Executive function in people who are somatically hypervigilant

Proposal details

Title: Executive function in people who are somatically hypervigilant
Research Area(s): PTSD and other Anxiety Disorders
Background: Statement of the research topic and rationale for research We know people with chronic pain evaluate their sensory and spatial environments differently to people without chronic pain (Moseley, Gallace et al. 2011). Magnification of bodily sensations (Vlaeyen and Linton 2000) and reduced ability to tell whether a stimulus is relevant or not, are common in chronic pain (Apkarian, Baliki et al. 2009). Clinically, we report these changes as ‘somatic hypervigilance’, while the person with chronic pain complains that “everything hurts”. Somatic hypervigilance emerges in people with chronic pain as their brains reorganise in response to sensitisation processes occurring in peripheral and central neurons(Apkarian, Baliki et al. 2009; Latremoliere and Woolf 2009). Somatic hypervigilance is the symptomatic manifestation of cortical reorganisation that includes an increase in the excitability of peripheral and central neurons, alteration of the area the neuron looks after and changes to the map of the body in the brain, its presence can be strongly implied by the presence of allodynia (Latremoliere and Woolf 2009). Resources required for cortical reorganisation leave other processes in the brain depleted of resources and people in chronic pain are likely to exhibit associated poor cognitive performance. . Recording brain activity in response to a given stimulus evokes event related potentials (ERPs). ERPs form the basis of a ‘neurophysiological profile’ of a given response for example, or of a given condition or diagnosis. Most neurophysiological studies in the pain literature use experimental pain paradigms (acute rather than chronic pain) and very few consider investigation during cognitive performance (Knudsen, Petersen et al. 2011). When they do, the majority consider modulation by attention or distraction. No study to date has explored the pattern of neurophysiological activity during a working memory task in people with chronic pain. That is, the neurophysiological profile of a working memory task for people with chronic pain, remains to be elucidated. However, one condition that shares many features with chronic pain, and on which the neurophysiological profile of working memory tasks has been well studied, is post-traumatic stress disorder (PTSD).PTSD is a disorder triggered by severe psychological trauma. The central component of the disorder is the repeated intrusion of traumatic memories which becomes associated with an exaggerated fear and stress response. The reactivity to the memories may build up over time as central brain regions reorganise and sensitise, gradually leading to a magnified perception of a number of stimuli including sounds and bodily perceptions (hypervigilance) (McFarlane 2010). People with PTSD demonstrate consistent changes in ERPs during tests of working memory (McFarlane, Weber et al. 1993; Shaw, Strother et al. 2002; Clark, McFarlane et al. 2003; Galletly, McFarlane et al. 2008; Moores, Clark et al. 2008; McFarlane 2010). The changes in ERPs during a working memory task show that people with PTSD are slower to detect the target stimulus, are less accurate at discriminating the stimulus and use more neurons than people without PTSD to complete the task. When it comes to evaluating the meaning or context of a stimulus, people with PTSD show a decreased activation of cortical neurons. The ERP trace of working memory can be considered a neurophysiological correlate of a magnified perception of the stimulus and a decreased ability to discern its relevance. In other words a neurophysiological correlate of ‘hypervigilance’. The central hypothesis of the current thesis is that chronic pain and PTSD share neurophysiological and perceptual characteristics. To fully interrogate this hypothesis the thesis asks several questions. First, what evidence is there for working memory and executive function changes in people with chronic pain? Second, do people with the shared perceptual change of somatic hypervigilance as measured by a sensitive scale, show changes on ERPs that are similar to changes characterised by PTSD during neuropsychological tasks? Third, do people in chronic pain demonstrate ERP changes that are similar to the changes in people with PTSD? These questions reflect a new line of enquiry in chronic pain research that could contribute to diagnostic accuracy (Falconer, Felmingham et al. 2008), improve treatment efficiency (McFarlane and Yehuda 2000), and characterise neurophysiological change associated with the disorder (Galletly, McFarlane et al. 2008). This is timely because the release of the Australian Government paper “When musculoskeletal conditions and mental disorders occur together” (Australian Institute of Health and Welfare 2010) details the comorbidity of musculoskeletal pain disorder and mental illness and calls for better integrated care of such disorders. Central hypothesis That chronic pain and PTSD share neurophysiological and perceptual characteristics.
