Insulin plays a crucial role in regulating the body's metabolism of glucose, fat and amino acids, the building blocks of protein. Insulin also is actively involved in transporting energy from the blood to the neurons in the brain. When insulin is absent or the body's insulin receptors are impaired, the brain suffers. A lack of insulin results in the formation of harmful plaque in the brain's memory center and cognitive regions.
The Role of Insulin in Metabolism
When you eat a normal meal, your digestive system converts carbohydrates into glucose, protein into amino acids and fat into protein-covered fat molecules. When glucose enters the bloodstream, the pancreas responds by producing insulin that is secreted into the bloodstream. Like glucose, fat and protein compounds affect the production of insulin but not nearly as much as glucose does. The insulin secreted by the pancreas binds to insulin receptors on liver and muscle cells. This causes a glucose transporter, GLUT-4, to move from the cell's interior to the cell membrane. This, in turn, allows the glucose transporter to carry glucose from the bloodstream and into the cell.
Insulin in the Brain
When insulin is present in the bloodstream, it can enter the brain. Insulin receptors are present in a number of areas of the brain, including the hippocampus, the brain's main memory center; the olfactory bulb, the brain's sensory area for smell; and the amygdala, the brain's center for fear processing. Once inside the brain, insulin binds to insulin receptors. This regulates the transportation of glucose from the bloodstream into the brain's neurons.
Impaired Insulin System in the Brain
A study published in the June 2010 issue of "Journal of Clinical and Experimental Neuropsychology" showed that when the brain's insulin levels are reduced or when the insulin receptors in the brain are damaged, the brain levels of the proteins amyloid beta and tau increase. These proteins have been associated with plaque formation in the hippocampus, the brain's main memory center. Plaque formation around the neurons in the hippocampus leads to tangles of the nerve cells. This, in turn, prevents the neurons from communicating properly with other neurons.
Memory Loss
The initial stages of plaque formations in the hippocampus lead to confusion and memory blending, which is the creation of artificial memories on the basis of stored pieces of information. For example, the brain might treat old memories as recent memories or blend together old memories with present experiences. Eventually the tangles of the neurons in the hippocampus lead to Alzheimer's disease, which is characterized by an inability to recall and store memories. Patients with Alzheimer's disease may still have a functional working memory, the ability to keep information in mind for a short time period, and they usually have relatively intact procedural memory, which is the memory required for knowing how to do things. In progressed stages of Alzheimer's disease, even these forms of memory deteriorate.
References
- Mayo Clinic: Diabetes treatment: Using Insulin to Manage Blood Sugar
- "Journal of Alzheimer's Disease"; An Integrated and Unifying Hypothesis for the Metabolic Basis of Sporadic Alzheimer's Disease; A. Erol; April 2008
- "Journal of Neurosciences"; Insulin Resistance, Inflammation, and Cognition in Alzheimer's Disease: Lessons for Multiple Sclerosis; G.S. Watson and S. Craft; April 2006
- "Experimental Gerontology"; The Role of Insulin and Neurotrophic Factor Signaling in Brain Aging and Alzheimer's Disease; G.M. Cole and S. A. Frautschy; January/February 2007
- "Journal of Clinical and Experimental Neuropsychology"; Cognitive Impairment in Nondiabetic Middle-Aged and Older Adults is Associated with Insulin Resistance; H. Bruehl, et al.; June 2010
