dorsal hippocampus (HPCd), a brain region recently linked to eating and social memory, as a candidate system where these functions overlap.

METHODS

HPCd OT signaling gain- and loss-of-function strategies were used in male Sprague Dawley rats that were trained in a novel social eating procedure to consume their first nocturnal meal under conditions that varied with regard to conspecific presence and familiarity. The endogenous role of HPCd OT signaling was also evaluated for olfactory-based social transmission of food preference learning, sociality, and social recognition memory.

RESULTS

HPCd OT administration had no effect on food intake under isolated conditions but significantly increased consumption in the presence of a familiar but not an unfamiliar conspecific. Supporting these results, chronic knockdown of HPCd OT receptor expression eliminated the food intake-promoting effects of a familiar conspecific. HPCd OT receptor knockdown also blocked social transmission of food preference learning and impaired social recognition memory without affecting sociality.

CONCLUSIONS

Collectively, the results of the current study identify endogenous HPCd OT signaling as a novel substrate in which OT synergistically influences eating and social behaviors, including the social facilitation of eating and the social transmission of food preference.

Taichi on the brain: an activation likelihood estimated meta-analysis of functional neuroimaging data

Introduction

Tai Chi Chuan (TCC) is an exercise regimen renowned for its comprehensive benefits to both physical and mental health. The present research endeavor aims to elucidate the neurocognitive impacts of TCC compared to alternative exercise modalities or therapeutic interventions.

Methods

A systematic meta-analysis was undertaken, encompassing a rigorous review of diverse datasets, wherein 422 scholarly articles were examined, with a subset of 18 articles meeting the stringent criteria for inclusion in the analytical framework.

Results

The study cohort comprised 677 participants, characterized by a mean age of 56.52 ± 14.89 years and an average educational attainment of 11.06 ± 3.32 years. Noteworthy alterations in functional neural activity were identified within the superior frontal gyrus.

Discussion

This comprehensive analysis provides significant insights into the enduring neural modifications and the distinctive contributions of TCC to cognitive health. Nevertheless, it is imperative to acknowledge the potential for bias in smaller functional magnetic resonance imaging studies owing to their inconclusive outcomes. This observation underscores the critical need for collaborative, multicenter research initiatives with expanded sample sizes to enhance the robustness and generalizability of future findings.

Efficiency of post-meal memory inhibition predicts subsequent food intake

Memory processes may contribute to appetite regulation. When people look at palatable foods, their desire to consume them depends upon memory retrieval (i.e., recalling if it will taste good). If memory inhibition occurs during satiety, then pleasant eating-related memories will not be retrieved, making eating less likely. In contrast, if memory inhibition is less efficient, pleasant food-related memories will be retrieved, the food will appear desirable, and the chance of consumption increases. Here we tested whether a putative measure of memory inhibition could predict post-meal snack food intake. Study participants looked at palatable snacks and judged their desire to eat them (i.e., a memory-dependent process), and then ate a small sample of each food, and rated them for liking (i.e., an orosensory-dependent process) - all using category rating scales. Following a filling meal, this test was repeated, alongside others. Finally, participants were given the opportunity for ad libitum snack food consumption, in addition to collecting measures such as impulsivity. Poorer memory inhibition (i.e., smaller changes in wanting relative to liking from pre-to post-meal) was associated with greater consumption of snacks on the ad libitum test (Sr2% = 4.4, p = 0.006) after controlling for other variables likely to influence eating (e.g., impulsivity). This effect was maintained even when the memory inhibition measure was based on foods different to those being consumed on the ad libitum snacking test. In conclusion, memory inhibition may contribute to food intake regulation, and when this is less efficient, more palatable food is likely to be eaten in the post-meal period.

Cue-potentiated feeding in rodents: Implications for weight regulation in obesogenic environments

Cue-potentiated feeding (CPF) describes instances where food intake is increased by exposure to conditioned cues associated with food, often in the absence of hunger. CPF effects have been reported in a range of experimental protocols developed by researchers working across diverse fields spanning behavioural neuroscience, social psychology and ecology. Here we review the evolution of research on cue-potentiated feeding in animal models to identify important behavioural parameters and key neural circuits and pharmacological systems underlying the effect. Overall, evidence indicates that social, discrete and contextual stimuli can be used to elicit CPF effects across multiple species, though effects are often subtle and sensitive to procedural variables. While regular exposure to food cues is thought to be a key risk factor for overeating in so-called 'obesogenic' environments, further work is needed to identify whether CPF promotes positive energy balance and weight gain over the longer term. We suggest several methodological and conceptual areas for inquiry to elucidate the contribution of CPF to the regulation of food choice and energy intake.

