1 Introduction
Disorders of consciousness can be grouped into two classes: local disorders and global disorders.
Local disorders of consciousness involve circumscribed deficits to a particular domain of con-
scious processing. Blindsight is perhaps the most well-known of all local disorders of conscious-
ness. Patients with blindsight have lesions in the visual cortex that result in a loss of conscious
experience for stimuli presented to certain regions of their visual field. Global disorders of
consciousness do not involve focal deficits of this kind, but instead involve impairments to the
subject’s overall state of consciousness—they are domain-general rather than domain-specific.
Some of the most intensely studied global disorders of consciousness involve patients who
have undergone a severe brain injury, typically caused by trauma or the loss of oxygen to the
brain. Those who sustain the most severe brain injuries will spend some time in a state of una-
rousable unawareness, also known as the comatose state (Young 2009). After a period of days
or weeks, some comatose patients may enter one of two post-comatose states: the Vegetative
State (VS) or the Minimally Conscious State (MCS). This chapter is concerned with these
post-comatose disorders of consciousness, the use of neuroimaging and electroencephalography
to detect preserved consciousness in post-comatose patients, and the ethical challenges that are
raised by the detection of consciousness in these patients.2 The Vegetative and Minimally Conscious States
Clinically, the VS, which is sometimes referred to as “unresponsive wakefulness syndrome”
(Laureys et al. 2010), is characterized by wakefulness without awareness. VS patients exhibit a
sleep/wake cycle and spontaneously open their eyes, but they do not manifest any behavioral
signs of awareness. In the words of the Royal College of Physicians (2003: §2.2), in the VS there
should be “no evidence of awareness of self or the environment, no responses to external stimuli
of a kind that would suggest volition or purpose (as opposed to reflexes), and no evidence of
language expression or comprehension.”
Although some patients remain in the VS indefinitely or die, others transition into the MCS
(Beaumont and Kenealy 2005). Patients with non-traumatic etiologies (e.g., cardiac arrest) are
unlikely to transition to the MCS if they remain in a VS for longer than three months, while26
POST-COMATOSE DISORDERS
OF CONSCIOUSNESS
Andrew Peterson and Tim Bayne
Andrew Peterson and Tim Bayne Post-Comatose Disorders of Consciousness