Synchronization and Inhibition of Saccade Action associated with Neurotypical Development and Psychiatric Disease

Abstract

Humans execute approximately 200,000 saccades daily, representing swift conjugate eye movements necessary to align areas of interest with the fovea. Despite their apparent simplicity, the neural mechanisms signaling saccadic execution are intricate, spanning multiple brain regions. Consequently, saccades serve as a valuable proxy for assessing brain function and can unveil alterations stemming from physiological and pathological factors such as maturation, aging, trauma, or disease. In Chapter 2 of this study, I explore the connection between alternating bilateral saccades in response to rhythmic visual cues and therapeutic outcomes in Eye Movement Desensitization and Reprocessing (EMDR), a widely utilized treatment for post-traumatic stress disorder (PTSD). I theorize that the eye movements employed in EMDR coincide with the activation of the default mode network, a neural circuit associated with relaxation and memory reprocessing, which likely contributes to clinical recovery. In Chapter 3 I establish that this form of saccadic synchronization reaches an adult-like level of proficiency by middle adolescence. Additionally, I observe that alternating saccades at a fixed rate correspond to a consistent blink pattern and autonomic relaxation, as evidenced by reduced pupil size. In Chapter 4, I assess motor synchronization in individuals with borderline personality disorder (BPD) both with and without a comorbid diagnosis of attention-deficit hyperactivity disorder (ADHD). My findings support the preservation of motor synchronization in these disorders. However, I note irregularities in saccades toward randomly timed targets, indicative of heightened anticipation of forthcoming visual stimuli. I also reveal disparities in blink and pupil responses between individuals with BPD and matched controls, possibly a consequence of dysregulated dopamine signaling. In Chapter 5, I investigate oculomotor impulsivity across different phases of the anti-saccade task within BPD and ADHD/BPD groups. My results demonstrate that while BPD and ADHD/BPD groups exhibit analogous behavior at the onset of the anti-saccade trial (i.e. delayed visual fixation), individuals with ADHD/BPD display an additional impairment characterized by reduced preparation for the task, leading to an increased frequency of directional errors with short latencies. This dissertation enriches the existing oculomotor literature by describing saccadic motor synchronization and inhibition in typical neurodevelopment and in psychiatric disease.