Consciousness encompasses a variety of functions and properties, such as awakening, awareness, and subjective aspects of both perception and volition (e.g., qualia and authorship, respectively). It remains to be seen whether these diverse functions are related to one another through common neural mechanisms, and if so how. Here, we advance the thesis that the neural mechanisms that give rise to conscious states share features with neural mechanisms that underlie simpler forms of decisions. The neurobiology of decision-making provides detailed insight into how the brain deliberates and reasons from evidence to make choices. The underlying mechanisms, mainly studied in animals, could support a variety of complex cognitive functions that probably operate independently of many aspects of consciousness. For example, many complex decisions in humans rely upon wakefulness but not upon awareness or authorship. In animal studies, decisions are typically embodied: they can be described as selection among possible actions. By substituting "circuits" for "actions" in the preceding phrase, we generalize from "deciding to do" to "deciding to consider" or, more generally, "deciding to decide to." This is an appealing notion from the perspective of brain evolution, because it allows us to recognize ideation as an elaboration of a simpler sensory-motor design. We propose that many of the functions of consciousness are simply ways of engaging the environment. Thus consciousness might be mediated by (nonconscious) decisions to engage, as in awakening, or to engage in a certain way, as when attaching narrative to action. Although the neural mechanisms underlying "decisions to engage" are unknown, they are likely to involve intralaminar (and matrix) thalamus and processes that "decide" to turn other circuits on. This idea invites an analogy between the functions of brain regions that project tomatrix thalamus, including the "default system", and the role of parietal cortex in perceptual decisions. While highly speculative, we think "decision to engage" provides a biologically plausible and computationally coherent hypothesis about the neural correlates of consciousness.