Abstract
Enhanced acquisition of eyeblink conditioning is observed in active duty military and veterans expressing PTSD symptoms (PTSD+) and those expressing temperamental vulnerabilities to develop PTSD after traumatic experiences, such as behaviorally inhibited temperament. There is a growing literature showing persistent cerebellar abnormalities in those experiencing mild traumatic brain injury (mTBI+) as well as linkages between mTBI and PTSD. With the dependency of eyeblink conditioning on cerebellar processes, the impact of mTBI on eyeblink conditioning in veterans expressing PTSD is unknown. The present study assessed eyeblink conditioning in veterans during two sessions separated by 1 week. With a focus on the accelerated learning of veterans expressing PTSD, training utilized a protocol which degrades learning through interspersing conditioned stimulus (CS) exposures amongst delay-type trials of CS and unconditional stimulus (US) co-terminating trials. Faster acquisition of the eyeblink conditioned responses (CR) was observed in PTSD during Week 1. The Week 2 assessment revealed an interaction of mTBI and PTSD, such that asymptotic performance of PTSD+ was greater than PTSD− among mTBI− veterans, whereas these groups did not differ in mTBI+ veterans. To further examine the relationship between enhanced sensitivity to acquire eyeblink conditioning and PTSD, cluster analysis was performed based on performance across training sessions. Those with enhanced sensitivity to acquire eyeblink conditioned responses expressed more PTSD symptoms, which were specific to Cluster C symptoms of avoidance, in addition to greater behavioral inhibition. These results support the continued investigation of the conditioned eyeblink response as a behavioral indicator of stress-related psychopathology.
Highlights
Diathesis models elaborate interactions between inherent vulnerabilities and experiential risk factors in the development of stress-related mental health problems, such as post-traumatic stress disorder (PTSD)
Of the 60 veterans that volunteered for the study, data for six participants was excluded from analysis
Consistent with prior research, acquisition of the classically conditioned eyeblink response was enhanced in veterans expressing current PTSD symptoms
Summary
Diathesis models elaborate interactions between inherent vulnerabilities and experiential risk factors in the development of stress-related mental health problems, such as post-traumatic stress disorder (PTSD). For PTSD, a learning diathesis model is proposed as a proxy for understanding the development and persistence of acquired changes in behavior and coping in the aftermath of trauma experience represented by intrusion and avoidance symptoms, in particular, and indirectly by arousal and enhanced reactivity symptoms (Allen et al, 2016, 2019; Servatius, 2016). A simple form of classical conditioning, provides a convenient methodology for assessing inherent learning biases in PTSD inasmuch as the critical stimuli used in the assessment of eyeblink conditioning are relatively independent of trauma occurrence. As an associative learning paradigm, eyeblink conditioning has high translational value for neurologic mental health influences (Steinmetz et al, 2001; Greer et al, 2005; Edwards et al, 2008; Myers et al, 2012b; Greer and Thompson, 2017; Handy et al, 2018) with protocols validated for humans and non-human mammals (e.g., Servatius, 2000) and strong evidence of neural substrates conserved across mammalian species (Miller et al, 2003; Cheng et al, 2008; Freeman and Steinmetz, 2011)
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