Endogenous Opioid Release After Orgasm in Man: A Combined PET/Functional MRI Study.

The endogenous µ-opioid receptor (MOR) system plays a key role in the mammalian reward circuit. Human and animal experiments suggest the involvement of MORs in human sexual pleasure, yet this hypothesis currently lacks in vivo support. Methods: We used PET with the radioligand [11C]carfentanil, which has high affinity for MORs, to quantify endogenous opioid release after orgasm in man. Participants were scanned once immediately after orgasm and once in a baseline state. Hemodynamic activity was measured with functional MRI during penile stimulation. Results: The PET data revealed significant opioid release in the hippocampus. Hemodynamic activity in the somatosensory and motor cortices and in the hippocampus and thalamus increased during penile stimulation, and thalamic activation was linearly dependent on self-reported sexual arousal. Conclusion: Our data show that endogenous opioidergic activation in the medial temporal lobe is centrally involved in sexual arousal, and this circuit may be implicated in orgasmic disorders.

Mu-opioid receptor system modulates responses to vocal bonding and distress signals in humans.

Laughter is a contagious prosocial signal that conveys bonding motivation; adult crying conversely communicates desire for social proximity by signalling distress. Endogenous mu-opioid receptors (MORs) modulate sociability in humans and non-human primates. In this combined PET-fMRI study (n = 17), we tested whether central MOR tone is associated with regional brain responses to social signals of laughter and crying. MOR availability was measured with positron emission tomography (PET) using the high-affinity agonist radioligand [11C]carfentanil. Haemodynamic responses to social laughter and crying vocalizations were measured using functional magnetic resonance imaging (fMRI). Social laughter evoked activation in the auditory cortex, insula, cingulate cortex, amygdala, primary and secondary somatosensory cortex, and primary and secondary motor cortex; crying sounds led to more restricted activation in the auditory cortex and nearby areas. MOR availability was negatively correlated with the haemodynamic responses to social laughter in the primary and secondary somatosensory cortex, primary and secondary motor cortex, posterior insula, posterior cingulate cortex, precuneus, cuneus, temporal gyri and lingual gyrus. For crying-evoked activations, MOR availability was negatively correlated with medial and lateral prefrontal haemodynamic responses. Altogether our findings highlight the role of the MOR system in modulating acute brain responses to both positive and negative social signals. This article is part of the theme issue 'Cracking the laugh code: laughter through the lens of biology, psychology and neuroscience'.

Brain structural alterations in autism and criminal psychopathy.

The goal of this study was to elucidate the anatomical brain basis of social cognition through two disorders with distinctively different phenotypes of social interaction. We compared structural MR images of 20 individuals with autism spectrum disorder (ASD), 19 violent offenders with high psychopathic traits, and 19 control participants using voxel-based morphometry (VBM). Our earlier study showed lower grey matter volume (GMV) values in the insula, frontal cortex, and sensorimotor cortex of the offender group compared to controls. In the present study, the images of the ASD group revealed lower GMV in the left precuneus, right cerebellum, and right precentral gyrus in comparison with controls. The comparison between the offender and ASD groups showed lower GMV values for the right temporal pole and left inferior frontal gyrus in the offender group. There was also an overlap of both disorders in the right pre-central cortex, showing lower GMV compared to controls. Our findings suggest structural differences between violent offenders with high psychopathy traits and ASD individuals in the frontotemporal social brain network areas, previously associated with empathy. We also provide evidence of similar abnormal structures in the motor cortex for both of these disorders, possibly related to uniting issues of social cognition.

Aberrant motor contagion of emotions in psychopathy and high-functioning autism.

Psychopathy and autism are both associated with aberrant social skills and empathy, yet only psychopaths are markedly antisocial and violent. Here, we compared the functional neural alterations underlying these two groups that both have aberrant empathetic abilities but distinct behavioral phenotypes. We studied 19 incarcerated male offenders with high psychopathic traits, 20 males with high-functioning autism, and 19 age-matched healthy controls. All groups underwent functional magnetic resonance imaging while they viewed dynamic happy, angry, and disgusted faces or listened to laughter and crying sounds. Psychopathy was associated with reduced somatomotor responses to almost all expressions, while participants with autism demonstrated less marked and emotion-specific alterations in the somatomotor area. These data suggest that psychopathy and autism involve both common and distinct functional alterations in the brain networks involved in the socioemotional processing. The alterations are more profound in psychopathy, possibly reflecting the more severely disturbed socioemotional brain networks in this population.

µ-opioid receptor availability is associated with sex drive in human males.

The endogenous mu-opioid receptor (MOR) system modulates a multitude of social and reward-related functions, and exogenous opiates also influence sex drive in humans and animals. Sex drive shows substantial variation across humans, and it is possible that individual differences in MOR availability underlie interindividual of variation in human sex drive. We measured healthy male subjects' (n = 52) brain's MOR availability with positron emission tomography (PET) using an agonist radioligand, [11C]carfentanil, that has high affinity for MORs. Sex drive was measured using self-reports of engaging in sexual behaviour (sex with partner and masturbating). Bayesian hierarchical regression analysis revealed that sex drive was positively associated with MOR availability in cortical and subcortical areas, notably in caudate nucleus, hippocampus, and cingulate cortices. These results were replicated in full-volume GLM analysis. These widespread effects are in line with high spatial autocorrelation in MOR expression in human brain. Complementary voxel-based morphometry analysis (n = 108) of anatomical MR images provided limited evidence for positive association between sex drive and cortical density in the midcingulate cortex. We conclude that endogenous MOR tone is associated with individual differences in sex drive in human males.

Brain Basis of Psychopathy in Criminal Offenders and General Population.

Psychopathy is characterized by persistent antisocial behavior, impaired empathy, and egotistical traits. These traits vary also in normally functioning individuals. Here, we tested whether such antisocial personalities are associated with similar structural and neural alterations as those observed in criminal psychopathy. Subjects were 100 non-convicted well-functioning individuals, 19 violent male offenders, and 19 matched controls. Subjects underwent T1-weighted magnetic resonance imaging and viewed movie clips with varying violent content during functional magnetic resonance imaging. Psychopathic traits were evaluated with Levenson Self-Report Psychopathy Scale (controls) and Psychopathy Checklist-Revised (offenders). Psychopathic offenders had lower gray matter density (GMD) in orbitofrontal cortex and anterior insula. In the community sample, affective psychopathy traits were associated with lower GMD in the same areas. Viewing violence increased brain activity in periaqueductal grey matter, thalamus, somatosensory, premotor, and temporal cortices. Psychopathic offenders had increased responses to violence in thalamus and orbitofrontal, insular, and cingulate cortices. In the community sample, impulsivity-related psychopathy traits were positively associated with violence-elicited responses in similar areas. We conclude that brain characteristics underlying psychopathic spectrum in violent psychopathy are related to those observed in well-functioning individuals with asocial personality features.