Carly K. Peterson

The role of asymmetric frontal cortical activity in emotion-related phenomena: A review and update

Conceptual and empirical approaches to the study of the role of asymmetric frontal cortical activity in emotional processes are reviewed. Although early research suggested that greater left than right frontal cortical activity was associated with positive affect, more recent research, primarily on anger, suggests that greater left than right frontal cortical activity is associated with approach motivation, which can be positive (e.g., enthusiasm) or negative in valence (e.g., anger). In addition to reviewing this research on anger, research on guilt, bipolar disorder, and various types of positive affect is reviewed with relation to their association with asymmetric frontal cortical activity. The reviewed research not only contributes to a more complete understanding of the emotive functions of asymmetric frontal cortical activity, but it also points to the importance of considering motivational direction as separate from affective valence in psychological models of emotional space.

PANAS Positive Activation Is Associated With Anger

As a prototypic negative emotion, anger would seem to have little in common with positive activation, as measured by the Positive and Negative Affect Schedule (PANAS; D. Watson, L. A. Clark, & A. Tellegen, 1988). However, growing evidence suggests that both anger and positive affect are associated with approach motivation. This suggests the counterintuitive hypotheses that positive affect should be increased by anger-evoking situations, and that positive affect and anger should be directly correlated in such situations. Four studies tested and supported these hypotheses. Discussion focuses on the implications of these results.

Supine Body Position Reduces Neural Response to Anger Evocation

Body movements affect emotional processes. For example, adopting the facial expressions of specific emotions (even via unobtrusive manipulations) affects emotional judgments and memories (Laird, 2007). Manipulated body postures can affect behavior: slumped postures lead to more ‘‘helpless behaviors’’ (Riskind & Gotay, 1982). Simple body postures may also affect other emotive responses and the neural activations associated with them. Lying flat on one’s back may be antithetical to approach motivation (i.e., the urge to move toward something). We sought to address this issue, which has implications not only for the study of embodiment, but also for the study of neural processes, because some neuroscience techniques rely on individuals being in supine positions. More than 15 studies using electroencephalographic (EEG) and repetitive transcranial magnetic stimulation (rTMS) methods have suggested that the left prefrontal cortex is more activated than the right prefrontal cortex during the experience of anger, particularly anger associated with approach motivational inclinations (Carver & Harmon-Jones, 2009; van Honk & Schutter, 2006). Tomarken and Zald (2009), however, questioned these effects when they reviewed some functional magnetic resonance imaging (fMRI) studies that failed to find greater relative left prefrontal cortical activations during anger. One possible explanation of the divergence of the EEG-rTMS and fMRI studies on anger is that the fMRI studies did not evoke anger associated with approach motivation. Research has shown that mild anger cues only evoke greater relative left frontal cortical activation when approach motivation is also activated (Harmon-Jones, Lueck, Fearn, & Harmon-Jones, 2006). Another possibility for the diverging findings is that the EEGrTMS studies test participants in an upright body position, whereas fMRI studies test participants in a supine body position. We measured relative left frontal EEG activity to an angerinducing insult while participants were upright or reclined. We expected the reclined position to produce less relative left frontal cortical activation than the upright position because a supine position may be antithetical to approach motivation.

Asymmetric frontal cortical activity and negative affective responses to ostracism

Ostracism arouses negative affect. However, little is known about variables that influence the intensity of these negative affective responses. Two studies fill this void by incorporating work on approach- and withdrawal-related emotional states and their associated cortical activations. Study 1 found that following ostracism anger related directly to relative left frontal cortical activation. Study 2 used unilateral hand contractions to manipulate frontal cortical activity prior to an ostracizing event. Right-hand contractions, compared to left-hand contractions, caused greater relative left frontal cortical activation during the hand contractions as well as ostracism. Also, right-hand contractions caused more self-reported anger in response to being ostracized. Within-condition correlations revealed patterns of associations between ostracism-induced frontal asymmetry and emotive responses to ostracism consistent with Study 1. Taken together, these results suggest that asymmetrical frontal cortical activity is related to angry responses to ostracism, with greater relative left frontal cortical activity being associated with increased anger.

