The four quadrants
The UPPER LEFT quadrant covers the inner-individual aspects of human consciousness, as studied by developmental psychology, in both it's coventional and contemplative forms.
The UPPER RIGHT quadrant covers the outer-individual aspects of human consciousness, as studied by neurology and cognitive science.
The LOWER LEFT quadrant covers the inner-collective aspects of human consciousness, as studied by the sciences of culture: cultural psychology and anthropology.
The LOWER RIGHT quadrant covers the outer-collective aspects of human consciousness, as studied by sociology.
Western culture tends to over-emphasize the Right Hand quadrants (brain science, sociology), and neglect the Left Hand quadrants (introspection, human culture). The integral model of consciousness redresses that imbalance by pointing out the importance of the Left Hand quadrants.
One way to make sense of the Four Quandrants model is to see the UPPER LEFT quadrant as primary, and the other three quandrants as the various ways individual human consciousness is conditioned, by the material brain, cultural influences and social structures.
A more radical view is to see the Four Quadrants as the four ways in which Universal Spirit is expressed simultaneously.
All of the quadrants mutually interact with eachother. A given stage of individual development (e.g. abstract mind) will be reflected in a stage of neurological development (e.g. the neocortex), a stage of cultural development (e.g. rationalisation) and a stage of societal development (e.g. industrialisation).
Each quadrant consists of nine levels/stages. Combining quadrants with levels gives the "all quadrants, all levels" approch of Integral Philosophy.