Deepa Issar
PhD Thesis Defense
Date: Thursday, April 16th , 2026
Advisor: Dr. Matt Smith, Dr. Jana Kainerstorfer
Committee: Dr. Steve Chase, Dr. Barbara Shinn-Cunningham, Dr. Laura Lewis
Abstract: Internally and externally driven arousal changes in behavior and cortical activity
Arousal is an internal state that describes our readiness to engage with our environment. Fluctuations in arousal, which occur both in health and in neurocognitive disorders, give rise to global changes across the brain, body, and behavior. It can be difficult to connect arousal findings across studies because they use various biomarkers of arousal and different measures of brain activity. In this work, we began to bridge this gap by quantifying arousal in terms of multiple physiological biomarkers and by measuring both cortical neural and vascular activity.
First, we investigated spontaneous drifts in arousal driven by internal processes such as fatigue and engagement. We linked variability in saccadic reaction time (RT), a common behavioral measure in cognitive neuroscience, to multiple physiological markers of arousal (heart rate and pupil diameter) across timescales. Next, we addressed the challenge of connecting arousal results between cortical neural and vascular studies. To our knowledge, this work is the first to simultaneously use non-invasive near-infrared spectroscopy (NIRS) to measure vascular changes and intracortical microelectrodes to measure neural changes in visual cortex area V1 of non-human primates. We report how these methods enable the investigation of arousal-linked variability in visually evoked vascular and neural responses. Lastly, we studied externally driven shifts in arousal by adjusting task demands over minutes in a color change detection task. We observed changes in behavior (false alarm rate and RT), physiological markers of arousal, and V1 population activity were aligned to changes in task difficulty. These findings indicated subjects could modulate their behavior and arousal level to meet fluctuating task demands. In summary, this work sheds light onto the link between arousal level and the variability observed in behavior as well as cortical neural and vascular activity. It also illuminates the potential of simultaneous multimodal measures of physiology and brain activity to better characterize arousal-linked processes that may affect these measurements to different extents.