Contributed by Jonathan Stevenson / On one level, in “Flex, Rot, and Sp(l)it,” a penetrating and conceptually cohesive show of paintings at Nathalie Karg Gallery, Heidi Hahn visually chronicles the tension between the unavoidable confinement of the body and the irrepressible expansiveness of the mind. While the so-called mind-body problem is as old as philosophy itself, to Western audiences it is perhaps most resonant in René Descartes’ exercise of systematic doubt, concluding with “I think therefore I am.” In terms of value, this ingrained formulation privileges the mind over the body. While philosophers are left to connect mental processes with gray matter, for painters and others it can be discomfiting to realize that although thinking is supposed to be the essence of being, a person’s mind is often prejudged on the basis of their body’s characteristics.