Electrodermal Activity (EDA) Overview

Electrodermal activity (EDA) refers to changes in the electrical properties of the skin, primarily influenced by sweat gland activity. It is monitored through two methods:

1. Galvanic Skin Resistance (GSR): An active method measuring electrical resistance when a current is applied.
2. Galvanic Skin Potential (GSP): A passive method measuring voltage without applied current.

Ohm's Law:

Describes the relationship between current (I), voltage (E), and resistance (R):

I = \frac{E}{R}

or, using conductance (G = \frac{1}{R}):

I = E \times G .

Units:

• Current (I): Amperes (A)
• Voltage (E): Volts (V)
• Resistance (R): Ohms (Ω)
• Conductance (G): Siemens (S)

Normal Conductance Values:

For human skin, normal conductance ranges from 1 to 20 microSiemens (μS).

Measurement Equipment:

The BIOPAC system uses a constant 0.5 V DC to measure the current required to maintain this voltage, with conductance inferred from current readings.

Anatomical Aspects

• Measurement Sites: Inner surfaces of palms and soles are commonly used due to rich eccrine sweat gland density in these areas.
• Neurotransmission: Eccrine glands are stimulated by acetylcholine, contrasting with other sympathetic nervous system components that are controlled by noradrenergic fibers.
• Sympathetic Activation: Increases in skin conductance occur with heightened sympathetic nervous system activation, characterized by decreased resistance.
• Function of Eccrine Glands: Primarily linked to thermoregulation through cooling via evaporation; however, in palms and soles, responses are often due to psychological stimuli.

Response Dynamics

• Measurement Protocol: Electrodes placed on fingers (index and middle or ring fingers). Skin must be cleaned with soap before placement, avoiding abrasion.
• Response Latency: The EDA response exhibits a 1-3 second delay before onset and a further 1-3 seconds to peak in response to stimuli due to physiological processing.
• Typical Changes: Short-term (phasic) conductance changes measured before and after stimuli typically range between 0.2 and 1 μS.
• Challenges in Measurement: Common artifacts from loose electrodes, movement, and deep breaths can affect readings.

Spontaneous Fluctuations

• Definition: Fluctuations in EDA can occur in the absence of external stimuli, termed spontaneous (non-specific) responses, often larger than 0.01 μS.
• Electrodermally Labile vs. Stable:
  • Labile: Individuals with high spontaneous fluctuations, greater emotional responsiveness.
  • Stable: Individuals with lower fluctuations, exhibiting regulated emotional responses.

Historical Context and Applications

• Historical Use: EDA has roots in clinical studies dating back to Jean Charcot and emotional research by Carl Gustav Jung.
• Research Applications: Widely studied in emotions, arousal, attention, and cognitive load since the early 20th century.
• Psychophysiological Traits: Differences in lability/stability are partly genetically determined (up to 50%).
• Behavioural Associations: Electrodermal lability corresponds with effective attention span and emotional regulation, while psychopathy often shows diminished EDA responses.

Utility in Investigative Contexts

• Polygraph Testing: EDA is a crucial component in polygraphic lie detection, a method based on monitoring psychophysiological responses, though its scientific validity is debated.

Class Goal

• Objective: Demonstrate basic EDA phenomena and the polygraphic method using the Biopac Student