Glucose is the main source of energy for the brain. So corn syrup, the Karo kind, being pure glucose produced by depolymerizing corn starch, is fine for the brain.

High fructose corn syrup, made by enzymatic conversion of about half the glucose to fructose, or cane sugar, which is a disaccharide consisting of paired molecules of glucose and fuctose, are not so fine. The fructose has to be processed by the liver before it can be used.