Jary Larsen

Impaired Response Inhibition in Veterans with Post-Traumatic Stress Disorder and Mild Traumatic Brain Injury

Combat veterans with post-traumatic stress disorder (PTSD) can show impairments in executive control and increases in impulsivity. The current study examined the effects of PTSD on motor response inhibition, a key cognitive control function. A Go/NoGo task was administered to veterans with a diagnosis of PTSD based on semi-structured clinical interview using DSM-IV criteria (n = 40) and age-matched control veterans (n = 33). Participants also completed questionnaires to assess self-reported levels of PTSD and depressive symptoms. Performance measures from the patients (error rates and reaction times) were compared to those from controls. PTSD patients showed a significant deficit in response inhibition, committing more errors on NoGo trials than controls. Higher levels of PTSD and depressive symptoms were associated with higher error rates. Of the three symptom clusters, re-experiencing was the strongest predictor of performance. Because the co-morbidity of mild traumatic brain injury (mTBI) and PTSD was high in this population, secondary analyses compared veterans with PTSD+mTBI (n = 30) to veterans with PTSD only (n = 10). Although preliminary, results indicated the two patient groups did not differ on any measure (p > .88). Since cognitive impairments could hinder the effectiveness of standard PTSD therapies, incorporating treatments that strengthen executive functions might be considered in the future. (JINS, 2012, 18, 1-10).

Attentional bias for trauma-related words: exaggerated emotional Stroop effect in Afghanistan and Iraq war veterans with PTSD.

BackgroundPost-traumatic stress disorder (PTSD) involves debilitating symptoms that can disrupt cognitive functioning. The emotional Stroop has been commonly used to examine the impact of PTSD on attentional control, but no published study has yet used it with Afghanistan and Iraq war veterans, and only one previous study has compared groups on habituation to trauma-related words.MethodsWe administered the emotional Stroop, the Beck Depression Inventory (BDI), and the PTSD Checklist (PCL) to 30 veterans with PTSD, 30 military controls, and 30 civilian controls. Stroop word types included Combat, Matched-neutral, Neutral, Positive and Negative.ResultsCompared to controls, veterans with PTSD were disproportionately slower in responding to Combat words. They were also slower and less accurate overall, did not show interference on Negative or Positive words relative to Neutral, and showed a trend for delayed but successful habituation to Combat words. Higher PCL and BDI scores also correlated with larger interference effects.ConclusionsBecause of its specificity in detecting attentional biases to trauma-related words, the emotional Stroop task may serve as a useful pre- and post task with intervention studies of PTSD patients.

Increased response variability as a marker of executive dysfunction in veterans with post-traumatic stress disorder.

The stability of cognitive control processes over time can be indexed by trial-to-trial variability in reaction time (RT). Greater RT variability has been interpreted as an indicator of executive dysfunction, inhibitory inefficiency, and excessive mental noise. Previous studies have demonstrated that combat veterans with post-traumatic stress disorder (PTSD) show substantial impairments in inhibitory control, but no studies have examined response variability in this population. In the current experiment, RT variability in the Go/NoGo response inhibition task was assessed for 45 veterans with PTSD and 34 control veterans using the intra-individual coefficient of variation (ICV) and ex-Gaussian analysis of RT distributions. Despite having mean RTs that were indistinguishable from controls, the PTSD patients had significantly greater RT variability as measured by ICV. More variable RTs were in turn associated with a greater number of false alarm errors in the patients, suggesting that less consistent performers were less successful at inhibiting inappropriate responses. RT variability was also highly correlated with self-reported symptoms of PTSD, depression, and attentional impulsiveness. Furthermore, response variability predicted diagnosis even when controlling for PTSD symptom severity. In turn, PTSD severity was correlated with self-rated attentional impulsiveness. Deficits in the top-down cognitive control processes that cause greater response variability might contribute to the maintenance of PTSD symptomology. Thus, the distractibility issues that cause more variable reaction times might also result in greater distress related to the trauma.

Right hemisphere reading mechanisms in a global alexic patient.

We investigated the implicit, or covert, reading ability of a global alexic patient (EA) to help determine the contribution of the right hemisphere to reading. Previous studies of alexic patients with left hemisphere damage have suggested that the ability to derive meaning from printed words that cannot be read out loud may reflect right hemisphere reading mechanisms. Other investigators have argued that residual left hemisphere abilities are sufficient to account for implicit reading and moreover do not require the postulation of a right hemisphere system that has no role in normal reading processes. However, few studies have assessed covert reading in patients with lesions as extensive as the one in EA, which affected left medial, inferior temporal-occipital cortex, hippocampus, splenium, and dorsal white matter. EA was presented with lexical decision, semantic categorization, phonemic categorization, and letter matching tasks. Although EA was unable to access phonology and could not overtly name words or letters, she was nevertheless capable of making lexical and semantic decisions at above chance levels, with an advantage for concrete versus abstract words. Her oral and written spelling were relatively intact, suggesting that orthographic knowledge is retained, although inaccessible through the visual modality. Based on her ability to access lexical and semantic information without contacting phonological representations, we propose that EAs implicit reading emerges from, and is supported, by the right hemisphere. Finally, we conclude that her spelling and writing abilities are supported by left hemisphere mechanisms.

