Rapid dynamics of dorsal raphe serotonin neurons regulate the strength of visual attention

Every moment, a spotlight of attention roams our visual field to enhance detection of salient stimuli. While recent work suggests how the brain selects salient relevant stimuli (attentional focus), it is unknown if there are mechanisms that modulate attention to suit fluctuating target salience or internal needs (attentional strength). Here, using optical recordings and perturbations in mice performing a cued detection task, we report that rapid dynamics in both dorsal raphe (DR) activity and cortical serotonin (5HT) release selectively regulate attentional strength. In contrast to these rapid DR-5HT dynamics, we found previously reported reward-associated and slower dynamics were both unrelated to attention. Brief optogenetic DR-5HT suppression increased attentional strength and performance, whereas optogenetic excitation reduced attentional strength and performance. A computational model suggests DR-5HT's inverse effects on attention arise from control of cortical suppression and divisive normalization. Collectively, our results demonstrate that the brain independently controls attentional strength and focus and defines rapid DR-5HT neuromodulation as a new regulator of attentional strength.