Episodic future thinking improves intertemporal choice and food choice in individuals with higher weight: A systematic review and meta-analysis

Episodic future thinking (EFT) strengthens self-regulation abilities by increasing the perceived value of long-term reinforcements and reducing impulsive choice in delay discounting tasks. As such, EFT interventions have the potential to improve dietary and eating-related decision-making in individuals with obesity or binge eating symptoms, conditions associated with elevated delay discounting. Here, we meta-analyzed evidence from 12 studies that assessed whether EFT interventions improve delay discounting and real-world food choice compared to control interventions. Included studies involved 951 adults with overweight or obesity (body mass index [BMI] ≥25). There were no studies involving participants with binge eating disorder. EFT intervention pooled effects were significant, improving delay discounting with a medium effect, g = 0.55, p < 0.0001, and subsequent food choice outcomes with a small effect, g = 0.31, p < 0.01. Notably, our review is the first to analyze mechanisms of effect in this population, demonstrating that improvements were greater when temporal horizons of EFT episodes were aligned with delay discounting tasks and more distant horizons predicted far-transfer to subsequent dietary and eating-related choices. Our findings thus show that EFT is an effective intervention for individuals with higher weight at risk of adverse health consequences.

Hunger, Satiety, and Their Vulnerabilities

The psychological states of hunger and satiety play an important role in regulating human food intake. Several lines of evidence suggest that these states rely upon declarative learning and memory processes, which are based primarily in the medial temporal lobes (MTL). The MTL, and particularly the hippocampus, is unusual in that it is especially vulnerable to insult. Consequently, we examine here the impact on hunger and satiety of conditions that: (1) are central to ingestive behaviour and where there is evidence of MTL pathology (i.e., habitual consumption of a Western-style diet, obesity, and anorexia nervosa); and (2) where there is overwhelming evidence of MTL pathology, but where ingestive behaviour is not thought central (i.e., temporal lobe epilepsy and post-traumatic stress disorder). While for some of these conditions the evidence base is currently limited, the general conclusion is that MTL impairment is linked, sometimes strongly, to dysfunctional hunger and satiety. This focus on the MTL, and declarative learning and memory processes, has implications for the development of alternative treatment approaches for the regulation of appetite.

Predictors of state-based changes in wanting and liking

People report wanting food when they are hungry, and on eating it they typically report liking the experience. After eating, both wanting and liking decline, but wanting declines to a greater extent, which we term the 'affective discrepancy effect'. In this study we examine the predictors - state, sensory and memory-based - of these affective changes. Hungry participants undertook three tasks: (1) written recollections of what certain foods are like to eat; (2) ratings of wanting and expected flavour liking and fillingness when looking at snacks, and ratings of food and flavour liking when eating them; (3) ratings of bodily state. These tasks were then repeated after lunch. State-based changes in food liking were best predicted by changes in flavour liking. For state-based change in wanting, memory-based information about flavour liking and fillingness from tasks (1) and (2) were all significant predictors. For recollections about eating (task 1), mentions of food fillingness significantly increased pre-to post-lunch and this was the best predictor of the affective discrepancy effect. Recollections of food fillingness are state-dependent, and can arise unbidden (i.e., such recollective content was unprompted). This may reflect one way that memory may selectively influence wanting, and hence whether food intake is initiated or not.

