  Cognitive states are involving in our daily life, which motivates us to
explore them and understand them by a vast variety of perspectives. Among these
perspectives, brain connectivity is increasingly receiving attention in recent
years. It is the right time to summarize the past achievements, serving as a
cornerstone for the upcoming progress in the field. In this chapter, the
definition of the cognitive state is first given and the cognitive states that
are frequently investigated are then outlined. The introduction of the methods
for estimating connectivity strength and graph theoretical metrics is followed.
Subsequently, each cognitive state is separately described and the progress in
cognitive state investigation is summarized, including analysis, understanding,
and decoding. We concentrate on the literature ascertaining macro-scale
representations of cognitive states from the perspective of brain connectivity
and give an overview of achievements related to cognitive states to date,
especially within the past ten years. The discussions and future prospects are
stated at the end of the chapter.
