5.5: Interbrain Neural Synchrony
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\(\newcommand{\avec}{\mathbf a}\) \(\newcommand{\bvec}{\mathbf b}\) \(\newcommand{\cvec}{\mathbf c}\) \(\newcommand{\dvec}{\mathbf d}\) \(\newcommand{\dtil}{\widetilde{\mathbf d}}\) \(\newcommand{\evec}{\mathbf e}\) \(\newcommand{\fvec}{\mathbf f}\) \(\newcommand{\nvec}{\mathbf n}\) \(\newcommand{\pvec}{\mathbf p}\) \(\newcommand{\qvec}{\mathbf q}\) \(\newcommand{\svec}{\mathbf s}\) \(\newcommand{\tvec}{\mathbf t}\) \(\newcommand{\uvec}{\mathbf u}\) \(\newcommand{\vvec}{\mathbf v}\) \(\newcommand{\wvec}{\mathbf w}\) \(\newcommand{\xvec}{\mathbf x}\) \(\newcommand{\yvec}{\mathbf y}\) \(\newcommand{\zvec}{\mathbf z}\) \(\newcommand{\rvec}{\mathbf r}\) \(\newcommand{\mvec}{\mathbf m}\) \(\newcommand{\zerovec}{\mathbf 0}\) \(\newcommand{\onevec}{\mathbf 1}\) \(\newcommand{\real}{\mathbb R}\) \(\newcommand{\twovec}[2]{\left[\begin{array}{r}#1 \\ #2 \end{array}\right]}\) \(\newcommand{\ctwovec}[2]{\left[\begin{array}{c}#1 \\ #2 \end{array}\right]}\) \(\newcommand{\threevec}[3]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \end{array}\right]}\) \(\newcommand{\cthreevec}[3]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \end{array}\right]}\) \(\newcommand{\fourvec}[4]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \\ #4 \end{array}\right]}\) \(\newcommand{\cfourvec}[4]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \\ #4 \end{array}\right]}\) \(\newcommand{\fivevec}[5]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \\ #4 \\ #5 \\ \end{array}\right]}\) \(\newcommand{\cfivevec}[5]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \\ #4 \\ #5 \\ \end{array}\right]}\) \(\newcommand{\mattwo}[4]{\left[\begin{array}{rr}#1 \amp #2 \\ #3 \amp #4 \\ \end{array}\right]}\) \(\newcommand{\laspan}[1]{\text{Span}\{#1\}}\) \(\newcommand{\bcal}{\cal B}\) \(\newcommand{\ccal}{\cal C}\) \(\newcommand{\scal}{\cal S}\) \(\newcommand{\wcal}{\cal W}\) \(\newcommand{\ecal}{\cal E}\) \(\newcommand{\coords}[2]{\left\{#1\right\}_{#2}}\) \(\newcommand{\gray}[1]{\color{gray}{#1}}\) \(\newcommand{\lgray}[1]{\color{lightgray}{#1}}\) \(\newcommand{\rank}{\operatorname{rank}}\) \(\newcommand{\row}{\text{Row}}\) \(\newcommand{\col}{\text{Col}}\) \(\renewcommand{\row}{\text{Row}}\) \(\newcommand{\nul}{\text{Nul}}\) \(\newcommand{\var}{\text{Var}}\) \(\newcommand{\corr}{\text{corr}}\) \(\newcommand{\len}[1]{\left|#1\right|}\) \(\newcommand{\bbar}{\overline{\bvec}}\) \(\newcommand{\bhat}{\widehat{\bvec}}\) \(\newcommand{\bperp}{\bvec^\perp}\) \(\newcommand{\xhat}{\widehat{\xvec}}\) \(\newcommand{\vhat}{\widehat{\vvec}}\) \(\newcommand{\uhat}{\widehat{\uvec}}\) \(\newcommand{\what}{\widehat{\wvec}}\) \(\newcommand{\Sighat}{\widehat{\Sigma}}\) \(\newcommand{\lt}{<}\) \(\newcommand{\gt}{>}\) \(\newcommand{\amp}{&}\) \(\definecolor{fillinmathshade}{gray}{0.9}\)Interbrain Neural Synchrony
Infants are active in their interactions with other people, engaging with them in synchronous and dynamic exchanges (De Jaegher & Di Paolo, 2007; Schilbach et al., 2013). Figure \(\PageIndex{1}\) displays two images, each showing a type of synchrony that takes place in the everyday interactions between infants and toddlers and their caregivers. The image on the left of Figure \(\PageIndex{1}\) shows an infant and caregiver engaged in dyadic synchrony–they are looking at each other’s faces, sharing eye gaze, emotions, behaviors, etc., The image on the right of Figure \(\PageIndex{1}\) shows a toddler and caregiver engaged in triadic synchrony–they are sharing interest in an object through their shared gaze, emotions, behavior, etc. Interactive coordination, like in these two types of synchrony, is often referred to as interpersonal synchrony, a “dynamic process by which hormonal, physiological, and behavioral cues are exchanged” and reciprocally adjusted between conversational partners (Feldman, 2012). In this way, a synchronous interaction between caregivers and infants and toddlers involves more than shared interest and eye gaze–sharing also takes place at the physiological (e.g., oxytocin, cardiac output) and neural level (Feldman, 2007; Markova & Nguyen, 2023). [1]
A dynamic process by which hormonal, physiological, and behavioral cues are exchanged and reciprocally adjusted between conversational partners
