Corrigendum to' The vagal paradox: A polyvagal solution' [Compr. Psychoneuroendocrinology 16C (2023) 100200].

[This corrects the article DOI: 10.1016/j.cpnec.2023.100200.].

The vagal paradox: A polyvagal solution.

Although there is a consistent literature documenting that vagal cardioinhibitory pathways support homeostatic functions, another less frequently cited literature implicates vagal cardioinhibitory pathways in compromises to survival in humans and other mammals. The latter is usually associated with threat reactions, chronic stress, and potentially lethal clinical conditions such as hypoxia. Solving this 'vagal paradox' in studies conducted in the neonatal intensive care unit served as the motivator for the Polyvagal Theory (PVT). The paradox is resolved when the different functions of vagal cardioinhibitory fibers originating in two anatomically distinguishable brainstem areas are recognized. One pathway originates in a dorsal area known as the dorsal motor nucleus of the vagus and the other in a ventral area of the brainstem known as nucleus ambiguus. Unlike mammals, in all ancestral vertebrates from which mammals evolved, cardioinhibitory vagal fibers primarily originate in the dorsal motor nucleus of the vagus. Thus, in mammals the vagus nerve is 'poly' vagal because it contains two distinct efferent pathways. Developmental and evolutionary biology identify a ventral migration of vagal cardioinhibitory fibers that culminate in an integrated circuit that has been labeled the ventral vagal complex. This complex consists of the interneuronal communication of the ventral vagus with the source nuclei involved in regulating the striated muscles of the head and face via special visceral efferent pathways. This integrated system enables the coordination of vagal regulation of the heart with sucking, swallowing, breathing, and vocalizing and forms the basis of a social engagement system that allows sociality to be a potent neuromodulator resulting in calm states that promote homeostatic function. These biobehavioral features, dependent on the maturation of the ventral vagal complex, can be compromised in preterm infants. Developmental biology informs us that in the immature mammal (e.g., fetus, preterm infant) the ventral vagus is not fully functional and myelinization is not complete; this neuroanatomical profile may potentiate the impact of vagal cardioinhibitory pathways originating in the dorsal motor nucleus of the vagus. This vulnerability is confirmed clinically in the life-threatening reactions of apnea and bradycardia in human preterm newborns, which are hypothetically mediated through chronotropic dorsal vagal pathways. Neuroanatomical research documents that the distribution of cardioinhibitory neurons representing these two distinct vagal source nuclei varies among mammals and changes during early development. By explaining the solution of the 'vagal paradox' in the preterm human, the paper highlights the functional cardioinhibitory functions of the two vagal source nuclei and provides the scientific foundation for the testing of hypotheses generated by PVT.

Association of Self-Reported Autonomic Symptoms With Sensor-Based Physiological Measures.

OBJECTIVE: Autonomic regulation of organ and tissues may give rise to disruptions of typical functions. The Body Perception Questionnaire Short Form (BPQ-SF) includes items that were developed to assess autonomic symptoms in daily life. This pair of studies aimed to establish previously unexplored psychometric properties of the BPQ-SF autonomic symptoms scale, develop normative values for clinical and research use, and assess the convergence of self-reports with sensor-based measures. METHODS: Study 1 reports exploratory and confirmatory factor analysis on BPQ-SF autonomic symptom items from a large US population-based online study ( n = 2048). In study 2, BPQ-SF scores were examined for associations with heart period, respiratory sinus arrhythmia, and skin conductance during seated leg lifts in a community sample ( n = 62). RESULTS: Study 1 results supported a two-factor supradiaphragmatic and subdiaphragmatic autonomic symptom solution (confirmatory factor analysis: root mean squared error of approximation = 0.040, Comparative Fit Index = 0.99, Tucker-Lewis Index = 0.99), although a one-factor solution also fit the data well (root mean squared error of approximation = 0.080, Comparative Fit Index = 0.99, Tucker-Lewis Index = 0.99). In study 2, heart period responses to leg lifts and rests were demonstrated at all autonomic symptom levels. However, low autonomic symptoms were associated with optimal autonomic nervous system patterns of activation and recovery to baseline levels. Moderate symptoms were associated with prolonged sympathetic activation. The highest symptom levels were associated with impaired autonomic nervous system coordination across activation and recovery. CONCLUSIONS: Results support the utility of self-reports of autonomic symptoms in research and clinical applications, with higher symptoms likely indicating autonomic impairment.

