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 oddly enough, 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 disclosed the discovery of three giant neurons that connect much of the brain of mice; Such neurons could be the physiological basis of consciousness, but other experts disagree.

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The three giant neurons

Christof Koch and his team gave a presentation to members of the neuroscientific community in which presented the methodology and results of their research on neuronal connectivity in the brains of mice.

The most outstanding 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 reaches 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 investigation, 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 coordinating the electrochemical impulses of 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 claims of Koch's team.

• Related article: "Parts of the human brain (and functions)"

What is the cloister?

The cloister is a layer of neurons attached to the lower face 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.

Not only do neurons in the cloister maintain relevant connections with other parts of the brain, but they are also very closely connected to each other. This has been associated with the uniform processing of stimulation passing through the cloister.

Koch's team proposal

Drawing on his recent research and others he had previously collaborated on, Koch defends that consciousness could be located in the cloister, which has been the main focus of her professional career.

According to the proposal of this team, the three giant neurons that they have found would allow the coordination of nerve impulses in the cloister: associate the reception and sending of signals from this structure with the appearance of the consciousness, taking into account the globality of this transmission and the functions that have been attributed to the cloister.

Another relevant research for 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 by electrodes "deactivated" consciousness of the patient, while the interruption of said stimulation made her regain it.

Investigation methodology

The Allen Institute research team triggered the production of fluorescent proteins in individual neurons originating from the cloister of various mice. For this they used a substance that, being present in the body, caused the activation of certain genes.

By propagating through the target neurons, these proteins gave the entire length of these cells a distinctive color. They later 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 experts in the neurosciences have disagreed with Koch's team's proposal. In a general way, the localizationism of his hypothesis has been criticized, which attributes to the cloister the main role in human consciousness without relying on a solid research base.

To study the veracity of these statements, Chau et al. (2015) carried out a study with 171 war veterans who had suffered head injuries. They found that injuries in the cloister were associated with a slower recovery of consciousness after damagebut not with more serious long-term sequelae.

At the moment the evidence in favor of the hypothesis that the cloister is key to consciousness is inconclusive, especially when it comes 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.

Bibliographic references:

• Chau, A.; Salazar, A. M.; Krueger, F.; Cristofori, I. & Grafman, J. (2015). The effect of claustrum lesions on human consciousness and recovery of function. Consciousness and Cognition, 36: 256-64.

• Crick, F. C. & Koch, C. (2005). What is the function of the claustrum? Philosophical Transactions of the Real Society of London B: Biological Sciences, 360 (1458): 1271-79.

• Koubeissi, M. Z.; Bartolomei, F.; Beltagy, A. & Picard, F. (2014). Electrical stimulation of a small brain area reversibly disrupts consciousness. Epilepsy & Behavior, 37: 32-35.

• 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.