anaesthetics in understanding the neural basis of consciousness raises the
important question of what we mean when we say they cause unconsciousness:
do we mean they take away wakefulness or awareness? What if the two are not
the same thing? (Shushruth, 2013).
Abolishing consciousness is not like pulling out a single component or switching
off a light. Nor, as we have begun to see, is the conscious–unconscious distinc-
tion necessarily an all-or-nothing difference, in terms of either brain function or
experience. Just as we can identify what seems like a spectrum of awareness from
coma to minimal conscious state or from heavily to lightly anaesthetised, we can
also talk about everyday cognitive processes as involving more or less awareness
(Chapter 8). Highly complex perceptual and learning processes go on all the time
apparently without awareness. For example, you have no conscious knowledge
of how you judge distances, recognise objects from unfamiliar angles, or make
aesthetic judgements. You once learned the quickest route to the shops, the
name of the highest mountain the world, and the dates of the Second World War,
but if we asked you now you would not be able to tell us when you learned them.
This is called ‘source amnesia’ and is related to ‘cryptomnesia’ or ‘unconscious pla-
giarism’, in which people falsely believe they invented an idea themselves when
in fact they learnt it from someone else.
Learning a new skill offers a good example of how blurry, and moveable, the
boundary may be between conscious and unconscious. You may once have
struggled to learn a new language, to ride a bike, or to master the skills of cooking,
but now you do these things easily and without paying them much attention.
FIGURE 4.6 • A comparison of average PET images of cerebral blood flow in a severely depressed patient for three states: awake,
sedated (drowsy with a low dose of propofol), and fully anaesthetised with propofol. Although some researchers
thought that anaesthetics might selectively depress specific brain areas associated with consciousness, many
studies have shown that the depression of activity is widespread across the brain (Ogawa et al., 2003).
