Kendra Pierre-Louis: For Scientific AmericanIt is Science quickly, My name is Kendra Pierre-Louis, I’m replacing Rachel Feltman.
The French philosopher and scientist René Descartes wrote: “I think, therefore I am.” What he meant, in part, was that although our senses could deceive us, the act of thinking was proof of our own existence.
But think again about this phrase: “I think, therefore I am.”
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Who am I in this short statement?
Scientists call this self, this subjective feeling of self, consciousness.
And understanding what consciousness is, how it works, and where it lives in the brain has plagued researchers for generations. I spoke with SciAmAllison Parshall, associate editor, for more on the search for consciousness.
We explore what consciousness is, how the brain creates it, and what current science says about dreams, anesthesia, animals, and even artificial intelligence.
So you recently pointed out an article in the February issue of Scientific American on consciousness. What sparked your interest in the subject?
Allison Parshall: Well, I studied cognitive science in college, and consciousness is sort of the big question that looms over a lot of neuroscience, whether it’s addressed head-on or not.
There were these famous split-brain studies decades ago. [with] people who were having seizures and trying to fix them by, essentially, cutting off the connections between the two brain hemispheres. And that would result in really strange things where, for example, there was information in your brain that you had but you weren’t aware of because consciousness was, like, in one side of the brain and couldn’t access the other.
It’s inherently very interesting, isn’t it? That’s the big question: “How do I get perspective? How does my brain make me feel like myself?” It’s a very philosophical question, so for someone who is interested in cognitive science as a very interdisciplinary field, the philosophy of it all was very interesting.
Pierre-Louis: One of the things I found really interesting in your article is this: scientists don’t have a precise definition of what consciousness is. But can you describe at a high level what they are trying to explore when they study consciousness?
Parhall: The English word “conscience” is a bit confusing, so we kind of have to forgive it, but it refers to a lot of things. I mean, first of all, you can just think about it like whether you’re conscious or not – are you awake or not? Are you… have you lost consciousness? Are you blinking? Are you aware?
And then there’s also what you experience when you’re aware of it, so there’s this sense of subjective first-person perspective that is sort of the source of a lot of the mystery here. It’s like, “Why, as I sit here, I see through my eyes and I have a holistic, unified experience of me as a person, and it’s connected to every other state I’ve ever been in, and it’s sort of this unified flow?”
We don’t know exactly how it leaves the brain, because the brain is a very complex piece of physical matter. So there’s this age-old question in philosophy of mind and philosophy of science and everything, [which] was like, “How are the mind and brain connected? Are they basically the same things, or are they two separate things?” It’s like this war between this idea of dualism, where, like, the mind is something separate from the brain and there’s, like, a gap between what you can explain by just looking at the physical object, and this idea of materialism, which is, like, everything that we are, everything that we perceive goes back to the physical matter of our brain.
Science tends to align itself with materialism, simply because it’s almost an assumption that you have to make in order to do something. But it’s been very difficult for neuroscientists to really bridge that gap, to understand what our first-person experience means, where it comes from in the brain, how is it that the brain comes together to make this happen for us – it’s very difficult to explain, and nothing has really been proven. [Laughs]that is indeed what happened.
Pierre-Louis: One of the things I found interesting, as someone who has been under anesthesia, is that when we are under anesthesia or hallucinogens, we lose consciousness. But when we dream, which many of us consider an altered state, we are still linked to consciousness. Can you talk a little about it?
Parhall: That’s a very good question. I think about it a lot. I had to remove my appendix while I was telling this story, and I was trying to get them to do this test on me to see if I remained conscious because sometimes people can maintain a certain connection, and they didn’t know what I was talking about. I was a little disappointed. [Laughs.]
Pierre-Louis: [Laughs.]
Parhall: Some scientists propose a kind of multi-pronged dimension, as a way of thinking about consciousness. There are sort of three dimensions that I think of when we think about consciousness. The awakening of one of them: Are your eyes open, honestly? Like, are you blinking? Are you aware of this? Another problem is internal consciousness. So do you have any insight into yourself, not necessarily your environment, but your own internal states? Do you have some sort of monologue going on? And then, thirdly, connectivity, and that’s where it’s at: are you connected to your environment? Are you sending and receiving signals from your brain to your body about what your body experiences and how your body interacts with the world?
So, while dreaming, you are not awake or connected, but you have an internal awareness. So it’s sort of a special altered state of consciousness. Under anesthesia you really don’t have any of that, ideally, but sometimes people maintain a connection, and that’s a problem; we don’t want that to happen. But yes, it’s fundamentally quite different. Obviously, there is a question like: “Do you completely lose consciousness when you are under anesthesia?” but that’s a little out of my wheelhouse.
Pierre-Louis: So we talk a lot about the difficulty of defining consciousness, and one of the things that stood out to me was this beautiful quote from Marcello Massimini, a neurophysiologist at the University of Milan, who… I’m going to, like, read the quote verbatim because I thought it was so beautiful, when he talks about the brain…
Parhall: Me too.
