INS and type 2 diabetes mellitus: Patients with T2DM have insulin resistance both centrally and peripherally, and the insulin that breaks through the blood-brain barrier and is transported to the brain tissue is also greatly reduced, which ultimately damages energy, a stable form of glucose metabolism, and white matter fiber structure and function (Hanyu, 2019; Kellar and Craft, 2020; Tamura et al., 2020).