Quantum coherence demonstrated in the brain

Quantum coherence has been demonstrated in the brain

A new imaging method for MRI is based on detection of quantum coherence
(Rizi et al, 2000). It turns out that quantum dipole couplings of entangled
nuclear spins in two molecules (e.g. water, protein) separated by distances
ranging from 10 microns to one millimeter are detectable in that they give
a measurable NMR signal. Applied to brain MRI, the technique enhances
contrast of conventional imaging and give an interesting brain mapping
which may be relevant to a neural correlate of consciousness.

This work has been developed by WS Warren and colleagues at Princeton,
University of Pennsylvania and elsewhere, and a list of some of their
references is below. Their goal has been strictly to develop new contrast
enhancement for MRI imaging, and for this they deserve congratulations.
They have not considered possible relevance of the quantum coherences to
brain function (and may not be aware of such proposals). Nancy Woolf at
UCLA who (among others) does consider quantum processes of possible
relevance to consciousness noticed the work in its other context. Thanks
again Nancy. Here are the references, followed by a summary..

Generation of impossible cross-peaks between bulk water and biomolecules in
solution NMR (1993) Richter W, Lee S, Warren WS, He Q Science 262:2005-2009

Imaging with intermolecular multiple quantum coherences in solution nuclear
magnetic resonance (1995) Richter W, Lee S, Warren WS, He Q Science 267:
654-657
Homogenous NMR spectra in inhomogeneous fields. Vathyam S, Lee S, Warren WS
(1996) Science 272: 92-96

Imaging contrast enhancement based on intermolecular zero quantum
coherences (1998) Warren WS, Ahn S, Mescher M, Garwood M, Ugurbil K,
Richter W, Rizi RR, Hopkins J, Leigh JS Science 281:247-251

Intermolecular zero-quantum coherence imaging of the human brain. (2000)
Rizi RR, Ahn S, Alsop DC, Garrett-Rose S, Mescher M, Richter W, Schnall MD,
Leigh JS, and Warren WS, Magnetic Resonance in Medicine 43:627-632

Summary

NMR and MRI use the magnetic properties of nuclei with spin (essentially
hydrogen protons) when the nuclei are immersed in a static magnetic field
and exposed to a second oscillating magnetic field or electromagnetic (e.g.
RF) radiation. Some nuclei with spins are altered and eventually relax to
their original orientation giving a measurable signal. The medium and other
conditions in which the protons find themselves determine the response, and
hence valuable information about structure and dynamics are obtained.

In the conventional approach to NMR and MRI, magnetic fields generated by
the bulk magnetization of the sample's nuclear spins are neglected. (The
sample may be.a solution of proteins in NMR, or a human brain in MRI.) With
newer, high strength magnets, bulk magnetization of the sample's protons
lead to interesting behavior when presented with excitatory pulses of RF
and/or variations in magnetic field gradient. For example two RF pulses
generate trains of large amplitude echoes in simple solutions. These
effects (generally ignored in most approaches) may be described using
classical physics, however Warren and colleagues have shown the effects are
better understood as quantum coherence, specifically as "intermolecular
multiple quantum coherences "('IMQC'). These are detectable because of
dipole couplings between distant spins; the paired spins are superpositions
of two eigenstates of the spin system which are separated in energy by more
than one spin flip.

The MRI IMQC signal involves flipping up one solute spin with simultaneous
flipping down of a nearby, quantum entangled solvent spin. (The NMR pulse
may be viewed as a measurement on an affected spin, causing its entangled
spin some distance away to simultaneously collapse.) Because the spins are
on two different molecules, only dipole-dipole interactions would provide
such a coupling, and this interaction is normally assumed to be averaged
away by diffusion or thermal noise ("decoherence"). However only the short
range dipolar couplings are motionally averaged out; the dipolar coupling
between spins separated by much more than, e.g. the distance molecules
diffuse on an NMR time scale (~10 micrometers to 1 millimeter) are
retained. The surviving dipole field generated by a single proton is
extremely small, less than 10^-16 Tesla at 10 microns, however there are
10^45 different pairs of spin in a typical 1 ml sample, and with various
processing steps a robust signal is obtained.

In human brain imaging (one axial slice is presented) Zizi et al (2000)
found sites of maximal IMQC
quantum coherence appearing in periventricular gray, and frontal,
pre-motor/parietal, and occipital cortex. A measure of the durations of the
quantum processes were 24.2 msec in the white matter region, 26.0 msec in
the gray matter region, and 293.8 msec in the ventricular region. (The
possible relation of white and gray matter durations of around 25 msec to
"40 Hz" periodicity is interesting). The CSF-containing ventricles (and/or
periventricular gray matter) are seen in the quantum coherence image, as
well as a control image of single, non-coupled spins and may reflect a
'flow' phenomenon. The cortical areas are seen only in the quantum
coherence image.

The enhanced contrast quantum coherence MRI imaging is potentially useful
clinically.
However if quantum states and processes play a significant role in
consciousness as many of us believe (e.g. see my website
www.consciousness.arizona.edu/hameroff), the images may be even more
interesting. Does this technique take us closer to imaging the neural
correlate of consciousness?

The occurrence of quantum coherence in the brain doesn't prove that quantum
coherence is relevant to consciousness, but it does show that quantum
coherence can, and does, occur in the brain. This is important as
consciousness models involving quantum states in the brain have come under
sharp criticism due to the issue of decoherence, and the question of
whether quantum processes of significance can exist in the brain at
physiological temperature. It appears that quantum coherence can, and does
occur in the brain.

Stuart Hameroff

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Stuart Hameroff M.D.
Professor, Departments of Anesthesiology and Psychology
Associate Director, Center for Consciousness Studies
The University of Arizona
hameroff@u.arizona.edu
http://www.consciousness.arizona.edu/hameroff

Consultant, Starlab
http://www.starlab.org
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Received on Mon Oct 09 11:52:01 2000