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Tomescu MI, Van der Donck S, Perisanu EM, Berceanu AI, Alaerts K, Boets B, Carcea I. Social functioning predicts individual changes in EEG microstates following intranasal oxytocin administration: A double-blind, cross-over randomized clinical trial. Psychophysiology 2024; 61:e14581. [PMID: 38594888 DOI: 10.1111/psyp.14581] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/03/2023] [Revised: 03/20/2024] [Accepted: 03/21/2024] [Indexed: 04/11/2024]
Abstract
Oxytocin (OXT) modulates social behaviors. However, the administration of exogenous OXT in humans produces inconsistent behavioral changes, affecting future consideration of OXT as a treatment for autism and other disorders with social symptoms. Inter-individual variability in social functioning traits might play a key role in how OXT changes brain activity and, therefore, behavior. Here, we investigated if inter-individual variability might dictate how single-dose intranasal OXT administration (IN-OXT) changes spontaneous neural activity during the eyes-open resting state. We used a double-blinded, randomized, placebo-controlled, cross-over design on 30 typically developing young adult men to investigate the dynamics of EEG microstates corresponding to activity in defined neural networks. We confirmed previous reports that, at the group level, IN-OXT increases the representation of the attention and salience microstates. Furthermore, we identified a decreased representation of microstates associated with the default mode network. Using multivariate partial least square statistical analysis, we found that social functioning traits associated with IN-OXT-induced changes in microstate dynamics in specific spectral bands. Correlation analysis further revealed that the higher the social functioning, the more IN-OXT increased the appearance of the visual network-associated microstate, and suppressed the appearance of a default mode network-related microstate. The lower the social functioning, the more IN-OXT increases the appearance of the salience microstate. The effects we report on the salience microstate support the hypothesis that OXT regulates behavior by enhancing social salience. Moreover, our findings indicate that social functioning traits modulate responses to IN-OXT and could partially explain the inconsistent reports on IN-OXT effects.
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Affiliation(s)
- Miralena I Tomescu
- Faculty of Educational Sciences, Department of Psychology, University "Stefan cel Mare" of Suceava, Bucharest, Romania
- CINETic Center, National University of Theatre and Film "I.L. Caragiale" Bucharest, Bucharest, Romania
- Faculty of Psychology and Educational Sciences, Department of Psychology, University of Bucharest, Bucharest, Romania
| | - Stephanie Van der Donck
- Center for Developmental Psychiatry, Department of Neurosciences, KU Leuven, Leuven, Belgium
- Leuven Autism Research (LAuRes), KU Leuven, Leuven, Belgium
| | - Emanuela M Perisanu
- Institute of Cardiovascular Diseases, Timisoara, Romania
- Faculty of Medicine, University of Sibiu, Sibiu, Romania
| | - Alexandru I Berceanu
- CINETic Center, National University of Theatre and Film "I.L. Caragiale" Bucharest, Bucharest, Romania
| | - Kaat Alaerts
- Neuromodulation Laboratory, Research Group for Neurorehabilitation, KU Leuven, Leuven, Belgium
| | - Bart Boets
- Center for Developmental Psychiatry, Department of Neurosciences, KU Leuven, Leuven, Belgium
- Leuven Autism Research (LAuRes), KU Leuven, Leuven, Belgium
| | - Ioana Carcea
- CINETic Center, National University of Theatre and Film "I.L. Caragiale" Bucharest, Bucharest, Romania
- Department of Pharmacology, Physiology, and Neuroscience, Rutgers Brain Health Institute, Rutgers, The State University of New Jersey, Newark, New Jersey, USA
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2
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Prinsen J, Alaerts K. In the eye of the beholder: Social traits predict motor simulation during naturalistic action perception. Neuropsychologia 2024; 199:108889. [PMID: 38670526 DOI: 10.1016/j.neuropsychologia.2024.108889] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/14/2023] [Revised: 03/22/2024] [Accepted: 04/22/2024] [Indexed: 04/28/2024]
Abstract
