DC magnetic fields from the human body generally: a historical overview

Area of Science:

• Biophysics
• Biomagnetism
• Neuroscience

Background:

• Early direct current magnetic field (dcMF) measurements were conducted between 1969 and 1983.
• These measurements mapped natural currents throughout the body, excluding the brain (dcMEG) due to interfering non-neural head sources.
• This historical mapping provides valuable context for interpreting contemporary biomagnetic data.

Purpose of the Study:

• To review and present early dcMF measurements of natural body currents.
• To highlight the utility of this historical data for interpreting modern dcMEG studies.
• To challenge the assumption of solely neural sources in recent dcMEG research by presenting alternative non-neural origins.

Main Methods:

• Review of dcMF measurements conducted from 1969 to 1983.
• Whole-body mapping of dcMFs, with specific exclusion of the brain.
• Analysis of potential sources including physiological reflexes, muscle fibers, hair follicles, and injury currents.

Main Results:

• dcMFs were detected across nearly the entire body, with higher magnitudes observed in limbs and the head.
• The abdomen exhibited particularly strong dcMFs, often the largest recorded.
• Identified sources included abdominal reflexes (e.g., from cold water ingestion), long muscle fibers, hair follicles, and cardiac injury currents.

Conclusions:

• dcMFs originate from diverse and complex sources within the body, not solely neural activity.
• Non-neural sources like hair follicles and physiological responses can influence head measurements, potentially confounding dcMEG interpretations.
• Understanding these varied sources is critical for accurate interpretation of biomagnetic data, particularly in the head.