Background Previous reports of abnormal auditory N2 and P3 event-related potentials (ERPs) suggest impaired discrimination, evaluation or context updating for infrequent target stimuli in post-traumatic stress disorder (PTSD). This study examines each of these processes by investigating high-resolution ERP topography during target detection for visual word stimuli.
Method ERPs were recorded at 124 electrodes from 10 PTSD patients and 10 matched controls. Target detection tasks comprised blocks of equally probable red and blue words, with low probability target events. Detection of fixed target words in one color provided the basis for measurement of selective attention for color, stimulus evaluation and target detection processing. Alternative task instructions, with the same stimuli, required detection of any consecutive word repeats in an attended color, which demands working memory updating for nontarget words. Comparison of attended non-target words from each task indicates the extra activity for updating working memory representations of target attributes. Thus, specific condition comparisons provide measures of stimulus discrimination and evaluation, working memory updating and target detection.
Results PTSD patients had slower and less accurate motor responses in both tasks, with greater inaccuracy during the variable target task. There was abnormal ERP activity in PTSD at 200-300 ms in the left posterior temporal region during stimulus discrimination and target recognition. During evaluation of attended non-target words, PTSD patients demonstrate deficits in frontal and parietal regions at 400-500 ms. During working memory updating, at 400-600 ms, there was a delay in frontal activation, followed by smaller activity in parietal areas in PTSD. During target word recognition, PTSD patients demonstrate deficits in frontal activity, with greater occipital and parietal activity.
Conclusions These findings indicate impaired evaluation and integration of new information in working memory. In particular, the results suggest failure in frontal executive systems, with greater dependence on visual processing for effective target detection. The current findings are consistent with neuropsychology studies that identify deficits of attention and memory for verbal information in PTSD. This study provides insight into the temporal components of attention and working memory in PTSD. It is proposed that working memory deficits arise from disruption to synchronized activity in distributed networks engaged in working memory processes.
| Identifer | oai:union.ndltd.org:ADTP/216450 |
| Date | January 2004 |
| Creators | Weber, Darren Lee, darrenleeweber@gmail.com |
| Publisher | Flinders University. Psychology |
| Source Sets | Australiasian Digital Theses Program |
| Language | English |
| Detected Language | English |
| Rights | http://www.flinders.edu.au/disclaimer/), Copyright Darren Lee Weber |
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