Can deep brain stimulation make you a ‘different person’?

Deep brain stimulation (DBS), a procedure in which implanted electrodes deliver current to a target region of the brain, might sound like the stuff of science fiction. In actuality, it’s been approved for the treatment of Parkinson’s disease, essential tremor, and dystonia. Experimental work is ongoing in DBS for obsessive-compulsive disorder, depression, Tourette syndrome, epilepsy, and more.

Among the potential side effects of DBS, however, are changes to one’s “personality, mood, behavior, or cognition.” This has led to concerns that DBS might threaten personal identity. To assess those worries, though, we need to ask: What is personal identity?

To bioethicists concerned with this question, personal identity is a term of art. It picks out the property of being the same individual over time. It is continuity of personal identity that makes me, today, the same individual as the child who grew up to be me, rather than our being two fundamentally distinct entities.

But what exactly is it that makes this so? Examining different views of personal identity can help us understand.

On psychological views of personal identity, continuity of identity amounts to continuity of some feature(s) of our psychology (typically continuity of memory, sometimes along with other features of us such as character traits and values). This view has been supported with some fascinating thought experiments and was the dominant theory among analytic philosophers for quite some time.

Particularly prominent are relational views of personal identity, on which personal identity is grounded partly in relationships with other people (and perhaps also culture). There are also biological views, according to which identity consists of being the same organism over time. Multi-faceted views that combine these and other theories have also been gaining traction.

But what do these views have to do with DBS research?

Asking whether DBS threatens personal identity is, at least to some extent, engaging with long-standing philosophical questions about what constitutes the self. These are challenging issues, especially in qualitative research on the attitudes of DBS subjects.

When such subjects describe changes (or a lack thereof) to their identity as a result of DBS, it isn’t always clear which way of thinking about identity is informing their reflections.

In one study of people undergoing DBS for obsessive-compulsive disorder, researchers asked, “Did you change as a person?” One of the researchers, Dr. Sanneke de Haan, succinctly characterizes the responses this way in a follow-up paper: Some patients effectively responded, “No, I have not changed; I have become more myself,” while others effectively responded, “Yes, I have changed; I have become more myself.”

Reflecting on these ambiguities in subjects’ answers, de Haan expresses skepticism that the concept of identity can be clinically useful due to this apparent vagueness. But it may be that DBS subjects, like theoretical bioethicists, have a range of views on what constitutes personal identity.

If that’s correct, we can take the apparent ambiguities in de Haan et al.’s findings as an occasion for deeper examination of DBS subjects’ thinking on identity. DBS subjects may possess rich insight based on their experience.

Finer-grained questions will be required to get a clearer picture of how DBS subjects understand the concept of personal identity and what sorts of considerations inform their views. Such questions will need to get at certain philosophical dimensions of the concept of identity without being overly abstract or confusing.

Might bioethics researchers utilize methods from experimental philosophy to accomplish this task? However it’s accomplished, the potential rewards are significant: DBS subjects may well have unique perspectives on identity that can inform both bioethical theory and clinical practice.

-By Peter Zuk, Ph.D. candidate in philosophy at Rice University and research associate in the Center for Medical Ethics and Health Policy at Baylor College of Medicine