Faculty Bibliography

Asymmetries in visual performance at isoeccentric locations are well-documented and functionally important. At a fixed eccentricity, visual performance is best along the horizontal, intermediate along the lower vertical, and poorest along the upper vertical meridian. These performance fields are pervasive across a range of visual tasks, including those mediated by contrast sensitivity. However, contrast performance fields have not been characterized with a systematic manipulation of stimulus spatial frequency, eccentricity, and size; three parameters that constrain contrast sensitivity. Further, individual differences in performance fields measurements have not been assessed. Here, we use an orientation discrimination task to characterize the pattern of contrast sensitivity across four isoeccentric locations along the cardinal meridians, and to examine whether and how this asymmetry pattern changes with systematic manipulation of stimulus spatial frequency (4 cpd to 8 cpd), eccentricity (4.5 degrees to 9 degrees), and size (3 degrees visual angle to 6 degrees visual angle). Our data demonstrate that contrast sensitivity is highest along the horizontal, intermediate along the lower vertical, and poorest along the upper vertical meridian. This pattern is consistent across stimulus parameter manipulations, even though they cause profound shifts in contrast sensitivity. Eccentricity-dependent decreases in contrast sensitivity can be compensated for by scaling stimulus size alone. Moreover, we find that individual variability in the strength of performance field asymmetries is consistent across conditions. This study is the first to systematically and jointly manipulate, and compare, contrast performance fields across spatial frequency, eccentricity, and size, and to address individual variability in performance fields.

Cerebral Palsy (CP) is one of the foremost causes of childhood motor disability and disrupts the individual's development and ability to function. Several factors contribute to the development of CP such as preterm delivery, low birth weight, infection/inflammation, and additional pregnancy complications, both in preterm and term infants. As there is no specific treatment for CP, rehabilitation is the current option for the management of patients. The serious nature of this condition creates deficits that last a lifetime.  We collected studies that were published in the past 10 years, using PubMed as our main database. We chose studies that were relevant to CP and stem cell therapy. We mainly focused on various types of stem cells that can be used in treatment, mechanism of action (MOA) of stem cells, routes, dosage, and adverse effects, their efficacy, and safety in CP patients. Of all the 38 studies we reviewed, we found that five articles discussed the utilization of human umbilical cord blood [hUCB], four articles discussed autologous bone marrow stem cells, and one discussed allogeneic umbilical cord blood usage. One article discussed neural stem-like cells (NSLCs) derived from bone marrow and the remaining 27 articles were about CP and its treatment. We reviewed detailed information about the possible stem cell therapies and their benefits in patients with CP. We found that immune modulation is the major mechanism of action of stem cells, and among all the types of stem cells. Autologous umbilical cord mesenchymal stem cells appear to be safe and most effective in treatment compared to other stem cell treatments. Among all symptoms, motor symptoms are best corrected by stem cell therapy. Still, it did not show any marked improvement in treating other symptoms like speech defects, sensory or cognitive defects, or visual impairment.

Avoidance behavior is a typically adaptive response performed by an organism to avert harmful situations. Individuals differ remarkably in their tendency to acquire and perform new avoidance behaviors, as seen in anxiety disorders where avoidance becomes pervasive and inappropriate. In rodent models of avoidance, the inbred Wistar-Kyoto (WKY) rat demonstrates increased learning and expression of avoidance compared to the outbred Sprague Dawley (SD) rat. However, underlying mechanisms that contribute to these differences are unclear. Computational modeling techniques can help identify factors that may not be easily decipherable from behavioral data alone. Here, we utilize a reinforcement learning (RL) model approach to better understand strain differences in avoidance behavior. An actor-critic model, with separate learning rates for action selection (in the actor) and state evaluation (in the critic), was applied to individual data of avoidance acquisition from a large cohort of WKY and SD rats. Latent parameters were extracted, such as learning rate and subjective reinforcement value of foot shock, that were then compared across groups. The RL model was able to accurately represent WKY and SD avoidance behavior, demonstrating that the model could simulate individual performance. The model determined that the perceived negative value of foot shock was significantly higher in WKY than SD rats, whereas learning rate in the actor was lower in WKY than SD rats. These findings demonstrate the utility of computational modeling in identifying underlying processes that could promote strain differences in behavioral performance.

Drug-resistant focal epilepsy (DRFE) in children can impair cognition and behavior, and lead to premature death. Increased pediatric epilepsy surgery numbers reflect the improvements in seizure control and long-term developmental outcomes. Yet, many children with DRFE are not candidates for surgical resection due to overlap of the seizure network with eloquent cortex or multiple seizure-onset zones, making surgery dangerous or ineffective. In adults, responsive neurostimulation (RNS System) therapy is safe and effective treatment for DRFE with one or two seizure foci, especially when the seizure focus is in eloquent cortex. We present six pediatric patients with DRFE who underwent RNS implantation. Our outcomes demonstrate safety, decreased clinical seizure frequency, as well as improved functional status and quality of life. Changes in the clinical seizure semiology and frequency occurred in conjunction with adjustments to the stimulation parameters, supporting the efficacy of responsive neuromodulation in children.

Recent research suggests that estrogen is protective against binge eating in adult females, and that pubertal estrogen may be critical for these effects. Nonetheless, to date, no study has examined the role of pubertal estrogen in adult binge eating phenotypes in females, potentially due to difficulties experimentally manipulating estrogen in humans to examine causal effects. We used a novel animal model to examine whether estrogen removal prior to puberty (via pre-pubertal ovariectomy (P-OVX)) increases rates of binge eating prone (BEP) phenotypes in adulthood in females. A total of 77 P-OVX and 79 intact rats were followed from pre-puberty into adulthood and phenotyped for BEP status in adulthood. Results showed significantly increased rates (~2-8x higher) of adult BEP phenotypes in P-OVX as compared to intact rats. Findings confirm that estrogen removal substantially increases later risk for binge eating in females, potentially by disrupting typical adolescent brain development.