Early visual processing deficits in the elderly: anterior increases and posterior decreases of electrical source activity
We compared temporal processing in elderly and young controls using EEG and electrical neuroimaging. Subjects discriminated the offset direction of Vernier stimuli in four conditions: Vernier only, mask only, Vernier immediately followed by a mask, and Vernier followed by a mask after a 150 ms SOA. The elderly showed a markedly decreased performance when the Vernier was immediately followed by a mask. Statistical analysis of the electrical sources in this condition showed decreased activity in occipital and fusiform areas at around stimulus onset, and increased activity in right inferior parietal area cortex (BA40) at around 170 ms. Hence, ongoing electrical activity in higher level visual areas is decreased in the elderly, while parietal cortex shows evoked increases that may reflect increased spatial attention. Across the four stimulus conditions elderly showed a distinct EEG scalp topography at around 150 ms that was not observed in young controls. In addition, elderly showed markedly decreased responses at around the N1 latency. Electrical source imaging across the stimulus conditions around this latency revealed decreased electrical activity in the precuneus and cingulate cortex, and increased activity in the inferior parietal, the medial and superior frontal gyrus, as well as in the caudate nucleus. Results are in line with the posterior–anterior shift account of aging and show that a reorganization is apparent around stimulus onset, as well as in visual processing before 200 ms.
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Record created on 2010-05-12, modified on 2016-08-08