A new study published in Neuropsychopharmacology has revealed how the drug ketamine changes the way our brains process touch, especially the difference between touch from ourselves versus someone else. Researchers found that under ketamine, the brain struggles to make this distinction, suggesting that ketamine may blur the boundaries of self-perception. These findings offer new insights into how certain psychiatric symptoms related to self-awareness could be mirrored in the brain.
Ketamine is a medication originally developed as an anesthetic, but it has gained attention for its ability to produce rapid antidepressant effects, even in people who haven’t responded to traditional treatments. Ketamine is a dissociative drug that can create an altered state of consciousness, where individuals experience a separation from their usual sense of self.
At lower doses, ketamine is used in treating depression and chronic pain, while higher doses are used in medical anesthesia. Because it temporarily disrupts the brain’s usual processing, ketamine offers a unique way to study how certain psychiatric symptoms, especially those related to self-awareness and perception, might be simulated.
The motivation behind this new study comes from the fact that many psychiatric conditions, such as schizophrenia and dissociative disorders, involve disturbances in self-perception or self-boundaries. Such disruptions can significantly impact a person’s social functioning and mental well-being, yet they are challenging to study in a controlled setting. By using ketamine to induce a temporary change in self-awareness, researchers hoped to gain insight into how our brains normally distinguish between self-generated sensations and those coming from outside.
“In our lab, we are very interested in the ‘sense of self’ — the feeling of ‘being you.’ We know that this sense of self is likely anchored in the fact that we can perceive our own bodies,” said study author Reinoud Kaldewaij, a postdoctoral fellow at the Center for Social and Affective Neuroscience at Linköping University.
“Touch, which reminds of us in a way of the border between our own body and the outside world, seems to play an important role in this. We also know that ketamine alters our general sense of self. Therefore, we expected that ketamine would also alter the way we perceive touch, especially the difference between touch generated by ourselves compared to touch from others.”
The study included 30 healthy participants between the ages of 19 and 39 who each underwent two separate sessions. In one session, participants received an intravenous infusion of ketamine, and in the other, they received a placebo (a saline solution), with the sessions occurring in a randomized and double-blind manner. This design ensured that neither the participants nor the researchers knew which infusion was being administered, minimizing biases and expectations. After each infusion, participants underwent a functional magnetic resonance imaging (fMRI) scan, which allowed researchers to observe and measure brain activity in real time as participants experienced different types of touch.
During the fMRI scans, participants engaged in a task that involved three types of touch: touching their own arm, being touched on the arm by a researcher, and stroking a soft object. These different conditions allowed the researchers to compare brain responses to self-generated touch, externally generated touch, and non-human touch. The self-other distinction was of particular interest, as it’s a key component of our sense of self and personal boundaries. Additionally, participants completed various assessments to gauge their levels of dissociation (a sense of disconnection from one’s self), awareness of bodily sensations, and comfort with social touch.
The study’s findings revealed that ketamine had a notable effect on how participants’ brains processed touch, especially touch generated by another person. In a typical (placebo) state, the brain’s right temporoparietal cortex—an area involved in distinguishing self-generated sensations from external ones—showed higher activity during externally generated touch than self-touch, which aligns with previous research.
However, during the ketamine session, this difference in brain activity was reduced, indicating that the brain was less able to distinguish between self-produced and other-produced touch. This effect was especially evident during the externally generated touch, where the neural response more closely resembled the response seen during self-touch. These findings suggest that ketamine blurs the brain’s ability to differentiate between self and other, leading to a reduced sense of self-boundaries.
Beyond the neural changes, ketamine also affected participants’ attitudes toward touch. During the ketamine session, participants showed a stronger inclination toward social touch, a shift that was linked to their decreased awareness of bodily sensations (interoceptive awareness). This suggests that under ketamine, individuals may feel less certain about the boundaries of their own body, potentially leading to an increased comfort with touch from others.
Interestingly, while ketamine altered the subjective and neural experiences of touch, it did not appear to affect basic touch sensitivity, as measured by the tactile detection thresholds for self- and other-generated touch.
“Ketamine changes the way we process touch from others in the brain, especially when we compare it to touch generated by ourselves,” Kaldewaij told PsyPost. “The signal becomes a bit weaker, and therefore a bit more like the signal we see when we touch ourselves. This may be (one of) the underlying reason(s) why people under the influence of ketamine experience a blurring of the sense of the self and a stronger connection with the outside world.”
The findings suggest an exciting path for future studies to explore how alterations in self-perception, brought about by substances like ketamine, might help address self-related challenges in mental health disorders. This line of research could eventually inform therapeutic strategies that harness sensory experiences, such as touch, to improve well-being for people who struggle with self-perception issues, bridging the worlds of sensory processing and mental health.
The study, “Ketamine reduces the neural distinction between self- and other-produced affective touch: a randomized double-blind placebo-controlled study,” was authored by Reinoud Kaldewaij, Paula C. Salamone, Adam Enmalm, Lars Östman, Michal Pietrzak, Hanna Karlsson, Andreas Löfberg, Emelie Gauffin, Martin Samuelsson, Sarah Gustavson, Andrea J. Capusan, Håkan Olausson, Markus Heilig, and Rebecca Boehme.
