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To be human is to think. To imagine. To dream. To hate. To love. We are able to do those things because we are conscious.

Now, imagine being able to do all those things, but nothing else — to be unable to move, speak or communicate with anyone around you. That’s what happened to Martin Pistorius of South Africa.

As Pistorius described it to WBUR’s On Point, he was “a vibrant mind hidden in plain sight.”

“On the outside, I looked empty,” he said. “Yet on the inside, I was very much alive.”

Pistorius relayed his experience as part of On Point’s special series “Brainwaves: The mysteries of the human brain.” His story provides enticing clues to a question science has not yet answered — how consciousness works.

Pistorius was 12 years old when he came home from school one day not feeling well. What he thought was just the flu, turned out to be a rare brain infection that gradually caused him to lose the ability to talk, walk and move, before he slipped into a deep coma.

“ For the first few years, I do not remember anything at all,” Pistorius said. “There are no memories from that time. No awareness, no sense of what was happening around me.”

But  then, at around the age of 16, his mind started to wake up. It was like a fog lifting, he said.

“I often describe it like an image coming into focus. At first, everything was gray and blurry. Then, little by little, the details and colors returned,” Pistorius remembered. “I started becoming aware of sounds, then voices. Over time, I became aware that I had thoughts again, memories, a sense of myself.”

But no one in the outside world was aware of his reawakening. And without the ability to talk or move, Pistorius had no way to let anyone know he was still in there.

“I often describe it as feeling like a ghost. I could see and hear what was happening around me, but I could not interact with it in any meaningful way,” he said. “That disconnect between who I was inside and how I was seen outside was devastating.”

Pistorius remained stuck in this state for years, and said he coped by letting his mind form a world of its own.

“I spent a lot of time in my own head thinking, remembering, imagining. I created stories, I replayed conversations,” he said. “I imagined myself doing ordinary things or simply choosing where I wanted to go and who I wanted to be with. In many ways, my imagination became my freedom.”

Finally, after nearly a decade in this state, one of his caretakers, Virna van der Walt, noticed Pistorius was reacting to the world around him. She convinced his parents to have him assessed. The testing proved he could make intentional eye movements in response to images, which showed he was in fact conscious.

This was an enormous relief, he said, but it wasn’t the end of his difficulties. Over time and through hard work, Pistorius regained control of his hands and upper body. This has allowed him to communicate using a speech computer.

Today, Pistorius is an author, an accessibility specialist and web developer. He’s also married and is the father of a 7-year-old son.

“The gift of communication has enormous power,” Pistorius said. “It brought my world back to life.”

So, after all this, how does he define consciousness?

“Based on what I have experienced, I would say that consciousness cannot be reliably judged from the outside,” Pistorius said. “During all those years when I could not move or speak, I still loved, I still hurt, I still hoped, I still imagined. Being human is not defined by how much you can do, but by your capacity to feel, to connect and to care. And I think that is something we all share regardless of how we look or how we communicate.”

There’s lots more to explore in On Point’s five-part series “Brainwaves: The mysteries of the human brain” — from what it means to have a healthy brain to how AI is advancing researchers’ understanding of how the brain works. Scroll and click below for more episodes from the series:

• Why is the brain such a mystery? The brain is the organ that makes us who we are. It’s our conduit between reality and thought. But somehow, we’ve only scratched the surface in understanding how the brain actually works.
• Is AI actually thinking? The rate at which artificial intelligence is able to replicate human behavior has increased in recent years. Does that mean it’s thinking like us?
• What happens between life and death? A tunnel. A bright light. Reuniting with deceased loved ones. Many people who have near-death experiences have remarkably similar stories. Why?
• How does a brain stay healthy? You might think a healthy brain starts and ends in your head — but there are miles and miles of neuron fibers that connect your brain with nearly every corner of your body. Here’s a look at why a healthy brain needs a healthy body.