Previous research has robustly demonstrated that eye contact between actor and observer promotes the simulation of perceived actions into the observer's own motor system, which in turn facilitates social perception and communication. The socially relevant connotation embedded in eye contact may however be different for individuals with differing social traits. Here, we examined how "normal" (i.e. non-clinical) variability in self-reported social responsiveness/autistic traits, social anxiety and interpersonal relationship style (secure, avoidant or anxious attachment) influences neural motor simulation during action observation in different gaze conditions. To do so, we analyzed an existing dataset involving 124 adult participants (age range: 18-35 years) who underwent transcranial magnetic stimulation (TMS) while observing an actor performing simple hand actions and simultaneously engaging in eye contact or gazing away from the observer. Motor evoked potential (MEP) amplitudes were adopted as an index of motor resonance. Regression-based analyses highlighted the role of social responsiveness and secure attachment in shaping motor resonance, indicating that socially responsive motor resonance during dyadic gaze (i.e., MEPdirect > MEPaverted) was only observed in participants displaying high levels of these traits. Furthermore, a clustering analysis identified two to three distinct subgroups of participants with unique social trait profiles, showing a clear differentiation in motor resonant patterns upon different gaze cues that is in accordance with a recent neurobiological framework of attachment. Together, results demonstrate that motor resonance within a given social interaction may serve as a sensitive tracker of socio-interactive engagement, which allows to capture subclinical inter-individual variation in relevant social traits.
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Affiliation(s)
- Jellina Prinsen
- Neurorehabilitation Research Group, Department of Rehabilitation Sciences, KU Leuven, Leuven, Belgium.
| | - Kaat Alaerts
- Neurorehabilitation Research Group, Department of Rehabilitation Sciences, KU Leuven, Leuven, Belgium
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3
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Prinsen J, Alaerts K. Broken or socially mistuned mirroring in ASD? An investigation via transcranial magnetic stimulation. Autism Res 2022; 15:1056-1067. [PMID: 35384338 DOI: 10.1002/aur.2720] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/08/2021] [Revised: 03/17/2022] [Accepted: 03/21/2022] [Indexed: 11/07/2022]
Abstract
Individuals with an autism spectrum disorder (ASD) experience persistent difficulties during social interactions and communication. Previously, it has been suggested that deficits in the so-called "mirror system," active during both action execution and observation, may underlie these social difficulties. It is still a topic of debate however whether deficiencies in the simulation of others' actions (i.e., "broken" mirroring) forms a general feature of ASD, or whether these mostly reflect a lack of social attunement. The latter would suggest an overall intact mirror system, but an impaired modulation of mirror activity according to variable social contexts. In this study, 25 adults with ASD and 28 age- and IQ-matched control participants underwent transcranial magnetic stimulation during the observation of hand movements under variable conditions. Hand movements were presented via a live interaction partner, either without social context to assess basic motor mirroring or in combination with direct and averted gaze from the actor to assess socially modulated mirroring. Overall, no significant group differences were revealed, indicating no generally diminished mirror activity in ASD. Interestingly however, regression analyses revealed that, among ASD participants, higher symptom severity was associated with both reduced basic motor mirroring and aberrant socially modulated mirroring (i.e., no enhancement of mirror system activity upon observation of the interaction partner's direct vs. averted gaze). These findings further challenge the notion that mirror system dysfunctions constitute a principal feature of ASD, but demonstrate that variations in mirroring may be related to differential expressions of ASD symptom severity. LAY SUMMARY: Our findings show similar activity levels in brain regions responsible for action simulation and understanding in adults with autism, compared to adults without autism. However, the presence of more severe autism symptoms was linked to reduced activity in these regions. This suggests lower levels of brain activity during action understanding in some, but not all, persons with autism, which may contribute to the social difficulties these persons experience in daily life.
