The relation between quantum mechanics and higher brain functions

Schrödinger's Cat: A cat, along with a flask containing a poison and a radioactive source, is placed in a sealed box. If an internal Geiger counter detects radiation, the flask is shattered, releasing the poison that kills the cat. The Copenhagen interpretation of quantum mechanics implies that after a while, the cat is simultaneously alive and dead. Yet, when we look in the box, we see the cat either alive ordead, not both alive and dead.

The conventional prediction would be
that as soon as the photons from this
quantum system encounter a classical
object, such as the retina of the observer,
quantum superposition (the cat is both alive and dead)  is lost and the cat
is either dead or alive.


Neuroscientific doubters:
The relation between quantum mechanics
and higher brain functions, including consciousness, is often discussed, but is far from
being understood. Physicists, ignorant of
modern neurobiology, are tempted to
assume a formal or even dualistic view of
the mind–brain problem. Meanwhile, cognitive neuroscientists and neurobiologists
consider the quantum world to be irrelevant
to their concerns and therefore do not
attempt to understand its concepts. What
can we confidently state about the current
relationship between these two fields of
scientific inquiry.



All biological organisms must obey the
laws of physics both classical and quantum.
In contrast to classical physics, quantum
mechanics is fundamentally indeterministic. It explains a range of phenomena that
cannot be understood within a classical
context:
a) the fact that light or any small particle can behave like a wave or particle
depending on the experimental setup
(wave–particle duality);
b) the inability to
simultaneously determine, with perfect
accuracy, both the position and momentum
of an object (Heisenberg’s uncertainty principle);
and the fact that the quantum states
of multiple objects, such as two coupled
electrons, may be highly correlated even
though the objects are spatially separated,
thus violating ong our intuitions about locality
(entanglement).

Major philosophical and conceptual
problems surround the process of making
measurements in quantum mechanics. To
illuminate the paradoxical nature of superposition — that is, the fact that particles or
quantum bits (qubits) are allowed to exist
in a superposition of states — Schrödinger
proposed a celebrated thought experiment: a sealed box containing the quantum superposition of both a dead and a live cat. (see above)


When an observer peers inside the
box, measuring its content, the wave function, which describes the probability that
the system will be found in any one particular state, is said to collapse, and the system will be found in one or the other state with known probability.


But
large quantum systems are notoriously difficult to analyse rigorously, except in highly
idealized models or limits. Estimates based
on the same unrealistic one-particle model,
applied to trillions of interacting particles,
show discrepancies of ten orders of magnitude in the work of different authors. It is
therefore better to turn to hard experimental realities and abstract computational
theory to find the neural correlates of
quantum processes in the brain.



Although brains obey quantum
mechanics, they do not seem to exploit any
of its special features.


Computational neuroscience is
a young field and theories of complex
neural systems, with all the variability of living matter, will never reach the precision of
physical laws of well-isolated simple systems. It has already been demonstrated,
however, that many previously mysterious
aspects of perception and action are
explainable in terms of conventional neuronal processing.

At this point, intrepid students of the mind
point to qualia, the constitutive elements of
consciousness. The subjective feelings associated with the redness of red or the painfulness of a toothache are two distinct qualia.
As long as it remains mysterious how the
physical world gives rise to such sensations,
could one of the more flamboyant interpretations of quantum mechanics explain consciousness?

In regard to which side to come down Christof Koch argues in his paper that instead of regarding such a proposition (as a QM brain) being 'far out', it would be healthy to move on and regard the proposition
at this scientific juncture, as 'very unlikely'.


Source: Christof Koch is in the Division of Biology and
Division of Engineering and Applied Science,
216-76, California Institute of Technology,
Pasadena, California 91125, USA.
Klaus Hepp and Christof Koch are at the
Institute of Neuroinformatics, the University
of Zürich and ETH, Zürich, Switzerland.


FURTHER READING
Hepp, K. in Quantum Future: Lecture Notes in Physics
(eds Blanchard, P. & Jadczyk, A.) 517, 92–104 (1998).
Koch, C. Biophysics of Computation: Information
Processing in Single Neurons(Oxford Univ. Press, N


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