Dopamine, polarised light micrograph. Dopamine is a neurotransmitter that plays an important role in the brain's reward and pleasure centres, as well as in regulating movement and mood. When dopamine is deposited onto a surface and allowed to dry, it can form thin crystalline films. When viewed through polarized light, a thin crystalline film of dopamine can exhibit interesting optical properties due to its molecular structure. It can reveal unique patterns of birefringence, or double refraction, which is the splitting of light into two separate beams with different polarizations. This occurs because the molecular arrangement of the dopamine crystals causes light to travel at different speeds in different directions. As the polarized light passes through the dopamine crystal, it can create a range of colours and patterns, depending on the orientation and thickness of the crystal.