What factors contribute to the decrease in brain volume as people age?

The reduction of neurons and lower synapse count is a significant factor contributing to the decrease in brain volume as people age. As individuals grow older, there is a natural decline in the number of neurons, a phenomenon that can lead to a decrease in overall brain mass. This neuron loss can be attributed to various factors, including genetic influences, lifestyle choices, and the cumulative effects of aging on cellular health.

Additionally, with fewer neurons, there is a subsequent reduction in synaptic connections. Synapses are the junctions through which neurons communicate, and a decrease in their count can significantly impact cognitive functions, memory, and overall brain capacity. This loss of synapses is often observed in aging individuals and can contribute to common age-related cognitive challenges.

In contrast, options discussing increased synapse count or longer axons, increased connectivity, or improved neuroplasticity do not accurately reflect the age-related changes observed in the brain. While neuroplasticity is the brain's ability to adapt and reorganize itself, it typically declines with age, leading to less efficient communication among neurons. Thus, the correct choice highlights the primary biological changes—reduction in neuron and synapse numbers—that directly correlate with the observable decrease in brain volume as people age.