Giant Neurons Associated With Consciousness Discovered
What is the nature of consciousness? This is one of the great mysteries of psychology, neuroscience and the philosophy of mind, and although it may seem curious, research on animals, whose sense of consciousness has to be somewhat different from ours, has helped to clarify it.
In fact, recently a team of researchers from the Allen Institute for Brain Sciences led by Christof Koch has reported the discovery of three giant neurons that connect much of the brain of mice; These neurons could be the physiological basis of consciousness, but other experts disagree.
Christof Koch and his team gave a presentation to members of the neuroscientific community in which they presented the methodology and results of their research on neuronal connectivity in mouse brains.
The most notable aspect of his presentation was the identification of three giant neurons that arise from the brain structure known as the “cloister” and connect it with a large part of the brain. The largest of the three comes to surround the entire brain while the other two also cover a significant portion of the hemispheres.
As revealed by the three-dimensional images obtained from the research, these three cells maintain strong synaptic connections with neurons in many different regions of the brain. This suggests that they may play a relevant role in the coordination of electrochemical impulses in the central nervous system.
However, for the moment The existence of these three neurons has not been confirmed in other species animals, including humans, so great caution must be exercised when attempting to generalize the Koch team’s claims.
The claustrum is a layer of neurons attached to the lower surface of the cerebral neocortex, very close to the insula and the basal ganglia; It is sometimes considered a part of this structure. Its amplitude is irregular, measuring several millimeters in some areas and much less than a millimeter in others.
This region of the brain synapses with many cortical and subcortical structures including the hippocampus, essential for long-term memory, and the amygdala, involved in emotional learning.
Neurons in the claustrum not only maintain relevant connections with other parts of the brain, but are also very closely connected to each other. This has been associated with the uniform processing of stimulation passing through the cloister.
The Koch team’s proposal
Based on his recent research and others on which he had previously collaborated, Koch defends that consciousness could be located in the cloister which has been the main focus of his professional career.
According to this team’s proposal, the three giant neurons they have found would allow the coordination of nervous impulses in the cloister: they associate the reception and sending of signals from this structure with the appearance of consciousness, taking into account the global nature of this transmission and the functions that have been attributed to the cloister.
Another research relevant to this hypothesis is the one carried out by Mohamad Koubeissi’s group (2014) with a woman affected by epilepsy. This team found that Stimulation of the cloister using electrodes “deactivated” consciousness of the patient, while the interruption of said stimulation caused her to recover it.
The Allen Institute research team triggered the production of fluorescent proteins in individual neurons originating from the claustrum of several mice. To do this, they used a substance that, when present in the body, caused the activation of certain genes.
By spreading through the target neurons, these proteins provided the entire length of these cells with a distinctive color. They then took 10,000 images of sections of the brains and used computer software to create three-dimensional maps of activated neurons
Criticisms of this hypothesis
Various neuroscience experts have disagreed with the Koch team’s proposal. In general, the localizationism of his hypothesis has been criticized, which attributes the main role to the cloister in human consciousness without being supported by a solid research base.
To study the veracity of these approaches, Chau and collaborators (2015) carried out a study with 171 war veterans who had suffered traumatic brain injuries. They found that injuries to the cloister were related to a slower recovery of consciousness after damage but not with more serious long-term consequences.
At the moment the evidence in favor of the hypothesis that the cloister is key to consciousness is inconclusive, especially when we refer to human beings. However, the evidence does suggest that this structure may be relevant for attentional control through the connection of different regions of both cerebral hemispheres.
Torgerson, C.M.; Irimia, A.; Goh, S.Y.M. & Van Horn, J.D. (2015). The DTI connectivity of the human claustrum. Human Brain Mapping, 36: 827-38.
