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Abstract

The general consensus is that the brain is something different from the mind: it is made of physical substance, and is subject to the laws of physics. The mind, however, cannot be described
by physical methods. It is considered to be related to experiences such as perceptions
or consciousness. The question of the connection between mind and brain, or that of body
and soul, is probably the most profound problem at the interface between the “sciences” and
the “arts”. That signals can be emitted by the brain and then enter our consciousness—and
thus that the brain influences the mind—is hardly in dispute. Indeed, psychophysics is even
capable of specifying a quantitative relationship between a physical stimulus and the sensation
it elicits. Opinion is more divided regarding the question of whether the mind can also influence
the brain. German criminal law presupposes that it does [1], and the sociologist J¨urgen
Habermas shares this view [2].The concept that the brain determines the mind is consistent
with the laws of physics. But this does not apply to the opposite concept, that the mind can
affect the brain: an ability of the “mind” to modify the activity of nerve cells would contradict
the principle of causality. Benjamin Libet [3], however, takes the latter concept as a starting
point in one of his much-discussed experiments on the question of conscious free will. He
measured how long it takes for us to make a voluntary movement after we become aware of the
fact that we want to make it, and found that the delay was about 200 ms. Surprisingly, however,
brain potentials that indicated the initiation of the movement were measurable more than 500
ms before the movement occurred. The conclusion: the “will” cannot trigger the movement,
because it is evidenced 300 ms too late. If the opposite result had been obtained, so that the
will to act was apparent prior to the brain activity, the conclusion would have been that this
result is indeed consistent with the notion that the “will” initiated the movement. Furthermore,
Libet concludes that “conscious control over the actual motor performance of the acts remains
possible”. Another interpretation of his results, which however can be reconciled with the laws
of physics, is as follows. Brain activity initiates both the activation of the muscles that produce
the movement, and also the perception that one is “willing” to make the movement. Which of
these processes first becomes apparent has no implications regarding the causal relationships.
As long as one takes it as given that laws of physics apply to the brain, the possibility that the
“will” initiates movements is ruled out.