Timothy Justus

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).

The Cerebellum and English Grammatical Morphology: Evidence from Production, Comprehension, and Grammaticality Judgments

Three neuropsychological experiments on a group of 16 cerebellar patients and 16 age-and education-matched controls investigated the effects of damage to the cerebellum on English grammatical morphology across production, comprehension, and grammaticality judgment tasks. In Experiment 1, participants described a series of pictures previously used in studies of cortical aphasic patients. The cerebellar patients did not differ significantly from the controls in the total number of words produced or in the proportion of closed-class words. They did differ to a marginally significant extent in the production of required articles. In Experiment 2, participants identified the agent in a series of aurally presented sentences in which three agency cues (subjectverb agreement, word order, and noun animacy) were manipulated. The cerebellar patients were less affected than the controls were by the manipulation of subjectverb agreement to a marginally significant extent. In Experiment 3, participants performed a grammaticality judgment task on a series of aurally presented sentences. The cerebellar patients were significantly less able to discriminate grammatical and ungrammatical sentences than the controls were, particularly when the error was of subject verb agreement as opposed to word order. The results suggest that damage to the cerebellum can result in subtle impairments in the use of grammatical morphology, and are discussed in light of hypothesized roles for the cerebellum in language.

The cognitive neuropsychology of the cerebellum

We review evidence from neuropsychological studies of patients with damage to the cerebellum that suggests cerebellar involvement in four general categories of cognition: (1) speech and language; (2) temporal processing; (3) implicit learning and memory; (4) visuospatial processing and attention. A relatively strong case can be made for cerebellar contributions to language (including speech perception, lexical retrieval, and working memory) and to temporal processing. However, the evidence concerning cerebellar involvement in non-motor implicit learning and visuospatial processing is more equivocal. We argue that cerebellar contributions to cognition are computationally plausible, given its reciprocal connectivity with the cerebral cortex, and suggest that this function of the cerebellum may be an example of an evolutionary process by which mechanisms originally evolved for one function (in this case, motor control) are adapted to other functions (cognition).

Reduced phonological similarity effects in patients with damage to the cerebellum.

Ten cerebellar patients were compared to 10 control subjects on a verbal working memory task in which the phonological similarity of the words to be remembered and their modality of presentation were manipulated. Cerebellar patients demonstrated a reduction of the phonological similarity effect relative to controls. Further, this reduction did not depend systematically upon the presentation modality. These results first document that qualitative differences in verbal working memory may be observed following cerebellar damage, indicating altered cognitive processing, even though behavioral output as measured by the digit span may be within normal limits. However, the results also present problems for the hypothesis that the cerebellar role is specifically associated with articulatory rehearsal as conceptualized in the Baddeley-Hitch model of working memory.

Auditory attention to frequency and time: an analogy to visual local–global stimuli

Two priming experiments demonstrated exogenous attentional persistence to the fundamental auditory dimensions of frequency (Experiment 1) and time (Experiment 2). In a divided-attention task, participants responded to an independent dimension, the identification of three-tone sequence patterns, for both prime and probe stimuli. The stimuli were specifically designed to parallel the local-global hierarchical letter stimuli of [Navon D. (1977). Forest before trees: The precedence of global features in visual perception. Cognitive Psychology, 9, 353-383] and the task was designed to parallel subsequent work in visual attention using Navon stimuli [Robertson, L. C. (1996). Attentional persistence for features of hierarchical patterns. Journal of Experimental Psychology: General, 125, 227-249; Ward, L. M. (1982). Determinants of attention to local and global features of visual forms. Journal of Experimental Psychology: Human Perception and Performance, 8, 562-581]. The results are discussed in terms of previous work in auditory attention and previous approaches to auditory local-global processing.

A neural instantiation of the motor theory of speech perception.

