Client Education

Memory Issues

The Biology of Memory Loss

By: Denise Hamilton, Special to AccentCare

Throughout your life, nerve cells are constantly dying and new ones are created. As you age, the rejuvenation process slows down in your brain as well as elsewhere and as cells die, fewer spring up to replace them, which means nearby cells must grow new neurological connections to compensate.

During early development and through adolescence, these connections between cells, called synapses, are formed at a tremendous rate of overproduction, says Albert Herrera, a professor of biological sciences at the University of Southern California who specializes in the development of synaptic connections.

The ability to remember something or learn it, including abstract skills such as writing poetry or motor skills such as playing the piano, has its focus in synaptic connections, scientists say. And recent studies have shown that the ability of the brain to form new synaptic connections persists throughout life.

In the 10 years after childhood, the brain selectively "prunes" the synaptic connections that are not used, eventually reducing them to the adult number. "The process is activity-dependent," says Herrera, meaning that how the brain gets used determines which connections remain and which get pared down.

Studies have shown that rats raised in rich, stimulating environments develop many more synaptic connections than rats raised in bare cages. While there are no analogous controlled studies for humans — that would be cruel and unethical — Herrera says it? reasonable to conclude that "the more you challenge yourself with novel and diverse experiences, the more you'll stimulate this growth of synaptic connections in the brain."

Synapse loss is the first thing to go in people with memory disorders. In fact, some theorize that the thicker the density of the synapses, the slower this happens, which may protect against Alzheimer? Disease. Additionally, nerve cells communicate via synapses by using chemicals called neurotransmitters that go from one cell to another. Over time, some of those neurotransmitters can wear out. For a while, other nerve cells may compensate by stepping up chemical production, but at some point they may get maxed out, Herrera says. And it is at that point that people may begin to notice memory problems.

That's why some of the Alzheimer? therapies currently under study involve neuroprotective agents such as Vitamin E and other chemicals that slow or prevent this deterioration or stimulate production of brain chemicals used in memory. That? also why doctors recommend staying mentally active: Doing crossword puzzles won? create new nerve cells, but it does create new connections between the nerve cells. Thus the more you stimulate yourself, the more connections you create.

Conversely, Herrera points out that because the brain compensates for loss of nerve cells throughout life, significant deterioration may occur before the compensating cells wear out and a patient begins having symptoms of memory loss.

"One theory is that the deficiency in nerve cells, while progressive, happens at different rates for different people, and as long as you stay above that threshold of loss, it? not obvious. Some individuals may cross that threshold at age 40 and others at 110," Herrera says, explaining why some 90-year-olds can have memories that are sharp as tacks while other people who are 65 may exhibit severe memory loss.