Researchers who studied the brains of adults age 43 to 87 found evidence that humans continue to make new neurons throughout their late adult life. The findings also show that the process is suspended in patients with Alzheimer's disease.
Neurogenesis, the growth of new neurons, occurs during embryonic development. By the time people are born, most of these neurons have already formed. The growth of new brain cells in adults was thought to rarely occur.
María Llorens-Martín, from the Severo Ochoa Molecular Biology Center in Spain, and colleagues, however, found evidence that suggest otherwise.
In a new study published in Nature Medicine on March 25, the researchers studied brain tissue samples to look for signs of new brain cells. The samples were taken from 13 deceased adults age between 43 and 87 years old who died of a range of reasons but were all considered neurologically healthy before their death.
Neurons are made in the brain's hippocampus, a region that plays a role in learning and memory. As these neurons mature from young to old, they make certain proteins.
The researchers used antibodies to detect these proteins and found they were drawn to thousands of neurons across the samples.
After examining the cells that make the proteins, Llorens-Martín's team found a range of neuron shapes and sizes, which indicates that the neurons are still in the process of maturing. This means that they were made later in life.
Neurons In Alzheimer's Disease Patients
The researchers also analyzed the brains of 45 deceased Alzheimer's disease patients whose age ranged between 52 and 97 years. They found that the brains showed few, if any, signs of new neurons in the hippocampus. Those in the course of the disease in particular exhibit less signs of new neurons.
This suggests that the loss of new neurons, if this could be detected in the living brain, may indicate the onset of Alzheimer's disease.
It may also mean that promoting new neuron growth may delay or prevent the onset of Alzheimer's, which now affects more than 5.5. million people in the United States.
"These results demonstrate the persistence of AHN during both physiological and pathological aging in humans and provide evidence for impaired neurogenesis as a potentially relevant mechanism underlying memory deficits in AD that might be amenable to novel therapeutic strategies," the researchers wrote in their study.