Adrenal Response

What Is the Adrenal Response?

The adrenal response refers to the release of stress hormones — primarily adrenaline (epinephrine) and cortisol — from the adrenal glands as part of the body's sympathetic nervous system stress reaction. This hormonal cascade is a key component of the fight-or-flight response and produces the measurable physiological changes that the polygraph instrument is designed to detect.

How the Adrenal Response Relates to Polygraph Testing

When a deceptive examinee hears a relevant question that threatens to expose their lie, their brain's threat detection system (centred in the amygdala) triggers a rapid signalling cascade:

• Hypothalamus activation — The brain's hypothalamus signals the adrenal glands via the sympathetic nervous system and the hypothalamic-pituitary-adrenal (HPA) axis
• Adrenaline release — The adrenal medulla releases epinephrine (adrenaline) into the bloodstream within seconds, producing immediate physiological effects
• Cortisol release — The adrenal cortex releases cortisol over a slightly longer timeframe, sustaining the stress response

Physiological Effects Measured by the Polygraph

The hormonal effects of the adrenal response directly produce the changes measured across all polygraph channels:

• Increased electrodermal activity — Adrenaline stimulates eccrine sweat glands on the fingertips, increasing skin conductance measured by the EDA electrodes
• Elevated blood pressure and heart rate — Adrenaline increases cardiac output, recorded by the cardio cuff
• Respiratory changes — Stress hormones alter breathing patterns, recorded by the pneumograph
• Vasoconstriction — Adrenaline causes peripheral blood vessels to narrow, reducing pulse amplitude in the fingertips

Why the Adrenal Response Makes Polygraph Testing Possible

The adrenal response is involuntary — it occurs automatically in response to perceived threat and cannot be consciously suppressed. This is the fundamental reason why polygraph testing works: even a highly motivated liar who appears calm and composed on the outside is experiencing internal physiological changes driven by the adrenal response that the polygraph can detect.

The speed of the adrenal response (seconds from threat perception to measurable physiological change) aligns with the typical 1–3 second latency between a polygraph question and the onset of a scorable phasic response in the physiological data.

Individual Variation in Adrenal Response

The magnitude and characteristics of the adrenal response vary between individuals, which has implications for polygraph testing:

• Hyperreactive individuals — May produce excessively strong adrenal responses to all question types, making differential scoring difficult
• Hyporeactive individuals — May produce weak adrenal responses, potentially due to adrenal fatigue, certain medications (particularly beta-blockers which block adrenaline receptors), or medical conditions
• Habituation — Repeated exposure to the same stimulus can reduce the adrenal response over time, which is why polygraph examinations typically limit the number of chart presentations

The suitability screening portion of the pre-test interview is designed to identify factors that may affect the examinee's adrenal responsiveness. For more on the physiology behind polygraph testing, visit the Polygraph Examiner Hub or learn how a polygraph works.