The effect would be that, an individual would always be at the grade level you were on when you caught the virus. An individual might be able to use very limited short term memory to cram for quizzes or tests but lasting learning would not be there. The hippocampus is a small organ located within the brain's medial temporal lobe and forms an important part of the limbic system, the region that regulates emotions. A group of aggressive viruses, including those responsible for common colds, polio and diarrhoea, may harm a crucial memory-processing region in the brain known as the hippocampus.