Appeasement: replacing Stockholm syndrome as a definition of a survival strategy.

Background: Stockholm syndrome or traumatic bonding (Painter & Dutton, Patterns of emotional bonding in battered women: Traumatic bonding. International Journal of Women's Studies, 8(4), 363-375, 1985) has been used in mainstream culture, legal, and some clinical settings to describe a hypothetical phenomenon of trauma survivors developing powerful emotional attachments to their abuser. It has frequently been used to explain the reported 'positive bond' between some kidnap victims and their captor's, although scarce empirical research has supported this assertion. It has been used in various situations where interpersonal violence and mind control are reported and where clear power differentials exist, such as in child sexual abuse, intimate partner violence, human trafficking, and hostage situation scenarios.Objective: We propose replacing Stockholm syndrome with 'appeasement,' a term that can be explained through a biopsychological model (i.e. Polyvagal Theory) to describe how survivors may appear emotionally connected with their perpetrators to effectively adapt to life-threatening situations by calming the perpetrator.Conclusion: We believe the term appeasement will demystify the reported survivor experiences and will, in the eyes of the public, victims, and survivors, provide a science-based explanation for their narratives of survival that may initially appear to be contradictory. By understanding the potent reflexive neurobiological survival mechanisms embedded in appeasement, individuals and families can operationalise their survival from a perspective that supports resilience, a healthy long-term recovery, and normalises their coping responses as survival techniques.

Changing and redefining how victims are viewed and portrayed in mainstream media.Appeasement emphasises the asymmetry and adaptive strategy used to regulate and calm the captor, thus minimising potential injury and abuse.Stockholm syndrome does not reflect the survivor's experience nor does it acknowledge the negative impact that the label has on the survivor.

Differential Momentary Reports of Stress and Affect Associated With Alcohol Consumption in Middle-Aged Versus Younger Adults.

Background: Stress is a motivator to consume alcohol, a well-documented relapse risk, and is known to differentially affect biological and psychological processes as people age.Objectives: Because alcohol consumption is known to acutely decrease stress and increase affect, this study examined differences in ratings of stress and affect in middle-aged versus younger adults who regularly consume alcohol.Methods: A sample of younger (n = 17) and middle-aged (n = 18) drinkers was studied during a 3-day period of typical alcohol consumption. Resting levels of respiratory sinus arrhythmia (RSA) were measured during a baseline study visit since RSA is a well-documented biomarker of stress and is known to decrease with age. Ecological momentary assessment (EMA) survey ratings (n = 1,598) were modeled using hierarchical regression to assess differences in stress and affect throughout the day between the two age groups.Results: As anticipated, middle-aged participants had lower RSA than those who were younger. Although the middle-aged adults showed overall lower stress, generally they also experienced higher affect than the younger adults. Middle-aged adults experienced a significant reduction in stress following drinking while no such effect was observed in the younger adults.Conclusions: To our knowledge, this is the first investigation using EMA methodology to examine stress and affect between younger and middle-aged adults who habitually consume alcohol. These cross-sectional data suggest potential momentary stress relief to engaging with moderate alcohol consumption in a middle-aged population. Future work must address this important motivational process in curtailing maintenance of alcohol consumption and preventing escalation of consumption.

A study of respiratory sinus arrhythmia and stuttering persistence.

INTRODUCTION: The present study investigated potential differences in respiratory sinus arrhythmia between preschool-age children with persisting stuttering, children who recovered from stuttering, and children who do not stutter. METHODS: Participants were 10 children with persisting stuttering (persisting group), 20 children who recovered from stuttering (recovered group), and 36 children who do not stutter (non-stuttering group). Participants viewed a neutral video clip to establish a pre-arousal baseline and then viewed two emotionally-arousing video clips (positive and negative, counterbalanced). Age-appropriate speaking tasks followed each of the video clips (post-baseline, post-positive, and post-negative). Respiratory sinus arrhythmia (RSA), an index of parasympathetic nervous system activity, was measured during the video clips and subsequent speaking tasks. RESULTS: First, the persisting group, recovered group, and non-stuttering group did not significantly differ in baseline RSA. Second, during the emotionally-arousing video clips, there was a significant group x condition interaction, with the recovered group exhibiting significantly lower RSA in the positive than negative condition, and the non-stuttering group exhibiting significantly higher RSA in the positive than negative condition. Third, in the narrative tasks, there was a significant group x condition interaction, with a greater difference in RSA between the post-baseline speaking task and the post-positive and post-negative speaking tasks for the persisting compared to the non-stuttering group. Lastly, a follow-up analysis indicated that the recovered and nonstuttering groups, compared to the persisting group, exhibited significantly greater RSA during the baseline (neutral) condition compared to the post-neutral narrative task. CONCLUSIONS: Findings provide a physiological perspective of emotion within children who stutter and persist and children who stutter and recover. Future investigations with larger sample sizes and diverse methodologies are necessary to provide novel insights on the specific emotion-related processes that are potentially involved with persistence of stuttering in young children.

