Page 195 - Visions of the Future Chemistry and Life Science

176 V. WALSH

it doesn’t possess any degree of temporal resolution. Temporal resolution
simply refers to the window of time which can be used to look at a func-
tion and it is critical when one considers the nature of psychological
models of brain function. Our models always contain stages of processing
that are part parallel and part serial. In other words, to understand brain
processes means understanding them in time as well as space. Knowledge
of precisely when the brain carries out specific functions is fundamental to
any accurate description of how the brain performs many complex tasks.
And it’s not just a matter of running a clock against brain functions. Indeed
the brain may invent some apsects of what you think of as real time. You
might think you experience a unified world in which objects have shape
and colour and movement – but you are deluded. The brain areas that deal
with the different attributes of an object all operate at different paces,
perhaps several milliseconds apart (several milliseconds is a long time in
the brain – while you’re larding about the brain is doing some impressive
housekeeping) and we don’t know how they are brought together in syn-
chrony.
The stimulation method could not address the role of the elaboration
areas and the study of brain damaged patients or lesion studies of animals
is hampered by the lack of temporal resolution. What is needed for another
wave of reverse engineering, then, is the ability to stimulate the brain
while it is doing something, or to be able to reversibly disrupt its function-
ing to give the lesion method a temporal dimension. The story of how we
are able to achieve both of these takes us back to Faraday. . . .
Recall that Faraday discovered electromagnetic induction and we
know the brain is a conductor of electricity. It follows that exposing the
brain to a changing magnetic field will result in an induced electrical field
and therefore neural activity in the brain. This was soon appreciated and
as the nineteenth century drew to its close Arsene d’Arsonval (1896)
reported the first production of visual percepts (spots or flashes of light
called phosphenes) induced by magnetic stimulation (Figure 10.3). The
subject also reported feelings of vertigo and under some conditions muscle
contractions as well.
One might have thought that d’Arsonval’s discovery would be suffi-
cient to generate further studies of brain function by magnetic stimulation,
but the technical solutions to this had to wait for the best part of the twen-
tieth century until 1985 when Anthony Barker and colleagues at the
University of Sheffield successfully stimulated the motor cortex and pro-