Verbal and working memory deficits in an impulsive aggressive college sample.
Impulsive aggressors often report difficulties remembering details of their aggressive outbursts. Additionally, researchers have found impairments in working and verbal memory and in executive functions in both impulsive and aggressive populations. However, previous studies have not distinguished between aggressive subtypes when studying memory. A major goal of this research was to extend previous studies and employ both neuropsychological assessment and event-related potentials (ERPs) to investigate memory impairment, especially verbal and working memory impairment, in a well defined, impulsive aggressive population. Participants were 58 college students comprised of two groups: impulsive aggressors and non-aggressive controls. The control group scored higher on several measures of verbal memory: Long Delay Free Recall (CVLT-II), Vocabulary (WASI), Logical Memory – 1st recall total and thematic total and Family Pictures I and II (WMS-III). These indicate both short- and long-term verbal memory differences. Additionally, we found that controls were more accurate on all measures of working memory: Letter-Number Sequencing and Spatial Span (WMS-III), n-back, Sequential Spatial Memory Task (SMT). Only the Sequential SMT reached statistical significance. However, a trend was seen such that as working memory load increased, the difference between group scores also increased. A significant group x stimulus (match/ no- match) interaction was found for P300 amplitude, with controls exhibiting larger P300 amplitudes for low probability match stimuli compared to high probability no-match stimuli during a high-load working memory task (3-back). This difference was not seen in impulsive aggressors, indicating impulsive aggressors process information differently than non-aggressive controls. Finally, as working memory load increases during an ERP task, it is expected that P300 amplitude at the Pz electrode will decrease continuously while the amplitude at Fz increases continuously. This was true of the controls. In the impulsive aggressive group, however, the continuous decrease in Pz amplitude was seen, but the continuous increase in Fz amplitude discontinued completely once they appeared to reach a working memory overload, dropping to a baseline level. Although memory deficits in this impulsive aggressive college sample are not blatantly obvious, when pushed to their cognitive limits, differences in information processing as well as in both verbal and working memory become apparent.