These examples reveal something quite extraordinary: Our memories, once formed, are not fixed. Each time we retrieve a memory, we strengthen the neural pathways that have created it, and in doing so, reinforce and consolidate that memory so that it becomes lodged more permanently in our minds. But for a short time during this retrieval process, our memory becomes malleable—we are able to reshape it and sometimes contaminate it.

We’ve explored the deepest depths of the ocean. We’ve sent robots to Mars. And yet, we still have a long way to go in trying to understand how that three-pound squishy mass between our ears can generate the entirety of the human experience. From the joys of gustatory delight to the ravages of a midlife crisis, our brain makes it all possible. And our intuitive understanding of how it works can be (and often is) wrong. That’s why Unthinkable by Helen Thomson is so fascinating.

The Unthinkable Inner Workings of the Brain

Perhaps one of the best ways we can come to understand the brain — or at least one of the more interesting ways — is to look at exceptional cases that deviate from the norm. We learned a lot about personality and behavior, for example, when Phineas Gage survived a tamping iron shooting straight through his skull. We learned a lot about how language “works” in our brains thanks to the work Paul Broca and Carl Wernicke.

It’s in that spirit that author Helen Thomson traveled to visit exceptional cases of people with unique conditions.

She spoke to someone with perfect memory, for example. We might think of memory as “taking a photograph” and then retrieving it from an album. In truth, we “recreate” our memories every time we think about them. Remember the invisible gorilla? This is why eyewitness testimony can be so unreliable, and why false memories can be so pervasive.

The Abnormality of Normal

But, we’ve also got a number of “conditions” and “experiences” that most people view as “abnormal.” It’s not “normal” to hallucinate, right? You shouldn’t see and hear things that aren’t really there… or should you?

In learning more about her life, I came across the most startling discovery of my journey so far. I found that hallucinations are not only common, but vital to producing our perception of reality. So vital, in fact, that you’re probably hallucinating right now.

From what I recall (there’s that imperfect memory again), the discussion of hallucination came up in the context of synesthesia. This is when the senses “cross over,” so to speak. Synesthetes with chromesthesia, for example, will “see” colors when they hear sounds. It’s actually more common than you might think: about 1 in 3,000 people. Some research says indicates that “around 4 percent of the population is naturally synesthetic all of the time.”

Consider this. We usually think that we perceive a thing (see it, hear it, smell it, etc.) and then our brains process that input to generate our experience of that thing. In truth, our brain does a lot more predicting and anticipating. In this way, a “hallucination” could just be a prediction gone awry.

Anil Seth, a cognitive and computational neuroscientist at the University of Sussex, suggests listening to sine-wave speech, a degraded version of a speech recording. The first time all you’ll hear is a jumble of beeps and whistles. But if you listen to the original recording and then switch back to the degraded version, you will suddenly be able to make out what is being said. All that has changed is your brain’s expectations of the input. It means it now has better information on which to base its prediction. “Our reality,” Seth once told me, “is merely a controlled hallucination, reined in by our senses.” Or, as psychologist Chris Frith once put it, “A fantasy that coincides with a reality.”

I Think Therefore I Am?

The human brain is truly remarkable. And psychology, along with related fields like neurology and developmental biology, is still a relatively young science. We still have so much to learn about that three-pound squishy mass. Maybe we’ll never fully understand it.

Put another way:

If the brain were so simple that we could understand it, we would be so simple that we couldn’t.

Unthinkable by Helen Thomson is available now in hardcover, paperback, Kindle e-book, and audiobook formats.