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Oades, R.D.,
Zerbin, D. & Eggers, C. (1994) Negative
difference (Nd), an ERP-marker of stimulus relevance: different lateral
asymmetries for paranoid and non-paranoid schizophrenics. Pharmacopsychiat.,
27, 65-67. (pdf file)
We
studied Nd in psychotic patients with varying degrees of paranoid
symptoms. Nd is an ERP measure of the difference registered by
a non-attended tone and the same tone used later as a discrimination
target.
Methods: In a 3-tone oddball paradigm we recorded from
19 sites in 22 young healthy subjects and 28 patients with schizophrenia
in a passive tone presentation and an active discrimination.
Results: 1/ Nd (200-260 ms) was fronto-central and
bilaterally symmetrical in healthy subjects. 2/ Paranoid
patients showed a left-frontal/right temporoparietal amplitude reduction
which was reversed in non-paranoid subjects, (reduced at right-frontal/left
posterior sites). 3/ These asymmetries were similar but clearer
when the groups were separated by active paranoid symptoms than by diagnosis.
Conclusions: Thus there are functional asymmetries mediating
stimulus relevance (controlled processing) in schizophrenic patients
which differ from controls and differ between patients with and without
active paranoid symptoms.
See other reports on Nd in healthy subjects (1995),
and in schizophrenia (1991 ,1996)
.
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