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.