Inhibiting ventral hippocampal NMDA receptors and Arc increases energy intake in male rats

Research into the neural mechanisms that underlie higher-order cognitive control of eating behavior suggests that ventral hippocampal (vHC) neurons, which are critical for emotional memory, also inhibit energy intake. We showed previously that optogenetically inhibiting vHC glutamatergic neurons during the early postprandial period, when the memory of the meal would be undergoing consolidation, caused rats to eat their next meal sooner and to eat more during that next meal when the neurons were no longer inhibited. The present research determined whether manipulations known to interfere with synaptic plasticity and memory when given pretraining would increase energy intake when given prior to ingestion. Specifically, we tested the effects of blocking vHC glutamatergic N-methyl-D-aspartate receptors (NMDARs) and activity-regulated cytoskeleton-associated protein (Arc) on sucrose ingestion. The results showed that male rats consumed a larger sucrose meal on days when they were given vHC infusions of the NMDAR antagonist APV or Arc antisense oligodeoxynucleotides than on days when they were given control infusions. The rats did not accommodate for that increase by delaying the onset of their next sucrose meal (i.e., decreased satiety ratio) or by eating less during the next meal. These data suggest that vHC NMDARs and Arc limit meal size and inhibit meal initiation.

Central Neurocircuits Regulating Food Intake in Response to Gut Inputs-Preclinical Evidence

The regulation of energy balance requires the complex integration of homeostatic and hedonic pathways, but sensory inputs from the gastrointestinal (GI) tract are increasingly recognized as playing critical roles. The stomach and small intestine relay sensory information to the central nervous system (CNS) via the sensory afferent vagus nerve. This vast volume of complex sensory information is received by neurons of the nucleus of the tractus solitarius (NTS) and is integrated with responses to circulating factors as well as descending inputs from the brainstem, midbrain, and forebrain nuclei involved in autonomic regulation. The integrated signal is relayed to the adjacent dorsal motor nucleus of the vagus (DMV), which supplies the motor output response via the efferent vagus nerve to regulate and modulate gastric motility, tone, secretion, and emptying, as well as intestinal motility and transit; the precise coordination of these responses is essential for the control of meal size, meal termination, and nutrient absorption. The interconnectivity of the NTS implies that many other CNS areas are capable of modulating vagal efferent output, emphasized by the many CNS disorders associated with dysregulated GI functions including feeding. This review will summarize the role of major CNS centers to gut-related inputs in the regulation of gastric function with specific reference to the regulation of food intake.

From Obesity to Hippocampal Neurodegeneration: Pathogenesis and Non-Pharmacological Interventions

High-caloric diet and physical inactivity predispose individuals to obesity and diabetes, which are risk factors of hippocampal neurodegeneration and cognitive deficits. Along with the adipose-hippocampus crosstalk, chronically inflamed adipose tissue secretes inflammatory cytokine could trigger neuroinflammatory responses in the hippocampus, and in turn, impairs hippocampal neuroplasticity under obese and diabetic conditions. Hence, caloric restriction and physical exercise are critical non-pharmacological interventions to halt the pathogenesis from obesity to hippocampal neurodegeneration. In response to physical exercise, peripheral organs, including the adipose tissue, skeletal muscles, and liver, can secret numerous exerkines, which bring beneficial effects to metabolic and brain health. In this review, we summarized how chronic inflammation in adipose tissue could trigger neuroinflammation and hippocampal impairment, which potentially contribute to cognitive deficits in obese and diabetic conditions. We also discussed the potential mechanisms underlying the neurotrophic and neuroprotective effects of caloric restriction and physical exercise by counteracting neuroinflammation, plasticity deficits, and cognitive impairments. This review provides timely insights into how chronic metabolic disorders, like obesity, could impair brain health and cognitive functions in later life.

Early life exposure to hypercaloric diet impairs eating behavior during weaning: The role of BDNF signaling and astrocyte marks

