Mossy cells of the DG are glutamatergic neurons that have intrinsic and circuit properties that make them ideal to activate granule cells, which is likely to be necessary because the granule cells are quiescent, hyperpolarized neurons. That quiescence seems necessary for cognitive functions such as pattern separation but leaves granule cells at risk of suboptimal activation. Mossy cells could serve to inhibit local granule cells so they are not activated too much by an input, supporting pattern separation, but activate granule cells in distal DG lamellae to relay or “broadcast” information that might otherwise be undetected, which may support heterassociative function. For this potentially important role, mossy cells may pay a “price”—vulnerability to insults or injuries that are associated with release of high concentrations of glutamate from the mossy fibers.