Consciousness And Theory Of Mind
In this chapter we
discuss what is meant by consciousness, and how this can be altered in certain
pathological conditions. This ability to be aware of what we are doing, namely
consciousness, is then discussed further in terms of how we can understand the
thought processes of others, so-called theory of mind, disorders of which may
underlie a range of conditions, especially autism.
Consciousness – what
is it?
In thinking about
consciousness, it is important to differentiate between the level and
the content of conscious experience. The level of consciousness may
also be referred to as the level of arousal while the contents of
consciousness refers to the objects and occurrences of which we are aware.
Of course, the contents of consciousness will be affected greatly by the level
of consciousness but these two phenomena are likely to be at least partly
dissociable. For example, people in hyperaroused states may be less aware of
surroundings than less-aroused individuals. Conversely, it has recently been
shown that individuals in a vegetative state may actually show neurophysiological
patterns of activity (as measured by functional magnetic resonance imaging
[fMRI]; see Chapter 53), indicating a much richer level of awareness than their
immobile unresponsive state would suggest.
In general, experimental
and clinical access to the contents of consciousness relies on verbal report
and certain behavioural indicators. We may ask a subject to tell us or to
indicate whether they are aware of a stimulus in the periphery of
their visual field. We may assess their memory by requiring them to
indicate whether they have an awareness of a particular stimulus that was
previously presented to them. We may also attempt to ascertain the richness of
their awareness through such measures; with respect to memory, for example,
does the subject truly recollect a prior presentation or do they simply have a
strong sense that it is familiar? An important observation with respect to the
contents of consciousness is that while our awareness obviously defines our
experience of the world, the explanations that they provide for our behaviour
is only partial and may be inaccurate. This was shown strikingly in an
experiment by Libet and colleagues, who required volunteers to make periodic
movements while simultaneously recording cerebral activity. They showed that
subjective assessments of becoming aware of an intention to move actually
occurred some 500 ms after there had been a brain response. This finding,
subsequently replicated, suggests that our brain can indicate what we are
about to do before we are aware of wanting to do it.
Further evidence of a
discrepancy between what we are aware of and what we actually do comes from
work by Castiello and colleagues. These authors showed that when subjects
receive incorrect feedback about the trajectory of an arm movement that they
are in the process of making, they will correct the movement without actually
being aware of doing so, even when the correction made is relatively large.
Furthermore, when asked to reproduce the movement that they have just
made, subjects will reproduce the one that mirrors the incorrect feedback
that they were given, further suggesting that they were unconscious of the
control that they have exerted over the movement.
It is also the case that
previously experienced events or objects may influence our ongoing actions and
decisions without necessarily re-emerging into consciousness. The occurrence of
basic processing outside our awareness would seem to be an efficient way of
freeing our conscious processing to deal with more complex problems. However,
it should be remembered that there are clear instances where the contents of
consciousness may have a marked impact on lower level processes. For example,
Haggard and colleagues showed that subjects who have made a willed (conscious)
movement are likely to link more closely in time that movement with an outcome
than when the movement is not felt to be consciously initiated (if it is
produced by application of a brief magnetic field over the motor cortex).
Thus, consciousness
enables actions to gain greater prominence in our memory, but much of what we
do routinely does not require this to happen. As to the precise neurobiological
origin of con- sciousness, this is unknown, but the coordinated activity of the
cortex and its reciprocal connections to the thalamus and diffusely projecting
brainstem nuclei is important. This is best illustrated in patients in a vegetative
state (see below) and blindsight (see Chapter 26). In
this latter condition there is damage to the primary visual cortex such that
individuals cannot consciously see but when tested it is clear that their
visual system can detect stimuli of different forms including colour and
motion. It is thought to arise from the intact extrastriate visual areas, which
cannot feedback to the primary visual cortex, as a result of which conscious
visual perception is lost.
Consciousness and
theory of mind
As humans, we may be
unique in being conscious of our conscious- ness. This “thinking about
thinking” has been referred to as ‘meta representation’ and it is perhaps the
ability to represent our own mental states and those of others that facilitates
and shapes our most complex social interactions. To be able to represent the
mental states of others has been referred to as having a theory of mind.
We use this theory of mind to interpret, explain and predict many of the
actions and utterances of other people. If someone is being sarcastic or deceitful, they
say and do precisely the opposite of what they feel. By understanding
these possibilities their behaviour may become more logical and predictable to
us.
What happens if we have
difficulty with theory of mind processing? It has been suggested that the
isolation and very limited social repertoire of individuals with autism may
arise from the difficulty that they have in understanding the mental states of
other people. There is also evidence that people with schizophrenia may
have deficits in theory of mind abilities and in both cases the abnormality
underlying this deficit is thought to reside in the prefrontal cortex (see
Chapter 34).
Vegetative state
Some patients who have a
major global brain injury (e.g. anoxia secondary to a cardiac or respiratory
arrest) can end up in a state of unresponsive wakefulness or a vegetative
state (which is said to be permanent if it continues for more than six
months to a year depending on the nature of the original insult). In this state
the patient clearly has periods of sleep and wakefulness, but during the latter
time they are unable to respond to any stimuli as there is extensive damage
above the level of the arousal systems in the brainstem. In some cases the
responses to such stimuli are present, but inconsistently so, and such
individuals are deemed to be in a minimally conscious state (MCS).
It is important that all
individuals in a vegetative state or MCS are investigated thoroughly over time
using a range of stimuli and functional imaging (see Chapter 53). This is
because although some patients appear not to be able to respond there is
evidence of cortical activation with sensory stimuli on functional imaging. In
these cases, the patient may have had a more focal injury to the upper
brainstem that prevents them from being able to make any clear motor responses
to stimuli – the so-called locked-in syndrome. Once diagnosed,
such patients may be able to communicate through the use of eye movements and
blinking (see Chapter 56).
