Memory loss due to shrinkage of the hippocampus increases and becomes more recurrent as people get older. In an attempt to find an inexpensive way to decrease the rate of memory loss, the study found that regular aerobic exercise for a year increases hippocampal volume, replacing about two years of lost memory, and improves spatial memory. The study also found that individuals who do aerobic exercises have increased levels of BDNF which is involved in neurogenesis and cell proliferation in the hippocampus, contributing to improved memory and increased size of the hippocampus.
The study chose elderly participants with no history of neurological diseases and split them randomly into two groups: the aerobic walking group and the stretching control group. Before the participants began their training, baseline measurements were taken of aerobic fitness, MRI, blood, and memory. Aerobic fitness levels were measured by monitoring heart rate and oxygen intake of participants walking on a treadmill. The aerobic exercise group walked 10 minutes a week, adding time each week, and wore heart monitors to ensure they met a certain heart rate that varied per person. The stretching control group attended classes that improved balance and toned muscles, increasing in intensity over the course of the year. After conclusion the study, the greatest changes in fitness and improved oxygen levels correlated to the greatest changes in hippocampal volume, but not in the caudate nucleus or the thalamus.
MRI images were taken to measure changes in the volume of the hippocampus, thalamus, and caudate nucleus before the start of the study as the baseline, after the sixth month, and at the one year after completion of the study. MRI images found that those in the aerobic exercise group had an increase in volume of the right and left hippocampus while the stretching control group showed a decrease in the right and left hippocampus. However, change only occurred in the anterior hippocampus and not in the posterior hippocampus because the anterior portion contains the cells responsible for attaining spatial memory. The study found that changes due to exercise happened mainly in the anterior hippocampus by finding little changes in the caudate nucleus, thalamus, and posterior hippocampus of the exercise group.
The participants had blood drawn prior to the study and after completion of the study to measure serum BDNF levels. Compared to the stretching control group, the study showed that the exercise group showed a greater increase in serum BDNF that controls cell proliferation in the dentate gyrus of the hippocampus, leading to increased hippocampal volume. Memory was tested using a spatial memory task prior to the study, after 6 months, and after completion of the study. The spatial memory test showed that participants with higher aerobic fitness levels performed faster and more accurately compared to the stretching group and the test result before the study began, showing that increase in the hippocampal volume in the aerobic fitness group leads to improved spatial memory.
In class, we discussed the development of neurons and the need for neurotrophic factors in order for neurogenesis to occur. BDNF stands for brain-derived neurotrophic factor that helps in the proliferation of the neuronal cells in the anterior hippocampus increasing in volume when exercise induced. This article shows that neurogenesis can occur in adults. Before reading this article, I assumed that after the first couple years of life, neurons could change because of neuroplasticity, but neurogenesis could not occur. I now understand that neurogenesis can occur within the brain later in life if stimulated, which can have profound effects on spatial memory function. From class, I understand that neurotrophic factors increase the likelihood that a neuron will survive, but I did not understand the extent of effectiveness of neurotrophic factors on neuronal growth until reading the article that showed how an increase in the BDNF led to a direct increase in hippocampal volume, meaning the neurotrophic factors contributed to the development of neurons to increase the volume in the anterior hippocampus, leading to increased spatial memory.
Based on the study, one question that remained unanswered was how exactly did exercise lead to an increase in BDNF? The study suggested there is a correlation, but did not examine how the correlation came about. If the reason for the increase is found, neuroscientists could find a way to stimulate the production of BDNF in a more direct and swift manner in order to increase hippocampal volume and could potentially lead to an increase in spatial memory in individuals with memory deficit.