Mental fatigue caused by prolonged cognitive load associated with sympathetic hyperactivity

Area of Science:

• Neuroscience
• Human Physiology
• Autonomic Nervous System Research

Background:

• Chronic fatigue is associated with sympathetic hyperactivity.
• The link between autonomic function and mental fatigue from prolonged cognitive load in healthy humans remains unclear.
• Investigating mental fatigue mechanisms requires understanding autonomic function changes.

Purpose of the Study:

• To examine the association between mental fatigue and autonomic functions in healthy humans.
• To clarify the physiological mechanisms underlying mental fatigue.
• To determine if prolonged cognitive load affects autonomic nervous system balance.

Main Methods:

• 10 healthy participants underwent an 8-hour mental task session (advanced trail making test, kana pick-out test, mirror drawing test) to induce mental fatigue.
• Autonomic functions were assessed using accelerated plethysmography before and after the mental tasks.
• A control session involved an 8-hour relaxation period to compare against the fatigue-inducing tasks.

Main Results:

• The relaxation session showed no significant changes in low-frequency (LF), high-frequency (HF), or LF/HF ratio from baseline.
• Following the mental fatigue session, high-frequency (HF) power significantly decreased.
• The low-frequency/high-frequency (LF/HF) ratio significantly increased after the mental fatigue session compared to baseline and the relaxation session.

Conclusions:

• Mental fatigue induced by prolonged cognitive load is associated with sympathetic hyperactivity.
• Decreased parasympathetic activity is a key factor contributing to sympathetic hyperactivity during mental fatigue.
• Autonomic nervous system imbalance, specifically reduced parasympathetic tone, underlies mental fatigue.