Like Nagel, with his “physico-mental intimacy” and his variability of relations, Merleau-Ponty also searches for new forms of physico-mental relations. He postulates a “circular causality” as a “chiasm” between mental states and physico-mental conditions. These terms characterize physico-mental relations as forms of organization within the structures of the “lived body” such that physico-chemical and mental states appear as the interior and the exterior, the concave and the convex side of a non-visible hinge, the “lived body” (Merleau-Ponty 1968, 295).
Source: wiktionary