How do we think and what is the neural circuit mechanism for it? Possible roles of working memory and inner speech in thinking.

Animals detect changes in the surrounding situation and predict what is likely to happen next by evaluating the current sensory information to that of a prior associative memory. Using working memory with inner speech, humans are able to flexibly predict the future situation and devise appropriate strategies to avoid dangers or achieve goals. This prospective thinking is supported not only by feed-forward sensory information with associative memory but also by working memory that maintains attended information for tens of seconds. Working memory is a type of short-term memory essential for providing the temporal and spatial continuity of attention during the transition from the current behavior to the next. We hypothesize that repeated associative learning of sensory signals with multisensory object imagery may form the reverberatory circuits between the sensory cortices and higher cognitive areas. The cortico-cortical reverberatory circuits may generate the cognitive scenes of objects. We also hypothesize that the cortico-thalamo-cortical loops may maintain the cognitive object-scenes as working memory to internally search for related memories of action planning and emotional self-state. Such internal search for relevant memory engrams may be a major role of working memory in thinking. In this perspective article, we discuss self-cognition and the circuit mechanism for it in the human brain.