Cardiac Vagal Regulation Is Impeded in Children With Cyclic Vomiting Syndrome.

INTRODUCTION: The pathophysiology underlying cyclic vomiting syndrome (CVS) remains undefined. Scant data and distinct clinical features point to altered autonomic nervous system function. Autonomic signaling can be noninvasively assessed through cardiac indices of parasympathetic vagal regulation, which is reduced in children with disorders of gut-brain interaction. We aimed to examine dynamic cardiac vagal regulation in children with CVS compared with that in healthy controls (HC). METHODS: A total of 31 children with CVS evaluated in a tertiary care CVS center and 66 HC (ages 8-18 years) underwent cardiac autonomic function assessment. Electrocardiogram recordings were conducted during 3-minute sit/stand/sit posture challenges. The electrocardiogram-derived variables heart period, respiratory sinus arrhythmia (RSA), and vagal efficiency (VE) were analyzed using linear regression and mixed-effects modeling. RESULTS: After exclusion of medication confounders, 23 patients with CVS were included in analyses. Both groups were comparable in age, gender, and body mass index. Compared with HC, children with CVS had shorter heart period (standardized mean difference range: 1.15-1.22, all P values < 0.05) and lower RSA (SMD range: 0.66-0.88, all P values < 0.05). Patients with CVS had significantly lower VE during the entire course of posture shifts, compared with HC ( B = -19.87, SE = 6.95, t = -2.86, P = 0.005, SMD = 0.76). DISCUSSION: Children with CVS have suboptimal parasympathetic autonomic regulation compared with HC, indexed by reduced RSA and VE, even during their interepisodic well phase. Abnormal vagal modulation may underlie CVS pathophysiology, comorbidities, and triggers. Assessing VE during posture stressors could inform therapeutic interventions.

Association of childhood maltreatment with adult body awareness and autonomic reactivity: The moderating effect of practicing body psychotherapy.

Research shows the disruptive effects of early maltreatment on the autonomic nervous system (ANS) functioning in adulthood. Psychotherapists not only tend to report higher rates of personal experience with early maltreatment, but also fewer mental problems and disturbances in adulthood, as compared to other professions. However, the role of the ANS in these processes has been understudied despite the relevance of the therapist's psychological state and related nonverbal communication for the therapeutic alliance. By comparing body psychotherapists to the general population, the present study aimed to explore the effects of practicing body psychotherapy (BPT) on the link between early maltreatment and autonomic reactivity in adulthood. An online study included 570 body psychotherapists from 35 countries (54% from the United States, Mage = 52.92, 81% of females) and 592 participants from the U.S. general population (Mage = 51.89, 78% females). We first inspected the factorial structure of the Body Perception Questionnaire-Short Form (Cabrera et al., 2018) in the specific population of BPT practitioners, confirming the three-factor model with one body awareness and two autonomic reactivity factors. Compared to the general population, BPT practitioners reported higher levels of childhood maltreatment, but fewer autonomic symptoms in adulthood, better differentiation of body awareness and autonomic reactivity, and a weaker association between childhood maltreatment experiences and present-day autonomic symptoms. Results are discussed in the framework of polyvagal theory (Porges, 1995, 2011). (PsycInfo Database Record (c) 2023 APA, all rights reserved).

Heart Rate Variability: A Personal Journey.