The interpersonal synchrony between an infant and caregiver can be seen in their brains. At the neural level, interbrain synchrony can be defined as a dyadic mechanism, wherein temporally coordinated patterns of brain activity between two interacting individuals supports aspects of their ongoing social interaction (Holroyd, 2022). Interpersonal synchronization of brain rhythms may play a substantive role for caregiver-child coordination, communication, and attachment formation (Atzil & Gendron, 2017). Caregiver and infant face-to-face communication that includes shared gaze and vocalizations elicits greater interbrain synchrony as compared with moments of similar caregiver and infant proximity that do not include facial or vocal communication. Based on existing evidence, short-term outcomes of interbrain synchrony include enhanced social connectedness, effective communication as well as interpersonal regulation (Feldman, 2007; Leong et al., 2017; Stephens et al., 2010). In the long term, interbrain synchronization has been linked to the development of social competence, secure attachment and bonding (Atzil & Gendron, 2017). [3] [4] [5]
Temporally coordinated patterns of brain activity between two interacting individuals supports aspects of their ongoing social interaction
To explore the interpersonal synchronization of brain activity between infants and caregivers engaging in face-to-face turn-taking conversations, researchers have used functional-near infrared spectroscopy (fNIRS) hyperscanning (Nguyen, Zimmer, & Hoehl, 2023). In developmental research, hyperscanning comprises the simultaneous measurement of brain activity in caregiver and child using different neuroimaging methods such as fNIRS, electroencephalography (EEG) and magnetoencephalography (MEG). [7]
A brain monitoring technique that allows for ongoing measurements of brain function, even in young infants
In developmental research, hyperscanning comprises the simultaneous measurement of brain activity in a caregiver and a child, sometimes using different neuroimaging methods
A brain monitoring technique that measures hemodynamic (blood flow) responses elicited from neuronal activation by shining near-infrared light into the brain
A brain monitoring technique that measures neuronal electrical activity using electrodes placed around the scalp
The results from the (fNIRS) hyperscanning (Nguyen, Zimmer, & Hoehl, 2023) study are eye-opening! The more turn-taking caregivers and infants shared, the more they displayed interpersonal neural synchrony during conversations. Figure \(\PageIndex{1}\) displays this data. Looking at Figure \(\PageIndex{1}\), the y-axis shows the level of neural synchrony between caregiver and infant, the x-axis shows the time engaged in the interaction and the colors represent the frequency of turn-taking, green being the highest frequency and red being the lowest frequency. The relation between neural synchrony and turn-taking frequency was stronger in the initial phase of the interaction and decreased over time. You can see this if you follow the green line across the chart, from left to right. The green line is the highest line early on in the interaction, showing that this is when the relationship between neural synchrony and turn-taking is the strongest. As interactions went on, the relationship between turn-taking and neural synchrony decreased (shown by the green line dropping downward across the chart). [9]
[10]
This relationship between neural synchrony and turn-taking primarily occurred in the medial prefrontal cortex (Nguyen, Zimmer, & Hoehl, 2023). Medial prefrontal regions have been implicated in caregiver–infant synchrony, especially in face-to-face exchanges (Piazza et al., 2020). This is consistent with the role of the medial prefrontal cortex in processing communicative signals (Amodio & Frith, 2006; Kampe et al., 2003; Schilbach et al., 2006). In addition, the number of turn-taking in general, but especially infants' turns, was related to a larger vocabulary at twenty-four months of age. [11]
Located in the middle area of the prefrontal cortex and has essential roles in various processes, such as early social cognition
Next, the researchers (Nguyen, Zimmer, & Hoehl, 2023) examined the relationship between caregiver–infant turn-taking and infant brain maturity, measured by inter-hemispheric functional connectivity. Functional connectivity within brain networks can be detected from very early in brain development, even in newborns (Fransson et al., 2009; Gao et al., 2015; Schöpf, Kasprian, Brugger, Prayer, 2012; Thomason et al., 2019; Zhang, Shen, & Lin, 2019). Research points to a developmental progression whereby functional connectivity in some brain networks are already in place at birth, whereas functional connectivity in higher-order brain networks show more protracted development during infancy (Gao et al., 2015; van den Heuvel & Thomason, 2016). Results