THE BRAIN
The brain controls all the body’s functions – from
consciousness and heart rate to thinking, memory
and emotion. It is the most complex thing we know of,
and the gaps ∈ our knowledge about how it works are
vast. Neuroscientists have the daunting job of making
sense of this complicated organ – to provide insights
into our minds and behaviour and to find ways to
tackle debilitating brain diseases and injuries. Brain
injuries can occur ∈ many ways, such as through
accidents, stroke or infections. The rehabilitation
group at the Medical Research Council Cognition
and Brain Sciences Unit ∈Cambridge specialises
∈ helping people with brain injuries to compensate
for cognitive problems and to cope with everyday life.
Its work includes developing new ways to measure
the problems faced by people with brain injuries and
developing new treatments. The scientists are also
interested ∈ finding out more about how people
recover from brain injury and related memory loss.
The brain stem controls our core body functions –
the things our body must do unconsciously to keep us
alive, such as altering our heart beat and regulating
our blood pressure and body temperature. It also
controls functions such as alertness, swallowing,
digestion and breathing.
Consciousness is part of what makes each of us
unique. It encompasses many of our ideas, thoughts,
feelings, plans and memories. Conscious thought is
different from the unconscious workings of the brain
– which enable us to breathe, walk and talk and our
hearts to beat automatically. There are two aspects to
consciousness: awareness and wakefulness.
— Awareness refers to our internal, subjective
experience. It includes self awareness – the ability to
understand that you exist, as an individual, separate
from other people and with private thoughts. It also
includes awareness of the relationship between
oneself and one’s environment through use of our
senses and by thinking about ideas and acting upon
them using judgement.
— Wakefulness refers to different levels of
conscious awareness. Each day we experience a
spectrum of wakefulness, from full attentiveness, such
as if we are involved ∈ an interesting conversation,
through inattentiveness, drowsiness and normal
sleep. Following some types of brain injury or during
anaesthesia people can’t be woken: they have a lower
level of wakefulness. Brain death lies at the far end of
this spectrum.
These two aspects of consciousness normally go
hand-in-hand; we don’t expect to have an interesting
conversation with someone who is asleep. However,
we can possess awareness when we are asleep, for
example when we dream.
Where does consciousness come from?
Scientists have amassed much evidence linking
different aspects of consciousness to our brain. We
now know that consciousness requires many parts of
the brain to work together. Parts of the cerebral cortex
act together to produce our thoughts and experiences.
A functioning thalamus is also required to produce
wakefulness – we know this because if a part of the
thalamus called the centromedian nucleus becomes
damaged, we become unconscious.
Unconsciousness can also be caused by
anaesthesia, or changes to the body’s internal
environment such as a rise or drop ∈ core body
temperature or a lack of oxygen. A prolonged period
of unconsciousness is known as a coma. Sometimes,
after a severe brain injury, a person can enter a
vegetative state (VS). Unlike coma patients, VS
patients show normal wake/sleep cycles, but even
when they are awake they show no external sign of
awareness. When all electrical activity ∈ the brain
stops irreversibly, this is known as brain death.
Scientists at the MRC Cognition and Brain
Sciences Unit ∈Cambridge study patients with
disorders of consciousness. Their work recently
revealed that a woman who was diagnosed as
being ∈a persistent vegetative state following
a car accident was aware of her surroundings.
Working with colleagues ∈Belgium, the scientists
used functional magnetic resonance imaging
(fMRI) to map the woman’s brain activity. She was
physically unresponsive and fulfilled all the criteria
for a diagnosis of vegetative state according to
international guidelines. But scans showed that her
brain responded to speech. Her brain also actively
processed the meaning of sentences, becoming
more active when she heard sentences containing
words with several meanings, like ‘rain’ and ‘reign’.
When asked to imagine playing tennis or moving
around her home, brain scans showed that the
woman could do this, activating various areas of her
brain ∈ the same way as healthy volunteers. “These
are startling results. They confirm that, despite the
diagnosis of vegetative state, this patient retained
the ability to understand spoken commands and
to respond to them through her brain activity,” said
one of the researchers. “Her decision to work with
us represents a clear act of intent which confirmed
beyond any doubt that she was consciously aware of
herself and her surroundings.”
Doctors use different levels of sedation to reduce
people’s awareness of their bodies and surroundings.
For example, high levels of anaesthetic drugs cause
general anaesthesia: a complete loss of consciousness.
Another team of scientists at the MRC Cognition and
Brain Sciences Unit used fMRI to study how sedation
affects the brain’s processing of speech. Working with
researchers at the Wolfson Brain Imaging Centre ∈
Cambridge, they found that during heavy sedation,
volunteers’ brains still responded to the sounds of
speech but they were unable to process or remember
it. The findings have important implications for the care
of patients undergoing general anaesthesia or coming
out of a coma.
Available at: <http://www.mrc.ac.uk/publications/browse/the-brain-mrc- -research-for-lifelong-health/>. Retrieved on: 28 June 2016. Adapted.
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