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Brain Bugs: Hallucinations, Forgotten Faces, and Other Cognitive Quirks

January 28, 2012, 12:00 AM
Hallucination

What's the Big Idea?

If seeing is believing, then how do we come to know? One common misperception holds that vision springs directly from the eyes. True, the eyes, ears, and skin bombard us with a constant stream of information. But sensory input is only the first step in a complex journey towards arriving at our understanding of the world. It's the brain that determines which details we pay attention to and why.

As neuroscientist V.S. Ramachandran writes in his book The Tell-Tale Brain,"Even though our picture of the world seems coherent and unified, it actually emerges from the activity those thirty (or more) different visual areas in the cortex, each of which mediates multiple subtle functions." Watch the video:

What's the Significance?

For neurologists like Ramachandran, "the question of how neurons encode meaning and evoke all the semantic associations of an object is the holy grail of neuroscience, whether you are studying memory, perception, art, or consciousness." Ramachandran studies patients with cognitive abnormalities for two reasons: clinical interest in improving the life of the patient, as well as the fact that cognitive quirks and disorders provide insight into the broader mystery of human perception. 

This is because brain damage is highly specialized. If you hit your head, you're not going to experience a general reduction in "brain power." Instead, a lesion to any area of the brain will in the loss of a specific function associated with that area. Ramachadran tells the story of John, a 68-year-old former fighter pilot who one day began to experience intense nausea and abdominal pain. He was rushed to the hospital, where doctors determined that he required immediate removal of his appendix. The surgery was successful -- but that's where the routine nature of the case ended.

John developed a blood clot in a vein in his leg, which traveled to his cerebral arteries, causing a stroke. Minutes later, when his wife walked into the recovery room, he found he could no longer recognize her face, even though he knew her by the sound of her voice.

There was nothing wrong with his vision or hearing. Another piece of the puzzle was missing: the unnamed, barely understood process of object recognition. John could describe objects in painstaking detail, but he was unable to say decisively what they were. When picking up a carrot, for instance, he noted that it was "long, with a tuft at the end," and wondered if it might be a paintbrush.

In John's case, the "wire between the vision and the amagydala," which regulates emotion, had been cut. Vision was normal, emotion was normal, "but the two [had been] uncoupled." Face blindness affects only 2.5% of the population, but this disconnect between sight and emotion inspired Ramachandran's theory that the brain perceives the identity of a person or object in a more fluid, interconnected way than previously imagined: "My hunch is that at each stage in processing, whenever the brain achieves a partial solution to a perceptual 'problem'--determining an object's identity, location, or movement--this partial solution is immediately fed back to earlier stages."

It's as if each of us is hallucinating all the time and what we call perception involves merely selecting the one hallucination that best matches the current input. 

Oliver Sacks, a neurologist at Columbia, told Big Think that how the mind works is indeed the biggest topic in neurology today. As someone who actually experiences clinical, non-drug induced visual hallucinations, Sacks has a particular interest in visual perception, especially the "higher reaches of imagination and thinking and creativity," which he associates with hallucinations. 

Far from being freakish or a sign of insanity, hallucinations are often entirely benign and more common than you'd think. They "start off as geometric patterns and colors," then sometimes "landscapes and sometimes enormous crystals or fields of flowers." For some people, they accompany migraines. Other people see them when listening to music or thinking of a number. (Editorial note: for more on this subject, see tomorrow's post on synesthesia.

Cognitive aberrations like hallucinations and lack of facial recognition also remind us of how little we can count on a single, unquestionable version of reality. Watch our interview with Oliver Sacks:

Dan Honan contributed to this article.

Image courtesy of Shutterstock.

 

Brain Bugs: Hallucinations,...

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