Anyone who has ever been acutely anxious can attest to the havoc that such a mood can wreak on the digestive system. Clearly the brain and the gut are closely connected, both circumstantially (I always spent a lot of time in the bathroom during my high school speech competitions) and physically (by the vagus nerve that runs from the head to the body's internal organs). By these measures, it stands to reason that your psychological state can affect your digestion. But a study released today in the journal PLoS One suggests an alternative theory. According to Stanford gastroenterologist Pankaj Pasricha, MD:
A lot of research has focused on understanding how the mind can influence the body. But this study suggests that it can be the other way around. Gastric irritation during the first few days of life may reset the brain into a permanently depressed state.
In the study, Pasricha and his colleagues applied a mild irritant to the digestive system of 10-day-old laboratory rats once a day for six days. When the rats were 8 to 10 weeks old, they then used a variety of psychological and behavioral tests to assess the animals. They found that rats with early gastric irritation were more likely to display depressed or anxious behaviors than their non-treated peers. Blocking the signaling of a hormone known to be associated with depression in humans alleviated the behaviors.
Clearly not every case of newborn colic will lead to lifelong depression. But according to Pasricha:
It seems that when the rats are exposed to gastric irritation at the appropriate point in time there is signaling across the gut to the brain that permanently alters its function.
The researchers are now planning to investigate exactly how that signaling is initiated and acts in the brain, and whether it might be possible to develop new ways to treat depression and anxiety in humans.