'Tree of Life' with knots by Leonardo Da Vinci in the Sala delle Asse in Milan.
Similar to arabesque art: "The very term arabesque is a rather diffuse one, sometimes used broadly to denote almost any style of geometric ornamentation prevalent in Islamic nations, but here I will take it as referring more specifically to stylised vegetal decoration ‘in which plants and leaves grow according to the laws of geometry rather than nature,’ forming ‘interlaced straps, zizags, spirals, scrolls and knots’ which tend to fall into complicated polygonal shapes, in turn forming separate frames for other patterns inside them. Use of this type of decoration, which apparently originated in 10th-Century Baghdad, became widespread throughout the Islamic world in the following centuries." - www.spamula.net
Related to Knot theory: “In topology, knot theory is the study of mathematical knots. While inspired by knots which appear in daily life in shoelaces and rope, a mathematician's knot differs in that the ends are joined together so that it cannot be undone.” - http://en.wikipedia.org/wiki/Knot_theory
But probably an homage to the astonishing Albrecht Dürer, a German painter, mathematician, and theorist who was a friend of Leonardo.
Though it might also have been a subliminal expression of the knots, wires and connections in his brain ; p