How can words make us laugh? Make us cry? During Nobel laureate Karl Deisseroth’s time at the College, the question went from a matter of literature and writing to one of biochemistry and science.

Deisseroth’s pursuit of those mysteries led him from a 1992 Harvard bachelor’s degree to a Stanford University M.D./Ph.D. and a career as a clinical psychiatrist and researcher.

Deisseroth’s work developing optogenetics, which uses light to activate single neurons in the brain, has opened new windows to observe and understand the brain. The work’s importance was recognized with this year’s Nobel Prize in Physiology or Medicine.

In this edited conversation, Deisseroth, Stanford University’s D.H. Chen Professor of Bioengineering and of Psychiatry and Behavioral Sciences, reflected on his undergraduate years and on the throughlines, apparent even then, that led from early lab experiences through his later work.

Gazette: Your family traveled when you were little. Do you consider Boston your childhood home or was there another city that your family settled in?

Karl Deisseroth: My father was a medical intern at the Beth Israel Hospital on the Longwood campus. I was born there. He was a Harvard affiliate but wasn’t a professor. He became a hematologist, oncologist, and had appointments around the country.

So I spent a lot of time in Northern California, when my dad was at the University of California in San Francisco; in Houston, when he was at the MD Anderson Cancer Center; and in Maryland, when he was at the NIH. I’ve been around, but I definitely see myself as a Boston native, a Red Sox fan, and a Patriots fan.

Who were you when you first got to Harvard?

We had just moved from Northern California to Texas, so I was coming from a one-year, senior-year stint at a high school in Texas. It was a good school.

The other thing unusual about me is that I was only 16 when I went to Harvard. I started school a year early and then skipped second grade, so it definitely was important that I got good preparation.

Did the fact that you were younger affect your course through Harvard?

It was not something I would necessarily recommend — I think that’s why you don’t see it much these days. But I had a great time at Harvard. I learned a ton and made some great friends.

I was in Winthrop House, and all my friends were physics and math folks. So I had breakfast, lunch, and dinner with physicists for at least three of the four years I was there.

I know you were busy in the lab, but did you have time for extracurriculars?

I did wrestling freshman year and focused on lab work after that.

I started as a developmental neurobiologist in the lab of Martin Shankland — he’s in Texas now. I worked on homeobox genes that regulate body plan formation in leeches.

I was always interested in the brain and thought I should start with the most accessible preparation. Leech development is pretty interesting. All the cells are accessible because the embryos are transparent, and you can actually track the lineage of each cell as it develops.

I thought that would be a cool opportunity to see how a nervous system is formed.

How much time were you spending in the lab at that point?

I did an honors thesis and spent as much time as I could in Martin’s lab. What was hard was that it was at the Medical School, and you have to take a shuttle bus to the Longwood campus and back. I rode the M2 more than I care to remember.

My major was biochemical sciences — I think they’ve reorganized the departments since then. We were based in the Sherman Fairchild building, and I took a lot of classes there. I also was a teaching fellow. I taught quantum biochemistry.

But you were first interested in creative writing?

My first semester, I took a creative writing course and that was the direction where I thought I was headed. I was writing poems and short stories, and I loved the power of the written word, how it could make me feel and make others feel.

I still feel that way. I just got distracted by science.

What made you decide to chuck writing for science?

It was gradual. I had taken introductory chemistry and biochemistry classes, and I started to get excited by how other fields — immunology, developmental biology — had made a lot of headway by getting to know the cells very deeply.

So my attraction to the leech system is that you could access the individual cells directly and consistently through the lifespan. I thought if we can do for the brain what was done for developmental biology and for immunology, that would be amazing. I got enthralled and headed in that direction.

Was there any connection between your interest in the brain and in creative writing, from the standpoint of where in the brain ideas come from?

There was definitely a connection, but it was more about where feelings come from, how this collection of cells can create a subjective feeling. To me, that seemed like a very deep mystery — it still does — and I wanted to understand that better.

Does your work in psychiatry follow that path as well?

Yes, but it was not clear from the beginning.

I was interested in feeling and how it could be assembled from cells. That was a nice connection with my interest in writing and words because I knew that words were a very precise way of causing feeling.

Of course, that only works with people, so I thought, “I’ve got to work with the human brain so I have to go to medical school.”

I did an M.D./Ph.D. program at Stanford though I wasn’t at all thinking psychiatry. I was thinking neurosurgery because I knew that neurosurgeons had direct access to the cells of the human brain. I was thinking that would be the route.

But time spent in a psychiatric ward put you on the path to psychiatry?

It was very unexpected. This was during the later stage of medical school. It was my first exposure and reset my path completely.

What was so moving or influential?

One was an encounter with a patient, and another was more cultural about the specialty. I had a very intense interaction with a patient with schizoaffective disorder, which is a schizophrenia-like symptom. It was a person who was otherwise healthy but was very upset and had a very deep paranoid delusion.

I was so struck by how different his reality was from mine and how his brain had constructed for him a different reality.

I thought, “Look at this guy. His brain is giving him this emotion, this anger, this altered perception.” That’s what I was interested in. Here’s somebody who’s suffering, maybe I could help people like this and increase understanding at the same time.

I hadn’t quite realized the clarity of this psychiatric state, how much help the patients needed, and how much it could teach everybody else.

The cultural aspect was that I also did a neurosurgery rotation, and I realized that the nature of psychiatry is that it gives more time to talk and think in an intellectual way. So I thought, all signs point to psychiatry.

It seems like progress on some of these psychiatric conditions has been stuck for a while. Are we starting to make progress with some of them?

I think things are starting to move. We went through a long time in psychiatry when there were neither new classes of medication nor new deep insights into the nature of psychiatric illness. Both of those are changing now.

Your development of optogenetics is being used in labs all over the world. Are there specific advances — whether in your lab or another — that are particularly gratifying to you and show how impactful that work has been?

Certainly, on the basic science side, there have been more than 10,000 papers — discoveries from labs around the world — using our methods. We’ve been teaching people how to use these methods. So it’s been very gratifying to see all the work that’s been done and all the insights that have emerged.

On the translational side, it’s also moving. For example, one issue in psychiatry is that we haven’t really known the cells that are causal — that are actually making the problems or that might correct the problems. There are ideas, there are correlations, but you don’t know what’s causing the problem.

With optogenetics, you can know that, because you’re having a direct, precise, real-time, causal impact on cells. And that brings me all the way back to my initial motivation of getting direct access to cells, except now we’re using light and a gene from algae.

We’ve been able to bring that causality to preclinical and then clinical work. For example, right now there are medications for autism and for schizophrenia that are well advanced in the clinical trial process.

For both, these treatments were validated with optogenetic causality. And these are pills — which makes them easier to give — and they have that crucial causal validation. It’s a firm bedrock to stand on.