Measuring the Brain’s Electromagnetic Field: How We Detect the Physical Substrate of Consciousness

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The Instruments That See Thought

If consciousness is an electromagnetic field — as McFadden, Pockett, and the Fingelkurts argue — then every instrument that measures the brain’s electromagnetic activity is, in a very real sense, a consciousness detector. Not a metaphorical consciousness detector. A literal one. An instrument that registers the physical phenomenon that IS subjective experience.

This reframing transforms the significance of every EEG, MEG, and electrocorticography recording ever made. These are not merely measurements of brain activity that correlates with consciousness. They are measurements of consciousness itself — the electromagnetic field in which thoughts, feelings, perceptions, and the experience of selfhood physically reside.

Understanding how these instruments work, what they measure, and what their measurements mean is essential for anyone who takes the electromagnetic theory of consciousness seriously. Each technology provides a different window into the field — a different angle of view on the same underlying reality.

Electroencephalography (EEG): The Pioneer

EEG, invented by Hans Berger in 1924, is the oldest and most widely used method for measuring the brain’s electromagnetic field.

How it works. Electrodes placed on the scalp detect the electrical potential differences (voltage fluctuations) generated by the brain’s electromagnetic field. These voltage fluctuations are primarily produced by the postsynaptic currents in cortical pyramidal neurons — the large, vertically oriented neurons in the cortex whose coordinated activity generates the strongest extracellular fields.

When tens of thousands of pyramidal neurons in a cortical column synchronize their activity, they generate a summed electrical field that is strong enough to propagate through the cerebrospinal fluid, skull, and scalp to be detected by surface electrodes. A single neuron’s field is far too weak to detect at the scalp. EEG requires the synchronized activity of approximately 10,000-50,000 neurons to generate a detectable signal.

What it measures. EEG measures the temporal dynamics of the brain’s EM field with excellent time resolution (millisecond precision) but poor spatial resolution (centimeter scale). It is best suited for detecting:

• Oscillatory activity at different frequency bands: delta (0.5-4 Hz, deep sleep), theta (4-8 Hz, meditation, memory), alpha (8-12 Hz, relaxed wakefulness), beta (12-30 Hz, active thinking), gamma (30-100 Hz, conscious perception, binding).
• Event-related potentials (ERPs): time-locked voltage changes in response to specific stimuli, including the P300 (a marker of conscious perception), the N400 (semantic processing), and the mismatch negativity (automatic change detection).
• Long-range coherence: the degree of synchronization between EEG signals at different scalp locations, indicating functional coupling between distant brain regions.

Relevance to consciousness. EEG has provided the primary empirical foundation for electromagnetic theories of consciousness. The correlations between EEG patterns and consciousness states are among the most robust findings in neuroscience:

• Waking consciousness: alpha and beta dominant, with gamma bursts during active perception
• Drowsiness: increased theta
• Light sleep (NREM Stage 1-2): theta dominant, with K-complexes and sleep spindles
• Deep sleep (NREM Stage 3): delta dominant
• REM sleep: mixed frequency, resembling waking
• Anesthesia: characteristic burst-suppression patterns, loss of gamma coherence
• Brain death: isoelectric (flat line) — total absence of EM field activity

These correlations are exactly what the EM field theory predicts: every change in consciousness corresponds to a measurable change in the brain’s electromagnetic field.

Limitations. EEG’s spatial resolution is poor — the signal at any scalp electrode is a blurred mixture of contributions from many brain regions (the “volume conduction” problem). This makes it difficult to localize the specific cortical sources of EEG signals. Additionally, EEG is most sensitive to activity in the cortical surface (gyral crowns) and relatively insensitive to activity in deep brain structures and cortical sulci.

Magnetoencephalography (MEG): The Magnetic Mirror

MEG, developed in the 1960s-1970s, measures the magnetic component of the brain’s electromagnetic field.

How it works. Moving charges (the currents in active neurons) generate both electric fields (measured by EEG) and magnetic fields (measured by MEG). MEG uses superconducting quantum interference devices (SQUIDs) — extremely sensitive magnetic sensors cooled to near absolute zero (-269°C) — to detect the tiny magnetic fields (on the order of femtotesla, 10^-15 Tesla) generated by neural currents.

Advantages over EEG. The magnetic field generated by neural currents is not distorted by the skull and scalp tissues (which are poor conductors of magnetic fields), unlike the electric field (which is significantly distorted by these tissues). This means MEG provides better spatial resolution than EEG — approximately 2-3 millimeters, compared to EEG’s centimeter-scale resolution.

Additionally, MEG is selectively sensitive to tangential currents — currents flowing parallel to the scalp surface, which are generated primarily by neurons in cortical sulci (the folds of the cortex). EEG, by contrast, is more sensitive to radial currents from gyral crowns. This means MEG and EEG provide complementary spatial information — together, they give a more complete picture of the brain’s EM field than either alone.

Relevance to consciousness. MEG has been particularly valuable for studying the timing of conscious perception. Because of its excellent temporal resolution (sub-millisecond) and improved spatial resolution, MEG can track the rapid propagation of electromagnetic activity through the cortex during the transition from unconscious processing to conscious perception.

Research by Dehaene, Del Cul, and colleagues using MEG has shown that conscious perception is associated with a specific electromagnetic signature: a late, widespread burst of gamma-band activity that propagates from posterior sensory cortex to frontal cortex approximately 270-300 milliseconds after stimulus onset. This “ignition” — a term from Dehaene’s Global Neuronal Workspace theory — is present when stimuli are consciously perceived and absent when they are not.

