Abstract
Rewards and reward expectations influence neuronal activity in many brain regions as stimuli associated with a higher reward tend to give rise to stronger neuronal responses than stimuli associated with lower rewards. It is difficult to dissociate these reward effects from the effects of attention, as attention also modulates neuronal activity in many of the same structures (Maunsell, 2004). Here we investigated the relation between rewards and attention by recording neuronal activity in the primary visual cortex (area V1), an area usually not believed to play a crucial role in reward processing, in a curve-tracing task with varying rewards. We report a new effect of reward magnitude in area V1 where highly rewarding stimuli cause more neuronal activity than unrewarding stimuli, but only if there are multiple stimuli in the display. Our results demonstrate a remarkable correspondence between reward and attention effects. First, rewards bias the competition between simultaneously presented stimuli as is also true for selective attention. Second, the latency of the reward effect is similar to the latency of attentional modulation (Roelfsema, 2006). Third, neurons modulated by rewards are also modulated by attention. These results inspire a unification of theories about reward expectation and selective attention.