Smooth pursuit eye movements in dementia of the Alzheimer type

Smooth pursuit eye movements (SPEM) to a sinusoidally modulated target moving horizontally across a cathode ray tube screen were examined for 17 patients with dementia of the Alzheimer type (DAT) and for 14 age-matched control subjects. There were 3 target-motion conditions at frequencies representing varying ranges of target velocity. DAT patients differed from controls on all measures of smooth pursuit quality: their gain was reduced at high target velocities and lower target accelerations, they made more frequent directionally appropriate saccades and had more saccadic intrusions, they led the target with their eyes (phase lead) in all 3 conditions, and lag-adjusted cross-correlation coefficients, computed between digitized eye-movement and target signals, were lower among patients. The cross-correlation measure was most sensitive to between-group variability. These results suggest that the impaired SPEM observed in DAT patients reflect degeneration of cortical oculomotor centers, either through inappropriate saccadic intrusions in smooth pursuit as a result of physiologic disinhibition or through effects on attentional processes or both.