Pierre-Louis: Like “an object with limits, with a given weight, a bit like tofu. It’s not particularly elegant”, but “inside this object that you can hold in your hand, there is a universe”, and I just feel like that really corresponds to the difficulty of what we’re trying to understand.
Parhall: Yeah, part of the reason I like this quote is because he was talking about his first experience in medical school with a brain. I never went to medical school, but I had a brain in college, and it shook me to my core because it was, like, it was someone – I think it was a woman – like, she’s a person, and I’m holding her, and, like, she’s not a person anymore.
There’s this interesting thought experiment from the philosopher Gottfried Leibniz, who sees the mind as an analogy to a mill, a mill that grinds…
Pierre-Louis: Like a grain mill.
Parhall: A grain mill, yes. And the question is if you could walk into your brain like you can walk into a mill and see all these, not levers but, you know, mechanistic things happening, the question is, “Where would you see the thought? Like, where would the thought emerge?” But it’s like… it’s a bit circular, isn’t it, because then you’re a being inside the mill, and you have a subjective experience, it’s a bit of a mess.
I think that’s why this topic is so fascinating to people and why this is so compelling to me: how do we bridge this gap? Some scientists think it’s impossible. And so that’s kind of where a lot of the story comes from: can we close this gap? Are scientific tools even capable of allowing us to understand what is happening when we fundamentally try to understand our own experience?
This is where the article’s tagline comes in, like “The Hardest Problem.” There is this idea of consciousness as a difficult problem. There is, for example, a simple problem: “Can you look at the brain and determine which areas are related to consciousness?” But then the larger question arises: “How does this subjective quality emerge?” Philosophers sometimes call this “the hard problem,” and I think there’s a case to be made that it’s one of the hardest problems for science to solve because we are fundamentally subjective beings who look outward from our inner selves and are locked in and we are, in this case, trying to access something that is fundamentally locked in. It’s very difficult to measure.
Pierre-Louis: It looks like this.
I know in this article you present several theories about where consciousness is located, and most of these theories look at different aspects of the brain. But one theory I wanted to highlight was integrated information theory. [IIT] …
Parhall: Yes.
Pierre-Louis: This is a mathematical and philosophical theory that stands out in some way. Can you talk about this theory?
Parhall: Yeah, you said it right: a lot of theories of consciousness look at the brain and look at which areas light up when you’re consciously aware of something versus where you’re not and basically squeeze the juice, as some say, squeeze the juice of consciousness out of the brain.
This theory is very interesting because it takes a rather opposite approach. It begins with our subjective philosophical observations of what consciousness looks like…
Pierre-Louis: Mm-hmm.
Parhall: And I try to sort of boil it down to a few principles. There are therefore five principles; I won’t go through them all. But ultimately they come down to this idea that your consciousness is unitary, so you only experience one stream of consciousness…
Pierre-Louis: Mm-hmm.
Parhall: Anytime. Even though, for example, you might feel like you have a toothache and also worry about your mother, and, and these are two separate things that you can separate, you experience them as a whole. So this is the g ent of intuition they draw there. And also this idea that it’s very rich in information. So even if you close your eyes, from an information theory perspective, there are many things that differentiate one state from another. For example, if I watch a film and I perceive one scene compared to the next scene, it is even very different. And these two ideas that everything is integrated and everything is very information-rich…
Pierre-Louis: Mm-hmm.
Parhall: It’s kind of like where the theory gets its name from, because when you combine those two things, you can say, “Okay, this is all about integrated information.” »
Now I feel like I’m already starting to lose the plot a bit…
Pierre-Louis: [Laughs.]
Parhall: Because we’re getting so abstract, but what that means in practice is you’re applying that to the brain – which is not, like, an insubstantial leap; To be clear, there is some extrapolation here – we all have these brain networks…
Pierre-Louis: Mm-hmm.
Parhall: And these brain networks communicate with each other and contain a lot of information, and then they transmit a lot of information between them. And one of the things that happens when you lose consciousness under anesthesia or in other forms, for example when you fall into dreamless sleep, is that these networks sort of stop talking to each other. Basically, your brain somehow operates with integrated information. When we lose consciousness, it is less integrated. Therefore, this is part of the reason why you lose consciousness.
And it’s a little weird, but we’ve developed some pretty interesting measures to study this, so there’s a way to use a magnetic coil to zap parts of the brain and see what happens. In [a] In a fully awake brain, there will be sort of ripples upon ripples upon ripples that propagate because everything is so information-rich and integrated. In an unconscious brain or in a brain that is perhaps in a minimally conscious state following a brain injury, you see a lot less of these ripples.
