Studies of the neural circuitry of food regulation has provided ample evidence that the hypothalamus (a structure the size of four peas which is suspended above the pituitary gland in the middle of the brain) plays a critical role in the hyperphagia seen in PWS. The hypothalamus is known to receive input from many other areas of the brain, and neuroimaging studies have begun to flesh out the precise connections of food-related information transfer in the brain, particularly in PWS.
The current study examined the neural mechanisms of hunger in 9 individuals with PWS and 10 non-PWS control subjects using a functional magnetic resonance imaging scanner (fMRI) (Food-related Neural Circuitry in PWS: Response to High- versus Low-calorie Foods , Dimitropoulos and Schultz, J Autism Dev Disord, 2008). Subjects were presented with pictures of both high- and low-calorie foods and were asked to rate how much they liked them. Subjects also performed a simple discrimination task by answering the question, â€œare these pictures of foods and objects the same or different?â€ The authors hypothesized that the abnormal hunger in PWS would be reflected by different patterns of activation in the brain. One of the strengths of this experiment was that the non-PWS control subjects had similar cognitive development and similar body-mass-indices (BMI) as the PWS subjects. This allows for more accurate statistical comparisons.
Functional neuroimaging studies are very elaborate to analyze, but the main findings were as follows: 1) individuals with PWS showed much more activation than control subjects in neural circuitry known to mediate food-related behavior, and 2) the caloric value of food plays an important role in determining the difference in how individuals with PWS process information about food. The areas which were seen to be most active in those with PWS compared to control subjects were the lateral hypothalamus (known to be important for regulating food behaviors), the thalamus and mid-insular cortex (important for the sensation of taste; particularly sweet tastes), the amygdala (crucial for arousal and emotionally complex feelings), the fusiform gyrus (which responds to objects that the viewer has a motivation for), and the orbitofrontal cortex (which contains a special taste region).
The limitations to this study include a wide range of ages of participants, a small sample size, and differences in how long it had been since subjects had last eaten. However, what is ultimately compelling about this study is its detailed description of the neural areas involved in eating in PWS which have previously been reported most reliably in animal preparations. Future studies will seek to increase subject size and statistical power and lead to a better understanding of how the brain in PWS responds differently to hunger and food stimuli. Understanding these neural mechanisms can make the treatment of eating problems in PWS more sophisticated and successful.