Literature shows that gestational and/or lactational exposure to hypercaloric diets induces long term effects on eating behavior and the involvement of neurochemical mechanisms. We hypothesized that the effects of hypercaloric diets in early development phases can precede an overweight or an obesity status. The aim of the present study was to evaluate the impact of gestational and lactational exposure to cafeteria diet on eating behavior and neurochemical parameters, BDNF signaling, epigenetic and astrocyte marks in the hippocampus and olfactory bulb during the weaning phase. Pregnant female rats were randomized between standard and cafeteria diet, the respective diet was maintained through the lactational period. The framework of feeding pattern, meal, and its microstructure, was observed in postnatal day 20. Exposure to cafeteria diet increased the number of meals, associated with a lower first inter-meal interval and higher consumption in both genders, without any changes in body weight. Diet exposure also reduced the number of grooming, a behavior typically found at the end of meals. Hypercaloric diet exposure reduced BDNF levels in the olfactory bulb and hippocampus from rats of both sexes and increased the content of the TrkB receptor in hippocampi. It was observed an increase in HDAC5 levels, an epigenetic mark. Still, early exposure to the hypercaloric diet reduced hippocampal GFAP and PPARγ levels, without any effect on NeuN content, indicating that alterations in astrocytes can precede those neuronal outcomes. Our results showed that changes in interrelated neurochemical signaling, BDNF, and astrocyte marks, induced by hypercaloric diet in early stages of development may be related to impairment in the temporal distribution of eating pattern and consequent amounts of consumed food during the weaning phase.

Beta and gamma synchronous oscillations in neural network activity in mice-induced by food deprivation

Food deprivation is known to trigger hunger sensation and motivation to eat for energy replenishing. However, brain mechanisms associated with hunger and neural circuitries that mediate hunger driven responses remained to be investigated. To understand neural signaling of hunger, local field potentials (LFPs) in the lateral hypothalamus (LHa), nucleus accumbens (NAc), dorsal hippocampus (HP) and olfactory bulb (OB) and their interconnectivities were studied in freely moving adult male Albino mice during 18-20 h food deprivation and fed periods. Raw LFP signals were recorded and analyzed for mean values of spectral frequency power and coherence values. One-way repeated measures ANOVA revealed significant increases in spectral powers of beta and gamma frequency ranges induced by food deprivation in the LHa, HP, NAc but not OB. No change of spectral power in these brain regions was induced by food feeding. The analyses of coherent activity between brain regions also deliniated some distributed neural network activities correlated with hunger. In particular, coherent function indicated the increased beta and gamma phase synchrony between the pairs of LHa-HP and NAc-OB regions, and decreased gamma synchrony between the pairs of LHa-NAc and NAc-HP induced by food deprivation. It was found that plasma glucose level, locomotor count, travelled distance and time spent on moving were not altered by food deprivation. These results suggest that changes in LFP hallmarks in these brain regions were associated with hunger driven by negative energy balance.

Regulation of Memory Function by Feeding-Relevant Biological Systems: Following the Breadcrumbs to the Hippocampus

The hippocampus (HPC) controls fundamental learning and memory processes, including memory for visuospatial navigation (spatial memory) and flexible memory for facts and autobiographical events (declarative memory). Emerging evidence reveals that hippocampal-dependent memory function is regulated by various peripheral biological systems that are traditionally known for their roles in appetite and body weight regulation. Here, we argue that these effects are consistent with a framework that it is evolutionarily advantageous to encode and recall critical features surrounding feeding behavior, including the spatial location of a food source, social factors, post-absorptive processing, and other episodic elements of a meal. We review evidence that gut-to-brain communication from the vagus nerve and from feeding-relevant endocrine systems, including ghrelin, insulin, leptin, and glucagon-like peptide-1 (GLP-1), promote hippocampal-dependent spatial and declarative memory via neurotrophic and neurogenic mechanisms. The collective literature reviewed herein supports a model in which various stages of feeding behavior and hippocampal-dependent memory function are closely linked.

Sucrose ingestion induces glutamate AMPA receptor phosphorylation in dorsal hippocampal neurons: Increased sucrose experience prevents this effect

Evidence suggests that meal-related memory influences later eating behavior. Memory can serve as a powerful mechanism for controlling eating behavior because it provides a record of recent intake that likely outlasts most physiological signals generated by ingestion. Dorsal (dHC) and ventral hippocampal (vHC) neurons are critical for memory, and we demonstrated previously that they limit energy intake during the postprandial period. If dHC or vHC neurons control intake through a process that requires memory, then ingestion should increase events necessary for synaptic plasticity in dHC and vHC during the postprandial period. To test this, we determined whether ingesting a sucrose solution induced posttranslational events critical for hippocampal synaptic plasticity: phosphorylation of AMPAR GluA1 subunits at 1) serine 831 (pSer831) and 2) serine 845 (pSer845). We also examined whether increasing the amount of previous experience with the sucrose solution, which would be expected to decrease the mnemonic demand involved in an ingestion bout, would also attenuate sucrose-induced phosphorylation. Quantitative immunoblotting of dHC and vHC membrane fractions demonstrated that sucrose ingestion increased postprandial pSer831 in dHC but not vHC. Increased previous sucrose experience prevented sucrose-induced dHC pSer831. Sucrose ingestion did not affect pSer845 in either dHC or vHC. Thus, the present findings show that ingestion activates a postranslational event necessary for synaptic plasticity in an experience-dependent manner, which is consistent with the hypothesis that dHC neurons form a memory of a meal during the postprandial period.