Heart rate variabfility (HRV) has been a focal point throughout my academic history. To put into perspective, I have published studies spanning seven decades focusing on HRV (1969-2022). My interest in HRV started early in graduate school and continues to be an important portal informing my theoretical perspective. The current paper tracks some of this history, which started as an empirical observation and moved through several scientific stages including development of quantitative methods and investigations of neural mechanisms. Along this journey a variety of hypotheses were tested including the relative sensitivity of HRV metrics to neural mechanisms, psychological processes, and medical diagnoses. In addition, the research led to the identification of portal of intervention that have become strategies to optimize mental and physical health. These apparent disparate programs of inquiry have been tightly merged as the Polyvagal Theory evolved. In the sections below, I have shared my personal journey through these stages of scientific inquiry and my attempts to integrate the new knowledge in an expansive theoretical model.

"A new measure of feeling safe: Developing psychometric properties of the Neuroception of Psychological Safety Scale (NPSS)": Correction.

Reports an error in "A new measure of feeling safe: Developing psychometric properties of the Neuroception of Psychological Safety Scale (NPSS)" by Liza Morton, Nicola Cogan, Jacek Kolacz, Calum Calderwood, Marek Nikolic, Thomas Bacon, Emily Pathe, Damien Williams and Stephen W. Porges (Psychological Trauma: Theory, Research, Practice, and Policy, Advanced Online Publication, Jul 18, 2022, np). In the original article, the first name of Jacek Kolacz was misspelled as "Jakec" in the author byline and twice in the acknowledgments. In addition, the affiliations of Jacek Kolacz and Stephen W. Porges were incorrect. All versions of this article have been corrected. (The following abstract of the original article appeared in record 2022-82545-001). OBJECTIVE: Psychological safety is increasingly recognized as central to mental health, wellbeing and posttraumatic growth. To date, there is no psychometrically supported measure of psychological safety combining psychological, physiological and social components. The current research aimed to develop and establish the neuroception of psychological safety scale (NPSS), informed by Polyvagal Theory. METHOD: The study comprised of 3 stages: (a) item generation, (b) item reduction, and (c) assessment of factor structure and internal consistency. Exploratory and confirmatory factor analysis was conducted from 2 samples who completed a survey online (exploratory n = 342, confirmatory n = 455). RESULTS: Initially, 107 items were generated. Item reduction and exploratory factor analysis resulted in a 29-item NPSS with subscales of compassion, social engagement and body sensations. The NPSS was found to have a consistent factor structure and internal consistency. CONCLUSION: The NPSS is a novel measure of psychological safety which can be used across a range of health and social care settings. This research provides a platform for further work to support and enhance understandings of the science of safety through the measurement of psychological, relational and physiological components of safety. The NPSS will help shape new approaches to evaluating trauma treatments, relational issues and mental health concerns. Research to establish the convergent, discriminant and concurrent validity of the NPSS and to explore its use with diverse community and clinical populations is underway. (PsycInfo Database Record (c) 2022 APA, all rights reserved).

A new measure of feeling safe: Developing psychometric properties of the Neuroception of Psychological Safety Scale (NPSS).

[Correction Notice: An Erratum for this article was reported online in Psychological Trauma: Theory, Research, Practice, and Policy on Sep 15 2022 (see record 2023-01894-001). In the original article, the first name of Jacek Kolacz was misspelled as "Jakec" in the author byline and twice in the acknowledgments. In addition, the affiliations of Jacek Kolacz and Stephen W. Porges were incorrect. All versions of this article have been corrected.] Objective: Psychological safety is increasingly recognized as central to mental health, wellbeing and posttraumatic growth. To date, there is no psychometrically supported measure of psychological safety combining psychological, physiological and social components. The current research aimed to develop and establish the neuroception of psychological safety scale (NPSS), informed by Polyvagal Theory. METHOD: The study comprised of 3 stages: (a) item generation, (b) item reduction, and (c) assessment of factor structure and internal consistency. Exploratory and confirmatory factor analysis was conducted from 2 samples who completed a survey online (exploratory n = 342, confirmatory n = 455). RESULTS: Initially, 107 items were generated. Item reduction and exploratory factor analysis resulted in a 29-item NPSS with subscales of compassion, social engagement and body sensations. The NPSS was found to have a consistent factor structure and internal consistency. CONCLUSION: The NPSS is a novel measure of psychological safety which can be used across a range of health and social care settings. This research provides a platform for further work to support and enhance understandings of the science of safety through the measurement of psychological, relational and physiological components of safety. The NPSS will help shape new approaches to evaluating trauma treatments, relational issues and mental health concerns. Research to establish the convergent, discriminant and concurrent validity of the NPSS and to explore its use with diverse community and clinical populations is underway. (PsycInfo Database Record (c) 2022 APA, all rights reserved).

