Measuring prefrontal cortex response to virtual reality exposure therapy in freely moving participants

Landowska, A

Abstract

Virtual Reality Exposure Therapy has demonstrated efficacy in the treatment of phobias; yet little is known about its underlying neural mechanisms. Neuroimaging studies have demonstrated that both traditional exposure therapy and virtual reality exposure therapy normalise brain activity within a prefrontal - amygdalar fear circuit after the treatment. However, the previous studies employed technologies that perhaps impact on ecological validity and naturalness of experience. Moreover, there are no studies investigating what is happening in the brain within a virtual reality session.
This PhD takes a multidisciplinary approach and draws upon research areas of cognitive neuroscience, neuropsychology, and virtual reality. The approach is twofold - developmental and experimental. A key methodological objective was to maximise ecological validity by allowing freedom of movement and sight of one’s own body. This was approached by combining wearable fNIRS within Immersive Projection Technology (IPT). The stimulus was adapted from a classic VR experiment - Pit Room. The scope of this PhD includes three experiments. The first pilot experiment tested the potential of combining the wearable Functional Near-Infrared Spectroscopy (fNIRS) device – NIRSport, with virtual reality (VR) display - CAVE-like Immersive Projection Technology (IPT) system – Octave. The aim was to test the feasibility of the protocol in terms of the design, integration of technology, and signal to noise ratio in the Pit Room study, which involved measuring brain response during exposure to heights in virtual reality. The study demonstrated that brain activity could be measured in IPT without a significant signal interference. Although there was no significant change in brain activity during exposure to virtual heights, the study found trends toward increased HbO in the prefrontal cortex. The second study investigated the brain activity indicative of fear inhibition and cognitive reappraisal within a single session of VRET in healthy controls. The heart rate was also measured as an indicator of emotional arousal (fear response) during the VRET session. 27 healthy volunteers were exposed to heights in virtual reality. Changes in oxygenated haemoglobin concentration in the prefrontal cortex were measured in three blocks using a wireless fNIRS, and heart rate was measured using a wireless psychophysiological monitor. Results revealed increased HbO concentration in the DLPFC and MPFC during exposure to the fear-evoking VR, consistent with fear inhibition and cognitive reappraisal measured in previous neuroimaging studies that had not used VR. Within-session brain activity was measured at much higher temporal resolution than in previous studies. Consistent with previous studies, a trend showed an increase of brain activity in the DLPFC indicative of cognitive reappraisal at the beginning of the session. Then additionally the MPFC was activated consistent with fear inhibition. The heart rate showed a trend towards a gradual decrease within a session. The aim of the third study was to investigate the neural basis of VRET in an acrophobic population. In particular, the study focused on measuring functional brain activity associated with both within- and between-session learning. Psychophysiological monitoring was also employed to measure levels of emotional arousal within- and between sessions. 13 acrophobic volunteers took part in three-session VRET for a fear of heights. Changes in HbO in the prefrontal cortex were measured in three blocks to investigate within–session brain activity and across three sessions to investigate between-session inhibitory learning. Results demonstrated that phobic participants have decreased activity in the DLPFC and MPFC at the beginning, however, after three sessions of VRET, activity in these brain areas increased towards normal (measured in healthy controls). Although there was no within-session learning during the first and second session, the study found a significant increase in the DLPFC at the beginning of a session. During the second block, additionally, the MPFC was activated. The magnitude of brain activity in those regions was negatively correlated with the initial level of acrophobia. Due to the technical difficulties, no significant results were found in psychophysiological measures. However, subjective fear ratings decreased significantly within- and between sessions. Moreover, participants who felt more present demonstrated stronger results in brain activity at the end of VRET. This is the first project that investigated the neural correlates of fear inhibition and inhibitory learning by combining a VR display in which people can move around and see their body, with wearable neural imaging that gave a reasonable compromise between spatial and temporal resolution.
This project has an application in widening access to immersive neuroimaging across understanding, diagnosis, assessment, and treatment of, a range of mental disorders such as phobia, anxiety or post-traumatic stress disorder. An application that is receiving an interest in the clinical community is repeatable, direct and quantifiable assessment within clinics, to diagnose, steer treatment and measure treatment outcome.

• Thesis Type: Thesis
• Acceptance Date: Oct 31, 2018
• Deposit Date: Nov 28, 2018
• Publicly Available Date: Nov 28, 2018
• Related Public URLs: http://usir.salford.ac.uk/48887/