Feeding cycle alters the biophysics and molecular expression of voltage-gated Na+ currents in rat hippocampal CA1 neurones

The function of hippocampus as a hub for energy balance is a subject of broad and current interest. This study aims at providing more evidence on this regard by addressing the effects of feeding cycle on the voltage-gated sodium (Na⁺ ) currents of acutely isolated Wistar rat hippocampal CA1 neurones. Specifically, by applying patch clamp techniques (whole cell voltage clamp and single channel in inside-out patches) we assessed the influence of feeding and fasting conditions on the intrinsic biophysical properties of Na⁺ currents. Additionally, mass spectrometry and western blotting experiments were used to address the effect of feeding cycle over the Na⁺ channel population of the rat hippocampus. Na⁺ currents were recorded in neurones obtained from fed and fasted animals (here termed "fed neurones" and "fasted neurones", respectively). Whole cell Na⁺ currents of fed neurones, as compared to fasted neurones, showed increased mean maximum current density and a higher "window current" amplitude. We demonstrate that these results are supported by an increased single channel Na⁺ conductance in fed neurones and, also, by a greater Nav1.2 channel density in plasma membrane-enriched fractions of fed samples (but not in whole hippocampus preparations). These results imply fast variations on the biophysics and molecular expression of Na⁺ currents of rat hippocampal CA1 neurones, throughout the feeding cycle. Thus, one may expect a differentiated regulation of the intrinsic neuronal excitability, which may account for the role of the hippocampus as a processor of satiety information.

Hippocampal dependent neuropsychological tests and their relationship to measures of cardiac and self-report interoception

The hippocampus is involved in interoceptive processing (i.e., perceiving internal bodily states), with much of this evidence relating to hunger and fullness. Here we examine whether cardiac and self-report measures of interoception are related to two measures of hippocampal dependent learning and memory (HDLM) - the Rey Auditory Verbal Learning Test (RAVLT) and Logical Memory. Healthy adults completed a neuropsychological test battery including all of these measures, along with assessments of intelligence and executive function. Biographical, medical and psychological-related data that might confound detecting an HDLM-interoception relationship was also collected. Both measures of HDLM were associated with cardiac interoception after controlling for confounding variables. More accurate cardiac interoception was linked to better HDLM performance. On the self-report measure of interoception, better performance on the RAVLT was associated with better-reported attention regulation, consistent with the hippocampus's known role in mindfulness. Overall, these findings suggest hippocampal involvement in cardiac and self-report interoceptive capacity. The broader functional role of the hippocampus in interoception is discussed.

The anterior medial temporal lobes: Their role in food intake and body weight regulation

The anterior medial temporal lobes are one of the most studied parts of the brain. Classically, their two main structures - the amygdalae and the hippocampi - have been linked to key cognitive and affective functions, related in particular to learning and memory. Based on abundant evidence, we will argue for an alternative but complementary point of view: they may also play a major role in food intake and body weight regulation. First, an overview is given of early clinical evidence in this line of thought. Subsequently, empirical evidence is presented on how food intake, including in the extreme case of obesity, may relate to amygdalian and hippocampal functioning. The focus is on the amygdala's role in processing the relevance of food stimuli, cue-induced feeding, and stress-induced eating and on the hippocampus' involvement in the use of interoceptive signals of hunger and satiety, as well as memory and inhibitory processes related to food intake. Additionally, an elaboration takes place on possible reciprocal links between food intake, body weight, and amygdala and hippocampus functioning. Finally, issues that seemed particularly critical for future research in the field are discussed.