The Edge Case Test: What Abnormal Brains Reveal About Consciousness
From Savants to Split Minds, How Neurological Outliers Forge New Theories of Mind
The most profound insights about consciousness often come from its edges. Earlier, I wrote about the P&O Test to explore a first limitation of what mental processes could possibly be. Before the P&O test, many magical things were considered possible that, with what is now known, could not be the case because they could not have come to be the case. This view of a whole system developing into existence is hidden from the view of a single individual within the system.
In an analogous way, “normal” thinking about thinking tends not to think about abnormal thinking. This was a problem for Descartes, who thought of his own mind as the central example of a mind. If he could envision his mind as existing without his body, then from his stance (in his own boots) that was a reasonable possibility. However, a theory of mind has to work not only for a “normal” thinker such as Descartes, but it must cover all the minds we encounter, including all those we consider abnormal, damaged or diseased. A theory that works for these cases as well as the “normal” case passes the “Edge Case Test” (ECT).
The Value of Edge Cases
In the philosophical history of mental self-reflection, it is only in modern times that the biological machinery that makes us function has become clear. Paralysis was an early edge case where damage to nerves in the spine stopped the action of what were otherwise perfectly good legs. However, it was only in recent times that damage or deformation of the biological machinery was associated with changes of the Mind.
Phineas Gage: Personality and the Frontal Lobe
The famous case of Gage (who survived an iron rod passing through his skull) demonstrated how damage to specific brain regions affects personality while leaving other functions intact. Recent research found that while only 4% of his cortex was damaged, about 10% of his white matter connections were disrupted, suggesting consciousness emerges from network connectivity rather than localized functions.
The terrible sadness of war has given us countless cases like Gage where parts of human brains have been damaged, and results have been studied and documented. Various tumors from brain cancer and other diseases have done so as well, and led to stimulation studies in open brain surgery. All of these are edge cases where theories of Mind are stripped away by failure to match reality.
The Savant Window: Kim Peek and Specialized Processing
Not all human brains are even anatomically the same as Descartes’ or each other. A well known case is that of Kim Peek, who was partially used as the basis for the movie character “Rain Man.” It is said that he memorized 12,000+ books but struggled with abstract thought. Peek's condition, "agenesis of the corpus callosum" is a malformation of brain structure in which the primary communication channel between the left and right hemispheres (the corpus callosum) does not form. A surgical procedure, corpus calloscotomy, sometimes produces this condition in what are called “split-brain” patients in order to treat severe epilepsy.
Dolphins and other marine mammals have brains that allow one half to sleep while the other half keeps working. Birds such as Corvids and Psittacids (parrots) have intelligent minds running on brains that have structures evolved to pack processing into size and weight constraints that would impact flying ability. Octopuses have a unique nervous system with about 500 million neurons, two-thirds of which are distributed across their eight arms.
Henry Molaison’s Neurosurgical Saga
After a 1953 lobotomy destroyed his hippocampus and medial temporal lobes, Molaison (Patient HM) lost the ability to form new memories. He could no longer form new declarative memories, despite retaining his personality, intelligence, and procedural memory abilities. H.M. maintained personal identity and character traits, raising philosophical questions about what constitutes the self across time. Molaison’s brain became an object of scientific custody battles postmortem, contrasting his subjective experience of perpetual "nowness" with researchers’ materialist focus on his physical brain.
Schizophrenia and Self-Awareness: The Nash Paradox
Nash experienced hallucinations and delusions that felt completely real to him, yet were generated by his own brain. This raises profound questions about the relationship between subjective experience and objective reality. He learned to "intellectually reject" delusions while retaining mathematical intuition. How does this edge case impact our trust in “reality”?
Nash reported that he became able to identify certain thoughts as symptoms of his illness, implying a meta-cognitive capacity where part of his consciousness could observe other parts. This suggests a layered model of mind that complicates straightforward mind-body reductionism.
Synesthesia: Cross-Sensory Perception of Solomon Shereshevsky
Solomon Shereshevsky experienced an extreme form of synesthesia where almost all of his senses were interconnected. When he heard a tone, he would simultaneously experience a color, a taste, and a tactile sensation. When he saw a number, he might experience it as a complex visual entity with specific texture and color. This pervasive cross-sensory perception gave him an extraordinary memory, but also created challenges in his daily life. His subjective experience was radically different from “normal” humans despite having the same basic neural architecture. This highlights how similar physical structures can give rise to profoundly different conscious experiences, complicating any straightforward mapping between neural activity and phenomenal experience.
Additional Edge Cases to Consider
Together with the edge cases listed above, many further cases can be studied to become aware of the much bigger picture of mental function and disfunction than considered by Descartes. These include:
1. Alien Hand Syndrome: Where one hand seems to act with its own agency, contradicting the person's conscious intentions. This directly challenges unified notions of self and agency.
2. Cotard's Syndrome: Where patients believe they are dead or don't exist despite being alive and conscious. This undermines the Cartesian certainty of one's own existence.
3. Blindsight: Where patients with visual cortex damage claim they cannot see objects but can "guess" their properties with surprising accuracy. This suggests consciousness can be dissociated from function.
4. Locked-In Syndrome: Where fully conscious individuals are almost completely paralyzed, demonstrating consciousness's independence from behavioral expression.
5. Dreamstate consciousness: How REM sleep and lucid dreaming reveal consciousness operating with different constraints and rules.
Conclusion
As in the application of the P&O Test, any Theory of Mind must stand up to the ECT, it must hold for the abnormal as well as the “normal.” The combination of the two tests require that, not only must whatever we find have a path through geologic time and organism development time, but also must extend to the edges. Theories of consciousness that don’t make it to the edge of human and animal experience, can be discarded. This suggests that consciousness is likely more distributed, heterogeneous, and varied than philosophical traditions have typically acknowledged. If human and animal consciousness manifests so diversely with the same basic neural hardware, what might this suggest about potential machine consciousness?