Changes in brain insulin metabolism and insulin resistance are associated with several CNS disorders such as Alzheimer’s disease (AD), depression [71,72,73], autism [74], schizophrenia [75], Huntington’s disease [76], Parkinson’s disease (PD) [77], etc. IN-insulin has shown an improvement in memory, metabolic integrity of the brain in patients with AD, and mild cognitive impairment [78]. Here, INS is linked to major depressive disorder.