Aims: 1. Whether event related potentials mapped during neurocognitive tests of working memory, and executive function in a group of people with somatic hypervigilance are similar to the outcomes reported in a group of people with PTSD during neurocognitive tests of working memory and executive function. 2. Whether people with somatic hypervigilance exhibit a worse performance to an inhibitory stimulus than people without somatic hypervigilance.
Method: The study will compare the ERP outcomes on an auditory oddball test , a test of continuous performance (n-back)(working memory) , a maze test (executive function), a startle test and a go/nogo test (inhibition) in people with somatic hypervigilance (score >3 on the SOMA-6 scale of the Sphere-12 questionnaire please see below) and people without somatic hypervigilance. Within their standardised methods of assessment, data are available in the Brain Resource Internation Database to form our inclusion and exclusion criteria and for the purpose of matching subjects: Inclusion and matching criteria: 1. Adults (greater than 18) 2. Males and females 3. Occupation 4. Number of years of education 5. Average sleep duration Groups: 1. Healthy normals, matched by the above criteria 2. Soma group; participants who score >3 on the Soma section of the Sphere-12 The SPHERE-12 – an adaptation of the 34 item sphere self-report questionnaire about general health. We would like to know about your general health. For ALL questions, please tick the appropriate box. Over the past few weeks have you been troubled by: SPHERE - 12 Never or some of the time A good part of the time Most of the time 1 Feeling nervous or tense? 2 Feeling unhappy and depressed? 3 Feeling constantly under strain? 4 Everything getting on top of you? 5 Losing confidence? 6 Being unable to overcome difficulties? 7 Muscle pain after activity? 8 Needing to sleep longer? 9 Prolonged tiredness after activity? 10 Poor sleep? 11 Poor concentration? 12 Tired muscles after activity? Two scores are extracted from the answers: The PSYCH score is the sum of answers to items 1 – 6 and the SOMA score is the sum of answers to items 7-12. Psych Soma Score: The Sphere 12 was designed for General Practitioners to use as a screening tool for mental health. It is an adaptation of the 34 item sphere self report questionnaire about general health. The six psychological and six somatic questions identify two levels and three types of mental disorder. A score of two or greater on the PSYCH questions and/or three or greater on the SOMA questions indicates a classification of a mental health disorder (Hickie, Davenport et al. 2001). Scoring at the threshold on both scales classifies the participant as having a level one, type one “mental health disorder”. This category predicts a disability of 8.2 days in the month where the participant is “out of role”. If an otherwise healthy participant scores 3 or more on the SOMA scale and below two on the PSYCH score, they are classified as having a mental health disorder manifested by somatic symptom presentation (Hickie, Davenport et al. 2001) People in this category are identified as a Level 2 (type 3) SOMA case. It is a sensitive identifier of people who magnify somatic symptoms (Kroenke, Spitzer et al. 2002). In a letter to the editor of the Medical Journal of Australia, Phillips et al (2002) make the point the SOMA scale will pick up many medical conditions including chronic fatigue syndrome, glandular fever, and fibromyalgia. They condemn the soma section as overinclusive because the participant is asked to relate the questions to their perceptions over the “past few weeks” allowing minor ailments and temporary states to be included, and oversensitive due to the non-specific nature of the wording of the questions. This can work in our favour by being a “catch all” net, specific for and sensitive to increased somatic perception (somatic hypervigilance). Exclusion criteria: 1. History of brain injury 2. Alzheimer’s disease 3. Suspected loss of consciousness 4. A history of chronic neurological or psychiatric disease 5. A history of stroke 6. Dementia 7. Trialling a new medication that has the potential to impair cognitive function 8. A history of mind altering drug use 9. Vision, Hearing or learning difficulties