E-Mail karger@karger.com Letter to the Editor 5 “I kind of enjoyed the next few hours till dinner. I was still kind of floating on air” (5:06) (T29). 6 “I had this awkward weight that I carried around me wherever I went (0:47) … Literally I had the sensation of this steal armor that I wore my entire life [that] – chunks of it – were falling off (3: 03)” (T16). 7 “I did immediately following the first session – and in the sec- ond and in the subsequent – feel a little bit of a lift to the weight on my chest. And if you suffer from depression I think you know what I’m talking about. You physically feel this turning in your stomach. It makes you physically nauseous (3: 30) … I didn’t experience what I call my breakthrough session until it was my ninth ketamine session and it was so profound and I felt like I broke through so many emotional barriers that I was able to see things differently (4: 35) … and during that time I was still progressively feeling lighter and lighter as each session went on (6: 10)” (T26). None of the testifiers were asked about experienced heaviness/ lightness/floating in these videos. Our finding that more than a quarter (17 out of 62, 27.4%) of the depressed testifiers spontane- ously report upon experiencing a sense of lightness – or less heavi- ness – that they associate with a reduction in depressive symptoms is in stark contrast with an extensive literature search that we con- ducted (see online supplement). We could not find a single article that addressed the question if a ketamine-induced sense of light- ness might be associated with antidepressant benefits for depressed individuals. Three testifiers (T4/11/26) mentioned body parts in relation to positively associated lightness (“head,” “throat,” “chest,” “neck”). Others might still have implicitly referred to bodily sensa- tions (e.g., T16, “I had this awkward weight that I carried around me wherever I went”). These testimonials suggest that the associa- tion between ketamine-induced lightness and other forms of light- ness induction might substantially differ; e.g., eliciting lightness through certain movements might evoke a pleasant “summer day” memory in healthy participants [9], while ketamine-induced light- ness seems associated with more profound psychological experi- ences such as breaking through emotional barriers (T26). Further- more, compared to depressed individuals receiving electroconvul- sive therapy (comparison group), an analogue systematic analysis of internet video testimonials showed that antidepressant-associ- ated lightness is rarely reported (4.0 vs. 27.4%, χ 2 = 10.78, p = 0.001 [see online suppl. material]). The aim of this letter is to highlight the need for future studies investigating the intriguing link between a subjective sense of light- ness and antidepressant benefits, as well as the need for therapeutic studies that investigate a potential antidepressant benefit from sta- bilization of the subjective feeling of lightness after ketamine infu- Dear Editor, There are two frequent effects of ketamine whose potential in- terrelationship has hardly been investigated: a feeling of lightness/ floating in healthy participants and recreational users [1–3], and temporary antidepressant benefits in individuals with treatment- refractory depression [4, 5]. Feelings of lightness/floating are a typ- ical occurrence in psychoactive-substance- or psychologically in- duced altered states of consciousness [6, 7]. As subjective lightness/ floating has been reported to be associated with elation [8], we hypothesized that depressed individuals receiving ketamine infu- sions associate it with an antidepressant state. In a systematic You- Tube search (online supplement; for all online suppl. material, see www.karger.com/doi/10.1159/000497441), we found 62 videos of depressed individuals reporting on experiences during and after ketamine infusions. Seventeen out of 62 testifiers spontaneously reported experiencing a sense of lightness – or less heaviness – that they associated with antidepressant benefits. Some examples are the following (for more, see online supplement): 1 “After my first treatment I woke up the next morning and I had less heaviness in my throat and my chest. The heaviness that you feel on an ongoing basis saps your energy (0:10)” (T4). 2 “The weight was gone. The heaviness, the darkness, the weird, awful thoughts, the sadness – I had completely forgotten what it felt like (2:22)” (T21). 3 “I felt happy and light (2:31)” (T19). 4 “Bubbles are rising from the back of my neck (3: 24) … all the pressure in my head just starts to feel light and normal again (4: 47)” (T11). Received: September 11, 2018 Accepted after revision: February 3, 2019 Published online: March 18, 2019 © 2019 S. Karger AG, Basel www.karger.com/pps Psychother Psychosom The Altered-State-of-Consciousness Aspect of a Feeling of Lightness Is Reported to Be Associated with Antidepressant Benefits by Depressed Individuals Receiving Ketamine Infusions: A Systematic Analysis of Internet Video Testimonials Kurt Stocker a–c Gregor Hasler d Matthias Hartmann c, e a Institute of Psychology, University of Zurich, Zurich, Switzerland; b Chair of Cognitive Science, ETH Swiss Federal Institute of Technology Zurich, Zurich, Switzerland; c Faculty of Psychology, Swiss Distance Learning University, Brig, Switzerland; d Unit of Psychiatry Research, University of Fribourg, Fribourg, Switzerland; e Department of Psychology, University of Bern, Bern, Switzerland Kurt Stocker, PhD Department of Psychology, University of Zurich Binzmühlestrasse 14, PO Box 25 CH–8050 Zurich (Switzerland) E-Mail kurt.stocker @psychologie.uzh.ch DOI: 10.1159/000497441 Downloaded by: Edward G Miner Library 128.151.10.35 - 3/19/2019 10:06:59 AM