Despite the rich literature on the consequences of selective attention to behavior and to neural responses, as well as a wealth of models of competitive selection, little is known about the circuit mechanisms by which the brain actually selects the highest priority stimulus as the next target of spatial attention. Following a first principles approach that breaks down selection into computational primitives, and with experiments in the barn owl midbrain selection network, Dr. Mysore and team recently discovered neural circuit mechanisms for categorical (robust-to-noise) selection as well as location-invariant selection (selection at all possible pairs of locations). Dr. Mysore shall describe these findings, and in doing so, highlight (a) the identification of a new form of population coding in the brain, namely, combinatorially optimized coding (relating to classic np-hard optimization problems), as well as of (b) a novel, multi-holed donut-like organization of inhibition in the brain. He shall then switch gears and describe their development of primate-like behavioral paradigms for the study of endogenous as well as exogenous control of visuospatial selective attention in freely behaving mice. He shall end with early results from their efforts involving endoscopic calcium imaging and optogenetic manipulations in mice that are aimed at identifying circuit mechanisms of selection for spatial attention in mammals.