Does the “hot- versus cold-blooded” distinction of reactive and proactive aggression extend to physiology?

Aggressive behavior is a multifaceted phenomenon encompassing various behaviors with distinct etiological, developmental, and motivational underpinnings. Reactive aggression is impulsive, emotionally charged, and triggered by real or perceived provocation, whereas proactive aggression is premeditated, controlled, and aimed at achieving specific goals. This review delves into the physiological aspects of aggression to explore the validity of the “hot-blooded” (reactive) versus “cold-blooded” (proactive) distinction, which are thought to be associated with hyper-arousal and hypo-arousal, respectively. To do so, we build on evidence from work investigating the role of heart rate (HR), skin conductance (SC), heart rate variability (HRV), and respiratory sinus arrhythmia (RSA) in the manifestation of reactive and proactive aggression. Our review points to contradicting findings in terms of the physiological arousal patterns associated with each aggressive behavior, although associations with HRV and RSA were more consistent compared to those found for HR and SC measures. We propose distinct possibilities that might explain the identified contradictory evidence. Specifically, we suggest that future research needs to test for (1) environmental moderation (e.g., parenting styles), (2) individual differences (e.g., negative emotionality and callous-unemotional traits), (3) potential associations with physiological responses to threat (e.g., fear conditioning and startle reactivity), and (4) the interaction between sympathetic and parasympathetic nervous systems. Despite its limitations, this line of work also has important implications and can guide more effective interventions for aggressive individuals who operate at a high cost to peers, family members and to the society in general.