Tuesday, February 23, 2010

♫ Oh, sugar sugar ♫

To say I had a sweet tooth as a child would be an understatement. I remember one Easter, I must have eaten over 40 Cadbury Creme Eggs in one sitting. My mom would put a chocolate centerpiece on the table, usually a bunny or an egg or something like that, and it would be surrounded with smaller treats, such as Creme Eggs. What ensued was a complex calculation of how many eggs I could eat before it would look like I ate them all. I had to factor in the fact that my brothers and sister would also eat some eggs, albeit at a slower rate. And I also had to squish all the little foil wrappers in the tiniest, most compact ball possible to make it look like I didn’t actually have that many. Those were the good days.

It’s no secret that children have a more pronounced preference for high-intensity sweetness. This preference may have evolved to make sure children seek out energy-rich nutrition during growth. Therefore, having a child with a sweet tooth was never really a cause for worry. Until now.

A recent study in the journal Addiction looks at the link between children with a sweet tooth and two other parameters: family history of alcoholism and depression. The researchers picked those two parameters because the pleasure derived from eating something sweet is generated by a reward system in your brain, and both alcoholism and depression affect this reward circuitry. The researchers looked at 300 healthy children, assessed their family history of alcoholism (via an interview with the mother), and tested them for depressive symptoms. They then tested the children for sweetness preference by having them taste sucrose solutions of different sucrose concentrations and asking them to choose which is their favorite. They also assessed the children’s liking for sweet treats in daily life.

The researchers found that almost half of the children were positive for family history of alcoholism, and one quarter of the children exhibited depressive symptoms, consistent with previous studies. When the researchers analyzed sweet preferences, it got messy. First, children with a family history of alcoholism preferred significantly higher sucrose concentrations compared with children with no such family history. Interesting, right? However, if from the total pool of children with a family history of alcoholism, you remove those who also show depressive symptoms, the alcoholism/sweet tooth link is no longer significant. Like I said, messy. Second, children who tested positive for depressive symptoms preferred significantly sweeter foods compared with children who didn’t exhibit depressive symptoms. Interesting, right? However, if you factor in the age of the children, this depression/sweet tooth link is no longer significant (this is because the intensity of the sweet tooth decreases with age). Guess what I’m about to say? That’s right, messy.

Overall, we can draw two conclusions. First, children with a family history of alcoholism AND exhibiting depressive symptoms prefer significantly sweeter solutions. Second, children exhibiting depressive symptoms MAY have a “sweeter tooth” compared with children who don’t exhibit depressive symptoms. Several theories, or a combination of these theories, could explain the associations observed in the study. First, if you read the fine print in the article, you’ll find that the mothers of children who have a family history of alcoholism and depressive symptoms are more likely to be obese. Perhaps these children are exposed to more sweets from an early age? Second, other studies have shown that adults with depression have a higher threshold for the detection of sweet taste. Therefore, it is possible that these children are less sensitive to sucrose and need a higher concentration of sugar to achieve the same level of sweet taste. Third, it is possible that the children with a family history of alcoholism and depressive symptoms have an altered brain reward system and require a higher concentration of sugar to activate the pleasure centers in the brain.

While this study suggests interesting associations, one thing is for sure, more experiments are needed to determine if having a sweet tooth means anything at all. Now excuse me while I unwrap the first Cadbury Creme Egg of the season.

Reference: Sweet preferences and analgesia during childhood: effects of family history of alcoholism and depression. (2010) Mennella JA, Yanina Pepino M, Lehmann-Castor SM, Yourshaw LM. Addiction. Feb 9 [Epub ahead of print].

Wednesday, February 10, 2010

Do you want to live? Yes or no?

In the early 2000’s, the Terry Schiavo case took the media by storm and pushed into the spotlight a number of ethical questions regarding patients in persistent vegetative state (awake but not aware). Evidently, none of this would have happened if we could just have asked her whether she wanted to continue living or not. A simple yes or no question. Could this be achieved? Can patients in a vegetative state communicate purposefully? A new study suggests they can.

The researchers looked at brain signals from 16 healthy patients and 54 patients with severe brain injuries who were in a vegetative state. The technique they used is called fMRI (for functional magnetic resonance imaging), a scan similar to one you would get for a joint injury, but instead of taking static images, fMRI measures blood flow in your brain. Presumably, if part of your brain is activated, there will be an increase in the blood flow in this area, and this will area will light up on the brain image.

The first experiment was done only with the healthy controls to establish that different cognitive tasks lead to the activation of different parts of your brain. While immobilized in the fMRI machine, the subjects were asked to imagine playing tennis. They then asked the healthy subjects to imagine walking through a familiar house. As expected, the brain scan images showed that each task activated a different brain region.

Armed with this control data, the researchers moved on to the patients in vegetative state. They asked each of the 54 patients to think about playing tennis and to think about navigating through a familiar house, and looked at the resulting brain signals. Of the 54, they found a grand total of five patients whose brain signals matched that of the healthy controls during a given task. This result suggests that some patients in a vegetative state can willfully influence their brain activity.

While this is an interesting finding in itself, there’s more. The researchers then took one of the five patients who showed the correct brain activity, and asked him yes or no questions. The patient was instructed to think about tennis when he wanted to answer yes, and think about the house when he wanted to say no. Out of the six yes or no questions he was asked (such as “Is your father’s name Alexander?”), he correctly answered five. Success!

The researchers and the media were quick to take these findings to the next level: with this new technique, we can now have brain damaged patients express their feelings! We can increase their quality of life! We can ask them important ethical questions! Well, hold on. While I do agree that this is a very interesting study, and that it will no doubt give a lot of hope to the families of patients in vegetative state, one has to be very careful with interpretation. First, let’s run the numbers: out of 54 patients, only five responded to the tasks. Out of those five, only one was tested. Out of the six questions asked, five were answered. While this represents a great achievement, we are very far from being able to extrapolate the potential of this technique. Second, the fMRI technique is expensive, imperfect, and very difficult to interpret. Third, certain words could possibly cue brain activity that may or may not be willful. I would like to see the researchers do an experiment where they just say the word “tennis” or “house” to healthy volunteers without asking them to imagine anything and see what kind of brain activity results. Finally, the fact that a patient has the cognitive ability to picture playing tennis does not mean he or she has the cognitive ability to make important, ethical decisions. So before we get all excited, I think we should keep things in perspective.
But one thing is for sure: in this age of medical technology, we can set the Ouija board aside.

This is what fMRI data looks like

Reference: Willful modulation of brain activity in disorders of consciousness. (2010) Monti MM, Vanhaudenhuyse A, Coleman MR, Boly M, Pickard JD, Tshibanda L, Owen AM, Laureys S. New Engl J Med Feb. 3 [Epub ahead of print].

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