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Affiliation(s)
- Jellina Prinsen
- Neurorehabilitation Research Group, Department of Rehabilitation Sciences, KU Leuven, Leuven, Belgium.,Leuven Autism Research Consortium (LAuRes), KU Leuven, Belgium
| | - Kaat Alaerts
- Neurorehabilitation Research Group, Department of Rehabilitation Sciences, KU Leuven, Leuven, Belgium.,Leuven Autism Research Consortium (LAuRes), KU Leuven, Belgium
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4
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Hietanen JK, Peltola MJ. The eye contact smile: The effects of sending and receiving a direct gaze. VISUAL COGNITION 2021. [DOI: 10.1080/13506285.2021.1915904] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/21/2022]
Affiliation(s)
- Jari K. Hietanen
- Human Information Processing Laboratory, Faculty of Social Sciences/Psychology, Tampere University, Tampere, Finland
| | - Mikko J. Peltola
- Human Information Processing Laboratory, Faculty of Social Sciences/Psychology, Tampere University, Tampere, Finland
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5
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Festante F, Rayson H, Paukner A, Kaburu SSK, Toschi G, Fox NA, Ferrari PF. Oxytocin promotes prosocial behavior and related neural responses in infant macaques at-risk for compromised social development. Dev Cogn Neurosci 2021; 48:100950. [PMID: 33831822 PMCID: PMC8042434 DOI: 10.1016/j.dcn.2021.100950] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/03/2020] [Revised: 02/12/2021] [Accepted: 03/30/2021] [Indexed: 01/30/2023] Open
Abstract
Although positive effects of oxytocin (OT) on social functioning are well-demonstrated, little is known about the mechanisms through which OT may drive early social development, or its therapeutic efficacy in infancy. To address these critical issues, we investigated the effects of exogenous OT on neural (EEG) and behavioral responses during observation of live facial gestures in infant macaques with limited social exposure (i.e. nursery-reared). Three key findings were revealed. First, OT increased alpha suppression over posterior scalp regions during observation of facial gestures but not non-biological movement, suggesting that OT targets self-other matching and attentional cortical networks involved in social perception from very early infancy. Second, OT increased infant production of matching facial gestures and attention towards the most socially-relevant facial stimuli, both behaviors typically silenced by early social deprivation. Third, infants with higher cortisol levels appeared to benefit the most from OT, displaying greater improvements in prosocial behaviors after OT administration. Altogether, these findings suggest that OT promotes prosocial behaviors and associated neural responses likely impacted by early social adversity, and demonstrate the potential of OT administration to ameliorate social difficulties in the context of neurodevelopmental and early-emerging psychiatric disorders, at a developmental stage when brain plasticity is greatest.
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Affiliation(s)
- Fabrizia Festante
- Department of Developmental Neuroscience, IRCCS Fondazione Stella Maris, 56128, Pisa, Italy; Department of Clinical and Experimental Medicine, University of Pisa, 56126, Pisa, Italy
| | - Holly Rayson
- Institut des Sciences Cognitives Marc Jeannerod, CNRS/Université Claude Bernard Lyon, Bron, Cedex, 69675, France
| | - Annika Paukner
- Psychology Department, Nottingham Trent University, Nottingham, NG1 4FQ, UK
| | - Stefano S K Kaburu
- Department of Biomedical Science & Physiology, University of Wolverhampton, Wolverhampton, WV1 1LY, UK
| | - Giulia Toschi
- Department of Medicine and Surgery, University of Parma, 43125, Parma, Italy
| | - Nathan A Fox
- Department of Human Development and Quantitative Methodology, University of Maryland, College Park, MD, 20740, USA
| | - Pier Francesco Ferrari
- Institut des Sciences Cognitives Marc Jeannerod, CNRS/Université Claude Bernard Lyon, Bron, Cedex, 69675, France; Department of Medicine and Surgery, University of Parma, 43125, Parma, Italy.
