Physical exercise may reduce dementia risk in aging, but varying reports on its effectiveness make it challenging to ascribe what level of exercise will have significant longer-term effects on important functions such as hippocampal-based learning and memory. This study compared the effect of three different 6-month exercise regimens on hippocampal-dependent cognition in healthy, elderly individuals. Participants, aged 65-85 with no cognitive deficits, were randomly assigned to one of three exercise interventions (low (LIT), medium (MIT), and High intensity interval training (HIIT), respectively). Each participant attended 72 supervised exercise sessions over a 6-month period. A total of 151 participants completed all sessions. Cognitive testing for hippocampal performance occurred monthly, as did blood collection, and continued for up to 5 years following initiation of the study. Multimodal 7 Tesla MRI scans were taken at commencement, 6 and 12 months. After 6 months, only the HIIT group displayed significant improvement in hippocampal function, as measured by paired associative learning (PAL). MRI from the HIIT group showed abrogation of the age-dependent volumetric decrease within several cortical regions including the hippocampus and improved functional connectivity between multiple neural networks not seen in the other groups. HIIT-mediated changes in the circulating levels of brain-derived neurotrophic factor (BDNF) and cortisol correlated to improved hippocampal-dependent cognitive ability. These findings demonstrate that HIIT significantly improves and prolongs the hippocampal-dependent cognitive health of aged individuals. Importantly, improvement was retained for at least 5 years following initiation of HIIT, suggesting that the changes seen in hippocampal volume and connectivity underpin this long-term maintenance. Sustained improvement in hippocampal function to this extent confirms that such exercise-based interventions can provide significant protection against hippocampal cognitive decline in the aged population. The changes in specific blood factor levels also may provide useful biomarkers for choosing the optimal exercise regimen to promote cognitive improvement.

High-Intensity Interval Training Shows Durable Hippocampal Benefits

A University of Queensland randomized controlled trial found that 6 months of high-intensity interval training (HIIT) using the Norwegian 4×4 protocol significantly improved hippocampal-dependent learning and memory in healthy elderly adults, with benefits lasting at least 5 years.[pmc.ncbi.nlm.nih]​

Study Design and Findings

The study randomly assigned 151 participants (aged 65-85) to three groups: low-intensity training (LIT), moderate-intensity training (MIT), or HIIT. All groups completed 72 supervised sessions over 6 months. The HIIT protocol specifically consisted of four 4-minute intervals at 85-95% of peak heart rate, interspersed with three 3-minute active recovery periods at 60-70% peak heart rate.[pmc.ncbi.nlm.nih]​

Only the HIIT group showed significant improvement in hippocampal-dependent spatial learning (measured by paired associative learning tests), with the largest gains occurring after 6 months of exercise. This cognitive improvement was maintained throughout a 5-year follow-up period, even though participants were not required to continue the exercise regimen.pmc.ncbi.nlm.nih+1

Neurobiological Changes

Brain imaging using 7 Tesla MRI revealed that HIIT prevented age-related hippocampal volume loss observed in the other groups. The right hippocampus remained stable in the HIIT group while decreasing significantly in both LIT and MIT groups. Additionally, HIIT increased functional connectivity between multiple neural networks, including the default mode network, motor network, visual network, and attention network.pmc.ncbi.nlm.nih+1

Biomarker Correlations

The study identified two blood biomarkers that predicted cognitive improvement in HIIT participants:pmc.ncbi.nlm.nih+1

• BDNF (Brain-Derived Neurotrophic Factor): Initial exercise-induced increases in BDNF levels predicted subsequent cognitive improvementpmc.ncbi.nlm.nih+1
• Cortisol: Higher exercise-induced cortisol responses correlated with better hippocampal-dependent cognitive performance at the end of the 6-month intervention[pmc.ncbi.nlm.nih]​

Long-Term Durability

The 5-year cognitive benefits appear directly attributable to the 6-month HIIT intervention rather than lifestyle differences, as accelerometry and questionnaire data showed no significant differences in physical activity patterns between groups during follow-up. The sustained improvement suggests that structural changes in hippocampal volume and neural connectivity established during the intervention underpin long-term cognitive protection.pmc.ncbi.nlm.nih+1