This article originally appeared in Psychology Today.

The brain is mainly made up of two types of substances: gray and white matter. White matter is made up of myelinated axons that connect different parts of the brain. They generate electrical signals and release chemicals to transmit information. As we age, white matter deteriorates; as a result, the signal becomes slower, misdirected, or lost. White matter degeneration is even more severe in people with cognitive impairment and/or dementia.

Because the global incidence of dementia is projected to double every 20 years [1], developing effective strategies to slow down cognitive decline—in both healthy and unhealthy brains—is critical. Learning about the brain pathologies that underlie age-related cognitive decline can help point scientists in the right direction. White matter deterioration, for example, leads to cortical “disconnection,” which is one of the main mechanisms of cognitive decline in healthy aging [2].