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Enhanced mirroring upon mutual gaze: multimodal evidence from TMS-assessed corticospinal excitability and the EEG mu rhythm. Sci Rep 2020; 10:20449. [PMID: 33235329 PMCID: PMC7687883 DOI: 10.1038/s41598-020-77508-x] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/24/2020] [Accepted: 11/11/2020] [Indexed: 01/10/2023] Open
Abstract
Previous research has demonstrated that eye contact between actor and observer specifically enhances the 'mirroring' of others' actions, as measured by transcranial magnetic stimulation (TMS)-induced motor evoked potentials (MEPs). However, it remains unknown whether other markers of mirror system activation, such as suppression of the EEG mu rhythm (8-13 Hz) over the sensorimotor strip, are also susceptible to perceived eye contact. Here, both TMS-induced MEPs and EEG mu suppression indices were assessed (in separate sessions) while 32 participants (mean age: 24y; 8m) observed a simple hand movement combined with direct or averted gaze from the actor. Both measures were significantly modulated by perceived eye gaze during action observation; showing an increase in MEP amplitude and an attenuation of the mu rhythm during direct vs. averted gaze. Importantly, while absolute MEP and mu suppression scores were not related, a significant association was identified between gaze-related changes in MEPs and mu suppression, indicating that both measures are similarly affected by the modulatory impact of gaze cues. Our results suggest that although the neural substrates underlying TMS-induced MEPs and the EEG mu rhythm may differ, both are sensitive to the social relevance of the observed actions, which might reflect a similar neural gating mechanism.
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Daniels N, Prinsen J, Soriano JR, Alaerts K. Oxytocin enhances the recovery of eye-contact induced autonomic arousal: A treatment mechanism study with placebo-controlled design. Eur Neuropsychopharmacol 2020; 39:87-98. [PMID: 32868176 DOI: 10.1016/j.euroneuro.2020.08.004] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 02/06/2020] [Revised: 07/22/2020] [Accepted: 08/09/2020] [Indexed: 12/19/2022]
Abstract
The neuropeptide oxytocin (OT) is suggested to exert a pivotal role in a variety of complex human behaviors, including trust, attachment, social perception and fear regulation. Previous studies have demonstrated that intranasal administration of OT reduces subjective and neuroendocrine stress responses and dampens amygdala reactivity. OT has also been proposed to modulate activity of the autonomic nervous system. Here, a randomized double-blind, placebo-controlled study (with parallel design) was conducted with 56 healthy adult men to investigate whether a single-dose of OT (24 IU) modulates sympathetic autonomic arousal upon live dyadic gaze interactions. To do so, electrodermal recordings of skin conductance were performed during the engagement of eye contact with a live model in a two-person social context. In accordance to prior research, direct eye gaze elicited a significant enhancement in skin conductance responses, but OT did not specifically enhance or dampen the overall magnitude (amplitude) of the skin conductance response. Administration of OT did facilitate the recovery of skin conductance responses back to baseline (reduced recovery time), indicating a role of OT in restoring homeostatic balance. Notably, the treatment-effect on autonomic recovery was most prominent in participants with low self-reported social responsiveness, indicating that person-dependent factors play an important role in determining OT treatment-responses. Exploratory, it was shown that OT also significantly reduced self-reported feelings of tension and (at trend-level) worrying about how one presents oneself. Together, these observations add further evidence to a role of OT in modulating activity of the autonomic nervous system, primarily by facilitating a restoration of homeostatic balance after stimulus-induced increases in sympathetically-driven autonomic arousal.
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Affiliation(s)
- Nicky Daniels
- KU Leuven, Department of Rehabilitation Sciences, Research Group for Neuromotor Rehabilitation, Tervuursevest 101 box 1501, 3001 Leuven, Belgium
| | - Jellina Prinsen
- KU Leuven, Department of Rehabilitation Sciences, Research Group for Neuromotor Rehabilitation, Tervuursevest 101 box 1501, 3001 Leuven, Belgium
| | - Javier R Soriano
- KU Leuven, Department of Rehabilitation Sciences, Research Group for Neuromotor Rehabilitation, Tervuursevest 101 box 1501, 3001 Leuven, Belgium
| | - Kaat Alaerts
- KU Leuven, Department of Rehabilitation Sciences, Research Group for Neuromotor Rehabilitation, Tervuursevest 101 box 1501, 3001 Leuven, Belgium.
