Several mechanisms might explain the relationship
between slow walking speed and subsequent decline in
cognitive function. One possible mechanism is that walking speed could be a marker of brain lesions (white matter disease) that are associated with future cognitive
decline [32]. Progression of these small white matter
lesions could produce abnormalities in walking speed
early in the process of decline, and only later might
impairments in cognition be detected [32]. Periventricular white matter hyper intensities (high signal) on magnetic resonance imaging (MRI) scans and increased
ventricular volume, even in apparently healthy older
adults, have also been associated with slowing of walking
speed [36]. These central nervous system changes con-
tribute to important markers of aging [35]. More recently,
changes on MRI scans in conjunction with presence of
apolipoprotein E epsilon 4 predicted future cognitive
decline and poor physical function in 444 older adults
over a 10 yr period. Radiological findings in conjunction
with apolipoprotein E epsilon 4 may single out a group at
higher risk for dementia [37]. Cognitive decline and poor physical function are risk factors for disability in old age
and were related in our sample.