Frontal and temporal sources of mismatch negativity in healthy controls, patients at onset of schizophrenia in adolesence and others at 15 years after onset
Introduction: Mismatch negativity (MMN) is an event-related potential measure of auditory change detection. It is widely reported to be smaller in patients with schizophrenia and may not improve along with otherwise successful clinical treatment (Oades et al., 1997). The main aim of this report is to explore ways of measuring and presenting four features of frequency-deviant MMN dipole sources (dipole moment, peak latency, brain location and orientation) and to relate these to the processes of psychopathology and illness progression. We already published a study of normal healthy subjects showing thew automatic processing sources for MMN bilaterally in the temporal lobes, left anterior cingulate and right inferiror frontal cortex (MMN, Jemel et al., 2002). [For sources of conscious controlled processing illustrated by the Negative Difference (Nd), see Jemel et al., 2003] Methods: Data from early onset patients (EOS) at the start of the illness in adolescence, and others who had their first break in adolescence 15 years ago (S-15Y) were compared with two groups of age-matched healthy controls (C-EOS, C-15Y). Putative generators in the 120-180 ms post-stimulus latency ranges were modelled with brain electrical source analysis (BESA) and mapped to the modified Montreal brain-atlas (Garneron algorhythm). Results: First: A 4-source model fitted the MMN waveform recorded from all 4 groups, whether MMN amplitude was more (EOS) or less (S-15Y) reduced. Second: The locations were in the left superior temporal and anterior cingulate gyri, right superior temporal and inferior/mid frontal cortices. Third: Dipole latencies confirmed a bottom-up sequence of processing and dipole moments were larger in the temporal lobes and on the left. Fourth: Patients showed small dipole location changes that were more marked in the S-15Y than the EOS group (more rostral for the left anteriorcingulate, more caudal for the right mid-frontal dipole) consistent with illness progression. Conclusions: The modelling of MMN dipole sources on brain atlas and anatomical images suggests that there is a degree of dissociation during illness between small progressive anatomical changes and some functional recovery indexed by scalp recordings from patients with an onset in adolescence 15 years before compared to adolescents in their first episode.
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