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8
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Soriano JR, Daniels N, Prinsen J, Alaerts K. Intranasal oxytocin enhances approach-related EEG frontal alpha asymmetry during engagement of direct eye contact. Brain Commun 2020; 2:fcaa093. [PMID: 32954338 PMCID: PMC7475692 DOI: 10.1093/braincomms/fcaa093] [Citation(s) in RCA: 9] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/26/2020] [Revised: 06/02/2020] [Accepted: 06/08/2020] [Indexed: 01/09/2023] Open
Abstract
The neuropeptide oxytocin is suggested to play a major role in a variety of complex human behaviours, including interpersonal bonding, trust and attachment. Recent theories have suggested that the role oxytocin plays in these complex social behaviours involves a modulation of motivational tendencies of approach-/avoidance-related behaviours. However, to date, direct neurophysiological evidence supporting this notion is limited. In this double-blind, randomized, placebo-controlled study with parallel design, we assessed the effects of administered intranasal oxytocin in 40 adult men on gaze behaviour and a neural marker of approach/avoidance motivational tendencies. Specifically, electroencephalography recordings were performed during the engagement of eye contact with a live model in a naturalistic two-person social context and electroencephalographic frontal alpha asymmetry, an established neurophysiological index of motivational tendencies for approach-/avoidance-related behaviours, was assessed. Compared to placebo, a single dose of oxytocin (24 international units) was shown to increase relative left-sided frontal asymmetry upon direct eye contact with a live model, which is indicative of an increase in approach-related motivational tendencies towards the presented eye contact stimulus. Notably, the treatment effect was most prominently observed in participants with lower self-reported social motivation (higher Motivation subscale scores on the Social Responsiveness Scale), indicating that participants with lower social motivation benefitted the most from the administered oxytocin. No treatment-specific changes were identified in terms of gaze behaviour towards the eye region of the live model. Together, these observations add neurophysiological evidence to the hypothesized role of oxytocin in modulating approach-/avoidance-related tendencies and suggest that inter-subject variability in person-dependent factors need to be considered to evaluate the potential benefit of intranasal oxytocin as a treatment. This notion is of particular relevance to the variety of neuropsychiatric populations such as autism spectrum disorder, social anxiety disorder and depression, for which intranasal oxytocin is increasingly considered a potential treatment.
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Affiliation(s)
- Javier R Soriano
- Research Group for Neurorehabilitation, Department of Rehabilitation Sciences, KU Leuven, 3001 Leuven, Belgium
| | - Nicky Daniels
- Research Group for Neurorehabilitation, Department of Rehabilitation Sciences, KU Leuven, 3001 Leuven, Belgium
| | - Jellina Prinsen
- Research Group for Neurorehabilitation, Department of Rehabilitation Sciences, KU Leuven, 3001 Leuven, Belgium
| | - Kaat Alaerts
- Research Group for Neurorehabilitation, Department of Rehabilitation Sciences, KU Leuven, 3001 Leuven, Belgium
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9
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Prinsen J, Alaerts K. Eye contact enhances interpersonal motor resonance: comparing video stimuli to a live two-person action context. Soc Cogn Affect Neurosci 2020; 14:967-976. [PMID: 31506688 PMCID: PMC6917019 DOI: 10.1093/scan/nsz064] [Citation(s) in RCA: 22] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/12/2019] [Revised: 07/26/2019] [Accepted: 08/10/2019] [Indexed: 12/12/2022] Open
Abstract
Previous research has shown a link between eye contact and interpersonal motor resonance, indicating that the mirroring of observed movements is enhanced when accompanied with mutual eye contact between actor and observer. Here, we further explored the role of eye contact within a naturalistic two-person action context. Twenty-two participants observed simple hand movements combined with direct or averted gaze presented via a live model in a two-person setting or via video recordings, while transcranial magnetic stimulation was applied over the primary motor cortex (M1) to measure changes in M1 excitability. Skin conductance responses and gaze behavior were also measured to investigate the role of arousal and visual attention herein. Eye contact significantly enhanced excitability of the observer's M1 during movement observation within a two-person setting. Notably, participants with higher social responsiveness (Social Communication subscale of the Social Responsiveness Scale) displayed a more pronounced modulation of M1 excitability by eye gaze. Gaze-related modulations in M1 excitability were, however, not associated with differences in visual attention or autonomic arousal. In summary, the current study highlights the effectiveness and feasibility of adopting paradigms with high ecological validity for studying the modulation of mirror system processes by subtle social cues, such as eye gaze.
