Increased Prefrontal and Parahippocampal Activation with Reduced Dorsolateral Prefrontal and Insular Cortex Activation to Food Images in Obesity: A Meta-Analysis of fMRI Studies

Abstract

Background and ObjectivesObesity is emerging as the most significant health concern of the twenty-first century. A wealth of neuroimaging data suggest that weight gain might be related to aberrant brain function, particularly in prefrontal cortical regions modulating mesolimbic addictive responses to food. Nevertheless, food addiction is currently a model hotly debated. Here, we conduct a meta-analysis of neuroimaging data, examining the most common functional differences between normal-weight and obese participants in response to food stimuli.Data SourceWe conducted a search using several journal databases and adhered to the ‘Preferred Reporting Items for Systematic Reviews and Meta-analyses’ (PRISMA) method. To this aim, 10 studies were found with a total of 126 obese participants, 129 healthy controls, equaling 184 foci (146 increased, 38 decreased activation) using the Activation Likelihood Estimation (ALE) technique. Out of the 10 studies, 7 investigated neural responses to food versus non-food images.ResultsIn response to food images, obese in comparison to healthy weight subjects had increased activation in the left dorsomedial prefrontal cortex, right parahippocampal gyrus, right precentral gyrus and right anterior cingulate cortex, and reduced activation in the left dorsolateral prefrontal cortex and left insular cortex.ConclusionsPrefrontal cortex areas linked to cognitive evaluation processes, such as evaluation of rewarding stimuli, as well as explicit memory regions, appear most consistently activated in response to images of food in those who are obese. Conversely, a reduced activation in brain regions associated with cognitive control and interoceptive awareness of sensations in the body might indicate a weakened control system, combined with hypo-sensitivity to satiety and discomfort signals after eating in those who are prone to overeat.

Obesity diminishes synaptic markers, alters microglial morphology, and impairs cognitive function

“…That is, obese individuals with lower numbers of dendritic spines and synapses in the frontal cortex may be incapable of sufficiently activating this brain region in response to cues that normally engage mechanisms necessary for self-control. Indeed, studies have shown that obese humans display hypoactivation of the anterior cingulate and dorsolateral prefrontal cortex in response to food cues (50)(51)(52). These changes may reflect a reduced synapse number in early obesity, leading to failure of mechanisms involving Fig.…”

IMAGING IN ENDOCRINOLOGY: The use of functional MRI to study the endocrinology of appetite

“…Cornier et al (41) recently showed that the measured neuronal response to the expectation of sweet taste (but not the response to taste receipt) is down-regulated in individuals prone to weight gain and obesity. A recent meta-analysis by Brooks et al (42) suggested that the areas linked to the evaluation of rewarding stimuli appear most consistently activated in response to images of food in those who are obese. However, they also noted that a reduced activation in brain regions associated with cognitive control and awareness of bodily sensations is often reported in the obese, which suggests that a weakened self-control system or hypo-sensitivity to satiety and discomfort signals after eating may also contribute to those who are prone to overeat (42).…”

“…A recent meta-analysis by Brooks et al (42) suggested that the areas linked to the evaluation of rewarding stimuli appear most consistently activated in response to images of food in those who are obese. However, they also noted that a reduced activation in brain regions associated with cognitive control and awareness of bodily sensations is often reported in the obese, which suggests that a weakened self-control system or hypo-sensitivity to satiety and discomfort signals after eating may also contribute to those who are prone to overeat (42). For example, Le et al (43) reported reduced activation in the prefrontal cortex, an area that has been described as playing a central role in the inhibition of inappropriate behaviours, in obese women in response to a meal as compared to lean or formerly obese women.…”

Roux-en-Y gastric bypass: effects on feeding behavior and underlying mechanisms

“…Furthermore, fMRI studies have demonstrated altered activation in key areas of the brain reward system in obese patients compared with normal-weight control subjects (17). For example, increased activation of prefrontal and parahippocampal reward centers observed in obese individuals might theoretically lead to an increased motivation to acquire food (18). On the other hand, a more pronounced inhibition of specific reward centers, such as the dorsal striatum, in obese individuals compared with normal-weight control subjects (19) might result in blunted reward responses after eating palatable foods, with subsequent compensatory overeating.…”