Neural Tissues Filter Electromagnetic Fields: Investigating Regional Processing of Induced Current in Ex vivo Brain Specimens

Abstract

As has been demonstrated experimentally, the living brain responds to pulsatile electromagnetic fields. Our aim was to investigate the capacities of ex vivo neural tissue to process and filter induced current generated by naturally occurring and laboratory-controlled electromagnetic fields. Microvolt potentials within the chemically fixed postmortem brains were collected throughout the field exposures. During strong geomagnetic storms there was a significant increase in power spectra within the 7.5 Hz to 14 Hz range within the right but not the left parahippocampal gyrus compared to days with relatively quiet geomagnetic activity. This finding indicated that ambient electromagnetic fluctuations from natural sources were processed differentially as a function of subsections of the postmortem tissue. Exposing a whole, fixed human brain to two physiologically patterned magnetic fields that have been associated with powerful subjective experiences reported by hundreds of human volunteers in the laboratory setting elicited increased power within the 7.5 Hz to 20 Hz range. The effects required 10 to 20 s to emerge and were primarily represented within tissue subsections of the right amygdala and orbitofrontal gyri. Other fields such as simple sine-wave (20 Hz) patterns of comparable intensity (2 to 10 μT) did not elicit the same configuration of changes. The results indicate that neural tissues filter electromagnetic fields non-randomly.

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“…EM-brain interactions are most associated with synchronous brain rhythms within the theta-alpha band with a temporal lobe and/or right hemispheric focus [139,150,151]. Whether the brain is exposed to natural EM field perturbances, experimental simulations, or is shielded from exogenous EM, it generally displays this peculiar selectivity.…”

“…Additionally, magnetite is highly concentrated within the neighboring hippocampus relative to most other brain regions. However, experiments with ex vivo brain tissues suggest theta rhythms are preferentially amplified by the same temporal regions post-mortem [139,150,151]. Indeed, when post-mortem human brain specimens fixed in ethanol-formalin-acetic acid (72% ethanol, C 2 H 6 O; 5% formaldehyde, CH 2 O; 5% acetic acid, C 2 H 4 O 2 ; 18% distilled water, dH 2 O; pH = 2.9) were directly injected with current or exposed to time-varying EM fields, mesial temporal lobe structures (e.g., hippocampus, parahippocampal cortex, entorhinal cortex, uncus) were found to selectively filter the induced signals with notable 4 Hz-7.5 Hz (theta) and 7.5 Hz-14 Hz (alpha) amplifications [150,151].…”

“…However, experiments with ex vivo brain tissues suggest theta rhythms are preferentially amplified by the same temporal regions post-mortem [139,150,151]. Indeed, when post-mortem human brain specimens fixed in ethanol-formalin-acetic acid (72% ethanol, C 2 H 6 O; 5% formaldehyde, CH 2 O; 5% acetic acid, C 2 H 4 O 2 ; 18% distilled water, dH 2 O; pH = 2.9) were directly injected with current or exposed to time-varying EM fields, mesial temporal lobe structures (e.g., hippocampus, parahippocampal cortex, entorhinal cortex, uncus) were found to selectively filter the induced signals with notable 4 Hz-7.5 Hz (theta) and 7.5 Hz-14 Hz (alpha) amplifications [150,151]. Interestingly, when the same post-mortem brain specimens were exposed to naturally occurring geomagnetic storm conditions (EM field perturbations on Earth caused by solar activity), right parahippocampal alpha activity became markedly amplified relative to non-storm conditions [151].…”

“…Quantitative modeling indicates that the permeability and permittivity of brain tissue predict a resonance frequency of approximately 7 Hz while bulk signaling within the spatial dimensions of the cerebrum predict 10 Hz [140,141]. Indeed, the finger-print-like, structural "identity" of each cytoarchitectonically distinct brain region may display a unique capacity to filter EM signals [139,150,151]. While largely speculative at this time, the brain's highly ordered, repetitive microstructure may provide the conditions for metamaterial-like interactions between EM fields and arrays of neural aggregates-particularly within the temporal lobes.…”