Decreased somatosensory activity to non-threatening touch in combat veterans with posttraumatic stress disorder

Abstract

Posttraumatic stress disorder (PTSD) is a severe psychiatric disorder prevalent in combat veterans. Previous neuroimaging studies have demonstrated that patients with PTSD exhibit abnormal responses to non-threatening visual and auditory stimuli, but have not examined somatosensory processing. Thirty male combat veterans, 16 with PTSD and 14 without, completed a tactile stimulation task during a 306-sensor magnetoencephalography (MEG) recording. Significant oscillatory neural responses were imaged using a beamforming approach. Participants also completed clinical assessments of PTSD, combat exposure, and depression. We found that veterans with PTSD exhibited significantly reduced activity during early (0 to 125 ms) tactile processing compared with combat controls. Specifically, veterans with PTSD had weaker activity in the left postcentral gyrus, left superior parietal area, and right prefrontal cortex in response to nonthreatening tactile stimulation relative to veterans without PTSD. The magnitude of activity in these brain regions was inversely correlated with symptom severity, indicating that those with the most severe PTSD had the most abnormal neural responses. Our findings are consistent with a resource allocation view of perceptual processing in PTSD, which directs attention away from nonthreatening sensory information.

Neuroimaging with magnetoencephalography: A dynamic view of brain pathophysiology

“…Of note, this group also found that the magnitude of neural activity in prefrontal and somatosensory cortices was correlated with symptom severity, indicating that those with the most abnormal response had the most severe symptoms. 66 A new study of verbal working memory from our laboratory reached a similar conclusion, as veterans with PTSD exhibited normal responses during both encoding and maintenance operations in left hemispheric language regions, but disturbed responses in right inferior frontal, right supramarginal and superior temporal cortices throughout the majority of encoding and maintenance periods (see Figure 5). 67 As with other studies, these right hemispheric responses correlated with PTSD symptom severity, and we propose that such activity in homologue areas reflects compensatory processing in veterans with PTSD.…”

“…65 However, a recent study demonstrated aberrant processing of non-threatening touch (i.e., an air-puff delivered to a finger) in veterans with PTSD compared to those without, with significant differences in primary somatosensory areas and the right prefrontal cortices. 66 This finding suggests aberrant sensory responses may be a more general phenomenon that is not tied directly to the valence of the stimuli, and again implicates right hemispheric cortices. Of note, this group also found that the magnitude of neural activity in prefrontal and somatosensory cortices was correlated with symptom severity, indicating that those with the most abnormal response had the most severe symptoms.…”

Resting State Functional Connectivity of the Thalamus in North Korean Refugees with and without Posttraumatic Stress Disorder

“…For example, PTSD patients exhibit increased activation in the postcentral cortex during tasks that reflect inhibitory responding 16 . Magnetoencephalography studies investigating veterans showed that PTSD patients exhibit weaker postcentral activity towards non-threatening stimuli 19 , and stronger precentral and postcentral activities during a resting state 20 . The present results are partially consistent with these findings showing stronger postcentral activity under resting conditions in PTSD patients than TECs.…”

Methodological considerations for a better somatosensory gating paradigm: The impact of the inter-stimulus interval

“…Ultimately, the data described herein provide novel insight into the effect of various ISIs on the filtering of redundant somatosensory information and may dramatically influence the design, analysis, and interpretation of future studies of SG. With numerous clinical conditions known to be associated with altered somatosensory processing, gating, and functional inhibition (e.g., HIV, posttraumatic stress disorder, cerebral palsy, schizophrenia; Badura-Brack et al, 2015 ; Spooner et al, 2018 ; Wilson et al, 2015 ; Wilson et al, 2019 ; Wilson et al, 2007 ; Wilson et al, 2009 ), the current study recommends that the use of paired-pulse paradigms with an ISI of ~200–220 ms may be ideal for eliciting optimal gating (i.e., best suppression of redundant information), and this may be most effective for distinguishing clinical populations from their healthy counterparts. However, previous studies have shown that the ISI optimal for distinguishing deficits in clinical populations (e.g., 500 ms) may differ from the ISI eliciting the best suppression (e.g., 100 ms) in the same patient group, suggesting that the two may serve dissociable mechanisms for sensory gating ( Nagamoto et al, 1991 ).…”