To What Extent Memory Could Contribute to Impaired Food Valuation and Choices in Obesity?

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.

The Bidirectional Relationship between Weight Gain and Cognitive Function in First-Episode Schizophrenia: A Longitudinal Study in China

Patients with schizophrenia often encounter notable weight gain during their illness, heightening the risk of metabolic diseases. While previous studies have noted a correlation between obesity and cognitive impairment in schizophrenia, many were cross-sectional, posing challenges in establishing a causal relationship between weight gain and cognitive function. The aim of this longitudinal study is to examine the relationship between weight gain and cognitive function in patients with first-episode schizophrenia (FES) during the initial 6-month antipsychotic treatments. Employing linear and logistic regression analyses, the study involved 337 participants. Significantly, baseline scores in processing speed (OR = 0.834, p = 0.007), working memory and attention (OR = 0.889, p = 0.043), and executive function (OR = 0.862, p = 0.006) were associated with clinically relevant weight gain (CRW, defined as an increase in body weight > 7%) at the 6-month endpoint. On the other hand, CRW correlated with improvements in the Brief Visuospatial Memory Test (p = 0.037). These findings suggest that patients with lower baseline cognitive performance undergo more substantial weight gain. Conversely, weight gain was correlated with cognitive improvements, particularly in the domain of visual learning and memory. This suggested a potential bidirectional relationship between weight gain and cognitive function in first-episode schizophrenia patients.

How are overweight and obesity associated with reinforcement learning deficits? A systematic review

Reinforcement learning (RL) refers to the ability to learn stimulus-response or response-outcome associations relevant to the acquisition of behavioral repertoire and adaptation to the environment. Research data from correlational and case-control studies have shown that obesity is associated with impairments in RL. The aim of the present study was to systematically review how obesity and overweight are associated with RL performance. More specifically, the relationship between high body mass index (BMI) and task performance was explored through the analysis of specific RL processes associated with different physiological, computational, and behavioral manifestations. Our systematic analyses indicate that obesity might be associated with impairments in the use of aversive outcomes to change ongoing behavior, as revealed by results involving instrumental negative reinforcement and extinction/reversal learning, but further research needs to be conducted to confirm this association. Hypotheses regarding how obesity might be associated with altered RL were discussed.

Review of Plant Extracts and Active Components: Mechanisms of Action for the Treatment of Obesity-Induced Cognitive Impairment

Obesity has been shown to negatively impact cognitive functions, but effective treatments for obesity-induced cognitive impairment are lacking. Natural dietary and plant products, functional foods, and plant-derived compounds have gained attention as potential remedies in part due to the nootropic properties of plants and certain plant-derived agents. This review discusses plant extracts and plant-derived substances that have been shown to ameliorate obesity-induced cognitive impairment in animal models. Mechanistic evaluations of their therapeutic effects are also summarized. A literature search was conducted using PubMed and Google Scholar databases, resulting in the review of 27 English language articles meeting the inclusion criteria. The nine plants (e.g., Ashwagandha, Adzuki bean, and olive) and 18 plant-derived substances (e.g., curcumin, Huperzine A, and Roxburgh's jewel orchid polysaccharides) included in this review improved obesity-induced cognitive impairment through several mechanisms, including attenuation of neuroinflammation, improvement in both central and peripheral insulin resistance, enhancement of neuroprotection and neurogenesis, and modulation of the synthesis and release of cognition-associated neurotransmitters. Based on these findings, plants and plant-derived substances may hold promise for the prevention and treatment of obesity-induced cognitive impairment. Further research is warranted to explore the clinical potential of these plant-derived treatments and to elucidate their underlying molecular mechanisms.

Adults with overweight or obesity use less efficient memory strategies compared to adults with healthy weight on a verbal list learning task modified with food words

Several studies suggest poorer episodic memory among adults with overweight (OW) relative to those with healthy weight (HW); however, few have used food stimuli. To understand the salience of food-related items when assessing memory, we adapted an episodic memory task, by replacing some non-food words with snack foods. Participants were 96 weight-loss seeking adults with OW compared to 48 adults with HW from the community matched on age, gender, ethnicity, and education. Overall memory ability was similar, although a trend showed the adults with HW performed better than adults with OW on immediate recall (d = 0.32, p = 0.07). However, there were clear differences in the use of learning strategies. Adults with HW utilized sematic clustering more effectively than adults with OW during all test phases (ds = 0.44-0.62; ps ≤ 0.01). Adults with HW also utilized serial clustering more effectively (d = 0.51; p < 0.01). Adults with HW showed better semantic clustering for both food and non-food words during immediate and short delay recall (ds = 0.42-0.78; ps ≤ 0.01) but semantic clustering was only better for the non-food category at long delay (d = 0.55; p < 0.01). These results show that adults with OW utilized less efficient learning strategies throughout the task and food-related content may impact learning. Clinically, these findings may suggest that weight-loss treatments should consider incorporating the teaching of learning and memory strategies to help increase utilization of new skills.

