Figure 1.

Functional changes in the blood oxygen level dependent (BOLD) and cerebral blood flow (CBF) response in the VC for mild hypercapnia and functional activation. The panels show average response curves and standard errors for the CBF activated voxels within healthy younger (n = 10) and older (n = 10) subjects. (A) Fractional changes in the CBF responses to hypercapnia, (B) Changes in the BOLD responses to hypercapnia, (C) Fractional changes in the CBF responses to activation, and (D) Changes in the BOLD responses to activation. A significant increase in the fractional changes in the CBF response to hypercapnia was seen in older subjects compared to younger subjects leading to a decrease in the M value for older subjects. For the functional activation task the BOLD response was greater for younger compared to older subjects. For all panels the solid bars indicate stimulus presentation. For all time series data the error bars are presented at every other time point that was sampled. [Color figure can be viewed in the online issue, which is available at www.interscience.wiley.com.]