Interpreting dissociations between regular and irregular past- tense morphology: Evidence from event-related potentials

Neuropsychological dissociations between regular and irregular English past-tense morphology have been reported using a lexical decision task in which past-tense primes immediately precede present-tense targets. We present N400 event-related potential data from healthy participants using the same design. Both regular and irregular past-tense forms primed corresponding present-tense forms, but with a longer duration for irregular verbs. Phonological control conditions suggested that differences in formal overlap between prime and target contribute to, but do not account for, this difference, suggesting a link between irregular morphology and semantics. Further analysis dividing the irregular verbs into two categories (weak irregular and strong) revealed that priming for strong verbs was reliably stronger than that for weak irregular and regular verbs, which were statistically indistinguishable from one another. We argue that, although we observe a regular-irregular dissociation, the nature of this dissociation is more consistent with single- than with dual-system models of inflectional morphology.

The role of Broca's area in regular past-tense morphology: An event-related potential study

It has been suggested that damage to anterior regions of the left hemisphere results in a dissociation in the perception and lexical activation of past-tense forms. Specifically, in a lexical-decision task in which past-tense primes immediately precede present-tense targets, such patients demonstrate significant priming for irregular verbs (spoke-speak), but, unlike control participants, fail to do so for regular verbs (looked-look). Here, this behavioral dissociation was first confirmed in a group of eleven patients with damage to the pars opercularis (BA 44) and pars triangularis (BA 45) of the left inferior frontal gyrus (i.e., Brocas area). Two conditions containing word-onset orthographic-phonological overlap (bead-bee, barge-bar) demonstrated that the disrupted regular-verb priming was accompanied by, and covaried with, disrupted ortho-phonological priming, regardless of whether prime stimuli contained the regular inflectional rhyme pattern. Further, the dissociation between impaired regular-verb and preserved irregular-verb priming was shown to be continuous rather than categorical; priming for weak-irregular verbs (spent-spend) was intermediate in size between that of regular verbs and strong verbs. Such continuous dissociations grounded in ortho-phonological relationships between present- and past-tense forms are predicted by single-system, connectionist approaches to inflectional morphology and not predicted by current dual-system, rule-based models. Event-related potential data demonstrated that N400 priming effects were intact for both regular and irregular verbs, suggesting that the absence of significant regular-verb priming in the response time data did not result from a disruption of lexical access, and may have stemmed instead from post-lexical events such as covert articulation, segmentation strategies, and/or cognitive control.

An event-related potential study of cross-modal morphological and phonological priming

The current work investigated whether differences in phonological overlap between the past- and present-tense forms of regular and irregular verbs can account for the graded neurophysiological effects of verb regularity observed in past-tense priming designs. Event-related potentials were recorded from sixteen healthy participants who performed a lexical-decision task in which past-tense primes immediately preceded present-tense targets. To minimize intra-modal phonological priming effects, cross-modal presentation between auditory primes and visual targets was employed, and results were compared to a companion intra-modal auditory study (Justus, Larsen, de Mornay Davies, & Swick, 2008). For both regular and irregular verbs, faster response times and reduced N400 components were observed for present-tense forms when primed by the corresponding past-tense forms. Although behavioral facilitation was observed with a pseudopast phonological control condition, neither this condition nor an orthographic-phonological control produced significant N400 priming effects. Instead, these two types of priming were associated with a post-lexical anterior negativity (PLAN). Results are discussed with regard to dual- and single-system theories of inflectional morphology, as well as intra- and cross-modal prelexical priming.

Event-related potentials demonstrate prolonged N400 priming effects for English irregular verbs

Evidence from event-related potentials has an important role to play in refining current models of inflectional morphology. Here, we present ERP data regarding the English past tense, using an immediate-priming design that frequently has been used in both healthy and neuropsychological populations (Tyler et al., 2002). The majority of extant ERP studies of inflectional morphology have adopted either priming designs based on lags of intervening items, which are argued to result in N400 effects specifically for regular morphology (Munte, Say, Clahsen, Schiltz, & Kutas, 1999), or designs employing morphological violations, which are argued to result in LAN-like effects specifically for overregularizations (Penke et al., 1997). The dissociations that have been found in the above work often have been used in support of dual-route models of the English past tense, in which regular past tenses are produced by affixation of the default (–ed) form, whereas irregular past tenses are stored in associative memory (Pinker & Ullman, 2002). Dual-system models have been challenged by connectionist theorists who argue that both regular and irregular morphology can be modeled within a single system that maps relationships between phonology, orthography, and semantics. Importantly, many such models specifically have been designed to account for behavioral data in immediate priming tasks (Plaut & Gonnerman, 2000). Thus, we wished to bridge these literatures with the ERP literature by using a more analogous design.