Oades, R. D., Wild-Wall, N., & Juran, S., (2005).
A comparison of bottom-up change detection with top-down controlled attention in schizophrenia.
World Journal of Biological Psychiatry, 6 (supplement 1), p. 51.

Introduction: Conscious awareness of a stimulus can occur ca. 200 ms after presentation (Libet 2002). Thus, MMN is a preconscious marker of auditory change detection, and the negative difference (Nd), a marker of target recognition, indicates postconscious processing. We trace the activation of MMN and Nd sources in the temporal and frontal lobes of healthy young subjects (Jemel et al 2002, 2003), and ask if these are altered in patients newly diagnosed with schizophrenia and others 14 years later (who often show reduced MMN).

Methods: Separate studies using tones deviating by frequency or duration were conducted with 14 healthy volunteers, then 28 adolescents (mean age 17.6y) and 18 adults with schizophrenia (mean age 32y) along with age-matched controls. Brain electrical source analysis (BESA) was based on EEG records from 32 sites.

Results:
First:
a) Peak MMN source activity had a similar latency in the auditory cortices and posterior left anterior-cingulate, but occurred later in the right inferior/mid-frontal cortex.
b) Nd sources were active subsequently in the adjacent right mid-frontal, then left superior frontal region before the temporo-parietal junction.
Second:
a) Frontal MMN sources migrated rostrocaudally, and temporal lobe sources laterally between the second and third decades in controls (Wild-Wall et al 2005).
b) The frontal maturational changes were disrupted, especially for the cingulate locus in older patients.
Third:
a) A more ventral locus for temporal lobes sources was evident in both patient groups, while right frontal changes tended to normalize in older patients
b) Functional and anatomical changes were not closely related.

Conclusions: Analyses of the MMN and Nd sources confirm a bottom-up followed by a top-down sequence of activations (Oknina et al 2005).
-- Some disturbances in MMN sources are evident from illness-onset.
-- Such preconscious impairments could contribute to a lack of insight in the psychotic experience.
-- However, tendencies for normalisation in right frontal function over time may underlie the heterogeneity in reports on MMN function, and represent the development of coping responses.

Support: N. W-W.: Alfried Krupp von Bohlen und Halbach Stiftung
References:
Jemel B et al (2002) Mismatch negativity results from bilateral asymmetric dipole sources in the frontal and temporal lobes. Brain Topogr 15: 13-27.
Jemel B et al (2003) Frontal and temporal lobe sources for a marker of controlled auditory attention: the negative difference (Nd) event-related potential. Brain Topogr 15: 249-62.
Libet B (2002) The timing of mental events: Libet's experimental findings and their implications. Conscious Cogn 11:291-99.
Oknina et al (2005) Frontal and temporal sources of mismatch negativity in healthy controls, patients at onset of schizophrenia in adolescence and others at 15 years after onset. Schizophr Res 76: 25-41.
Wild-Wall et al (2005) Maturation processes in automatic change detection as revealed by event-related brain potentials and dipole source localization. Int J Psychophysiol in press