A promising alternative to GPUs and FPGAs, Neurogrid will make the computational power required to explore various hypotheses about how the cortex works affordable. Neurogrid's speciality is modeling interactions between cortical areas, of which there are over three dozen in the visual system alone, connected by lateral, feedforward, and feedback projections. Feedback projections constitute about half the total—virtually every area projects back to the areas that feed it—yet their role remains mysterious. One hypothesis is that they integrate these areas' myriad representations into a coherent percept. Another hypothesis is that they mediate attention, zooming in on the most informative area and excluding the others.