The brain has a limited capacity to process the myriad sensory signals in the environment. To overcome this, the brain focuses to situationally relevant stimuli while filtering out irrelevant stimuli, a process known as attention. Volitional, or "top-down" attention (as opposed to reflexive or "bottom-up" attention) involves the coordination of frontal, more executive cortices with posterior, more primary cortices. Here, we hypothesize that the claustrum mediates top down signaling through its numerous cortical projections. Using optogenetic techniques in mice, projections between an executive region, anterior cingulate cortex (ACC), and the claustrum were manipulated in order to ascertain the role of the claustrum during performance on an attentional task. Silencing ACC afferents to claustrum or activating claustral afferents to ACC disrupted task performance. We conclude that the claustrum is involved with top-down preparatory attention and may also be involved in bottom-up attention.