Skin color and autonomic nervous system measures

Racial differences in sympathetic nervous system indicators: Implications and challenges for research

Growing evidence indicates the presence of racial differences in sympathetic nervous system (SNS) functioning, yet the nature of these differences is unclear and appears to vary across different indices of SNS activity. Moreover, racial differences among commonly used indices of SNS activity are under-investigated. This systematic review examines racial differences among widely used resting SNS indices, such as electrodermal activity (EDA), pre-ejection period (PEP), and salivary alpha-amylase (sAA). Our review reveals that Black participants have consistently been found to display lower resting EDA compared to White participants. The few studies that have investigated or reported racial differences in PEP and sAA yield mixed findings about whether racial differences exist. We discuss potential reasons for racial differences in SNS activity, such as index-specific factors, lab confounds, psychosocial environmental factors, and their interactions. We outline a framework characterizing possible contributors to racial differences in SNS functioning. Lastly, we highlight the implications of several definitional, analytic, and interpretive issues concerning the treatment of group differences in psychophysiological activity and provide future recommendations.

Electrodermal Activity Is Sensitive to Sleep Deprivation but Does Not Moderate the Effect of Total Sleep Deprivation on Affect

Emotion is characterized by dimensions of affective valence and arousal, either or both of which may be altered by sleep loss, thereby contributing to impaired regulatory functioning. Controlled laboratory studies of total sleep deprivation (TSD) generally show alterations in physiological arousal and affective state, but the relationship of affect and emotion with physiological arousal during TSD has not been well characterized. Established methods for examining physiological arousal include electrodermal activity (EDA) measures such as non-specific skin conductance responses (NSSCR) and skin conductance level (SCL). These measures are robust physiological markers of sympathetic arousal and have been linked to changes in experienced emotion. To explore the link between physiological arousal and affect during sleep deprivation, we investigated individuals’ EDA under TSD and its relationship to self-reported affect. We also investigated the relationship of EDA to two other measures known to be particularly sensitive to the arousal-decreasing effects of TSD, i.e., self-reported sleepiness and performance on a vigilant attention task. Data were drawn from three previously published laboratory experiments where participants were randomly assigned to either well-rested control (WRC) or 38 h of TSD. In this data set, comprising one of the largest samples ever used in an investigation of TSD and EDA (N = 193 with 74 WRC and 119 TSD), we found the expected impairing effects of TSD on self-reported affect and sleepiness and on vigilant attention. Furthermore, we found that NSSCR, but not SCL, were sensitive to TSD, with significant systematic inter-individual differences. Across individuals, the change in frequency of NSSCR during TSD was not predictive of the effect of TSD on affect, sleepiness, or vigilant attention, nor was it related to these outcomes during the rested baseline. Our findings indicate that while physiological arousal, as measured by EDA, may be useful for assessing TSD-related changes in non-specific arousal at the group level, it is not associated with individuals’ self-reported affect at rest nor their change in affect during TSD. This suggests that an essential aspect of the relationship between physiological arousal and self-reported affect is not well captured by EDA as measured by NSSCR.

Does physiologic response to loud tones change following cognitive-behavioral treatment for posttraumatic stress disorder?

This study examined responses to loud tones before and after cognitive-behavioral treatment for posttraumatic stress disorder (PTSD). Seventy-four women in a PTSD treatment outcome study for rape-related (n = 54) or physical assault-related PTSD (n = 20) were assessed in an auditory loud tone paradigm. Assessments were conducted before and after a 6-week period of cognitive-behavioral therapy. Physiologic responses to loud tones included heart rate (HR), skin conductance (SC), and eye-blink electromyogram (EMG). Groups were formed based upon treatment outcome and included a treatment responder group (no PTSD at posttreatment) and a nonresponder group (PTSD-positive at posttreatment). Treatment was successful for 53 of 74 women (72%) and unsuccessful for 21 women (28%). Responders and nonresponders were not significantly different from each other at pretreatment on the main outcome variables. Treatment responders showed a significant reduction in loud tone-related EMG, HR, and SC responses from pre- to posttreatment (partial η(2) = .24, .31, and .36, respectively; all p < .001) and the EMG and HR responses were significantly smaller than nonresponders at posttreatment (partial η(2) = .11, p = .004 and .19, p < .001, respectively). Successful cognitive-behavioral treatment of PTSD is associated with a quantifiable reduction in physiological responding to loud tones.

Affective reactions to pictures of ingroup and outgroup members

A pervasive form of social categorization among humans is between us and them. In this study, we assessed emotional reactions when people viewed pictures depicting members of the same or different ethnic group. African American and European American participants viewed a series of pleasant and unpleasant pictures portraying either ingroup or outgroup members, while physiological, behavioral, and evaluative judgments were measured. Two hypotheses were assessed. The outgroup antipathy hypothesis predicts that people will respond to outgroup pictures with more negative affect than to ingroup pictures. In contrast, the ingroup empathy hypothesis predicts that people will show exaggerated (pleasant and unpleasant) affective responses to pictures of ingroup members, due to group identification or personal relevance. The data provided no support for the antipathy hypothesis, whereas facial EMG, skin conductance, rating, and viewing time data lent support to the ingroup empathy hypothesis, in which greater pleasure and displeasure were apparent when viewing ingroup pictures.

