Regional fMRI brain activation does correlate with global brain volume.

In healthy elderly participants, there has been little correlation found between measures of global brain atrophy and functional magnetic resonance imaging activated voxel counts and mean percent magnetic resonance signal change. We used a validated passive viewing task to calculate the fMRI activated voxel counts and mean percent MR signal change from the striate and ventral extrastriate cortices of 24 healthy control subjects (age range=33-89, mean age=66). We correlated these data with three measures of atrophy - percent brain volume, normalised brain volume and grey matter volume - to evaluate the relationship between global brain atrophy and regional fMRI activation. There was a strong positive correlation (r>0.90) between regional activation volume in striate and ventral extrastriate cortex and decreasing total brain volume when results were averaged by decade. Correlation with percent brain volume was particularly strong. In addition, we found a strong negative correlation between mean percent MR signal change and brain volume measures. Within-subject individual correlation was less strong, highlighting the problem of individual variability in brain volume and regional activation measures.