Writing about the brain can sometimes bring me amazingly close to my readers–so close that I feel like I’m inside their minds. Case in point: my new column for Discover, on the subject of the mind’s eye.

Here’s how it begins:

One day in 2005, a retired building surveyor in Edinburgh visited his doctor with a strange complaint: His mind’s eye had suddenly gone blind.

The surveyor, referred to as MX by his doctors, was 65 at the time. He had always felt that he possessed an exceptional talent for picturing things in his mind. The skill had come in handy in his job, allowing MX to recall the fine details of the buildings he surveyed. Just before drifting off to sleep, he enjoyed running through recent events as if he were watching a movie. He could picture his family, his friends, and even characters in the books he read.

Then these images all vanished. The change happened shortly after MX went to a hospital to have his blocked coronary arteries treated. As a cardiologist snaked a tube into the arteries and cleared out the obstructions, MX felt a “reverberation” in his head and a tingling in his left arm. He didn’t think to mention it to his doctors at the time. But four days later he realized that when he closed his eyes, all was darkness.

I describe the singular case of MX, and what he tells scientists about our mind’s eye. The original paper that inspired the column compared MX to a group of normal men of his age and profession to figure out what was unique about him. But to my surprise–and to the surprise of the scientists I wrote about–a lot of readers felt a great kinship with MX.

Discover is running a selection of letters to the editor about the column, and a response from the scientists. It won’t be available online, but I was so fascinated by the exchange that I’m reprinting it here.

In March’s “The Brain” [page 28], Carl Zimmer assumes that having a mind’s eye is a normal function of the human senses. Yet I have never had a mind’s eye, and when I bring this up in conversation others often voice the same complaint. How common is this?
Marshall Krause San Geronimo, CA

Neuroscientists Adam Zeman and Sergio Della Sala reply:
We have encountered people who report that they have never experienced imagery; they seem little if at all disabled by their deficiency. We hope to study this neglected phenomenon using psychological and brain imaging techniques like those with which we explored the case of MX. Such research may help explain both the basis of imagery production in the brain and how (if at all) imagery is useful to us.

I enjoyed reading about MX and his mind’s-eye blindness. Were MX’s dream experiences also affected by this affliction?
Arlene Barker Homer City, PA

Zeman and Della Sala reply:
For about a year after the loss of his mind’s eye, MX reported that he dreamed without visual imagery. But then his visual dreaming recovered at night, even though his mind’s eye remained blank by day. This suggests that the brain mechanisms involved in dreaming can be teased apart from those involved in deliberate imagery formation.