Limitations. MEG requires a magnetically shielded room (to block the Earth’s magnetic field and environmental electromagnetic noise), making it expensive and non-portable. It also requires cryogenic cooling of the SQUID sensors, which is technically demanding and costly. Recent development of optically pumped magnetometers (OPMs) — room-temperature magnetic sensors — may overcome some of these limitations.

Local Field Potentials (LFP): The Inside View

LFPs are measured by electrodes inserted directly into brain tissue — either in animal experiments or in human patients undergoing neurosurgery for epilepsy or other conditions.

How it works. A microelectrode (typically with a tip diameter of 10-100 micrometers) is inserted into the brain and records the voltage fluctuations in the extracellular space surrounding neurons. These fluctuations reflect the summed synaptic currents, intrinsic membrane oscillations, and afterpotentials of neurons within approximately 250 micrometers of the electrode tip.

What it reveals. LFPs provide the most direct measurement of the brain’s local electromagnetic field. They reveal:

• Oscillatory activity at specific frequencies, with spatial resolution far superior to EEG
• Phase-amplitude coupling: the relationship between the phase of low-frequency oscillations and the amplitude of high-frequency oscillations — a phenomenon thought to be involved in information coding and consciousness
• Sharp wave ripples: brief, high-frequency bursts in the hippocampus associated with memory consolidation
• Gamma oscillations: high-frequency activity associated with conscious perception and the binding of perceptual features

Critical finding for consciousness theory. LFP studies have provided the most direct evidence that the brain’s EM field carries information beyond what neural spike patterns encode. Einevoll et al. (2013, Nature Reviews Neuroscience) reviewed evidence showing that LFPs contain information about sensory stimuli that is not present in the spike patterns of nearby neurons — information encoded in the field patterns themselves.

This finding directly supports the CEMI/Pockett/OA theories: the EM field is not merely a byproduct of neural firing. It carries additional information that is not reducible to spike patterns. If consciousness is this field, then consciousness contains information that is not available at the neural spike level — a prediction that distinguishes the EM field theory from purely computational theories of consciousness.

Electrocorticography (ECoG): The High-Resolution Surface Map

ECoG uses electrode grids placed directly on the surface of the cortex — typically during neurosurgery for epilepsy, when the brain is exposed and electrodes can be placed on the cortical surface without penetrating the tissue.

Advantages. ECoG provides:

• Superior spatial resolution (millimeter scale) compared to EEG
• Superior signal quality (no skull or scalp attenuation)
• Access to high-frequency activity (up to 200 Hz) that is attenuated by the skull and undetectable by scalp EEG
• Direct measurement of the cortical EM field at the surface where consciousness-related processing occurs

Consciousness-relevant findings. ECoG studies have revealed the detailed spatial pattern of the brain’s EM field during specific conscious experiences. For example, Parvizi and colleagues at Stanford used ECoG to map the electromagnetic signatures of specific emotional experiences — showing that laughter, sadness, and pain each produce distinctive spatial patterns of high-gamma activity across the cortical surface.

These findings directly support Pockett’s hypothesis that specific conscious experiences are identical to specific spatial EM field patterns.

Emerging Technologies: The Next Generation

Several emerging technologies promise to advance our ability to measure the brain’s EM field:

Optically pumped magnetometers (OPMs). Room-temperature magnetic sensors based on the optical pumping of alkali metal vapor. OPMs are approaching the sensitivity of SQUIDs but without the need for cryogenic cooling, enabling wearable MEG systems that can measure the brain’s magnetic field during natural behavior.

Nitrogen-vacancy (NV) diamond sensors. Quantum sensors based on the spin properties of nitrogen-vacancy defects in diamond crystals. NV sensors can measure magnetic fields with nanometer spatial resolution, potentially enabling measurement of the EM field generated by individual neurons.

High-density EEG. Modern high-density EEG systems use 256 or more electrodes, providing improved spatial resolution and enabling more sophisticated source localization algorithms.

Multimodal integration. The combination of EEG, MEG, fMRI, and diffusion tensor imaging (DTI) in a single experimental session enables the construction of comprehensive models that relate the brain’s electromagnetic field (measured by EEG/MEG) to its metabolic activity (measured by fMRI) and structural connectivity (measured by DTI).

The Emerging Picture: What the Measurements Reveal

Across all measurement modalities — EEG, MEG, LFP, and ECoG — the evidence converges on a consistent picture:

The brain’s EM field is not noise. It is a highly organized, information-rich, dynamically structured phenomenon that carries information about the brain’s representational content beyond what neural spike patterns encode.

The field tracks consciousness. Every transition in consciousness state — from waking to sleeping, from anesthesia to recovery, from inattention to awareness — is accompanied by a measurable change in the brain’s EM field. The correlation is so robust that EM field measurements are used clinically to monitor consciousness during surgery (bispectral index monitoring) and to assess consciousness in brain-injured patients.

The field has causal effects. Experimental evidence (Anastassiou, Fröhlich, and others) demonstrates that the endogenous EM field influences neural firing — meaning the field is not merely generated by neurons but feeds back to influence them. This closes the causal loop required for consciousness (as EM field) to influence behavior (through neural activity).

The field is unified. At any given moment, the brain’s EM field is a single, spatiotemporally continuous entity — not a collection of separate fields. This physical unity provides the natural basis for the phenomenological unity of consciousness.

The instruments exist. The measurements are being made. The data are accumulating. And the data consistently support the hypothesis that consciousness is an electromagnetic phenomenon — a field generated by the brain, carrying information beyond what neurons alone can encode, and exerting causal influence on the very neurons that generate it.

We have been measuring consciousness for over a century. We just did not know it.