Researchers report that intermittent electrical stimulation of an area deep inside the brain that degenerates in Alzheimer’s appears to improve working memory. Conversely, continuous deep brain stimulation, like the type used for Parkinson’s impairs memory, according to study results in adult non-human primates reported in the journal Current Biology. Intermittent stimulation helped the monkeys to remember things up to five times longer in a standard test of working memory.
In the new studies, scientists used the technique of placing hair-thin electrodes into the brain to deliver electricity and increase the activity of the nucleus basalis of Meynert, a small area in the forebrain that is inexplicably degenerated in both Parkinson’s and Alzheimer’s.
Their goals included making more of the chemical messenger acetylcholine available in the region. The nucleus basalis has a large concentration of neurons that are connected to brain areas critical for memory and cognition, and under healthy conditions have a ready supply of acetylcholine that enables the important communication between them.
As we age, acetylcholine levels in the brain naturally decrease, but Alzheimer’s causes a dramatic multiplier effect, resulting in a shortage.
The researchers started with continuous stimulation, like the clinical approaches, and saw an unexpected decline in performance. Equally surprising, they found intermittent stimulation resulted in more available acetylcholine in the region and better performance.
In fact, use of the cholinesterase inhibitor donepezil restored memory performance in animals that received constant stimulation but had no impact on those whose memory was already enhanced by intermittent stimulation.
The scientists suspect the benefit resulted from the impact of increased levels of acetylcholine directly on neurons and their supportive cells in that region. However it may also result from a slight increase in blood flow to the brain region, they write. Cholinesterase inhibitors, drugs used to treat Alzheimer’s, are known to increase blood flow to the brain about 10-15 percent in humans. Blood flow is typically reduced in Alzheimer’s.
After months of intermittent stimulation, the monkeys got more adept at the memory test even without the stimulation. The reason for the enduring effect is not 100 percent clear: it could be the brain cells make more connections, it could be more acetylcholine keeps getting released, it could be both, the scientists note.
Paper: “Intermittent Stimulation of the Nucleus Basalis of Meynert Improves Working Memory in Adult Monkeys”
Reprinted from materials provided by the Medical College of Georgia at Augusta University.