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Abstract:
Cognitive and neural mechanisms underlying neglect syndrome
were studied in 20 well defined cases of visuospatial neglect with
detection tests and ERP measurements (nine neglect patients;
visual, tactile and auditory stimulation). In addition to the
clinical features, neglect can be used as manipulation of the
threshold for conscious information processing. The results showed
first of all that neglect - defined often as visuospatial - is
multimodal. All our nine patients had neglect covering at least two
of the three modalities tested; in seven patients neglect covered
all three modalities. In acute phase of neglect the ERP
measurements showed disappearance or attenuation of N1 deflections
in responses to stimulation of the neglected side. In contrast, the
responses elicited by stimulation of the non-neglected side
contained pathologically large N1 deflections. Recovery from
neglect coincided with reappearance and normalization of the N1
deflections. These results suggest that the primary deficit in
neglect lies in orienting mechanisms. Despite the failure to orient
to the stimuli and thus difficulties in conscious perception of the
stimuli, the sensory apparatus is able to receive and discriminate
the stimuli. This was shown by the large auditory MMN responses to
deviant stimuli (1100 Hz, p=.15; among standards, 1000 Hz, p=.85;
delivered via speakers) in oddball paradigm, especially when
stimulating the neglected side.
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