David Baxter PhD
Late Founder
Anorexics May Have Altered Sense of Taste
Tuesday, October 09, 2007
Anorexia studies often focus on the powerful social pressure exerted by unrealistic images and critical peers, but recently there have been a few noteworthy searches for a pysiological component to the eating disorder. Last week, we discussed the parallel between anorexia and ecstasy. Starvation and drug both trigger similar pleasure mechanisms in the brain. In fact, when naltrexone, an opioid receptor antagonist commonly prescribed to heroin addicts, is given to anorexics, patients often return to a healthy weight.
While the view of anorexia as an addiction is intriguing, there are other possible physiological explanations for the disorder. Dr. Angela Wagner performed an experiment to study the reactions of 16 recovered anorexics to sugar. Recovered anorexics were chosen to avoid the confounding psychological factors that might be present in still-struggling subjects. Recovered anorexics took the sweet drink without protest, but an fMRI revealed that while their behavior may have returned to normal, their brains have not. Compared to the control subjects, there was much less activation of the insular cortex, especially the primary cortical taste region. This suggests the possibility that rather than missing meals to feel high, anorexics don?t eat because they simply find normally pleasant tastes less appealing.
There are a few alternative ways to view the evidence gathered by Dr. Wagner. Firstly, the order of causation is uncertain; it is unclear whether lack of neural excitation diminishes interest in food, or whether strict caloric restriction diminishes the amount of processing power allocated for taste. Further studies may be able to settle the chronology by scanning subjects before they develop an eating disorder. Another possibility to explore is that abnormal activation of the insular cortex has a larger effect than muted taste. The insular cortex is associated with self-regulation of heartbeat and many internal states requiring delicate balance. Some scientists have speculated that the insular cortex feedback loops between internal states and conscious action control our basic self-awareness. This could explain why anorexics are unable to maintain a healthy weight and a realistic body image. Conscious desire for weight-loss overpowers the unconcious system that is supposed to regulate hunger.
At this point, we can only say that physiological theories are interesting but lack the evidence behind therapy treatments. Some of the theories are mutually exclusive, meaning that some of the evidence must be misleading. For example, the aforementioned theory that anorexia is an addiction has some compelling evidence behind it, but the study by Dr. Wanger seems to directly contradict it because the insular cortex is supposed to contribute to cravings when it activates. Anorexia cannot be caused both by apathy and intense desire. This is more than just an interesting academic question. Anorexia is the deadliest of mental illnesses and every year that we remain ignorant of its cause means more lives lost.
Tuesday, October 09, 2007
Anorexia studies often focus on the powerful social pressure exerted by unrealistic images and critical peers, but recently there have been a few noteworthy searches for a pysiological component to the eating disorder. Last week, we discussed the parallel between anorexia and ecstasy. Starvation and drug both trigger similar pleasure mechanisms in the brain. In fact, when naltrexone, an opioid receptor antagonist commonly prescribed to heroin addicts, is given to anorexics, patients often return to a healthy weight.
While the view of anorexia as an addiction is intriguing, there are other possible physiological explanations for the disorder. Dr. Angela Wagner performed an experiment to study the reactions of 16 recovered anorexics to sugar. Recovered anorexics were chosen to avoid the confounding psychological factors that might be present in still-struggling subjects. Recovered anorexics took the sweet drink without protest, but an fMRI revealed that while their behavior may have returned to normal, their brains have not. Compared to the control subjects, there was much less activation of the insular cortex, especially the primary cortical taste region. This suggests the possibility that rather than missing meals to feel high, anorexics don?t eat because they simply find normally pleasant tastes less appealing.
There are a few alternative ways to view the evidence gathered by Dr. Wagner. Firstly, the order of causation is uncertain; it is unclear whether lack of neural excitation diminishes interest in food, or whether strict caloric restriction diminishes the amount of processing power allocated for taste. Further studies may be able to settle the chronology by scanning subjects before they develop an eating disorder. Another possibility to explore is that abnormal activation of the insular cortex has a larger effect than muted taste. The insular cortex is associated with self-regulation of heartbeat and many internal states requiring delicate balance. Some scientists have speculated that the insular cortex feedback loops between internal states and conscious action control our basic self-awareness. This could explain why anorexics are unable to maintain a healthy weight and a realistic body image. Conscious desire for weight-loss overpowers the unconcious system that is supposed to regulate hunger.
At this point, we can only say that physiological theories are interesting but lack the evidence behind therapy treatments. Some of the theories are mutually exclusive, meaning that some of the evidence must be misleading. For example, the aforementioned theory that anorexia is an addiction has some compelling evidence behind it, but the study by Dr. Wanger seems to directly contradict it because the insular cortex is supposed to contribute to cravings when it activates. Anorexia cannot be caused both by apathy and intense desire. This is more than just an interesting academic question. Anorexia is the deadliest of mental illnesses and every year that we remain ignorant of its cause means more lives lost.
