Nonlinear EEG activation evoked by low-strength low-frequency magnetic fields

Area of Science:

• Neuroscience
• Biophysics
• Sensory Physiology

Background:

• Electrophysiological studies suggest humans possess a magnetic sense.
• The specific dynamical laws governing the human magnetic sense remain unestablished.

Purpose of the Study:

• To test the hypothesis that brain potentials evoked by magnetic fields are nonlinearly related to the stimulus.
• To characterize the stimulus-response relationship in the human magnetic sense.

Main Methods:

• Applied a weak, low-frequency magnetic field (1G, 60 Hz) to eight subjects.
• Recorded brain potentials from occipital electrodes.
• Analyzed signals using nonlinear (recurrence analysis) and linear (time averaging) methods.

Main Results:

• Magnetosensory evoked potentials (MEPs) were detected using recurrence analysis in most subjects.
• MEPs showed nonlinear relationships with the magnetic stimulus, confirmed by the failure of linear time averaging to detect them.
• Detected MEPs exhibited expected latency but varied dynamical characteristics.

Conclusions:

• Human brain responses to magnetic fields are nonlinear.
• This nonlinearity suggests a complex sensory mechanism distinct from simpler linear transduction observed in other life forms.
• Human magnetic sense may confer vulnerability to man-made environmental electromagnetic fields.