Altered neural correlates of episodic memory for food and non-food cues in females with overweight/obesity

Episodic memory formation is fundamental to cognition and plays a key role in eating behaviors, indirectly promoting the maintenance and acceleration of weight gain. Impaired episodic memory function is a hallmark of people with overweight/obesity, nevertheless, little research has been conducted to explore the effects of overweight/obesity on neural networks associated with episodic memory. The current study aimed to unravel the behavioral responses and neurocognitive mechanisms underlying the episodic memory for food and non-food cues in females with overweight/obesity. To explore this issue, a group of females with overweight/obesity (n = 26) and a group of age-matched females with healthy weight (n = 28) participated in a functional magnetic resonance imaging (fMRI) event-related episodic memory paradigm, during which pictures of palatable food and pictures of neutral daily necessities were presented. Whole-brain analyses revealed differential engagement in several neural regions between the groups during an episodic memory task. Specifically, compared to the healthy weight controls, females with overweight/obesity exhibited reduced brain activity in the temporal, parietal, and frontal regions during episodic memory encoding and successful retrieval of both food and non-food cues. Additionally, activation patterns in the left hippocampus and right olfactory cortex of females with and without overweight/obesity suggested that item memory changed according to the type of stimuli presented during item memory. Specifically, females with overweight/obesity showed greater engagement of the left hippocampus and right olfactory cortex when processing food cues, but less activation of the left hippocampus and right olfactory cortex when presented with non-food cues. Consistent with the obesity and suboptimal food-related decision theoretical model, these findings provide evidence of dissociation of the neural underpinnings of episodic memory in females with overweight/obesity and underline important effects of overweight/obesity on brain functions related to episodic memory.

Orexin-A and endocannabinoids are involved in obesity-associated alteration of hippocampal neurogenesis, plasticity, and episodic memory in mice

The mammalian brain stores and distinguishes among episodic memories, i.e. memories formed during the personal experience, through a mechanism of pattern separation computed in the hippocampal dentate gyrus. Decision-making for food-related behaviors, such as the choice and intake of food, might be affected in obese subjects by alterations in the retrieval of episodic memories. Adult neurogenesis in the dentate gyrus regulates the pattern separation. Several molecular factors affect adult neurogenesis and exert a critical role in the development and plasticity of newborn neurons. Orexin-A/hypocretin-1 and downstream endocannabinoid 2-arachidonoylglycerol signaling are altered in obese mice. Here, we show that excessive orexin-A/2-arachidonoylglycerol/cannabinoid receptor type-1 signaling leads to the dysfunction of adult hippocampal neurogenesis and the subsequent inhibition of plasticity and impairment of pattern separation. By inhibiting orexin-A action at orexin-1 receptors we rescued both plasticity and pattern separation impairment in obese mice, thus providing a molecular and functional mechanism to explain alterations in episodic memory in obesity.

The authors show that adult hippocampal neurogenesis is altered in the dentate gyrus of obese mice with subsequent inhibition of long-term potentiation and impairment of pattern separation. Inhibition of orexin-A action at orexin-1 receptors rescued both impairments in obese mice.

Diet, inflammation and the gut microbiome: Mechanisms for obesity-associated cognitive impairment

Poor diet and obesity are associated with cognitive impairment throughout adulthood, and increased dementia risk in aging. Here we review the current literature interrogating the mechanisms by which diets high in fat, or fat and sugar lead to cognitive impairment, focusing on changes to gut microbiome composition, inflammatory signalling and blood-brain barrier integrity. Preclinical studies indicate weight gain is not necessary for diet-induced cognitive impairment. Rather, gut microbiome composition, and systemic and central inflammatory processes appear to contribute to diet-induced cognitive impairment. While both obese humans and rodents exhibit reduced blood-brain barrier integrity, cognitive impairments precede these changes, suggesting other mechanisms may underly diet-induced cognitive changes. Other potential candidates include hormone, glucoregulatory and cardiovascular changes. Poor diet and obesity act through multiple mechanisms to affect cognitive health and the challenge for future research is to identify key processes that can be reversed to improve cognition and quality of life.

Weight gain is associated with changes in neural response to palatable food tastes varying in sugar and fat and palatable food images: a repeated-measures fMRI study

BACKGROUND

Emerging data suggest that weight gain is associated with changes in neural response to palatable food tastes and palatable food cues, which may serve to maintain overeating.

OBJECTIVE

We investigated whether weight gain is associated with neural changes in response to tastes of milkshakes varying in fat and sugar content and palatable food images.

METHODS

We compared changes in neural activity between initially healthy-weight adolescents who gained weight (n = 36) and those showing weight stability (n = 31) over 2-3 y.

RESULTS

Adolescents who gained weight compared with those who remained weight stable showed decreases in activation in the postcentral gyrus, prefrontal cortex, insula, and anterior cingulate cortex, and increases in activation in the parietal lobe, posterior cingulate cortex, and inferior frontal gyrus in response to a high-fat/low-sugar compared with low-fat/low-sugar milkshake. Weight gainers also showed greater decreases in activation in the anterior insula and lateral orbitofrontal cortex in response to a high-fat/high-sugar compared with low-fat/low-sugar milkshake than those who remained weight stable. No group differences emerged in response to a low-fat/high-sugar compared with a low-fat/low-sugar milkshake. Weight gainers compared with those who remained weight stable showed greater decreases in activation in the middle temporal gyrus and increases in cuneus activation in response to appetizing compared with unappetizing food pictures. The significant interactions were partially driven by group differences in baseline responsivity and by opposite changes in neural activation in adolescents who remained weight stable.

CONCLUSIONS

Data suggest that weight gain is associated with a decrease in responsivity of regions associated with taste and reward processing to palatable high-fat- and high-fat/high-sugar food tastes. Data also suggest that avoiding weight gain increases taste sensitivity, which may prevent future excessive weight gain.This trial was registered at clinicaltrials.gov as NCT01949636.