showed that more frequent infant and caregiver turn-taking was positively related to brain maturation. This means that when caregivers and infants engage in more turn-taking, infants show greater inter-hemispheric functional connectivity. These results support previous research finding that infants' individual differences in inter-hemispheric connectivity can be identified and related to the individual differences they experience, such as turn-taking frequency (Allievi et al., 2016; Kelsey, Farris, & Grossmann, 2021; Nguyen, Zimmer, & Hoehl, 2023). The results emphasize the role of interpersonal neural synchrony in early turn-taking as well as brain maturation as a potential outcome related to early caregiver–infant interactions. [13] [14]
Taken together, interbrain research shows that caregiver–infant interactions and conversations involve a complex exchange where the two become synchronized, even at the neural level. To establish interbrain synchronization, caregivers should ensure that they tune-in to children’s cues and take the time to engage with infants and toddlers, irrespective of the activity, whether it's playing with materials, meal time or changing diapers. Importantly, synchronization involves the caregiver and children–interactions should not be one-sided. Additionally, caregivers who are more sensitive in their interactions show more caregiver–infant neural synchrony (Endevelt-Shapira & Feldman, 2023). When caregivers are synchronized with children, it leads to greater interbrain synchronization and brain maturation, which supports developmental outcomes. [16]
Attributions:
- [1] Markova et al., (2019). Neurobehavioral interpersonal synchrony in early development: The role of interactional rhythms. Frontiers in Psychology, 10, 2078. CC-BY
- [2] Image from Markova et al., (2019). Neurobehavioral interpersonal synchrony in early development: The role of interactional rhythms. Frontiers in Psychology, 10, 2078. CC-BY
- [3] Marriott Haresign et al., (2023). Gaze onsets during naturalistic infant-caregiver interaction associate with ‘sender’ but not ‘receiver’ neural responses, and do not lead to changes in inter-brain synchrony. Scientific Reports, 13(1), 3555. CC by 4.0
- [4] Endevelt-Shapira et al., (2021). Maternal chemosignals enhance infant-adult brain-to-brain synchrony. Science Advances, 7(50), eabg6867. CC by 4.0
- [5] Markova et al., (2019). Neurobehavioral interpersonal synchrony in early development: The role of interactional rhythms. Frontiers in Psychology, 10, 2078. CC-BY
- [6] Image from Marriott Haresign et al., (2023). Gaze onsets during naturalistic infant-caregiver interaction associate with ‘sender’ but not ‘receiver’ neural responses, and do not lead to changes in inter-brain synchrony. Scientific Reports, 13(1), 3555. CC by 4.0
- [7] Turk et al., (2022). Brains in sync: Practical guideline for parent–infant EEG during natural interaction. Frontiers in Psychology, 13, 833112. CC-BY
- [8] Image by Chajes et al., (2022). Examining the role of socioeconomic status and maternal sensitivity in predicting functional brain network connectivity in 5-month-old infants. Frontiers in Neuroscience, 16. CC by 4.0
- [9] Nguyen et al., (2023). Your turn, my turn. Neural synchrony in mother–infant proto-conversation. Philosophical Transactions of the Royal Society B, 378(1875), 20210488. CC by 4.0
- [10] Image from Nguyen et al., (2023). Your turn, my turn. Neural synchrony in mother–infant proto-conversation. Philosophical Transactions of the Royal Society B, 378(1875), 20210488. CC by 4.0
- [11] Nguyen et al., (2023). Your turn, my turn. Neural synchrony in mother–infant proto-conversation. Philosophical Transactions of the Royal Society B, 378(1875), 20210488. CC by 4.0
- [12] Image from Turk et al., (2022). Brains in sync: Practical guideline for parent–infant EEG during natural interaction. Frontiers in Psychology, 13, 833112. CC-BY
- [13] Nguyen et al., (2023). Your turn, my turn. Neural synchrony in mother–infant proto-conversation. Philosophical Transactions of the Royal Society B, 378(1875), 20210488. CC by 4.0
- [14] Kelsey et al., (2021). Variability in infants' functional brain network connectivity is associated with differences in affect and behavior. Frontiers in Psychiatry, 12, 685754. CC-BY
- [15] Image from Hirata et al., (2014). Hyperscanning MEG for understanding mother–child cerebral interactions. Frontiers in Human Neuroscience, 8, 118. CC-BY
- [16] Nguyen et al., (2023). Your turn, my turn. Neural synchrony in mother–infant proto-conversation. Philosophical Transactions of the Royal Society B, 378(1875), 20210488. CC by 4.0