Effects of MDMA on attention to positive social cues and pleasantness of affective touch

MDMA (±3,4-methylenedioxymethamphetamine) is described as an "empathogen-entactogen" that increases feelings of empathy, trust and interpersonal closeness. Laboratory work in animals and humans has documented prosocial effects that appear distinct from those of other psychostimulants, but the psychological and neurobiological processes that produce these effects remain unclear. The sense of touch, and specifically "affective" touch mediated by C-tactile (CT) afferents on hairy (non-glabrous) skin, is a socially relevant modality that is rated as hedonically pleasant at intermediate stroking velocities (1–10 cm/s). Prior reports link CT-optimal touch to activity in affective tactile brain regions and to neuromodulators influenced by MDMA, such as serotonin and oxytocin, yet human psychopharmacology studies have rarely examined touch as an outcome. Bershad and colleagues designed a placebo-controlled, double-blind, within-subject study to test whether MDMA selectively enhances responses to affective touch and biases visual attention toward positive social cues. They compared two doses of MDMA (0.75 and 1.5 mg/kg) with methamphetamine (MA; 20 mg) and placebo in healthy young adults, measuring subjective pleasantness, facial electromyography (EMG) during experienced and observed touch, and eye-movement indices of attention to emotional faces. The main hypotheses were that MDMA, but not MA, would increase pleasantness and positive psychophysiological responses to CT-optimal touch and would increase attentional bias toward happy facial expressions.

The study employed a four-session, within-subjects, double-blind design. Thirty-six healthy volunteers aged 18–40 years attended four 4.5-h laboratory sessions in randomized order, receiving placebo, 0.75 mg/kg MDMA, 1.5 mg/kg MDMA, or 20 mg methamphetamine (MA). Sessions were separated by at least 2 days. Participants were recruited with a history of 4–40 lifetime uses of MDMA and were screened for psychiatric and medical exclusions; women who were pregnant, lactating or planning pregnancy were excluded. Body-mass index eligibility was 19–30 kg/m2. Procedures began with orientation and informed consent. On session days participants abstained from drugs and alcohol for 48 h and underwent urine drug and breath-alcohol tests, and pregnancy testing when applicable. Capsules (drug or placebo) were administered at 09:30, subjective and cardiovascular measures were collected at multiple time points, and psychophysiological sensors were attached at 10:45 for facial EMG and electrooculography (EOG). The experimental tasks—the experienced touch task, the observed touch task, and the attention bias task—were completed in randomized order and psychophysiological sensors were removed after task completion. Experienced touch was delivered with a 5-cm-wide goat-hair brush over a 9-cm section of forearm using two velocities: CT-optimal slow stroking at 3 cm/s and non-optimal fast stroking at 30 cm/s. Each trial comprised 6 s of stimulation followed by self-report pleasantness ratings on a 7-point Likert scale; facial EMG (zygomatic and corrugator muscles) was recorded throughout. Observed touch consisted of 6-s videos showing touch to several skin surfaces at 0 (static), 3 or 30 cm/s; participants rated pleasantness after each video while EMG was recorded. For comparability with the experienced task, analyses of observed touch focused on arm locations. Attention to emotional faces was measured using a dot-probe style attention bias task adapted for eye-movement recording (EOG). Face pairs comprised one neutral and one emotional expression (happy, fearful, sad, angry) from a standard stimulus set; the initial eye-fixation toward the emotional versus neutral face (orienting) was the primary outcome. Trials with poor fixation, very short initial fixations (<100 ms), or noisy signals were discarded, and sessions with less than 4 h of prior sleep were excluded for attentional analyses. Heart rate and blood pressure were monitored at five time points and mean arterial pressure was calculated. Statistical analyses were conducted in SPSS. Missing cases were removed listwise. For repeated-measures subjective measures, peak or peak change from baseline was used. Repeated-measures ANOVAs tested drug effects with within-subject factors of dose and touch velocity where appropriate. MDMA vs placebo and MA vs placebo were analysed separately; linear contrasts were used across the two MDMA doses. Significant effects were followed with post hoc t-tests corrected by the Benjamini-Hochberg procedure (false discovery rate 0.05).

