How to evaluate and predict the degrees of language aptitude and language proficiency is one of the controversial issues in the world of second language learning. To address this matter, the use of clinical devices such as EEG (electroencephalogram) and ERP (Event-related potential) has recently been a hotly debated area of discussion. In the current paper, a history of using such devices has been collected and discussed to depict a comprehensive map for further research. The online search was accomplished using two major and reliable databases (Google Scholar and Research Gate). The study found some interesting investigations on the theory of language aptitude defined in various articles as well as the different uses of EEG and ERP in evaluating brain function of participants with different levels of language aptitude and proficiency showing various degrees of brain waves while performing a task or at the resting state of the brain.