Hypoarousal and Hyperarousal

Hypoarousal and hyperarousal are dysregulated nervous system states that result from trauma. These states represent the body’s adaptive responses to threat, but when they persist beyond the traumatic event, they become problematic patterns that interfere with daily functioning and well-being.

Hyperarousal

Hyperarousal is a state of heightened nervous system activation characterized by constant vigilance, reactivity, and a sense of being “on edge.” It represents the body’s attempt to remain ready to respond to perceived threats.

Characteristics of Hyperarousal

• Hypervigilance: Constant scanning of the environment for potential threats
• Irritability: Heightened reactivity to stimuli, both internal and external
• Difficulty sleeping: Trouble falling asleep, staying asleep, or feeling rested
• Startle response: Exaggerated responses to unexpected sounds or movements
• Racing thoughts: Mind constantly active, difficulty quieting thoughts
• Muscle tension: Chronic physical tension throughout the body
• Difficulty concentrating: Mind jumps from threat to threat
• Physical symptoms: Rapid heart rate, shallow breathing, sweating, digestive issues

Hypoarousal

Hypoarousal is a state of nervous system shutdown or collapse, characterized by numbing, dissociation, and a sense of being “checked out” or disconnected. It represents the body’s attempt to conserve energy when fighting or fleeing is not possible.

Characteristics of Hypoarousal

• Emotional numbing: Difficulty feeling emotions or feeling disconnected from them
• Dissociation: Feeling disconnected from self, body, or surroundings
• Fatigue and exhaustion: Persistent tiredness despite adequate rest
• Brain fog: Difficulty thinking clearly or processing information
• Depression: Low mood, lack of motivation, feelings of hopelessness
• Social withdrawal: Desire to isolate and disconnect from others
• Physical numbness: Reduced sensation in the body
• Feeling “frozen”: Difficulty taking action or making decisions

The Window of Tolerance

In a healthy nervous system, there’s a “window of tolerance”—a range of arousal where an individual can function effectively, process information, and respond appropriately to situations. Trauma narrows this window, making it easier to move into either hyperarousal (too much activation) or hypoarousal (too little activation) states.

Why These States Persist

After trauma, the nervous system can become “stuck” in these states because:

• The body learned that the world is dangerous (hyperarousal) or that there’s no escape (hypoarousal)
• These states became habitual responses to any stress, not just life-threatening situations
• The nervous system hasn’t learned that it’s safe to return to baseline regulation
• Physical patterns of tension and shutdown have become chronic

Moving Toward Regulation

Recovery involves learning to recognize these states, understand their protective function, and gradually expand the window of tolerance. This often involves:

• Somatic practices: Body-based approaches that help regulate the nervous system
• Mindfulness: Developing awareness of arousal states without judgment
• Breathing techniques: Using breath to shift between arousal states
• Grounding exercises: Techniques to anchor in the present moment
• Building safety: Creating internal and external conditions that support regulation

Neuroscience of Arousal States

The Autonomic Nervous System

Arousal states are regulated by the autonomic nervous system (ANS), which has two primary branches:

• Sympathetic nervous system: Activates the body for action (fight or flight), responsible for hyperarousal
• Parasympathetic nervous system: Calms the body and promotes rest, but can also trigger hypoarousal through shutdown responses

As Stephen Porges explains in his Polyvagal Theory, the parasympathetic system has two branches: the ventral vagal complex (associated with social engagement and safety) and the dorsal vagal complex (associated with shutdown and collapse, which produces hypoarousal states).

The Polyvagal Theory

Porges’ Polyvagal Theory explains that the vagus nerve, which connects the brain to the body, has evolved in three hierarchical stages:

1. Ventral vagal: Social engagement system—promotes connection, communication, and regulation (optimal functioning)
2. Sympathetic: Mobilization system—prepares for fight or flight (hyperarousal)
3. Dorsal vagal: Immobilization system—freeze, collapse, shutdown responses (hypoarousal)

Trauma can cause individuals to get stuck in sympathetic (hyperarousal) or dorsal vagal (hypoarousal) states, unable to access the ventral vagal state of social engagement and regulation.

The Brainstem’s Role

The brainstem, particularly the reticular activating system (RAS), plays a crucial role in arousal regulation. During trauma, this system becomes dysregulated, leading to persistent hypervigilance (hyperarousal) or shutdown (hypoarousal).

Amygdala Hyperactivity in Hyperarousal

In hyperarousal states, the amygdala—the brain’s threat detection center—remains highly active, constantly scanning for danger. This heightened amygdala activity keeps the sympathetic nervous system activated, maintaining a state of hypervigilance and reactivity.

As LeDoux (1996) explains, “The amygdala is like the smoke detector of the brain. In trauma survivors, it becomes hypersensitive, detecting threats everywhere, even when none exist” (p. 187).

Prefrontal Cortex Impairment

Both hyperarousal and hypoarousal states can impair prefrontal cortex functioning, which is responsible for executive functions like decision-making, emotional regulation, and rational thought. This makes it difficult to “think your way out of” these states or use cognitive strategies effectively.

Hypothalamic-Pituitary-Adrenal (HPA) Axis

The HPA axis, the body’s primary stress response system, becomes dysregulated in trauma survivors. In hyperarousal, the HPA axis may be chronically activated, flooding the body with stress hormones. In hypoarousal, the system may be exhausted or shut down, but still reactive to triggers.

Neurotransmitter Imbalances

• Hyperarousal: Often associated with elevated levels of norepinephrine and adrenaline, keeping the body in a state of alert activation
• Hypoarousal: Often associated with reduced neurotransmitter activity, particularly in systems related to motivation, engagement, and emotional experience

The Default Mode Network (DMN)

The default mode network, a network of brain regions active during rest and self-referential thought, can be disrupted in both hyperarousal and hypoarousal states. In hyperarousal, there may be difficulty quieting this network. In hypoarousal, the network may be underactive, contributing to feelings of disconnection.

Memory and Arousal

Arousal states can trigger traumatic memories stored in implicit memory systems. Hyperarousal can activate the sympathetic nervous system in ways that feel identical to the original trauma. Hypoarousal can recreate the shutdown response from the traumatic event.

Somatic Markers and Interoception

The ability to sense internal body states (interoception) is often impaired in trauma survivors. In hyperarousal, interoceptive signals may be amplified and misinterpreted as threats. In hypoarousal, interoceptive signals may be diminished, contributing to feelings of disconnection from the body.

References

LeDoux, J. E. (1996). The emotional brain: The mysterious underpinnings of emotional life. Simon & Schuster.

Porges, S. W. (2011). The polyvagal theory: Neurophysiological foundations of emotions, attachment, communication, and self-regulation. W. W. Norton & Company.