This study investigates the mechanisms by which type 2 diabetes affects brain parenchyma and impairs higher brain functions, focusing on insulin resistance. The analysis included 20 participants with an average age of 72.5 years and an average diabetes duration of 12 years. The study found a significant positive correlation between insulin resistance (CPR-IR) and general cognitive function (MoCA-J), but no significant correlations with executive function (FAB) or attention function (TMT-A and TMT-B). These findings suggest that insulin resistance contributes to cognitive decline in diabetic patients, likely due to impaired insulin signaling in the brain. This study highlights the importance of evaluating and addressing both insulin resistance and secretion capacity in diabetes treatment, particularly for Japanese patients who often have lower insulin secretion. The results underscore the potential benefits of exercise therapy in improving cognitive functions and suggest that designing treatment programs to enhance behavioral modifications could be beneficial for diabetes management. Future research should involve larger sample sizes and more detailed evaluation items to further explore these relationships and improve therapeutic strategies for cognitive decline in diabetic patients.