Electrophysiologic correlates of age effects on visuospatial attention shift.

The effects of age on the neural processes underlying shifts in visuospatial attention were studied by non-invasive recording of brain electrical activity. Event-related evoked potentials (ERPs) were recorded in young (age 28-36 years old) and elderly (59-74 years old) subjects during a target detection task. Targets were preceded by central or peripheral informative cues, which are hypothesized to provoke voluntary and reflexive shifts of spatial attention, respectively. There were no age-related differences in the effects of cue validity on reaction times. Elderly subjects had longer reaction times to both the valid and invalid targets. The ERP recordings demonstrated that attention shift-related negativities (ARNs) were generated over the hemisphere contralateral to the central cue direction with the same amplitude in young and elderly subjects. However, the onset latency was delayed for the elderly at anterior scalp sites. Peripheral cues enhanced the N1 component (140-200 ms post-cue) over the contralateral hemisphere comparably in the two age groups. The ARNs following N1 enhancement demonstrated delayed onset and restricted scalp distributions in the elderly group compared with the young group. These results suggest that resistance of cue validity effects to aging is consistent with existence of the N1 enhancement and ARNs, even in elderly subjects. Different age effects on ERPs generated by central and peripheral cues support the notion that voluntary and reflexive mechanisms of attention shift involve distinct neural systems with different vulnerability to aging.