When Biology Alters Behavior
Neurology, free will, and the uneasy question of accountability.
Posted May 18, 2026 | Reviewed by Devon Frye
A recent Psychology Today post titled “The Forensic Evolution of Compulsive Sexual Behavior Disorder” explored the definition of compulsive sexual behaviors and the debate that surrounds them.
The authors, Dr. Beata Bőthe and Dr. Mónika Koós, note that at the core of the debate is a difficult question: If one cannot control sexual impulses, a basic human instinct, is this a personal failure requiring responsibility and accountability, or is it a medical condition requiring treatment? After all, the struggle to push aside sexual fantasies or opportunities in favor of higher objectives is a near-universal human experience.
As a neurologist, I have long been interested in this question.
I knew that the experts who collaborated on the DSM-5 had considered a new diagnostic category, “Hypersexual Disorder,” but ultimately did not include it in the final version. What I did not know was that the major reason for this was fear of forensic misuse.
One line especially stood out to me: “While science requires rigorous empirical evidence before naming a disorder, the law works differently: It is an adversarial process that must resolve individual conflicts, even when the science is unsettled.”
In criminal matters, the concern was sentencing mitigation for offenders. Where would accountability lie for the suffering of victims?
In the 11th edition of the International Classification of Diseases (ICD-11), the World Health Organization (WHO) introduced “Compulsive Sexual Behavior Disorder” (CSBD). To address earlier concerns about misuse in legal settings, the WHO integrated several safeguards: only when the loss of control is persistent, causes meaningful functional impairment, and is accompanied by personal distress.
Parkinson's, Dopamine Agonists, and Impulse-Control Disorders
Neurology introduces another complication to this debate: Sometimes the loss of impulse control is clearly linked to biology and pharmacotherapy.
In Parkinson’s disease, for instance, medications to treat the motor symptoms, particularly dopamine agonists, can result in impulse control disorders , likely from excessive dopamine receptor stimulation. This may result in behaviors such as compulsive gambling, shopping, binge eating, and hypersexuality . Patients often cannot control these impulses, even when they retain awareness of them.
Symptoms can improve after withdrawal of the medication , but not always. And even when they do, irreparable harm may already have occurred.
With colleagues, we recently wrote an editorial drawing attention to this issue , particularly the fact that the harm caused by these prescriptions often extends beyond the patient to partners, caregivers, and families. Prescribers need stronger safeguards and better education for both patients and their loved ones.
Free Will and Accountability Debate
Neuroscience complicates simplistic ideas of personal responsibility. Philosophy and neuroscience have long debated whether we truly possess free will , or whether our behaviors ultimately reduce to neuronal activity in the brain.
This discussion is not just academic. If free will is more constrained than we assume, it raises difficult questions about accountability.
Philosopher Stephen Cave, in a recent article titled “ There is No Such Thing As Free Will ,” suggested a possible third perspective:
Our everyday experience does feel consistent that some degree of free will and choice exists, but we also need to be compassionate about those who have failed. There may be many underlying factors, including genetics , circumstances, disease, medications, among others.
Dr. Cave writes that vengeance usually does not lead to better outcomes. Understanding failure calmly, while searching for possible solutions, may be the best way to move forward.
I do not have a full answer for how an adversarial legal system should account for these complexities. But as a physician, I have come to believe that human behavior is rarely reducible to a single cause. Biology, circumstance, disease, medication, trauma , and choice all interact in ways that are difficult to disentangle. Our legal and moral frameworks assume stable agency, but neurology repeatedly shows us situations where agency becomes biologically altered.
Our “self” is not as static as we tend to believe.
Perhaps recognizing this complexity does not eliminate accountability, but it may encourage a little more humility and compassion toward ourselves and others.
Silveira-Moriyama, L., Bruno, M.K., Schneider, S.A., Ganos, C., Williams, L., Munhoz, R.P., Pringsheim, T., Alcalay, R.N., Subramanian, I. and Lang, A.E. (2026), Addressing Care Partner Burden from the Underrecognition of Iatrogenic Sexual Behavior Changes in Parkinson's Disease. Mov Disord. https://doi.org/10.1002/mds.70315
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Michiko Kimura Bruno, M.D., is a Movement Disorder Neurologist, practicing in Honolulu.
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This article is part of the Bringwise Psychology Journal — daily insights on human behavior, mental health, and personal growth.