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Affiliation(s)
- Jellina Prinsen
- Research Group for Neurorehabilitation, Department of Rehabilitation Sciences, KU Leuven, Leuven, Belgium
| | - Kaat Alaerts
- Research Group for Neurorehabilitation, Department of Rehabilitation Sciences, KU Leuven, Leuven, Belgium
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10
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Festante F, Ferrari PF, Thorpe SG, Buchanan RW, Fox NA. Intranasal oxytocin enhances EEG mu rhythm desynchronization during execution and observation of social action: An exploratory study. Psychoneuroendocrinology 2020; 111:104467. [PMID: 31630052 PMCID: PMC6897365 DOI: 10.1016/j.psyneuen.2019.104467] [Citation(s) in RCA: 14] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 08/27/2018] [Revised: 09/22/2019] [Accepted: 09/24/2019] [Indexed: 01/09/2023]
Abstract
Intranasal administration of oxytocin (OT) has been found to facilitate prosocial behaviors, emotion recognition and cooperation between individuals. Recent electroencephalography (EEG) investigations have reported enhanced mu rhythm (alpha: 8-13 Hz; beta: 15-25 Hz) desynchronization during the observation of biological motion and stimuli probing social synchrony after the administration of intranasal OT. This hormone may therefore target a network of cortical circuits involved in higher cognitive functions, including the mirror neuron system (MNS). Here, in a double-blind, placebo-controlled, between-subjects exploratory study, we investigated whether intranasal OT modulates the cortical activity from sensorimotor areas during the observation and the execution of social and non-social grasping actions. Participants underwent EEG testing after receiving a single dose (24 IU) of either intranasal OT or placebo. Results revealed an enhancement of alpha - but not beta - desynchronization during observation and execution of social grasps, especially over central and parietal electrodes, in participants who received OT (OT group). No differences between the social and non-social condition were found in the control group (CTRL group). Moreover, we found a significant difference over the cortical central-parietal region between the OT and CTRL group only within the social condition. These results suggest a possible action of intranasal OT on sensorimotor circuits involved in social perception and action understanding, which might contribute to facilitate the prosocial effects typically reported by behavioral studies.
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Affiliation(s)
- Fabrizia Festante
- Department of Developmental Neuroscience, IRCCS Fondazione Stella Maris, 56128, Pisa, Italy,Department of Medicine and Surgery, University of Parma, 43125, Parma, Italy
| | - Pier Francesco Ferrari
- Department of Medicine and Surgery, University of Parma, 43125, Parma, Italy,Institut des Sciences Cognitives Marc Jeannerod, CNRS, Bron, Cedex 69675, France
| | - Samuel G. Thorpe
- Department of Human Development and Quantitative Methodology, University of Maryland, College Park, MD 20740, USA
| | - Robert W. Buchanan
- Maryland Psychiatric Research Center, University of Maryland School of Medicine, Baltimore, MD 21228, USA
| | - Nathan A. Fox
- Department of Human Development and Quantitative Methodology, University of Maryland, College Park, MD 20740, USA
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