Non-invasive localization of P300 sources in normal aging and age-associated memory impairment.

Cognitive event-related potentials were recorded from 17 EEG leads in an auditory two-tone paradigm in 43 patients aged 51-79 years with the diagnosis of age-associated memory impairment (AAMI), in age-and sex-matched normal controls and in a control group 10 years older than the AAMI patients. In addition to P300 latencies, amplitudes and topographies, three-dimensional current density distribution utilizing low-resolution brain electromagnetic tomography (LORETA) was computed. P300 latency was delayed and P300 amplitude was reduced in both AAMI and older subjects. Topographically this amplitude reduction was most pronounced frontally. LORETA revealed medial (frontal and parietal) and lateral (dorso- and ventrolateral prefrontal, middle/superior temporal, posterior superior temporal/inferior parietal) sources. Significant reductions in LORETA source strength in normal aging and in AAMI were found mainly medially frontally, right dorsolaterally prefrontally and right inferiorly parietally. Since these anatomically highly interconnected brain regions in the right hemisphere are part of a network associated with sustained attention, the results speak for a decline in attentional resource capacity in AAMI patients and elderly subjects.