Related Stimuli in PTSD Potential for Scenario Adaptation in VR Exposure Therapy

Tanja JOVANOVICM, Sinisa POPOVICb, and Dragica KOZARIC-KOVACIC c

",IDepartment of Psychiatry and Behavioral Sciences, Emory University School of Medicine,

Atlanta, GA, USA

bUniversity of Zagreb, Faculty of Electrical Engineering and Computing, Zagreb, Croatia cReferral Centre for the Stress Related Disorders of the Ministry of Health of the Republic of Croatia, Department of Psychiatry, Dubrava University Hospital, Zagreb, Croatia

Abstract. The following article reviews the use of psychophysiological tools in diagnosis and treatment assessment of posttraumatic stress disorder (PTSD). Several different psychophysiological systems are described and evaluated in terms of their diagnostic utility. The article further makes recommendations regarding strategies for the use of psychophysiology in future assessment of the disorder and for implementation within virtual reality exposure therapy.

Keywords. Combat related Posttraumatic Stress Disorder, War veterans, Psychophysiological responses, Startle, Heart rate, Skin Conductance, Blood Pressure

Introduction

One of the central symptoms of posttraumatic stress disorder (PTSD) is hyper-arousal in response to trauma reminders. Such arousal induces physical symptoms, such as racing heart, sweating, and shortness of breath. These symptoms are controlled by the autonomic nervous system and can be measured using psychophysiological equipment. Psychophysiological measurements include recordings of several autonomic nervous system outputs, such as heart-rate, blood pressure, skin conductance, respiratory rate, and body temperature. Thus, these measurements provide an objective way to measure the

1 Corresponding Author: Tanja JOVANOVIC, Department of Psychiatry & Behavioral Sciences, Emory University School of Medicine, 1365 Clifton Road, Atlanta, Georgia 30322, E-mail: [email protected]

hyper-arousal symptoms related to trauma reactivity. Technological advances in the last decade have made such measurements possible with only a few pieces of equipment and without extensive training in psychophysiology. In other words, hyper-arousal can be measured in most clinical settings, and can be used in the diagnosis and treatment of PTSD.

1. Overview of psychophysiological measures

Based on the DSM-IV criterion of hyper-arousal in PTSD [1], several investigators have examined the utility of psychophysiological recording in diagnosing the disorder (see [2] for recent review). Most of these studies have recorded from multiple psychophysiological systems, namely, the cardiovascular, electrodermal, electromyographic, and electrocortical systems. The first two systems are under the control of the autonomic nervous system (ANS), whereas the second two are under the control of the central nervous system (CNS) [3]. The cardiovascular measurements include electrocardiograms (ECG), blood pressure (systolic BP and diastolic BP), and respiratory rate (see Figure 1). Electrodermal responses measure changes in sweat gland activity and are measured from the skin on the fingers (see Figure 2). Electromyographic (EMG) measurements include measuring the muscles that control facial expression and eyeblink [3]. Electrocortical recordings are made from the scalp and record evoked response potentials from cortical areas—as opposed to the first few measurements, these require much more sophisticated equipment and are not as readily interpreted; therefore, we will focus on the first three systems.

1.1. Cardiovascular system

Electrocardiograms can be used to analyze heart-rate in beats per minute (BPM), heart-rate variability (inter-beat interval, IBI), and respiratory sinus arrhythmia (RSA). Heart-rate is a direct index of sympathetic nervous system activation and is a very good indicator of hyper-arousal. Heart-rate variability and RSA are measures of parasympathetic nervous

system activity which inhibits arousal; therefore, these measures are good indicators of individual differences in resilience to trauma. These measures can be easily recorded from electrodes placed on the wrist or on the chest. The chest placement is less sensitive to motion artefact and is therefore preferred over the wrist placement. Blood pressure and respiration rate can also be automatically measured using a wrist sensor and chest band, respectively (see Figure 1). These measures are useful concomitants to ECG, and respiration rate is necessary in order to assess RSA.

1.2. Electrodermal system

Electrodermal measurements assess changes in sweat gland activity in the skin (Figure 2) that affect the electrical conductivity of the skin [3]. The electrodermal response measures skin conductance level (or skin resistance) and is also a direct index of sympathetic nervous system activation and thus a good measure of arousal. Historically it has been termed the Galvanic skin response (GSR) and is the most commonly used indicator of physical arousal. It has been used to measure habituation and learning effects as well as hyper-arousal. Electrodes can be placed either on the index and middle finger (Figure 2) or on the palm.

Figure 2. Placement of electrodes for measuring skin conductance response

1.3. Electromyographic system

Electromyographic measurements target the muscles in the face that control facial expression (Figure 3) [3], most commonly the zygomaticus muscles (cheek muscles that stretch the face during smiling, Figure 3A), the corrugator muscles (eyebrow muscles that control frowning, Figure 3B), and the frontalis muscles (forehead muscles that arch the eyebrows, Figure 3C). Electromyographic recordings are also made of the orbicularis muscles (Figure 3D) that contract during the eyeblink component of the startle reflex. Since these are under the control of the central nervous system, they are also under some degree of voluntary control. Thus, facial expressions, such as smiling or frowning can be purposefully generated or suppressed by the individual. For this reason, these measures are not as objective as the cardiovascular or electrodermal responses, which are not under voluntary control. However, electromyographic measurements of facial muscles are preferred when the stimuli can have either negative or positive interpretations [4]. Studies that examine positive as well as negative emotions can measure facial expressions using this system. While these muscle groups would not necessarily be of interest in analyzing hyper-arousal to trauma reminders, it may be useful in investigations of emotional numbing symptoms of PTSD.

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