So they tested that and, like, developed these measures to be able to sort of see what level of consciousness a person is at. But that can’t really explain, for example, if you’re fully aware, what the difference is between having a toothache and hearing the siren outside that’s so loud it makes your ears ring. Like this difference in what they call qualia, or, like, the qualitative state…
Pierre-Louis: Mm-hmm.
Parhall: It’s very difficult to assess.
Pierre-Louis: Does that also suggest, because I feel like we’re in a moment with all of this, like AI speaks where people – and, you know, we grew up with…
Parhall: Mm-hmm.
Pierre-Louis: Movies like The terminator– where people really want to believe that machines can be conscious, and this model also, because it doesn’t come directly from the brain, suggests that in theory we could create a conscious network?
Parhall: Yes and no. [Laughs.]
Pierre-Louis: [Laughs.]
Parhall: I think there are some ways in which this theory, because it doesn’t assume that consciousness needs a brain, right…
Pierre-Louis: Mm-hmm.
Parhall: That’s one of the reasons why it’s sometimes criticized, and I don’t know if it’s a very fair criticism, but the idea that, like, “Oh, if consciousness is just a matter of information, you could imagine a computer chip that is conscious,” it’s like, “Well, yeah, okay, sure, we could go to the extreme.” »
The prominent thinkers who support IIT right now don’t think our current major linguistic models could do this, in part simply because of their structure. Basically, it comes down to this: these computer chips aren’t actually integrated one way or another; they simulate integrated neural nodes. And it’s a little difficult to cut hair. Proponents of this theory don’t necessarily think that, like the ChatGPTs, you know, they’re on the verge of becoming conscious.
But this question of AI is, I think, really what has driven a lot of my interest in understanding where the field of consciousness research is right now, because it kind of lights the fire in everyone, right? For example, when Google’s LaMDA model, the machine said it was sensitive…
Pierre-Louis: Mm-hmm.
Parhall: A lot of people were turning to these consciousness researchers and asking, “Okay, what have we learned about consciousness? Can you extrapolate it from the brain to these machines?” And most AI people don’t think AI is close to consciousness, but I think it really highlights some of the limitations of neuroscientists’ understanding of consciousness, which is that you can’t take it out of the brain. And even theories that don’t involve the brain have a really hard time figuring out, like, what ground truth elements are we going to transfer from our brain theory to the AI theory?
Pierre-Louis: I guess my final, very pressing question: Is my sister’s cat conscious? [Laughs.]
Parhall: [Laughs.] Well, the question of consciousness of non-human animals is also one that has gained a lot of momentum in the past, about five to ten years. We’ve come a long way since the ’90s, according to the sources I spoke to, where we could really only assume that the only animals that had consciousness were humans because we can’t ask the cat, can we? But we can do carefully designed experiments so that the most parsimonious explanation is that this animal is conscious. And we did them, and we did them – also neurobiological studies. And I think at this point there’s a pretty broad consensus that all mammals are [probably] aware.
Just because they are conscious beings navigating the world doesn’t mean they have the cognitive capacity to threaten us or anything. And it’s exactly the same case with AI: just because they’re able to do things that humans can’t do and they’re considered quite intelligent, if you want to give them that, doesn’t mean there’s a first-person subjective conscious experience.
And then there’s another important distinction to make, which is that, as I said, the English word for conscience is really complicated…
Pierre-Louis: Mm-hmm.
Parhall: And that sort of encompasses both this sense of being an agent in the world, like sentience – like, a rock isn’t sentient, but a nematode probably is – with self-awareness, like this self-awareness and this ability to think back to oneself and reflect. When animal consciousness researchers talk about consciousness, they are simply talking about sentience.
And so there’s a question like, okay, at this point, a lot of researchers I’ve talked to have said that the boundary is sort of with fish and insects…
Pierre-Louis: Mm-hmm.
Parhall: So this is where the main question area lies. For example, we practically ran mammals. Fish and insects, we have some very interesting preliminary research that, for example, fish can recognize themselves in mirrors. It is not clear where the limit lies.
So all that to say that your cat is probably conscious, in my opinion. [Laughs] …
Pierre-Louis: [Laughs.]
Parhall: But what, what it will take for science to prove it, I think, illustrates very well some of the limitations of proving consciousness, anyway.
Pierre-Louis: Where can we find your work?
Parhall: You can find the feature article that this conversation was primarily based on at ScientificAmerican.com. It’s in the February 2026 issue of the magazine.
Pierre-Louis: Thank you very much for your time today.
Parhall: Of course. THANKS.
Pierre-Louis: That’s all for today. Join us Friday, when we explore the mystery of long-lost DNA.
Science quickly is produced by me, Kendra Pierre-Louis, with Fonda Mwangi, Sushmita Pathak and Jeff DelViscio. This episode was edited by Alex Sugiura. Shayna Posses and Aaron Shattuck check in on our show. Our theme music was composed by Dominic Smith. Subscribe to Scientific American for more recent and in-depth scientific news.
For Scientific American, This is Kendra Pierre-Louis. See you next time!
