ALL insect brains contain mushroom-shaped neural bodies which are implicated in associative learning. Here we show that the mushroom bodies of the locust brain have a remarkable and hitherto undescribed neural organisation consisting of six tubular structures in which bundles of axons are enclosed by cylindrical walls of nitric oxide synthase (NOS) expressing processes. A dynamic temporo-spatial simulation shows that the tubular organization allows NO to attain and maintain locally elevated concentrations within highly structured domains in the CNS. A diffusible gaseous signalling molecule such as NO can therefore selectively affect computational processes occurring in discrete parallel channels of information flow in the brain. The implications of this are discussed in relation to the role of NO in a compartmental model of the mushroom bodies and more generally in the context of the targetting of diffusible messenger molecules in the brain.