Functional MRI Evaluation of Brain Response to Visual Food Stimulation in Morbidly Obese Patients Before and After Bariatric Surgery
Condition: Morbid Obesity; Satiety
MeSH terms: Obesity, Morbid
Study type: Interventional

Summary: 
      Aim of study:

      To evaluate changes in feeding-related neural activity after different bariatric procedures
      in morbidly obese patients. Relationship of gut hormone levels will be assessed as well.
    

Detailed description: 
      Bariatric surgery mediates weight-loss via one or several mechanisms inherent to each
      technique used. Surgical restriction is the "lowest common denominator" shared, to various
      extent, by all procedures. Different degrees of malabsorption are utilized in "bypass
      procedures" such as Roux-Y gastric bypass (GBP), biliopancreatic diversion (BPD) and
      biliopancreatic diversion with duodenal switch (BPD-DS). These surgical options differ, also,
      in the degree of weight loss they promote. This difference is due to several factors
      including the extent of appetite suppression, increase in energy expenditure and degree of
      malabsorption achieved by the different procedures.

      A post-operative change in the gut-brain hormonal axis is a component that has recently drawn
      much attention and research but is still ill defined. It is an effect, presumably mediated by
      a change in a myriad of peptides and hormones originating mostly from the intestinal tract,
      eliciting a change in hunger and satiety feelings as well as a change in the drive to eat.
      Generally speaking, patients after sleeve gastrectomy (SG) and the bypass procedures
      mentioned, have a decreased appetite and report a reduced drive to seek food, which
      presumably contributes to their weight loss.

      Functional magnetic resonance imaging (fMRI) is an imaging modality which measures the
      hemodynamic response (change in blood flow) related to neural activity in the brain,
      therefore allowing mapping of areas in the brain which become active due to discrete stimuli.

      Recent studies utilizing fMRI to study neural response to hunger and satiety states, as well
      as to food anticipation and ingestion, have mapped discrete areas in the brain which respond
      to these stimuli. Fuhrer and colleagues found that during hunger, significantly enhanced
      brain activity is found in the left striate and extrastriate cortex, the inferior parietal
      lobe, and the orbitofrontal cortices. Stimulation with food images was associated with
      increased activity in both insulae, the left striate and extrastriate cortex, and the
      anterior midprefrontal cortex. Nonfood images were associated with enhanced activity in the
      right parietal lobe and the left and right middle temporal gyrus1. Stice and colleagues
      reported brain imaging studies which suggested that obese relative to lean individuals show
      greater activation of the gustatory cortex (insula/frontal operculum) and oral somatosensory
      regions (parietal operculum and Rolandic operculum) in response to anticipated intake and
      consumption of palatable foods.

      Ghrelin is an orexigenic (appetite stimulating) peptide secreted by the foregut prior to
      meals and is therefore considered a "meal initiator". Obese patients have low ghrelin levels
      but maintain a normal diurnal variation of this peptide, while patients after GBP, have
      reduced ghrelin levels which remain low throughout the day 3. Malik and co-workers
      demonstrated that when ghrelin was administered intravenously to healthy volunteers during
      fMRI the neural response to food pictures was affected. The neural effects of ghrelin were
      correlated with self-rated hunger ratings.

      Leptin is an adipocyte-derived circulating hormone that provides information to the brain
      regarding energy stores. The brain's response to leptin involves changes in energy
      expenditure and food intake. Farooqi and co-workers reported data suggesting that leptin acts
      on neural circuits governing food intake to diminish perception of food reward while
      enhancing the response to satiety signals generated during food consumption.

      Peptide YY3-36 (PYY) is a gut-derived satiety signal whose levels increase after meal
      ingestion. Intravenous infusion of PYY to human volunteers has been shown to cause a decrease
      in food consumption and self-reported feelings of hunger. It has also been able to alter
      neuronal activity in within both corticolimbic and higher-cortical areas as well as
      homeostatic brain regions. Levels of PYY are low in obese subjects, and have has been shown
      to gradually increase as early as 2 days after GBP, perhaps contributing to the success of
      this procedure in terms of appetite control.

      GLP-1 (glucagons-like peptide 1), like PYY, is an anorexigenic (appetite suppressing) signal.
      It is secreted from the gut after meals and reduces food intake by an effect on the
      brain-stem, as well as by decreasing the rate of gastric emptying which adds to the feeling
      of fullness after a meal. Like PYY, GLP-1 levels are low in obese patients and increase
      dramatically following GBP, contributing both to the weight loss as well as to the
      improvement in glucose tolerance after this operation.

      Several correlations will be assessed:

        1. Correlation between subjective reporting of hunger/satiety and fMRI images.

        2. Change in neural response to food-neutral and food-related pictures, following the
           operation (before vs. 1m and vs. 6m after the procedure).

        3. Difference between the two surgical procedures (SG vs.GBP) in regard to the neural
           response to food images.

        4. Correlation between gut-derived appetite-regulating hormone blood levels to subjective
           reporting of hunger/satiety and fMRI images at the different time points.

        5. Correlation of measured parameters to changes in weight, BMI and excess weight loss.
    

Intervention name(s): fMRI imaging following visual stimulation of food and non-food images
Intervention type(s): Procedure
Intervention description(s): fMRI Scans will be performed in a 3 tesla MRI scanner. All subjects will be scanned for anatomical imaging without injection of contrast material. These structural images will be used to localize the functional data obtained. Functional test will include several measurements of brain activity while viewing visual stimuli.
fMRI allows collection of information about brain activity with good spatial and temporal resolution. Protocols allow rapid assessment of regional activation in different brain regions during exposure to different visual stimuli.It provides a detailed functional map.
Scan test protocol includes anatomical measurement - 3D FSPGE T1w sequence, Asset DTI and repeated fMRI measurements (based on echo EPI, T2 * w, BOLD sequences). Test paradigms include picture collections of various foods non-food objects similar in size, color and shape.
Allocation: Non-Randomized
Intervention model: Single Group Assignment
Masking: Single (Investigator)
Primary purpose: Other