Sensory Transduction and Subjective Experience: Expression of eight genes in three senses suggests a radical model of consciousness
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- University of Auckland
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- Date:
- Received 29 December 2007 22:36 UTC; Posted 01 January 2008
- Subjects:
- Genetics & Genomics, Neuroscience
- Abstract:
Recent research into whole genome mapping of the mouse brain has made possible direct investigation of the brain expression of unusual genes. A search of the Allen Brain Atlas database has provided genetic and neuro-anatomical evidence for widespread specific expression in the brain of eight genes specific to sensory transduction, in vision, hearing and touch. A novel biophysical model is proposed for the function of these proteins, in generating the internal model of experiential reality.
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9 comments
I can accept the sensory part of your argument all right, but don’t see how you can say anything about consciousness. Consciousness is not just about sensation but rather more about integration, and I did not get that from your article.
To Camilo: We currently have no explanation for which physiological processes support subjective consciousness. Purely internal mental states, such as dreaming, are capable of manifesting the full sensory experience of the uniquely different qualia of visual and auditory perception. Electrophysiological excitation alone doesn’t explain these deep qualitative differences. Ultimately the differences between the senses arise form the very different types of quantum transformation involved, e.g. in sight and sound. Since sensory genes are paradoxically expressed in the CNS, a compact explanation is that the brain may be using them to elicit distinct quantum transformations in each sense mode, possibly of a resonant nature, to evoke the diverse qualitative manifestations of subjective experience.
To Kojiro: Yes consciousness is also about integration, but it is the integration of subjective sensory experiences, even when these are purely internal mental states. The ‘Cartesian theatre’ is richly colourful and sonorous. To explain how the brain can evoke a complete conscious experience may require the same biophysical transformations.
Without further meta-analysis of the gene regulatory mechanisms controlling the expression of these genes, it is very difficult to even say that there is something unique and special amongst the expression patterns of these genes. Many CNS genes are under the control of the REST transcriptional repressor, which is active in all cells that are NOT neurons. In CNS cells, REST is inhibited or eliminated, releasing the “brake” on neuronal gene expression. Without further control, it is possible that some (many) genes involved in transduction can be expressed in cell types that have nothing to do with sensory activities due to the leakiness of releasing the “brake.” However, this does not mean that therefore, these genes take on a greater role, like in consciousness. Your view ignores the fact that leakiness in the gene expression systems throughout the body cause the expression of thousands of gene products in places and cell types that may have no use for that particular protein.
In fact, several of the genes you identify are not even specific to the CNS, calling into question why some consciousness genes would be expressed in the gut, for instance, unless that is where the seat of consciousness lies (but I’ll leave that for the tantra philosophers to decide…).
To Noah: Your critique is a good one and a meta-analysis is a desirable step to clarify which (if any) of these genes are functionally active in the CNS. However their expression does show anatomical specificity and some opsin variants do have known CNS expression e.g. in the pineal. As an interesting example, the gene KLK8 making a splice variant opsin, neuropsin II, implicated as vital in mouse memory and learning is also present in humans, although absent in apes, and is thus cited as a trigger for human emergence – (Human Mutation, DOI: 10.1002/humu.20547)
Chris, this is a common mistake researchers make about KRK8, it is not an opsin, it was simply called neuropsin as a mistake but it is a serine protease as opposed to G-coupled protein receptor… OPN5 is an Opsin, also called neuropsin, but since this has caused so much confusion, researchers are now distinguishing them as KRK8 and OPN5 rather than using the term Neuropsin. I read your paper, I think this kind of outside thinking is needed for neuroscience, but you have to be careful…
Dear Noah Gray,
Are there some genes related to consciousness that are expressed in the gut / enteric nervous system? Will you be able to elaborate?You might be aware about the suggestion [may see reference 5 cited in the link given below] that ENT might be the brain of tubular animals. Was this suggestion already made by tantra philosophers?
[1] http://en.wikiversity.org/wiki/User_talk:DMR_Sekhar
Also Jiddu Krishna Murty [not a tantric] is of the opinion that there is no specific body part/location in the body [including brain] that is responsible for the consciousness.
Thanks,
DMR Sekhar.As noted in previous comments, one line of caution about interpreting actual function of genes expressed in the brain is that neuronal cells have relatively open transcription, due to the very low levels of REST, the zinc finger protein RE-1 silencing transcription factor in neuronal cells. The transcriptional repressor REST (Eur. J. Biochem. 271, p2855 2004) controls neuron-specific gene transcription via recruitment of histone deacetylases. “In neurons, only very low levels of REST can be detected. In fact, a decrease in the REST concentration during neuronal differentiation is most probably the essential prerequisite for transcription of neuronal genes. The chromatin configuration of neuronal genes is open, due to an extensive acetylation of the core histones. Transcriptional activators, as well as the RNA polymerase II complex, can gain access to the DNA and trigger gene transcription. In non-neuronal cells, however, REST is present and binds in a sequence-specific manner to several neuronal genes.”
The relatively open transcription of neuronal cells has led some researchers to suggest that transcription in neurons is not a reliable indicator of gene expression since the relaxation of REST allows for wholesale expression of neuronal-related genes, which may not be actually translated due to RNA processing after transcription. This however runs counter to the fact that neurons, participating in the most complex finely tuned organ of all – the brain – need to have corresponding acuity of gene transcription. The idea that neurons are simply an open Pandora’s box of randomly transcribed genes is not an accurate assessment.
Other evidence suggests that the influence of RNA may occur at a pre-transcriptional level and in a highly elegant manner that would permit just the sort of very specific gene expression required in the brain. Kuwabara et. al. (Cell 116:779-93 2004) describe a small dsRNA that activates the expression of neuron-specific genes at a transcriptional level and that alone is capable of inducing the differentiation of neuronal progenitor cells into neurons. This RNA may represent the first member of a group of small RNAs that directly modulate gene expression at the transcriptional level. Intriguingly, this RNA, which is expressed in the nucleus, rather than the cytoplasm where most miRNAs and siRNAs are found, neither inhibits expression of REST (not having sequence correspondence with REST mRNA), nor does it inhibit REST’s binding to DNA transcription sites, but rather alters REST’s activity, from binding to other repressors, such as CoREST 31 to binding with activators of gene expression.
The purpose of the current paper is not to establish beyond doubt that sensory transduction molecules are functionally expressed in the brain, but simply to show that gene expression at the level of anatomical investigation is consistent with this idea. Several of the genes cited, particularly rhodopsin, appear to be functionally transcribed as their pattern of occurrence is anatomically specific and in the latter case, correlated with the visual cortex, suggesting that at least some of these candidates do have functional expression in the CNS.
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King, Chris. Sensory Transduction and Subjective Experience: Expression of eight genes in three senses suggests a radical model of consciousness. Available from Nature Precedings <http://hdl.handle.net/10101/npre.2007.1473.1> (2007)
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Camilo Libedinsky on 02 January 2008 06:25 UTC
Let me see if I understood your main argument correctly. Let us focus on vision. If some opsin is responsible for phototransduction in a retinal photoreceptor, and this same gene is expressed in, say, primary visual cortex, are you saying that activity of these opsin-expressing cortical neurons are responsible for phenomenal consciousness? If so, why?