The dissociation of articulatory rehearsal and phonological representation also makes clear that there could be multiple neural bases for dyslexia. Poorly developed phonological representations could result from (1) an impairment in articulation, (2) the consolidation of such representations, or (3) the access of these representations from systems involved in the conversion of orthography to phonology. The striking degree of clumsiness in dyslexia 12xPerformance of dyslexic children on cerebellar and cognitive tests. Fawcett, A.J and Nicolson, R.I. J. Mot. Behav. 1999; 31: 68–78Crossref | PubMedSee all References12, in addition to the impairments on temporal processing tasks associated with the cerebellum 13xTime-estimation deficits in developmental dyslexia: evidence of cerebellar involvement. Nicolson, R.I et al. Proc. Roy. Soc. London Series B. 1995; 259: 43–47Crossref | PubMed | Scopus (133)See all References13 are consistent with the idea that an articulatory problem is at the head of the causal chain.However, it might also be that these children exhibit a host of subclinical neural abnormalities, only one of which involves the cerebellum. Unlike acquired language disorders such as alexia without agraphia in which, by definition, the deficit is restricted, people with developmental dyslexia typically exhibit below normal performance on a host of linguistic and non-linguistic tasks. Even if future imaging studies were to identify structural abnormalities in the cerebellum, it is probable that abnormalities will also be found in other brain areas. Anatomical studies using in vivo MRI have identified cerebellar hypoplasia in several psychiatric disorders including autism 14xBrainstem, cerebellar and limbic neuroanatomical abnormalities in autism. Courchesne, E. Curr. Opin. Neurobiol. 1997; 7: 269–278Crossref | PubMed | Scopus (259)See all References14, schizophrenia 15xAn MRI study of cerebellar vermis morphology in patients with schizophrenia: evidence in support of the cognitive dysmetria concept. Nopoulos, P.C et al. Biol. Psychiatry. 1999; 46: 703–711Abstract | Full Text | Full Text PDF | PubMed | Scopus (136)See all References15, and attention deficit and hyperactivity disorder 16xCerebellum in attention-deficit hyperactivity disorder: a morphometric MRI study. Berquin, P.C et al. Neurology. 1998; 50: 1087–1093Crossref | PubMedSee all References16. Correspondingly, causal accounts based on the cerebellar abnormalities have been proposed for autism and schizophrenia. Nonetheless, the pathology does not appear to be restricted to the cerebellum: structural differences have also been found in cortical regions.What then are we to make of this revisionist literature in which the cerebellum is suddenly being elevated from the low-level slave of the motor system to the key link of disorders as varied as schizophrenia and dyslexia? A sceptical position would be to argue that the cerebellar impairment is a correlate of the disorders, but not causal. For unknown reasons, the cerebellum is especially sensitive to problems that occur during neurodevelopment, but abnormalities in other, cortical regions are pre-eminent. Interestingly, the hypoplasia in autism, schizophrenia, and attention-deficit hyperactive disorder (ADHD) is associated with different cerebellar lobules. Knowing the time course of cerebellar neurogenesis and maturation might provide clues to windows during which the development of the CNS goes awry 17xEmbryonic development of the rat cerebellum. III. Regional differences in the time of origin, migration, and settling of Purkinje cells. Altman, J and Bayer, S. J. Comp. Neurol. 1985; 231: 42–65Crossref | PubMedSee all References17.Alternatively, it is an important enterprise to consider causal accounts that include the cerebellum. The target article offers a fine example of how these can be developed and tested. Nicolson et al.s working hypothesis for dyslexia builds upon a well-specified psychological model and, by emphasizing articulation as a skilled motor process, connects with more-traditional views of the cerebellum. As such, the ideas resonate with the central premise of the motor theory of speech perception and this theorys more recent progeny (e.g. mirror neurons, see Ref. 18xLanguage within our grasp. Rizzolatti, G and Arbib, M.A. Trends Neurosci. 1998; 21: 188–194Abstract | Full Text | Full Text PDF | PubMed | Scopus (1566)See all ReferencesRef. 18). Perception and action are intimately linked, interactive processes. Our knowledge, be it linguistic, perceptual, or conceptual is constrained by the actions we can produce, for it is their production, as well as our ability to understand the actions of others, that renders this knowledge adaptive.

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.

A mismatch negativity study of local–global auditory processing

We used mismatch negativity (MMN) to examine structural encoding of local and global auditory patterns in perceptual memory. Unlike previous MMN studies of local-global auditory perceptual organization that used interval-contour stimuli, here we presented hierarchical stimuli in which local pattern organization formed global patterns. Importantly, our stimuli allowed independent manipulation of the two structural levels. In separate blocks, participants were exposed to frequent local standard patterns and rare local deviant patterns, or to frequent global standard patterns and rare global deviant patterns. Within each deviant pattern, the variation from the standard pattern could occur at onset (early), towards the end of the pattern (late) or over both time windows (both). To isolate pattern indexing at one level, the other level continuously changed (e.g., in a global standard block, local elements varied trial-by-trial). MMN was found only for global deviant patterns, and only when deviation occurred late in the pattern. In a separate behavioral experiment, global deviants were detected more often than local ones, although initial similarity followed by a late deviation from the standard pattern was not required for explicit deviant detection (as with the MMN). This report demonstrates neural structural encoding for global information, when independently manipulated from local information. Furthermore, it extends previous MMN findings that have revealed indexing of complex abstract auditory information to the realm of hierarchical perceptual organization.

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.