IRS1 and Insulin resistance: In this study, increased IRS-1 Ser 307 phosphorylation and decreased Akt phosphorylation, both indictors of impaired insulin receptor signaling, were observed in the hippocampus and frontal cortex of HFD rats, although a recent study demonstrated that IRS-1 Ser 307 is a positive regulatory site that sustains peripheral insulin signaling and moderates the severity of insulin resistance in mice [38].