The Neurochemistry of Love, Lust, Anger, and Aggression

Posted on Oct 7, 2025 in Psychology

Passionate Love: Neurochemical Profile

  • High densities of dopamine (DA) and norepinephrine (NE), but low levels of serotonin (5-HT).
  • Displays subcortical activity in the Ventral Tegmental Area (VTA), caudate nucleus, and putamen.
  • Functions on dopaminergic-rich pathways, resulting in brain activation similar to cocaine use. It is rewarding, positive, and motivating.
  • In response to seeing a loved one, the VTA uses chemical messengers (dopamine, serotonin, and oxytocin) to send signals to the nucleus accumbens.
  • The amygdala and the prefrontal cortex are deactivated.

Companionate Love

  • Less intense, characterized by feelings of calm, social comfort, and security.
  • Animal studies associate it with oxytocin and vasopressin activity in the nucleus accumbens and ventral pallidum.

Unconditional Love

  • Studies showing pictures of individuals with an intellectual disability revealed significant brain activity in the reward and dopaminergic systems.
  • Areas involved include reward, emotion, and social cognition: Insula, globus pallidus, caudate nucleus, VTA, and Periaqueductal Gray (PAG).

Maternal Love

  • Activity observed in the insula and anterior cingulate cortex.
  • Also shows activation in dopaminergic-rich areas.
  • Specific activation of the Periaqueductal Gray (PAG) was observed in maternal love only (not passionate love). This may be because the PAG contains a high density of vasopressin receptors, crucial for maternal bonding.

Lust and Sexual Arousal

  • Dopamine, serotonin, and oxytocin rush to the nucleus accumbens to initiate sexual wanting.
  • Serotonin turns off sexual wanting; serotonin levels decrease after ejaculation.
  • Sexual arousal activates the reward system pathway:
  1. Ventral striatum, Nucleus accumbens, amygdala
  2. Anterior cingulate cortex (initiates autonomic output)
  3. Orbitofrontal cortex (responds to the level of perceived arousal and genital swelling)

The Neurobiology of Negative Emotions

Defining Anger, Disgust, and Contempt

Anger is the feeling of being injured or offended, accompanied by a desire to hurt or threaten the offending person. It can be a direct response to an event or displaced onto others when an individual is out of homeostasis.

Core Violations Associated with Negative Emotions:

  • Anger: Violation of autonomy.
  • Disgust: Violation of purity or divinity.
  • Contempt: Violation of community standards.

Assessment and Physiology of Anger

Self-Reporting Tools for Anger:

  • Multidimensional Anger Inventory: Measures frequency, duration, magnitude, mode of expression, hostile outlook, and range of anger-eliciting situations.
  • STAXI (State-Trait Anger Expression Inventory): Assesses state anger, trait anger, and anger expression, measuring how these components contribute to medical conditions.
  • Constructive Anger-Behavior Verbal Style Scale: Can predict blood pressure.

Physiological and Neural Correlates of Anger:

  • Physiological Changes: Angry facial expressions, perceived increase in body size, deeper voice, widening eyes, and tightening lips.
  • Brain Activity: Activation of the Amygdala and lower levels of prefrontal cortex activity (similar to aggression, where inhibition is reduced).

Aggression: Types and Neural Pathways

Aggression often arises when a goal is blocked, leading to frustration and subsequent aggressive behavior directed at the source of that frustration.

Types of Aggression:

  • Hostile Aggression: Characterized by violent behaviors.
  • Fear-Induced Aggression: Accompanied by fear, usually occurring when escape is impossible; associated with previous unpleasant experiences.
  • Maternal Aggression: Protection of young; a variant of dominant aggression.
  • Intermale Aggression: Fighting between males, including elements of competitive, territorial, and sexual aggression.
  • Territorial Aggression: Behavior directed toward the defense of an area by an individual (e.g., traits developed in guard dogs protecting property).

Motor Pathway for Aggression:

Limbic system → Hypothalamus → Brainstem (initiates motor movements)

Rage and Neurochemical Factors

Neural Pathway for Rage:

Medial Amygdala → Medial Hypothalamus → Periaqueductal Gray (PAG) (leads to aggression)

Key Brain Regions:

  • PAG: Helps determine the next behavioral move.
  • Insula: Monitors internal bodily state (interoception).

Neurochemical Factors Increasing Aggression:

  • Low Serotonin (5-HT) levels
  • High Norepinephrine (NE) levels
  • High Monoamine Oxidase A (MAO-A) activity
  • High Substance P levels
  • Testosterone

Disgust: Neural Correlates

  • Scientific Definition: Offense taken to a noxious object.
  • Lay Definition: Often described as a combination of disgust and fear.
  • Brain Regions Involved: Insula, hippocampus, anterior and posterior cingulate cortex, thalamus, and primary visual cortex.