What do we know about the effects of bilingualism on cognitive development? Our world is becoming progressively bilingual; in the United States, 21% of school-age children between the ages of 5 and 17 can speak something other than English at home, and this number is expected to increase in the coming years. In addition to social reasons, the positive effects on the cognitive development of the brain when introduced to a second language are multiple. The age of acquisition is vital because of the plasticity of the brain, which according to the critical period hypothesis, begins to level out after five years of age. In addition to plasticity, bilingual speakers are better able to focus their attention to solve complex problems than monolingual speakers. Therefore an individual will have a greater cognitive advantage if he or she is more proficient in his or her languages. Bilingualism itself may be held responsible for greater levels of executive control; To maintain balance between two languages, the bilingual brain depends on a system for monitoring general cognitive abilities that includes attention and inhibition processes. Additionally, studies have shown that bilingual patients suffer less from dementia and other aging-related diseases in the brain than monolingual patients. Neurolinguistic research has recently shown that knowledge of a second language affects structural changes in the brain. Mechelli et. al. demonstrated in one study that the acquisition of a second language increases gray matter density in the left inferior parietal cortex; the amount of structural reorganization in this region is controlled by achieved competence and age at acquisition. This study used voxel-based morphometry (VBM) to examine structural plasticity… middle of paper… children. Given the extent of exposure and age of acquisition, there is sufficient evidence showing that the bilingual brain can exhibit advanced cognitive abilities compared to the monolingual brain. Technological advances such as PET and other functional neuroimaging techniques have provided direct insight into the complex arrangements between language systems in the bilingual brain. The higher executive function used by bilingual speakers to switch between tasks between two languages ​​strengthens control mechanisms in different brain regions. Therefore consistent practice of control using both languages ​​will delay the onset of dementia, Alzheimer's disease and other diseases related to brain aging. Factors to consider when measuring neural function in bilingual and monolingual brains include age at onset, gender, education, and significant language experience.