Changes in cell density within the human hippocampal formation as a function of age

Area of Science:

• Neuroscience
• Aging Research
• Human Anatomy

Background:

• Previous studies on aging hippocampus neuron density yielded conflicting results.
• Classical stereological techniques and electron microscopy showed no age-related increase in grey matter neuron density.
• This study investigated neuron and glia density in the entire hippocampal formation, including white matter.

Purpose of the Study:

• To determine neuron and glia population density per unit weight in the entire human hippocampal formation.
• To investigate age-related changes in neuron density within the hippocampus.
• To compare age-dependent neuronal changes in the hippocampus with those in the visual cortex.

Main Methods:

• Analysis of the entire hippocampal formation (grey and white matter) from 25 human brains.
• Determination of neuron and glia counts per unit weight using cell dispersion and hemacytometer counting.
• Comparison of findings with a previous study on the aging visual cortex using similar techniques.

Main Results:

• A slight increase in neuron population density was observed between 20 and 87 years of age.
• The apparent increase in neuron density is attributed to senescent shrinkage of the hippocampal formation, particularly white matter.
• Neuron lifespan in the hippocampus appears considerably longer than in the visual cortex.

Conclusions:

• Age-dependent neuron loss occurs at varying rates across different human brain regions.
• The methodology of analyzing the entire hippocampal formation, including white matter, provides a different perspective on aging.
• The human hippocampus exhibits a greater resilience to age-related neuronal loss compared to the visual cortex.