Psychophysiology, 42, S72, 2005.
Identifying generators of visual recognition memory (old/new) effects in affective disorders: A Principal Components Analysis (PCA) of Laplacian waveforms
Jürgen Kayser, Craig E. Tenke, Nathan A. Gates, Chris J. Kroppmann, James P. Sedoruk, Carlye B. Griggs, Jonathan W. Stewart, Frederic M. Quitkin, Gerard E. Bruder
New York State Psychiatric Institute, New York, USA
Abstract
Event-related potential (ERP) correlates of mnemonic processes have rarely been assessed in mood disorders, despite considerable behavioral evidence of impairment. The typical ERP finding for healthy adults during explicit memory tasks is the so-called Âold/new effect, an enhanced posterior positivity between 300 and 800 ms for repeated items, which is assumed to index conscious recollection. This study compared 67-channel, reference-free current source densities (CSD; Laplacian) derived from surface potential ERPs recorded during visual recognition memory tasks using unknown faces (college yearbook) and pronouncable pseudo-words (e.g., ÂcernorÂ) from 30 unmedicated outpatients (major depressive disorder or dysthymia, DSM-IV) and 30 healthy adults, all right-handed. Patients performed more poorly than controls, with both groups having better memory for faces than pseudo-words. Unrestricted principal components (Varimax) were derived from CSD waveforms to identify and measure neuronal generator patterns. Two prominent CSD factors, related to current sources at parietal and temporal sites, revealed old/new effects at mid-frontal (422 ms peak latency) and inferior-parietal sites (809 ms). These sources and their old/new effects were reduced in patients at parietal and mid-central sites, especially for faces. Task-specific CSD topographies (< 300 ms) were comparable across groups, dissociating neuronal generators of early word and face processing. The combination of PCA and CSD methodologies can help to identify neuronal generators underlying memory impairments in depression.
Keywords: event-related potentials (ERP), recognition memory, old/new effect, current source density (CSD), faces, pseudo-words, visual modality, depression