Do two consciousnesses appear when dividing the brain?

One of the most important therapeutic advances in the field of epilepsy and neurosurgery is the section of the hard body. This structure links the two hemispheres and, among other things, allows information from one side to pass to the other. It also allows the electrical activation of epilepsy to spread, so that its section and separation of the two hemispheres prevents the epileptic seizures from going further.

What happens when we cut the brain in two? It has been described how the disconnect between the two brain hemispheres causes difficulties and changes in the execution of tasks that require the integration of information. When this happens, it acts as if one part of the brain knows the information and the other does not, as if we have a double brain. Can we speak, then, of a double consciousness?

The divided brain

When the researchers tested the visual functions of callosotomy patients, they found a curious phenomenon. Apparently, when we present an object to them in their right visual field, they are able to recognize it and point to it both verbally and by raising their right hand. However, when the object to be recognized is in the left field, while the patient claims to see absolutely no object, his left hand points to it.

This apparent contradiction is quickly resolved if we know that control over the body is crossed.: The right hemisphere controls the left part of the body, while the left hemisphere controls the right part. In this way, when the object is presented in the right field, the left hemisphere responds by raising the right hand and verbally, since speech is on the left side. On the other hand, when the object is in the left field, the right hemisphere responds by lifting the left hand, but cannot express it verbally because the language is housed in the other hemisphere.

However, this view of the phenomenon of brain divided is not as conclusive as we would like. The evidence in favor of this phenomenon is limited and less and less due to the fact that today we have better alternatives to callosotomy to treat epilepsy. This generates replicability problems that are difficult to overcome. On the other hand, there are doubts about whether the classic cases described in the literature are really as representative as they pretend, since that within the already small sample of callosotomized patients there are exceptions that do not comply with what is predicted according to the theory.

Theories about consciousness

The two most relevant theories for understanding the split brain phenomenon are the global workspace theory. (Global Workspace Theory or GWT) of Bernard Baars and the theory of the integration of the information (Integration Information Theory or IIT).

The GWT proposes the metaphor of theater to understand consciousness. All those processes and phenomena of which we are aware are those that are illuminated by the attentional focus, in the same way as in a play, the spotlights shed light on those parts of the stage that are relevant to the action. In the shadows all kinds of processes occur that, not being focused, do not reach consciousness. Thus, consciousness is a unitary process and the section of the brain in two should give rise either to a double consciousness, or to a consciousness focused on only one hemisphere of the two.

The IIT proposes that it is the sum of informational integration that builds consciousness. The more information integrated, the higher the level of consciousness. In a unitary brain, all the information converges at the same point, forming a single consciousness. In a divided brain in which information from one side does not reach the other, two different points of convergence of information, leading to the formation of two different consciences, each with its own information hemispherical.

Are two consciousnesses really formed?

Researchers tested the immobility of the classical theory of the divided brain through the section of the corpus callosum. For this, they recruited two individuals who had undergone said injury therapeutically and carried out five visual recognition experiments.

Contrary to what is described in the textbooks, the participants were perfectly able to indicate where the found the visual stimulus, if it appeared, in any part of the visual field, both by pointing with the hand and verbally. In one experiment, it was found that one of the two participants was better able to name the stimulus that was used (an animal) when presented in the right visual hemifield, due to the location of the language. Although the visual information did appear to be disintegrated, the place of presentation of the stimulus was not found to be associated with a specific type of response.

Conflict with classical theories

These data, although they are far from conclusive due to the small sample, show that what is predicted by classical theory is not rigidly fulfilled. In fact, it has yet to be shown that it is met in most patients. The truth is that the evidence with these two patients in five tasks that challenge the basic assumptions not only conflicts with the old clinical cases, but also with the theories of consciousness described before.

Both the GWD and the IIT predict that following the section of the corpus callosum and the interruption of the flow of information from one side to the other, two separate consciousnesses will form. The truth is that none of these patients showed signs of double consciousness and explained feeling that they had a single, very well integrated consciousness. These data do fit well with another of the theories of consciousness: that of recurrent local processing. This theory predicts that the mere interaction and exchange between two different areas of the brain is already enough to bring the information to consciousness. Thus, it does not take two connected hemispheres to bring separate information through callosotomy to the same consciousness.

Other possible explanations

Results are not final and should be taken with tweezers. It is possible to offer alternative explanations that integrate what has been described in the typical cases and what was found in this study. For example, it must be taken into account that the patients taken as subjects were callosotomized more than 15 years ago. It could be that after the operation the information is effectively disintegrated, but over time the brain has found a way to unite the double consciousness and re-form a single one.

Even so, it is fascinating that these patients with a perception divided in two are able to gather information and represent it in a single consciousness, giving a unified response. This is a phenomenon that will undoubtedly have to be answered one day if we are to have a truly explanatory theory of consciousness.