An interesting article Coupling the State and Contents of Consciousness has me thinking of an idea that has been in the back of mind for a while – the temporal resolution of conscious experience. If different stimuli (different color flashing lights for example) are presented too quickly, they will either tend to fuse into one or, depending on timings, the second stimuli may mask the first. Research suggests that consciousness operates somewhat in frames with a lag time of somewhere between 50-100 milliseconds or more.
Before I get to that topic, however, let me discuss a little about the paper itself.
While most consciousness studies study state (wakefulness, sleeping, dreaming) or content of consciousness, this paper tries to unify state and contents and link both to activity of the cortical layer 5 pyramidal (L5p) neurons. “These neurons affect both cortical and thalamic processing, hence coupling the cortico-cortical and thalamo-cortical loops with each other. Functionally this coupling corresponds to the coupling between the state and the contents of consciousness.”
The most basic definition of consciousness involves wakefulness. A person in a coma or passed out from drugs or alcohol is not regarded as conscious. We could debate whether someone dreaming or in deep sleep is conscious, but the important point is that the state of consciousness is controlled by the reticular formation with its projections into the thalamus. Damage to cells in these areas will result in permanent coma. Unquestionable these areas of the brain must be intact for any consciousness to occur.
However, one cannot be awake and conscious without being conscious of something and vice versa. “One cannot be conscious of the coconut taste while being in an unconscious state. And the other way around: in typical healthy subjects, one cannot be in a conscious state while not being conscious of anything at all. In other words, contents of consciousness and states of consciousness make up an integrated whole. Studying one while disregarding the other can only provide half of an answer.”
Certainly most of the content or “action” of consciousness in mammals, however, occurs the cortex or outermost layer of the brain. The cortical layer 5 pyramidal (L5p) neurons are a type of neuron that links the thalamus to the cortex.
The paper makes two noteworthy related predictions:
- Cortical processing that does not include L5p neurons will be unconscious. More generally, the present perspective suggests that L5p neurons have a central role in the mechanisms underlying consciousness.
- Cortical processing in itself, when not integrated with the non-specific pathway thalamic nuclei via L5p neurons, is not conscious. In particular, feedforward cortical processing, where information is mainly flowing within the cortical superficial layers bypassing thalamocortical neurons, is non-conscious.
The paper cites several studies linking L5p neurons to states of consciousness and the contents of perceptions.
This paper is only one I have seen in recent years that has attempted to link with this degree of specificity a type of structure in the brain to consciousness and make what seem to be testable predictions. I think it is noteworthy in that regard. Probably someone will point out others and I can revise that statement.
The paper makes an additional observation regarding the temporal resolution of consciousness. Since “conscious perception is based on the processing within the thalamocortical loop, then it is hard for conscious perception to resolve anything that happens faster than the processing time of this loop. In other words, we claim that the temporal resolution of conscious experience stems from the propagation time between the L5p neurons, NSP [non-specific pathway] thalamus and higher cortical areas.” It also tries to explain backward masking where a second stimulus masks the first one from consciousness by this same lag.
This lag in processing has been on my mind for a while. In 2012, I wrote:
The fact is that everything we perceive really is phantasma. The red of the rose is not real. It is a particular wavelength of light. The sound of the distant thunder is not real. It is an acoustic wave moving through the air. Solid objects don’t really exist. We might kick a large rock and we might hurt our foot but physics says the rock is mostly empty space and the pain in our foot is the product of a nerve impulse. Our experiences are all in the past, delayed by a neurological time-lag and assembled into a coherent whole bearing perhaps no resemblance to what is actually “out there” in the world.
What if this time-lag isn’t a feature of consciousness but is the explanation for it?
Consciousness is what emerges to assemble experience into a whole because the pathway from the thalamus to the cortex takes time. What’s more, the bigger the brain, the longer the pathway, the longer the lag time, and… can we assume the more consciousness would be required. Does it even make sense to talk of more or less consciousness? I’m not sure. In this view, consciousness emerges as brains gets larger, not because there are more neurons or more information processing happening. It emerges as a remedy or fix for the lag time in the thalamocortical loop.
Is this idea original? Probably not.
It will be interesting to see if the predictions of this paper work out.
Have you read “The User Illusion”? It is not just a processing lag, but a data handling capacity which affects the “inputs” to our brain. Much of the data coming in has to be summarized or gleaned heavily just to be processable.
I am glad to be alive when the tools have become available to get tangible answers to some of these questions. I hope to be alive when a consensus picture arises for what consciousness is and how it is created. I suspect it is a consequence of a mental tool (my definition of a mind is a collection of mental abilities) being applied to itself again and again. (I suspect that tool is the ability to imagine.)
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Haven’t read that but I did just buy it.
I’ve had a suspicion for a while that consciousness is more of an accident or side effect than it is something fundamental in itself. I wrote on another post: “The development of consciousness may be more or less equivalent in the grand scheme of things to the evolution of eyes or ears. Quite remarkable and amazing but not something we should regard as sui generis.”
I just got the “The User Illusion” after some initial glitch at Amazon.
It looks like a pretty wide ranging book and I was surprised it was written more than 20 years ago. The “user illusion” is almost exactly the same as Hoffman desktop analogy of consciousness. I wonder if he borrowed it from this book or they came at it independently.
Really interesting. It occurred to me at a very young age that we are not experiencing actual reality, rather something that has already happened. Reality itself can never be lived. As for consciousness, I’ve always thought of consciousness as the mental delay/feedback, which I think is what you’re hitting at.
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