Tangled Web (IMAGE) Princeton University Caption Pictured is a mouse hippocampal neuron studded with thousands of synaptic connections (yellow). The number and location of synapses -- not too many or too few -- is critical to healthy brain function. The researchers found that MHCI proteins, known for their role in the immune system, also are one of the only known factors that ensure synapse density is not too high. The protein does so by inhibiting insulin receptors, which promote synapse formation. Credit Image courtesy of Lisa Boulanger, Department of Molecular Biology Usage Restrictions None License Licensed content Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.