The concept of thought has always been central to understanding the nature of human thinking in psychological studies. However, the main question of what is thought still remains unanswered. The origins of the issue lie in the definition of the original unit of analysis, i.e. in the definition of what lies at the heart of image, belief, imagination, speech, consciousness, and thinking. Based on available studies, results of which were reflected in recent publications, it was argued that thought should be such an original unit of analysis. This article explores the concept of thought based on cognitive constructs and the neurophysiological correlates of mental activity. The present study is addressed to discuss issues dealing with the nature of thought, its content and structure, and the relationships between indicators of substantial thought and the neurobiological correlates of the process of thinking. Structurally thought is based on needs, emotions and intensions, and as such, thought defines the substantive essence of an image and also represents consciousness. Coherence of thoughts and consciousness, their integrity reflect the connectivity of things from the external world in their entirety. Thus, the ability to generate thoughts and build relationships within the stream of consciousness characterizes the human mind. It is shown that thought as a cognitive substance emerges from desires and experiences, as well as from conscious perception. Taken together, the described psychological and neurophysiological assumptions open up new horizons for research into human mental activity, thinking abilities and consciousness.