You Actually Share Your Brain With a Silent Stranger

CGP Grey7 HN recommenders · 2016–2025
20.2M views · explainer · evergreen · Uploaded 2016-05-31

CGP Grey explains split-brain patients, where severing the corpus callosum lets the two hemispheres act independently. He uses this to explore the idea of two minds in one head.

HN returns to it constantly in consciousness and decision-making threads as a clear, entertaining explanation of split-brain.

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12 comments from Hacker News

@BoppreH2016 · in “My Subconscious Is a Better Developer Than I Am”

For mind bending check the great explanation from CGP Grey, "You are two"[1], which argues the two brain hemispheres can operate independently. [1]: [VIDEO]

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@branchless2016 · in “My Subconscious Is a Better Developer Than I Am”

You are two [VIDEO] I always come up with good ideas when relaxed, usually when not working on the problem (showering / running). God why are they working us to death?!

@otto_ortega2017 · in “Split Brain Does Not Lead to Split Consciousness”

If you just learned that "Split Brain" was thing, I recommend watching this video by GPGrey, one of the best educational channels on YouTube: [VIDEO]

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@glenneroo2018 · in “The limits of information (2014)”

Kurzgesagt[0] and CGP Grey[1] did a fun little 2-part intro into "split mindedness" i.e. the idea that we may have multiple consciousnesses(?) contending for control. [0] [LINK] [1] [VIDEO]

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@teddyh2019 · in “Self-distancing can help you make better decisions”

> how can there be two selfs in a single mind. Oh wow, do I have a YouTube video for you: [VIDEO] ( You Are Two , by CGP Grey)

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@surround2020 · in “A man who can read letters but not numbers exposes roots of consciousness”

This reminds me of two mind-boggling discoveries I’ve had about the human mind. The first is that the two halves of your brain act somewhat independently. And in rare cases, people’s left and right halves are “split” apart, and they act entirely independently - e.g. their left and their right hands will act separately, or even argue with each other. CGP Grey made a great video about this: [VIDEO] The other is that most people have a “voice” inside their head - e.g. when they read, they hear their own voice inside their head reading; their thoughts are like sentences they “hear;” they could look in the mirror have a conversation with themselves. Some ~10% of people do not have this internal monologue. [LINK] [LINK]

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@midjji2021 · in “Making the hard problem of consciousness easier”

Is it hard though? Or is the hard part ethics i.e. personhood, and because the terms are conflated that makes consciousness hard, since it means you cannot accept what consciousness is without needing to also define ethics. Drop the idea that consciousness is sufficient or required for personhood in favor for something more behaviourally consistent like cuteness or power, and things become clearer. There is a part of you which simulates social interaction by learning models of various other agents it has inferred the existence of. As can be expected from something which is looking for agents based on indirect clues, we know this part does struggle with accidentally assigning agency to things which clearly lack consciousness i.e that damned sharp rock you stepped on twice. This part of you is capable of simulating a finite number of simultaneous such agents at a time, meaning it will focus on, as a whole, being able to predict the actions of the agents most often observed. It is also why we would expect it to replace groups of people you only interact with as a group as a "them". It is also very common that the most significant agent to simulate would be you. Hence one of the models being simulated is you. This is what generates the perception of consciousness, why it is you yet separate. It predicts the cognitive bias of the mind body duality, yet maintains the perception of consciousness. A part of you is constantly trying to explain your own actions, but critically, while w

@tick_tock_tick2021 · in “Spinoza’s God: Einstein believed in it, but what was it?”

Every time someone brings up consciousness I like to bring up [VIDEO] . Split brains imply some very interesting ideas around of consciousness.

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@throwaway30932023 · in “If I Know what's good for me, why am I sabotaging myself?”

Also, neurologically you are not one person. You are two: [VIDEO] It's not hard to imagine the nearly constant competition that erupts between neural sub-networks in your brain -- their collective output signals vying to be the dominant signal. Just stand in front of a bowl of ice cream and try to predict whether you will or won't actually eat it. (Impulse control, etc) Sensory awareness is helpful towards guiding these competitions and impulses into a direction (and a longer term habit) that is more aligned with your longer-term values. Also helpful: engineering your environment. [LINK]

@patmorgan232023 · in “Decades-long bet on consciousness ends – it’s philosopher 1, neuroscientist 0”

You're probably right. We have a couple examples of this happening. There's the interesting quarks that people with split brain hemispheres experience. [VIDEO] And dissociative identity disorder where there arguably multiple consciousnesses inhabiting the same brain. It is probably an evolutionary advantage that humans have a ( mostly) uniform singular consciousness.

@teekert2024 · in “New research on anesthesia and microtubules gives new clues about consciousness”

Consciousness must be much more high level than microtubules and quantum effects. I think the split brain "experiments" (not really experiments [0, 1]) are much more useful than the experiments presented in tfa. [0] [LINK] [1] [VIDEO]

@alexpotato2025 · in “The language brain matters more for programming than the math brain? (2020)”

This reminds me of the following quote: "Coding largely involves the 'logical part' of your brain. It tends to not include the 'language part' of your brain. This is one reason why comments you add to code are so useful: they force you to engage both parts of your brain and therefore get better results. This is also why when you go to explain a problem to a colleague, you often have a flash of brilliance and solve the problem: you are reframing the problem using a different part of your brain and the different part of your brain helps solve the problem." I'm sure some readers here will say this is preposterous and there is no such thing as having "two parts of your brain". To them I suggest watching: 1. "You are are two" (about people with their corpus callosum being severed) [VIDEO] 2. "Conscious Ants and Human Hives" by Peter Watts [LINK]

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