For the first time, scientists have detected a giant neuron wrapped around the entire brain circumference of a mouse, and it is so closely connected across both hemispheres that it could finally explain the origins of consciousness.
Using a new imaging technique, the team detected the giant neuron emanating from one of the best-connected regions of the brain, and said it could be to coordinate signals from different areas to create a conscious thought.
This newly discovered neuron is one of the three that has been detected for the first time in a mammalian brain, and the new imaging technique could help us determine if similar structures have gone unnoticed in our own brain since centuries.
At a recent meeting of brain research through the advancement of innovative neurotechnology initiative in Maryland, a team at the Allen Institute for Brain Science described how the three neurons extend across both hemispheres of the brain, and the larger one wraps around the circumference of the organ like a “crown of thorns.”
You can see them highlighted in the image at the top of the page.
Principal Investigator Christof Koch told Nature’s Sara Reardon that he had never seen neurons in the two brain regions before.
Curiously, the three giant neurons come from a part of the brain that has shown intriguing connections to human consciousness in the past – the claustrum, a thin layer of gray matter that could be the most connected structure in the entire brain, based on the volume.
This relatively small area is hidden between the inner surface of the neocortex at the center of the brain communicating with almost all regions of the cortex to achieve many higher cognitive functions such as language, long-term planning and advanced sensory tasks such as vision and hearing.
“Advanced brain imaging techniques that examine the white matter fibers circulating to and from the claustrum reveal that it is a large neural central station,” Koch wrote for Scientific American in 2014. “Almost all regions of the cortex send fibers to the cloister. “
The claustrum is so closely related to several crucial areas in the brain that Francis Crick renamed this double DNA helix a “consciousness driver” in a 2005 paper co-authored with Koch.
They suggested that he link all our external and internal perceptions into one unifying experience, as a conductor synchronizes an orchestra, and strange medical cases in recent years have reinforced this suggestion.
In 2014, a 54-year-old woman was admitted to the Medical Faculty Associates of George Washington University in Washington, DC, for treatment for epilepsy.
This involved gently probing different areas of her brain with electrodes in order to refine the potential source of her epileptic seizures, but when the team began to stimulate the woman’s claustrum, she discovered that she could actually ‘disconnect’ his consciousness.
Helen Thomson reported for New Scientist at the time:
“When the team touched the area with high frequency electrical impulses, the woman lost consciousness, she stopped understanding and stared into space, she did not respond to auditory or visual commands and her breathing slowed down. As soon as the stimulation stopped, she immediately regained consciousness without remembering the event. The same thing happened every time the area was stimulated during the two days of experiments. “
According to Koch, who was not involved in the study, this type of abrupt and specific stopping and starting of consciousness had never been seen before.
Another experiment in 2015 examined the effects of claustrum injury on the awareness of 171 combat veterans with traumatic brain injury.
They found that claustral damage was associated with the duration, but not the frequency, of unconsciousness, suggesting that it could play an important role in the activation and deactivation of conscious thought, but another region could be involved in its maintenance.
And now, Koch and his team have discovered extended neurons in the mouse brain emanating from this mysterious region.
In order to map neurons, researchers usually need to inject individual nerve cells with a dye, cut the brain into thin sections, and then trace the path of the neuron by hand.
This is a surprisingly rudimentary technique for a neuroscientist, and since they must destroy the brain in the process, it can not be done regularly on human organs.
Koch and his team wanted to develop a less invasive technique and design mice that could have specific genes in their claustral neurons activated by a specific drug.
“When the researchers fed the mice a small amount of medication, only a handful of neurons got enough to activate these genes,” says Reardon in Nature.
“This resulted in the production of a green fluorescent protein that spread throughout the neuron.” The team then took 10,000 transverse images of the mouse brain, and used a computer program to create a 3D reconstruction of the brain. only three bright cells. “
We need to keep in mind that just because these new giant neurons are connected to the claustrum does not mean that Koch’s hypothesis on consciousness is correct – we are far from proving it.
It is also important to note that these neurons have only been detected in mice so far, and the research has yet to be published in a peer-reviewed journal, so we have to wait for further confirmation before we can really study this discovery for what it means for humans.
But this discovery is an intriguing piece of the puzzle that could help make sense of this crucial but enigmatic region of the brain, and how it might relate to the human experience of conscious thought.
The research was presented at the February 15 meeting of the Brain Research through Advancing Innovative Neurotechnologies initiative in Bethesda, Maryland.