Layer 3 (L3) pyramidal neurons are involved in intrinsic and extrinsic corticocortical communications that are integral to area specific cortical functions. The functional and morphological properties of these neurons are altered in the lateral prefrontal cortex (LPFC) of aged rhesus monkeys, changes which parallel the decline of working memory (WM) function. What is not yet understood is the time course of these neuronal alternations during the aging process, or the impact of neuronal changes on the function of local networks that underlie WM. By comparing the properties of L3 pyramidal neurons from the LPFC of behaviorally characterized rhesus monkeys over the adult lifespan using whole cell patch clamp recordings and neuronal reconstructions, the present dissertation demonstrates that WM impairment, neuronal hyperexcitabilty and spine loss begin in middle age. We use bump attractor models to predict how empirically observed changes affect performance on the Delayed Response Task and Delayed Recognition Span Task (spatial). The performance of both models is affected much more by neuronal hyperexcitability than by synapse loss. In a separate study, we examine pathological changes of L3 pyramidal neurons in the perilesional ventral premotor cortex following acute ischemic injury to the primary motor cortex. Neurons from lesioned monkeys exhibit hyperexcitability and changes the excitatory:inhibitory synaptic balance in favor of inhibition. As oxidative stress and inflammation are known to exacerbate both age-related and injury-induced neuronal pathology, we characterize neuronal properties in both conditions after administering therapeutic interventions which target inflammatory pathways and which have previously been shown to ameliorate behavioral deficits. Chronic dietary curcumin treatment dampens neuronal hyperexcitability in middle-aged subjects, but the neuronal changes are not correlated with WM improvements. Treatment with mesenchymal-derived extracellular vesicles lowers firing rates and restores excitatory:inhibitory synaptic balance, and importantly, these changes correlate significantly with motor function.