The sixth sense: Are there genes associated with it?
Last Updated on December 13, 2022 by Joseph Gut – thasso
December 11, 2022 – We’re all familiar with the five senses that allow us to experience our surroundings, namely sight, hearing, smell, taste, and touch. However, equally important but much less well known is the so called Sixth Sense. Sixth sense stands for extrasensory perception or ability pertaining to reception of information not gained through the recognized physical senses mentioned above, but sensed with the mind.
Thus, in order to perform coordinated movements, we rely on special sensory neurons in our muscles and joints. Without them, the brain wouldn’t know what the rest of our body was doing or where in space we are, which, at times, may be important information to have, such as, for example, for athletes in plain competitions on the highest level possible. As some recents studies (overviewed and databased here) suggest, the involved circuits and pathways which make up for this particular sense, also known as proprioception, are thought of sharing some biological mechanisms with aging, cognition, habituation, innervation, sensitization, sensory-perception, sensory-processing, and spatial visual-perception to name only a few. Similarly, quite a number of genes have been thought to play roles in proprioception, such as ACLY, BDNF, CARD16, CAT, CRAT, FLT4, GLYAT, GRIP, and many more. In most cases however, it remained unclear how exactly these genes would relate to the phenomenon “Sixth Sense”. One important study has now shown that, using a twins model, there exist a heritability of proprioception and that genetic and environmental factors that contribute to this complex
human trait can effectively be disentangled. The study revealed that proprioception, expressed as movement sense, position sense, and force sense, is substantially heritable, and it is conceivable that this may have implications for motor learning and control, neural development, and neurorehabilitation.
Overall, the sixth sense (or proprioception) is what allows the central nervous system to send the right signals through motor neurons to muscles so that we can perform a specific movement and orient ourselves in space. This sense is entirely unconscious and is what stops, at least some of us, from falling over in the dark, what allows us to raise a cup of coffee to our mouth with our eyes shut in the morning, or what allows us to jump off the balance beam and re-land on it safely after a somersault. But seemingly, that’s not all: People without proprioception can’t actually perform coordinated movements at all.
That is why the work of a research team in Germany who recently published in Nature Communications its findings on how molecular markers may collect information from our muscles and joints about our movements, our posture and our position in space, and then pass that on to our central nervous system becomes so important. They describe the molecular markers of the cells involved in this “sixth sense”. The findings should help researchers to better understand how proprioceptive sensory neurons (pSN) work.
Precise connections are crucial
The pSN cell bodies are located in the dorsal root ganglia of the spinal cord. They are connected via long nerve fibers to the muscle spindles and Golgi tendon organs that constantly register stretch and tension in every muscle of the body. The pSN send this information to the central nervous system, where it is used to control motor neuron activity so that we can perform movements. However, up to now, almost nothing was known about the molecular programs that enable these precise connections and lend the muscle-specific pSN their unique identity. So, the research team specifically looked for molecular markers that differentiate the pSN for the abdominal, back and limb muscles in a mice experimental design.
Guidance for nascent nerve fibers
Using single-cell sequencing, the team investigated which genes in the pSN of the abdominal, back and leg muscles are read and translated into RNA. They found characteristic genes for the pSN connected to each muscle group. They also showed that these genes are already active at the embryonic stage and remain active for at least a while after birth. This may mean that there are fixed genetic programs that decide whether a proprioceptor will innervate the abdominal, back or limb muscles.
The team identified several genes for ephrins and their receptors which are involved in guiding nascent nerve fibers to their target during development of the nervous system. The team found that the connections between the proprioceptors and the rear leg muscles were impaired in mice that can’t produce ephrin-A5.Both ephrins and ephrin (Eph) receptors are membrane-bound proteins that require direct cell-cell interactions for Eph receptor activation. Eph/ephrin signaling has been implicated in the regulation of a host of processes critical to embryonic development including axon guidance, formation of tissue boundaries, cell migration, and segmentation. Additionally, Eph/ephrin signaling has been identified to play a critical role in the maintenance of several processes during adulthood including long-term potentiation, angiogenesis, and stem cell differentiation and cancer. It would be phantastic to more precisely know the role of genetic (allelic) variants of ephrins and receptors in the development and the interindividuel differences in the sixth sense.
See here a sequence on the “sixth sense”, a topic not yet easily to comprehend, with or without genes behind it:
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