What happens when the two halves of the brain can’t communicate? Philosopher Azenet Lopez explores this question in her new paper, “A Layered Unity Model of Split-Brain Consciousness.” Split-brain patients sometimes seem to have two separate streams of experience — yet they still feel like one person. Azenet’s model suggests that while detailed information may be split, a broader, global sense of awareness remains unified.
Here, she unpacks what this means for consciousness, identity, and how the mind holds together — even when the brain does not.
Mi3: For those who aren’t philosophers or neuroscientists, can you explain in simple terms: what exactly is split-brain consciousness?
Azenet: Split-brain consciousness refers to what happens when the main connection between the two halves of the brain—the corpus callosum—is severed, usually to treat severe epilepsy. People with this procedure seem completely normal in everyday life, but in lab experiments, it gets weird. For example, each side of their brain can process things separately. If you show a circle to the left eye and a square to the right, they can describe each, but oddly, they can’t tell you if those two shapes are the same or different. It’s like the brain’s two halves are having separate experiences.
Mi3: So are they two people in one body? Is that how it works?
Azenet: That’s the million-dollar question, isn’t it? Some have argued that maybe, after this surgery, the person becomes two separate conscious beings. But it’s not that simple. In my paper, I argue that even though there’s a breakdown in some types of conscious experience—like noticing detailed comparisons between left and right—the person still has a kind of overall, global awareness that’s shared. It’s not two people; it’s one person with some local disconnects.
Mi3: I love this idea of “global” and “local” experiences you mention. Can you give us an analogy?
Azenet: Sure! Imagine you’re at a music festival. You can hear the whole vibe—the buzz of the crowd, the thump of the bass—that’s the global experience. But then, focusing on the specific lyrics of the band or noticing the colour of someone’s funky hat next to you—that’s the local detail. For split-brain patients, the brain’s left and right sides can still share that general vibe of what’s going on, but when it comes to detailed comparisons—like matching two hats on either side—they struggle.
Mi3: So if the two brain halves struggle with sharing local details, how do you think they still maintain this sense of unity?
Azenet: I argue that it’s largely thanks to how attention works. While some automatic, reflexive kinds of attention split between the two hemispheres, other types—like consciously deciding what to focus on—still seem unified. So, both halves remain synced in terms of general awareness, emotions, and goals, even if they handle details independently. It’s a bit like having two camera feeds going into the same control room.
Mi3: And why should the average person care about this? How does this change how we think about ourselves?
Azenet: I think it challenges how we think about the self. We tend to imagine consciousness as this all-or-nothing thing—you’re either one person or you’re not. But what I found suggests that unity isn’t absolute; it’s layered and partial. And if that’s true for people with split brains, maybe it’s also true, to some degree, for all of us. Our minds might be more fragmented—and more resilient—than we usually believe.
Check out the original article and Azenet Lopez’s profile.
References:
Lopez, A. A layered unity model of split-brain consciousness. Philos Stud (2025). https://doi.org/10.1007/s11098-025-02339-3