The human brain does not use statistical methods for learning, language understanding, or sentiment detection.
Statistical methods are very useful as an *adjunct* to symbolic methods, but they cannot, by themselves, do the complete task. For an overview of issues about how the brain works and how it processes various aspects of human language, see the following compendium of slides and the references they contain:
http://www.jfsowa.com/talks/goal.pdf
The goal of language understanding
John Sowa