Skin colour, measures of socioeconomic status, and blood pressure among blacks in Erie County, NY

This study examined (1) the construct validity of an observational skin colour measure and (2) the interrelationships of skin colour, measures of socioeconomic status (SES), and blood pressure (BP) in a random survey of black male (n = 354) and black female (n = 641) household residents aged 18-86 in Erie County, NY. Significant associations between lighter skin colour and older age (p < 0.05), and being female (p < 0.01) were observed, confirming known findings. Lighter skin colour was also marginally associated with higher SES (p = 0.06) in females only. Darker skin colour was associated with higher diastolic BP (p < 0.05). The association of skin colour and BP may be explained by considering skin colour as: (1) a marker for socioenvironmental events (i.e. discrimination) and its consequences (i.e. impact on self-esteem), (2) a marker for genes of West African origin, or (3) related directly to BP through a biochemical pathway as yet unknown.

Skin color and education effects on blood pressure

This study reports that education effects but not skin color effects were associated with blood pressure and the incidence of hypertension in a cohort of Black females in Charleston, South Carolina, observed over the period 1960-1975. The authors suggest that skin color may be a secondary (non-causal) associate of blood pressure in Blacks.

Skin color, ethnicity, and blood pressure II: Detroit whites

Census areas in Detroit were ranked for their stress scores based on instability (e.g., crime, marital break up) and socioeconomic status. Four areas were selected for detailed study: 1) high stress, population predominantly black and 2) white, and 3) low stress, population predominantly black and 4) white. A sample was drawn from each area of persons of the predominant race, 25-60 years old, married and living with spouse, and having relatives in the Detroit Area. Nurses interviewed such persons; three blood pressure readings were taken during the first half-hour of medical history, and skin color was rated. While lighter skin color showed a negligible relation to higher blood pressure, a four-category division of European national background based on a skin color cline in Europe from Northern areas to the Mediterranean was significantly associated with a nurse-rating of skin color. The rank order of this four category variable, white ethnicity, was related linearly to both systolic and diastolic blood pressure means. Respondents with parents from Mediterranean countries had the lowest pressures and those from Northern Europe had the highest. The relationship is stronger for women than men. The relationship was independent of nine other control variables including age, overweight, smoking etc., and high and low stress areas, although of greater magnitude for the high than low stress groups. In this article, findings in whites are compared with prior results in blacks. Findings suggest that physiological and biological correlates exist that can be explored profitably by future research.

Skin color, ethnicity, and blood pressure I: Detroit blacks

Census areas in Detroit were ranked for their stress scores based on instability (e.g., crime, marital break up) and socioeconomic status. Four areas were selected for detailed study: 1) high stress, population predominantly black, 2) white, 3) low stress, population predominantly black, 4) white. A sample was drawn from each area of persons of the predominant race, 25-60 years old, married and living with spouse, and having relatives in the Detroit Area. Nurses interviewed such persons; three blood pressure readings were taken during the first half-hour of medical history, and skin color was rated. Results show that darker skin color, for black males especially, is related to higher pressure, independently of nine control variables (e.g., age, weight, socioeconomic status, etc.). However, younger black males (25-39 years of age) in high stress areas had higher pressure than counterparts in low stress areas, regardless of skin color and relative weight; for older black males (40-59 years of age) darker skin color was correlated with higher pressure, regardless of relative weight or stress area. For 35 blacks whose fathers were from the West Indies, pressures were higher than those with American-born fathers. These findings suggest that varied gene mixtures may be related to blood pressure levels and that skin color, an indicator of possible metabolic significance, combines with socially induced stress to induce higher blood pressures in lower class American blacks.

An examination of the relationship between race, skin color and a series of autonomic nervous system measures

In the total population of 75 subjects, the skin albedo correlated significantly with skin resistance, a relationship which was not maintained when the total population was separated into its component subgroups of whites, blacks and Indians. The Indians, "anthropologically Caucasians" but skin color more akin to the blacks, exhibited mean skin reflectance and skin resistance intermediate to that obtained in the black and white groups respectively. Other differences and significant correlations between the autonomic functions in the three groups indicated a higher level of sympathetic tone in the Indians, although this could be attributed to the older age of this group. It was suggested from the results that skin color rather than race has a greater influence on skin resistance.

Use of the pigmentometer, a new device for measuring skin albedo: relating skin color with a series of physiological measures

Use of the Pigmentometer, a new device for measuring skin albedo: Relating skin color with a series of physiological measures. An apparatus has been described for the indirect measurement of skin albedo in human subjects. This device operates on the principle of the reflectance of light as influenced by the lightness or darkness of the skin. This new equipment was used to examine the relationship between lightness or darkness of the skin and the basal level and responsivity of some autonomic nervous system physiological variables in a series of 46 black and 47 white male and female subjects. It was observed that blacks had significantly lower (darker) skin albedo (PI), a significantly higher skin resistance (SR) and amplitude of the galvanic skin response (GSR), and an insignificant higher basal heart rate (HR). Pearson Product-Movement correlations between all measures from the total population showed significant relationships between PI and SR, SR and GSR and HR and HRR (heart rate response). The further separation of the total population into subgroups of blacks, whites, males, females, and black and white male and female goups, respectively, altered some of these differences and relationships previously observed. These results appeared to support the premise that race is more responsible for influencing the measured physiological responses, particularly SR, than is the lightness or darkness of the skin.