The topography of the scalp-recorded visual N700.
OBJECTIVE
To describe the topography of the N700 component of the scalp-recorded visual event-related potential (ERP) and to provide fundamental knowledge of the conditions under which it occurs.


METHODS
We examined the time-course of visual ERP in response to the short (100ms) and prolonged (7s) presentation of simple salient visual stimuli separated by long interstimulus intervals employing high-resolution 64-channel DC-EEG. Current source density (CSD) mapping and spatio-temporal dipole source analysis were performed.


RESULTS
CSD analysis revealed highly significant bilateral current sinks over occipito-temporal areas from about 450ms up to 1s after stimulus offset (visual N700). CSD topography and dipole source analysis suggested late prolonged activation of extrastriate visual areas which did not depend merely upon a stimulus offset response, afterimages or blinking, as confirmed by control conditions.


CONCLUSIONS
Our findings provide basic knowledge about the time-course of sensory activation. We found that passive watching of rare salient short stimuli automatically evoked sustained activity in the extrastriate visual cortex up to 1s after stimulus offset.


CONCLUSIONS
Visual N700 provides a promising tool for important insights into the cortical mechanisms of stimulus post-processing. Its role in associative learning of temporally non-overlapping stimuli (automatic ultra-short-term sensory memory) should be explored.
Bender
S
S
Department for Child and Adolescent Psychiatry, University of Heidelberg, Blumenstraße 8, D-69115 Heidelberg, Germany; Section for Experimental Psychopathology, Psychiatric Hospital, Voßstraße 4, University of Heidelberg, D-69115 Heidelberg, Germany; Psychosomatic Hospital, University of Heidelberg, Im Neuenheimer Feld 410, D-69120 Heidelberg, Germany. Electronic address: Stephan.Bender@med.uni-heidelberg.de.
Oelkers-Ax
R
R
Department for Child and Adolescent Psychiatry, University of Heidelberg, Blumenstraße 8, D-69115 Heidelberg, Germany.
Hellwig
S
S
Section for Experimental Psychopathology, Psychiatric Hospital, Voßstraße 4, University of Heidelberg, D-69115 Heidelberg, Germany.
Resch
F
F
Department for Child and Adolescent Psychiatry, University of Heidelberg, Blumenstraße 8, D-69115 Heidelberg, Germany.
Weisbrod
M
M
Department for Child and Adolescent Psychiatry, University of Heidelberg, Blumenstraße 8, D-69115 Heidelberg, Germany; SRH-Klinikum Karlsbad-Langensteinbach, Psychiatric Hospital, Guttmannstraße 1, 76307 Karlsbad, Germany.
D000328:Adult; D000704:Analysis of Variance; D001931:Brain Mapping; D004569:Electroencephalography; D005074:Evoked Potentials, Visual / Q000502:physiology*; D005260:Female; D006801:Humans; D008297:Male; D010775:Photic Stimulation / Q000379:methods; D011930:Reaction Time / Q000502:physiology; D012016:Reference Values; D012535:Scalp; D013997:Time Factors; D014785:Vision, Ocular / Q000502:physiology; D014793:Visual Cortex / Q000502:physiology*; D014796:Visual Perception / Q000502:physiology