input, imagery arises from our interpretation of stored, memory-based information. Thus
the process of generating a mental image may be understood crudely as running
perception backwards (Behrmann, 2000). As we shall see later, the term “mental
practice” (MP) refers to a particular application of mental imagery in which performers
“practise” in their heads, or rehearse their skills symbolically, before actually executing
them. MP is also known as motor imagery (Slade, Landers and Martin, 2002).
If imagery resembles perception, then there should be similarities between the
measurable cortical activity involved in these psychological processes. Put simply,
similar parts of the brain should “light up” when we imagine things as when we actually
perceive them. For example, visual imagery should be associated with neural activity in
the cortical areas that are specialised for visual perception. Until relatively recently, this
hypothesis remained untested simply because no technology was available to allow
researchers to peer into the brain in order to measure the neural substrates of “real time”
or ongoing cognitive activities. Over the past decade, however, a variety of neuroimaging
techniques have been developed to allow brain activation to be measured objectively.
What are these dynamic brain techniques and how do they work?
According to Kolb and Whishaw (2003), the modern era of brain imaging began in the
early 1970s with the development of an X-ray procedure called “computerised
tomography” (derived from the word “tomo” meaning “cut”) or the CT scan. The logic of
this approach is that a computer may be used to draw a three-dimensional map of the
brain from information yielded by multiple X-rays directed through it. With the advent of
more sophisticated computational strategies to reconstruct images, three other brain
imaging procedures emerged: positron-emission tomography (PET scans), magnetic
resonance imaging (fMRI) and transcranial magnetic stimulation (TMS). These
procedures are designed to detect changes in metabolism or blood flow in the brain as
people are engaged in cognitive tasks. Such changes are correlated with neural activity.
Briefly, in the PET scan, people are given radioactively labelled compounds such as
glucose which are metabolised by the brain. This radioactivity is subsequently recorded
by special detectors. For reasons of convenience, however, PET scan measurement of
metabolism was replaced by the measurement of blood flow. Magnetic resonance
imaging is a less invasive technique and is based on two key principles. First, blood
oxygenation levels tend to change as a result of neural activity. Second, oxygenated
blood differs from non-oxygenated blood in its magnetic properties. When combined,
these principles allow researchers to detect changes in brain activity using special
magnets. TMS is a procedure in which a magnetic coil is placed over the skull either to
stimulate or to inhibit selectively certain areas of the cortical surface.
Using these neuroimaging techniques, research shows that the occipital cortex or
visual centre of the brain (which is located at the back of our heads) is activated when
people are asked to imagine things (Kosslyn, Ganis and Thompson, 2001). In addition,
these brain-imaging studies have also shown that, contrary to what most people believe,
mental imagery is not a single undifferentiated ability but, instead, a collection of
different cognitive capacities localised in different brain regions. To illustrate, brain
imaging studies show that when we “rotate” images in our mind (as happens, for
example, when we try to imagine what an object would look like if it were turned upside
down), neural activity is detected in the parietal lobes (which are located behind the
frontal lobe and above the temporal lobe). By contrast, visualising previously memorised
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