Memory Modulation in Humans
The majority of my doctoral work at the University of Utah’s INMAN Lab
investigated why sometimes direct brain stimulation of the human amygdala enhanced memories and
other times impaired memories or had no change in memory. My interests involved the patients’
demographic, neural, and medical profiles, which are understudied in the human memory enhancement
with direct brain stimulation field. The main reason for this lack is the extremely rare subject
pool of human patients with drug-resistant epilepsy who undergo surgery to implant electrodes into
their brain to triangulate seizure activity. Our research is completely voluntary while the
patients are under clinical care, and we do not dictate where the electrodes are implanted;
therefore, our participants are unique in many ways. Through the five years of my doctoral research
I discovered that patients with poorer existing long-term memory capacity are more vulnerable to
amygdala stimulation, and males compared to females are more likely to have memory enhancement
from the stimulation (Hollearn et al., 2024). In my more recent works I discovered that the
entorhinal and perirhinal cortices are the most affected by amygdala stimulation at multiple
timepoints, leading to changes in memory at both single trials and across trials (Hollearn et al.,
in prep). Perhaps with more research these undersampled regions may serve as a future biomarker
of differentiating memory enhancement practices from memory impairment when stimulating the
amygdala. Finally, I discovered that the combination of amygdala stimulation and hippocampal
interictal epileptic activity, especially bilaterally, results in the most extensive subsequent
memory loss (Hollearn et al., in prep). Because of my findings on differentiating memory
enhancement from impairment, I also wrote a review paper on which patient characteristics (e.g.,
demographic, medical, and neural) should be accounted for or investigated based on my and other
preliminary findings from animal and human models (Hollearn & Inman, under review).
In addition to human brain stimulation work, I was involved in naturalistic learning and spatial
navigation research in the same lab. Here we tested event segmentation of first-person perspective
continuous videos of people navigating a real environment that shifted between indoors and
outdoors. Across several subject pools, we tested event segmentation ability on undergraduate
students and patients with brain stimulators (Responsive NeuroStimulator) for epilepsy. Neural
results from these patients’ hippocampus during navigation have revealed intriguing patterns we
have never considered before. In addition, the participants who navigated the route wore
additional biomarker sensors to track heart rate, breathing, skin conductance, eye-tracking, and
velocity. This comprehensive capture of the navigating humans between indoor and outdoor spaces
will help answer basic scientific questions about perception, memory, navigation, event
segmentation, and naturalistic learning from biometric and direct hippocampal neural recordings.
While carrying the weight of my graduate work’s demands amongst personal challenges, I gained
vital professional, management, and research skills that I intend to embed into my future career.
I grew very fond of teaching and deepened my scientific communication skills through extensive
outreach efforts. The faculty and peer support from my lab was some of the most unforgettable
experiences that ensured me that science is a collaborative effort.
Prior to entering graduate school, I worked at the University of California, Irvine in the
Translational Neurobiology lab. Here my main duties involved recruitment and data collection of
healthy older adults’ cognitive tests, collecting saliva and blood samples, assisting in PET scans,
and operating an MRI machine to gather functional and structural scans. While my data analysis skills
were not well-developed yet at this time, I learned a lot about proper project management and data
acquisition skills, and I mentored dozens of students in data entry and small projects so they
could get involved in research. Some of my most amazing memories learning about and conducting
research come from this lab and the inclusive and highly collaborative setting I was placed in.
My experience in this lab set my expectation for how science should be done.
During my undergraduate years at California State University, Long Beach, I was advised by two
professors with whom I pursued very different projects. For one of the projects, I surveyed
undergraduate peers on personality and academic achievement and concluded that academic
self-efficacy is negatively associated with class dropout rates, which pinpoints a unique behavior
that academic advisors may use to evaluate student success (Domingo & Hollearn, 2022). The other
project involved observing undergraduate students’ ability to switch between multiple tasks while
driving with an automated driver. We concluded that switching tasks is most difficult when taking
over from automation because the driver must monitor what the automation is doing, therefore
taking on the driving task at double weight and monitoring more extensively to avoid collision
(Hollearn & Miles, 2019). This preliminary research was a helpful foundation to build more
extensive tasks on humans’ ability to interact with automated machines and safely carry out a
driving task.
Concurrent with these ongoing projects, I completed two cellular neuroscience internships, one
at the Yale School of Medicine and another at the University of California, Irvine. These projects
involved mouse models of anxiety biomarkers, one with retrograde tracer injections and the other
of co-localization of two proteins in pre- and post-synaptic space of newborn and teen mice. I
pursued these projects to get more cellular neuroscience experience, and I shifted to human
cognitive neuroscience because I was not entirely comfortable with conducting animal research. I
recognize the immense value of animal studies, whose discoveries serve as the backbone of our
theories on human cellular neuroscience and countless life-saving medications. Yet I prefer to
work with humans because I can ask my participants questions while also measuring their responses.
