I investigate the effects of scopolamine-induced cholinergic disruption on the working memory performance of rhesus macaques. Working memory plays a critical role in cognitive function and relies heavily on cholinergic signaling in the brain. To explore this relationship, I designed and implemented a delayed match-to-sample (DMTS) task to optimize the accuracy and reliability of the data collected. The DMTS trials involve three phases: stimulus, delay, and choice. Monkeys are presented with a sample stimulus they must memorize. After a variable delay period of 5 to 30 seconds, they select the target image from a set of options. Performance is tracked by calculating the percentage of correct, incorrect, and omitted responses. Daily DMTS sessions provide longitudinal data on memory performance, allowing me to analyze patterns before and after scopolamine administration. I am also learning to analyze spike-spike coherence to investigate changes in neuronal synchronization associated with memory performance. Upon inducing amnesia-like conditions under scopolamine, an M1 muscarinic antagonist, the delayed match-to-sample task evaluates memory performance under baseline and drug-induced conditions. The primary objective of my project is to understand how scopolamine-induced disruptions affect working memory performance and to investigate the underlying cortical mechanisms involved. Based on existing literature and preliminary observations, I anticipate observing a measurable decline in memory performance following scopolamine administration, with older macaques likely exhibiting more pronounced deficits compared to younger macques. This project aims to contribute to the understanding of how cholinergic mechanisms influence working memory performance and to provide insights into the cognitive impairments associated with neurodegenerative diseases.

The orofacial sensorimotor cortex plays an important role in controlling tongue and jaw movements, such as speaking and eating. Being able to reliably perform these movements has critical implications for people suffering from neurological diseases such as stroke and Alzheimer’s disease, which are known to affect orofacial functions. However, the features of the complex lingual function that drive motor cortical activity are still poorly understood. Here, we investigate how information in the orofacial primary motor cortex (MIo) varies based on factors such as availability of tactile sensation, axis of motion, and specific regions of the tongue. To answer this question, we tracked marker-based movements of the tongue and jaw while recording neural activity from implanted microelectrode arrays in the MIo of two rhesus macaques (Macaca mulatta) engaged in feeding. Decoding accuracies of models based on (i) axis of motion, i.e., antero-posterior (x-axis), supero-inferior (y-axis), medio-lateral (z-axis), (ii) tongue marker region (superficial vs. deep, anterior vs. intermediate vs. posterior), and (iii) local anesthesia applied to sensory branches of the trigeminal nerve, were then compared to evaluate the ability to predict marker position. Generally, decoding performance was best using the y-axis and worst with the z-axis. Additionally, model performance was best in the x-axis of posterior tongue markers. Lastly, we found significant differences in model performance between control and nerve block conditions across all motion axes, with the x-axis showing the largest decrease in performance post-nerve block. These findings indicate that information carried by MIo neurons differ as a function of the tongue's motion axis, region, available tactile information, and varying combinations of these factors. These have important implications for the development of evaluation tools, rehabilitation strategies, and neural prostheses to restore orolingual function in particular and limb sensorimotor function in general.