Effect of Normal Aging and of Mild Cognitive Impairment on Event-Related Potentials to a Stroop Color-Word Task.

Event-related potentials (ERPs) were recorded from 84 adults (51 to 87 years old) with the aim of exploring the effects of aging (middle-aged and older groups) and cognitive status (healthy or with amnestic mild cognitive impairment, aMCI) on the neural functioning associated with stimulus and response processing in a Stroop color-word task. An interference (or Stroop) effect was observed in the Reaction Time (RT), and the RT and number of errors results were consistent with the age-related decline in performance. Cognitive status did not affect the behavioral performance of the task, but age and cognitive status affected several ERP parameters. Aging was associated with a) slowing of the neural processing of the stimuli (P150, N2, and P3b latencies were longer), b) greater activation of the motor cortex for response preparation (LRP-R amplitude was larger), and c) use of more neural resources for cognitive control of stimuli (N2 amplitude was larger to the congruent and incongruent stimuli than to the colored X-strings, in the older group). Independent of age, aMCI dedicated more neural resources to processing the irrelevant dimension of the stimulus (they showed a greater difference than the control participants between the P3b amplitude to the colored X-strings and to the congruent/incongruent stimuli) and showed a deficit in the selection and preparation of the motor response (with smaller LRP-S and LRP-R amplitudes). Furthermore, the middle-aged aMCI participants evaluated and classified both congruent and incongruent stimuli more slowly (they showed longer P3b latencies) relative to middle-aged controls.