Increased Autonomic Reactivity and Mental Health Difficulties in COVID-19 Survivors: Implications for Medical Providers.

Background: Because there is a relationship between mental health (MH) and medical adversity and autonomic dysregulation, we hypothesized that individuals infected with COVID-19 would report greater current autonomic reactivity and more MH difficulties (emotional distress, mindfulness difficulties, and posttraumatic stress). We also hypothesized that individuals diagnosed with COVID-19 who are experiencing difficulties related to their prior adversity and those providing medical care to COVID-19 patients would be more negatively impacted due to their increased stress and infection rates. Method: US participants (N = 1,638; 61% female; Age M = 46.80) completed online self-report measures of prior adversity, current autonomic reactivity and current MH difficulties, and COVID-19 diagnosis history. Participants diagnosed with COVID-19 (n = 98) were more likely to be younger and providing medical care to COVID-19 patients. Results: Individuals diagnosed with COVID-19 reported increased current autonomic reactivity, being more negatively impacted by their prior MH/medical adversities, and currently experiencing more MH difficulties with an increased likelihood of clinically-significant PTSD and depression (p < 0.01 - p < 0.001). Current autonomic reactivity mediated 58.9% to 85.2% of the relationship between prior adversity and current MH difficulties; and COVID-19 diagnosis moderated and enhanced the effect of prior adversity on current autonomic reactivity (p < 0.01). Being a medical provider was associated with increased current autonomic reactivity (p < 0.01), while moderating and enhancing the relationship between current autonomic reactivity and emotional distress and posttraumatic stress symptoms (p < 0.05). Combining COVID-19 diagnosis with being a medical provider increased likelihood of clinically-significant PTSD and depression (p < 0.01). Conclusion: Individuals diagnosed with COVID-19, particularly medical providers, have increased current autonomic reactivity that is associated with their prior adversities and current MH difficulties.

Childhood Maltreatment Influences Autonomic Regulation and Mental Health in College Students.

Childhood maltreatment history may influence autonomic reactivity and recovery to stressors. Hypothetically, the maltreatment history may contribute to a retuned autonomic nervous system that is reflected in a novel metric, vagal efficiency (VE), designed to assess the functional efficiency of vagal cardioinhibitory pathways on heart rate. We explored whether VE mediates the well-documented relationship between maltreatment history and psychiatric symptoms. We also investigated the relationship between measures of autonomic regulation in response to the physical and emotional challenges and psychiatric symptoms. Participants (n = 167) completed self-report measures of psychiatric symptoms and had continuous beat-to-beat heart rate monitored before, during, and after physical and emotional stressors. Participants with maltreatment histories exhibited lower VE, which mediated the association of maltreatment history and the psychiatric symptoms of anxiety and depression. Consistent with prior literature, there were significant associations between maltreatment history and autonomic reactivity (i.e., heart rate and respiratory sinus arrhythmia) during emotional and physical challenges; however, when VE was entered as a covariate these associations were no longer statistically significant. Blunted VE may reflect a neural pathway through which maltreatment retunes autonomic regulation and provides a neurophysiological platform that increases mental health risk.

Polyvagal Theory: A Science of Safety.

Contemporary strategies for health and wellbeing fail our biological needs by not acknowledging that feelings of safety emerge from internal physiological states regulated by the autonomic nervous system. The study of feelings of safety has been an elusive construct that has historically been dependent upon subjectivity. Acknowledging that feelings of safety have a measurable underlying neurophysiological substrate would shift investigations of feelings of safety from a subjective to an objective science. Polyvagal Theory provides an innovative scientific perspective to study feelings of safety that incorporates an understanding of neuroanatomy and neurophysiology. This perspective identifies neural circuits that downregulate neural regulation of threat reactions and functionally neutralize defensive strategies via neural circuits communicating cues of safety that enable feelings of safety to support interpersonal accessibility and homeostatic functions. Basically, when humans feel safe, their nervous systems support the homeostatic functions of health, growth, and restoration, while they simultaneously become accessible to others without feeling or expressing threat and vulnerability. Feelings of safety reflect a core fundamental process that has enabled humans to survive through the opportunistic features of trusting social engagements that have co-regulatory capacities to mitigate metabolically costly defense reactions. Through the study of neural development and phylogeny, we can extract foundational principles and their underlying mechanisms through which the autonomic nervous system leads to feelings of safety and opportunities to co-regulate. Several principles highlight the validity of a science of safety that when implemented in societal institutions, ranging from healthcare to education, would enhance health, sociality, and lead to greater productivity, creativity, and a sense of wellbeing. By respecting our need to feel safe as a biological imperative linked to survival, we respect our phylogenetic heritage and elevate sociality as a neuromodulator that functionally provides the scientific validation for a societal focus on promoting opportunities to experience feelings of safety and co-regulation.

