What exactly is monosodium glutamate and what effect does it have on the brain?

MSG: Msg is a flavoring agent and Amino Acid commonly used in asian cooking. It imparts a meaty taste to food. It is not toxic but in some causes a feeling of dizziness and even nausea. The effects, if they occur are not serious or dangerous but most foods with msg are labeled so they can be avoided and Asian restaurants will frequently list foods as msg free.