Posttraumatic Stress Disorder-Associated Cognitive Deficits on the Repeatable Battery for the Assessment of Neuropsychological Status in a Veteran Population

Discussion

The findings of the present study suggest that veterans with PTSD perform worse on specific RBANS subtests compared with veterans without PTSD. Specifically, worse performance on the Story Recall subtest of the RBANS memory index was a significant predictor of a diagnosis of PTSD within the statistical model. This association with PTSD was not seen in other demographic (excluding education) or cognitive measures, including other memory tasks, such as List Recall and Figure Recall, and attentional measures, such as WAIS-IV Digit Span, and the Trail Making Test. Overall RBANS index scores were not significantly different between groups, though this is not surprising given that recent research suggests the RBANS composite scores have questionable validity and reliability.³⁴

The finding that a measure of episodic memory is most influenced by PTSD status is consistent with prior research.³⁵ However, there are several possible reasons why Story Recall in particular showed the greatest association, even more than other episodic memory measures. A review by Isaac and colleagues found a diagnosis of PTSD correlated with frontal lobe-associated memory deficits.⁶ As Story Recall provides only 2 rehearsal trials compared with the 4 trials provided in the RBANS List Learning subtest, it is possible that Story Recall relies more on attentional processes than on learning with repetition.

Research has indicated attention and verbal episodic memory dysfunction are associated with a diagnosis of PTSD in combat veterans, and individuals with a diagnosis of PTSD show deficits in executive functioning, including attention difficulties beyond what is seen in trauma-exposed controls.^4,7,8,11,35Furthermore, a diagnosis of PTSD has been shown to be associated with impaired performance on the Logical Memory subtest of the Wechsler Memory Scale-Revised, a very similar measure to the RBANS Story Recall.³⁶

The present finding that performance on a RBANS subtest was associated with a diagnosis of PTSD but not a history of TBI is not surprising. The majority of the present sample who reported a history of TBI met criteria for a remote head injury of mild severity (86%). Cognitive symptoms related to mild TBI are thought to generally resolve over time, and recent research suggests that PTSD symptoms may account for a substantial portion of reported postconcussive symptoms.^37,38Similarly, recent research suggests a diagnosis of mild TBI does not necessarily result in additive cognitive impairment in combat veterans with a diagnosis of PTSD, and that a diagnosis of PTSD is more strongly associated with cognitive symptoms than is mild TBI.^5,39,40

The lack of association with RBANS performance and co-occurring PTSD and TBI is less clear. Although both conditions are heterogenous, it may be that individuals with a diagnosis solely of PTSD are quantitively different from those with a concurrent diagnosis of PTSD and TBI (ie, PTSD presumed due to a mild TBI). Specifically, the impact of PTSD on cognition may be related to symptom severity and indexed trauma. A published systematic review on the PTSD-related cognitive impairment showed a medium-to-strong effect size for severity of PTSD symptoms on cognitive performance, with war trauma showing the strongest effect.⁴In particular, individuals who experience repeated or complex trauma are prone to experience PTSD symptoms with concurrent cognitive deficits, again suggesting the possibility of qualitative differences between outpatient veterans with PTSD and those with mild TBI associated PTSD.⁴¹While disentangling PTSD and mild TBI symptoms are notoriously difficult, future research aiming to examine these factors may be beneficial in the ability to draw larger conclusions on the relationship between cognition and PTSD.