A new Mayo Clinic study finds that after memory begins to decline, executive function is the next brain function to deteriorate in the progression from mild cognitive impairment, a pre-Alzheimer's disease condition, to Alzheimer's disease.
Ron Petersen, M.D., Ph.D., Mayo Clinic neurologist and senior study investigator, says executive function includes concentration, decision making, and higher-order problem solving.
"If someone with mild cognitive impairment starts having trouble staying on task, concentrating, multitasking, making decisions or paying attention to several things at once, that would mean they are progressing toward dementia," he says. "A decline in executive function will cause people to become more impaired in their daily activities, as it is pretty important in daily function."
Dr. Petersen says that awareness of the typical progression to Alzheimer's will be useful for patients, their families and their doctors. In order to convert from mild cognitive impairment to Alzheimer's disease, patients must have impairment in memory and one other aspect of brain function.
"Knowing what area of cognitive function is likely to become impaired after memory helps us as we try to keep our eyes out for people when they are worsening," he says.
Awareness of a patient's functional decline informs neurologists what areas of the brain are being affected as mild cognitive impairment progresses to Alzheimer's: the medial temporal lobe is affected as memory declines, and then the frontal regions of the brain are affected as executive function worsens, according to Dr. Petersen. The lessening of these abilities indicates the buildup of more plaques and tangles in the brain. The buildup results from abnormal protein accumulation inside the cells and the deposit of abnormal material outside the cells in the brain, leading to a slowly degenerating neuron death and shrinkage of the affected brain regions.
No one knows why mild cognitive impairment affects the memory then spreads to executive function as the disease moves toward Alzheimer's, says Dr. Petersen.
In future studies of mild cognitive impairment, measuring whether a patient has moved from memory impairment alone to weakened executive function could help determine whether a particular drug is successful in slowing or stopping the disease, he says.
If patients or their families notice progress from memory decline to problems with executive function, they should inform their physicians and consider medication to potentially slow the patient's deterioration, if they have not already done so, says Dr. Petersen.
Although previously neurologists have speculated that executive function may be next to wane following memory as one develops Alzheimer's, this study represents a systematic demonstration of the progression of impairment.
To conduct this study, the researchers identified 354 patients with amnestic mild cognitive impairment, a pre-Alzheimer's disease condition, and followed them for an average of 3.1 years, assessing them for impairment in the brain's executive function, and visuospatial and language abilities. Early in the course of mild cognitive impairment, the patients' attention capacity began to diminish. Executive function continued to decline steadily over the course of follow-up.