Correction: Peterson et al. Influence of Heart Rate Variability on Abstinence-Related Changes in Brain State in Everyday Drinkers. Brain Sci. 2021, 11, 817.

In the original article [...].

Autonomic Measures in Differentiating Depressive Disorders: A Potential AID.

Objective: The present study aimed at exploring the potential utility of autonomic regulation as a useful marker in the diagnostic differentiation between unipolar and bipolar depression. Method: Respiratory sinus arrhythmia (RSA), low-frequency (LF) of heart rate variability, and systolic blood pressure (SBP) were assessed in patients with bipolar depression (31) and major depressive disorder (MDD=32), and in healthy controls (HCs=32). Since bipolar depressed subjects were maintained on specific medications to manage manic/hypomanic symptoms, we explored whether mood stabilizers (atypical antipsychotics and anticonvulsants or their combinations) could independently affect the physiological parameters. Results: When the autonomic measures were analyzed by a multivariate analysis of variance (MANCOVA), after controlling for BMI, the combination of variables (RSA, LF, SBP) discriminated patients with bipolar depression and MDD from HC (F(6, 178)=3.036, p=0.007, Λ=0.823, partial η2=0.093). In any case, we cannot exclude that mood stabilizers might have affected SBP values in the bipolar group. To deconstruct this multivariate effect, pairwise ANOVAs and discriminant analyses contrasted groups and documented that RSA was the primary variable distinguishing the groups. Discriminant function analyses showed that RSA had a significant discriminating weight between bipolar depressed patients and HC subjects (p<0.0005). By contrast, RSA showed a trend towards the statistical significance in discriminating between bipolar depression and MDD patients (p=0.06). Conclusions: The assessment of RSA and SBP in outpatient settings might be helpful in the differential diagnosis of affective disorders.

Breastfeeding is related to atypical autonomic and behavior regulation in infants with a history of excessive crying.

The study investigated autonomic regulation during feeding in six-month old infants with a history of excessive crying (EC) and social-behavioral development at 12 and 24 months. When contrasted with non-EC infants (NEC), EC infants had atypical autonomic responses observed as dampened reductions in respiratory sinus arrhythmia (RSA) and decreases in heart period (HP) during feeding. EC infants demonstrated atypical autonomic regulation only if they were bottle-fed, while breastfed EC infants had patterns of autonomic regulation similar to NEC infants. Behavioral data suggest that while a history of EC was related to social-emotional behaviors at 12 and 24 months, breastfeeding may buffer the behavioral effects of EC on sociability at 24 months.

Associations between acoustic features of maternal speech and infants' emotion regulation following a social stressor.

Caregiver voices may provide cues to mobilize or calm infants. This study examined whether maternal prosody predicted changes in infants' biobehavioral state after the still face, a stressor in which the mother withdraws and reinstates social engagement. Ninety-four dyads participated in the study (infant age 4-8 months). Infants' heart rate and respiratory sinus arrhythmia (measuring cardiac vagal tone) were derived from an electrocardiogram (ECG). Infants' behavioral distress was measured by negative vocalizations, facial expressions, and gaze aversion. Mothers' vocalizations were measured via a composite of spectral analysis and spectro-temporal modulation using a two-dimensional fast Fourier transformation of the audio spectrogram. High values on the maternal prosody composite were associated with decreases in infants' heart rate (ß = -.26, 95% CI: [-0.46, -0.05]) and behavioral distress (ß = -.23, 95% CI: [-0.42, -0.03]), and increases in cardiac vagal tone in infants whose vagal tone was low during the stressor (1 SD below mean ß = .39, 95% CI: [0.06, 0.73]). High infant heart rate predicted increases in the maternal prosody composite (ß = .18, 95% CI: [0.03, 0.33]). These results suggest specific vocal acoustic features of speech that are relevant for regulating infants' biobehavioral state and demonstrate mother-infant bi-directional dynamics.