Asymmetrical frontal ERPs, emotion, and behavioral approach/inhibition sensitivity

Abstract The present study sought to extend past research on frontal brain asymmetry and individual differences by examining relationships of individual differences in behavioral inhibition/approach system (BIS/BAS) sensitivity with asymmetrical frontal event-related brain responses to startle probes presented during viewing of affective pictures. One hundred and ten participants were shown unpleasant, neutral, and pleasant affective pictures, and presented startle probes during picture presentations. Individual differences in BIS sensitivity related to relatively greater right frontal N100 amplitude to startle probes presented during pleasant and unpleasant pictures, whereas individual differences in BAS sensitivity related to reduced left frontal P300 amplitude to startle probes presented during pleasant pictures. The results of this study suggest that BIS sensitivity is related to greater relative right frontal cortical activity during affective states, while BAS sensitivity is related to greater relative left frontal cortical activity during appetitive states.

Anger and testosterone: evidence that situationally-induced anger relates to situationally-induced testosterone.

Testosterone has been shown to relate to power, dominance, social status, and aggression. However, no research has related situationally induced changes in testosterone to subjective emotional experience. Based on the fact that anger relates to power, dominance, social status, and aggression, we predicted that testosterone would be uniquely related to the subjective experience of anger. In this study, salivary testosterone and cortisol were measured both prior to and following an anger-inducing event. In line with predictions, anger was associated with increased testosterone but not cortisol. These results provide the first evidence of a subjective emotional experience linked with changes in testosterone.

Circadian and seasonal variability of resting frontal EEG asymmetry

Asymmetrical frontal cortical activity at resting baseline relates to important aspects of personality and psychopathology. However, some research has failed to replicate these relationships, perhaps because of situational influences. The present research investigates two situational variables, circadian and seasonal variability. These variables affect basal cortisol levels and mood, which have also been found to relate to resting asymmetrical frontal activity. Results of two correlational studies revealed that relative right frontal activity was greatest during fall mornings. These results suggest the importance of assessing time of day (TOD) and time of year (TOY) effects on resting frontal EEG asymmetry, which could reflect circadian and seasonal influences, but also selection effects when participants are free to select among study session times.

Anger, Motivation, and Asymmetrical Frontal Cortical Activations

This chapter reviews research on the motivational functions of anger and their association with asymmetric frontal cortical activations. In particular, anger is often associated with approach motivational inclinations, though certain individuals in certain situations may manifest anger that is associated with withdrawal motivational inclinations. Because anger is often associated with approach motivation, it is different from other negative emotions and thus is an emotion that permitted testing whether asymmetric (left vs. right) frontal cortical activity was due to positive vs. negative affect or approach vs. withdrawal motivation. Results of several studies revealed that anger is associated with greater relative left frontal activation. Moreover, manipulated increases in the approach motivation of anger cause even greater relative left frontal activation. These results support the idea that greater relative left frontal activity is associated with approach motivation and not positive affective valence. The chapter ends by discussing how this research challenges the idea that the frontal cortex is only involved in down-regulating negative emotions and by suggesting directions for future research examining connectivity among brain regions involved in anger and motivational processes.

Proneness to hypomania predicts EEG coherence between left motor cortex and left prefrontal cortex.

Previous research has demonstrated that hypomania is associated with approach motivation and activity in the left prefrontal cortex (PFC). Other research has linked left motor cortex excitability to approach motivation, suggesting the existence of connections between the motor cortex and PFC. The present research extends this work using unilateral hand contractions to manipulate contralateral cortical activity, and examining the relationship between motor cortex and PFC inter-electrode EEG coherence and hypomania. Within the right-hand contraction condition, hypomania related to greater connectivity between the left motor cortex and left PFC, relative to connectivity between the left motor cortex and right PFC. No relationships were found within the left-hand condition. The present research provides additional support for the role of the left PFC in bipolar disorder, as well as an important extension of research linking motor cortex excitability to emotion and approach motivation.

Toward an Understanding of the Emotion-modulated Startle Eyeblink Reflex: The Case of Anger

Three studies investigated the effect of angering pictures on the startle eyeblink response, based on angers unique identity as an approach-oriented negative affect. In Study 1, eyeblinks to startling noise probes during angering and neutral pictures did not differ, despite angering pictures being rated higher on arousal and anger and more negative in valence. Study 2 replicated Study 1; also, dysphoric participants exhibited potentiated eyeblinks to probes during angering pictures much like those to probes during fear/disgust stimuli. A follow-up study revealed that dysphoric participants rated angering pictures higher in fear. Study 3 again found that eyeblinks to probes during angering and neutral pictures did not differ. Taken together, these results suggest that probes during angering stimuli elicit eyeblinks much like those during neutral stimuli, perhaps due to the competing influences of arousal, valence, and motivation on the startle eyeblink reflex.