Diabetes is known to damage nerves in the arms and legs, sometimes leading to the painful condition known as diabetic neuropathy or the need to amputate limbs. Research since the 1960s has suggested the disease may also affect the brain itself; for example, people with diabetes are twice as likely as the general population to develop depression.
To find out whether the depression is a "psychological" response to the illness or results from structural brain changes, Alan Jacobson and colleagues at the Joslin Diabetes Center and Harvard Medical School, Boston, examined levels of gray matter-brain tissue rich in cell bodies, which constitutes key areas such as the cerebral cortex and the movement centers known as the basal ganglia.
The team used voxel-based morphometry, which creates detailed, three-dimensional representations of magnetic resonance imaging (MRI) scans. Reporting in the February issue of the journal Diabetes, the researchers found that diabetes patients had decreased levels of gray matter density in areas of the brain responsible for memory, language processing, and attention, compared with healthy controls. The decreases were more prevalent in patients with wide fluctuations of blood sugar, particularly in those with many episodes of low blood sugar resulting in unconsciousness.
Although cognitive tests revealed few differences between diabetes patients and controls, "it's possible that the structural changes we observed signal future cognitive problems," says study author Perry Renshaw of McLean Hospital in Belmont, Mass. Future studies will use MRI to help measure any cognitive and emotional changes, with the goal of treating and preventing depression in diabetic patients.