As outlined in the research reported here, the variable physiology of the hippocampus allows for an interesting natural experiment to determine the degree to which blood supply is important in the aging of the brain. It is known that capillary density declines with age throughout the body, and this affects the supply of oxygen and nutrients to tissues. The brain is a particularly energy hungry organ, and reduced supply produces consequences. It isn't just capillary density that is important in aging, however, but also the general decline in physical fitness and ability of the heart to pump blood uphill to the brain. This lost performance becomes particularly profound in heart failure patients, but is no doubt producing detrimental consequences even when present to a lesser degree.
The hippocampus exists twice: once in each brain hemisphere. It is considered the control center of memory. Damage to the hippocampus, such as it occurs in Alzheimer's and other brain diseases, is known to impair memory. But what role does blood supply in particular play? To answer this questions, researchers used high-resolution magnetic resonance imaging (MRI) to examine the blood supply to the hippocampus of 47 women and men aged 45 to 89 years. The study participants also underwent a neuropsychological test battery, which assessed, in particular, memory performance, speech comprehension, and the ability to concentrate.
"It has been known for some time that the hippocampus is supplied by either one or two arteries. It also happens that only one of the two hippocampi, which occur in every brain, is supplied by two vessels. This varies between individuals. The reasons are unknown. Maybe there is a genetic predisposition. However, it is also possible that the individual structure of the blood supply develops due to life circumstances. Then the personal lifestyle would influence the blood supply to the hippocampus. In the cognition tests, those study participants in whom at least one hippocampus was doubly supplied generally scored better. The fact that the blood supply is fundamentally important for the brain has been extensively documented. We were therefore particularly focused on the hippocampus and the situation of a disease of the brain vessels. Little is actually known about this."
Of the study subjects, 27 did not manifest signs of brain diseases. The remaining twenty participants showed pathological alterations in brain blood vessels, which were associated with microbleeding. "In these individuals, sporadic cerebral small vessel disease had been diagnosed prior to our investigations. These individuals exhibited a broad spectrum of neurological anomalies, including mild cognitive impairment. The healthy subjects generally scored better on cognitive tests than the study participants with small vessel disease. Among the participants with disease, those with at least one hippocampus supplied by two arteries reached better scores in cognition. They particularly benefited from the double supply. This may be due to a better supply not only of blood but also of oxygen."