Thirty-six participants (mean age 24.8 ± 4.2 years; 61% Caucasian) completed the study; they reported a mean of 11.1 ± 9.8 lifetime uses of MDMA. Experienced touch: self-report ratings confirmed the expected velocity effect, with CT-optimal slow touch (3 cm/s) rated as more pleasant than fast touch (30 cm/s) [F(1,35) = 38.0, p < 0.001]. MDMA increased pleasantness ratings for slow touch [dose main effect F(2,70) = 7.27, p < 0.05], with the low dose producing a marginal enhancement (p = 0.051) and the high dose producing a significant enhancement relative to placebo (p = 0.012). There was no significant effect of MDMA on ratings of fast touch, and MA produced no significant changes in pleasantness ratings for either velocity. Facial EMG during experienced touch showed a linear dose effect of MDMA on zygomatic activity across velocities [F(1,33) = 8.04, p < 0.01], whereas MA did not affect zygomatic responses. Corrugator activity showed the expected effect of velocity (greater activity for fast than slow touch) [F(1,31) = 13.9, p < 0.01], but no significant main effect of drug or dose on corrugator measures. For the high MDMA dose, zygomatic responses during slow touch correlated with pleasantness ratings (r = 0.54, p < 0.01). The authors note a possible confound that increased zygomatic activation could partly reflect MDMA-induced bruxism contaminating the recording. Observed touch: videos of slow touch were rated as more pleasant than fast or static touch [F(2,70) = 21.4, p < 0.001], replicating the velocity effect in vicarious ratings. However, there was no significant main effect of drug or drug × velocity interaction on observed-touch pleasantness ratings. Zygomatic EMG during observed touch showed a non-significant trend toward increased activity with MDMA [F(1,30) = 3.83, p = 0.06]; corrugator EMG showed no drug effects. Attention bias task: at the higher MDMA dose (1.5 mg/kg) participants showed an increased number of initial gazes orienting toward happy faces compared with placebo, whereas MDMA did not significantly affect initial gazes to fearful, sad or angry faces. MA did not alter orienting to emotional faces. Other subjective drug-effect questionnaires and cardiovascular monitoring were collected during sessions but specific cardiovascular results are not clearly reported in the extracted text. Participants' guesses about which drug they had received were mixed; analysis indicated that expectancy did not account for the observed touch pleasantness effects when comparing MA sessions in which participants mistakenly believed they had received MDMA versus other beliefs.

Bershad and colleagues interpret the results as evidence that MDMA uniquely enhances components of social experience: it selectively increased subjective pleasantness of CT-optimal (slow) affective touch and biased visual attention toward positive facial expressions. These effects were dose dependent and were not produced by the prototypic stimulant MA, suggesting a pharmacological profile beyond general stimulant action. The authors propose that MDMA's enhancement of CT-optimal touch could reflect modulation of neural circuits implicated in affective tactile processing, including dorsal posterior insula and orbitofrontal cortex, which have been linked to CT stimulation and to MDMA-induced connectivity changes in prior work. Potential mechanistic pathways discussed include serotonergic, oxytocinergic, noradrenergic and dopaminergic signalling. MDMA reliably increases plasma oxytocin in some studies and influences serotonin release, and these systems have been implicated in social behaviour; by contrast, MA does not increase oxytocin in the same way. The authors note mixed evidence from SSRI and other pharmacological manipulation studies about which neurotransmitter systems mediate MDMA's social effects, and they emphasise that their study did not measure plasma oxytocin or directly probe neurotransmitter mechanisms. The discussion acknowledges possible alternative explanations and methodological caveats. Increased zygomatic EMG at both touch velocities may partly reflect MDMA-related bruxism contaminating recordings, although the correlation between zygomatic activation and pleasantness at the high MDMA dose supports a psychophysiological relation to positive affect in that condition. The sample comprised healthy volunteers without psychiatric pathology, limiting generalisability to clinical populations. The touch manipulation used a brush rather than interpersonal skin-to-skin contact and was delivered in a controlled laboratory setting, so ecological validity for real-world social touch is constrained. The authors also note they focused on non-glabrous skin innervated by CT afferents and did not compare touch responses across glabrous versus non-glabrous sites. Strengths highlighted include the within-subject, double-blind design, two MDMA doses, the use of a stimulant comparator (MA) to dissociate MDMA-specific effects, and convergent subjective and psychophysiological measures. The authors conclude that enhanced pleasantness of affective touch and biased attention toward happy faces are plausible contributors to MDMA's prosocial profile and may be relevant to its therapeutic potential in disorders such as PTSD and autism spectrum disorder, while emphasising that questions about precise mechanisms and clinical relevance remain to be addressed in future research.