Andrew Peterson and Tim Baynebehaviorally-based methods for assaying consciousness.) Although the discussion of these
methods has focused on the question of whether they can be used to support the ascription of
consciousness to patients who appear from the bedside to be VS, it is worth noting that they
might also be used to show that some MCS patients enjoy a much wider range of conscious
states than might be apparent on the basis of their overt behavior.
The first neuroimaging data to provide robust evidence of consciousness in a VS patient were
obtained in a functional magnetic resonance imaging (fMRI) study of a 23-year-old woman
who had been in a VS for five months (Owen et al. 2006). While lying in the scanner, the
patient was given the auditory command to imagine one of two activities—playing tennis
or visiting the rooms of her home—for discrete and repeated 30-second intervals. The brain
activity preferentially involved in the two tasks (compared with rest) was indistinguishable from
that seen in 34 healthy volunteers: the instruction to play tennis was associated with increased
activation in the supplementary motor area (SMA), while the spatial navigation instruction was
associated with increased activation in the parahippocampal gyrus, posterior parietal lobe, and
the lateral premotor cortex (Boly et al. 2007; Owen et al. 2006).
In the decade since the publication of this ground-breaking paper, a number of other
command-following studies have been conducted. Some of these studies have followed Owen
et al. in using fMRI to assess command-following (Stender et al. 2014; Bardin et al. 2011; Monti
et al. 2010), whereas others have used EEG (Goldfine et al. 2011; Cruse et al. 2011). Some of
these studies have followed Owen et al. in assessing the capacity of patients to engage in imagery
involving spatial navigation or simple motor responses, whereas others have instructed patients
to perform tasks that involve attending to certain aspects of their environment. For example,
some studies have examined the capacity of VS and MCS patients to attend to instances of
particular words (such as their own name) that are presented in an auditory stream. Neural evi-
dence of the capacity for selective attention has been found in some VS (Naci and Owen 2013)
and MCS patients (Schnakers et al. 2008; Monti et al. 2015). Interestingly, the capacity of the
MCS patients to follow commands in the aforementioned studies was not manifest in their overt
behavior, and they had been classified as MCS only because of the low-level behaviors (such as
visual fixation and pursuit) that they had shown.
The most striking command-following studies have used neuroimaging as a channel of
communication. The first of these studies was conducted by Monti et al. (2010), who asked a
VS patient six yes/no autobiographical questions (such as, “Is your father’s name Alexander?”).
The patient was instructed to engage in either motor imagery or spatial imagery (depending
on the trial) to answer “yes” or “no.” The patient produced activation indicative of a cor-
rect answer in response to five of the six questions. The sixth question elicited no significant
activation in the regions of interest. These findings have been replicated in other VS patients
(Naci and Owen 2013; Bardin et al. 2011). In the most extensive communication study to
date, a patient diagnosed as being in a VS for 12 years answered ten yes/no questions, includ-
ing “Are you in pain?” (Fernández-Espejo and Owen 2013). Some authors have argued that,
given certain technological advances, these methods might allow some post-comatose patients
to participate in some medical decisions (Cairncross et al. 2016; Glannon 2016; Peterson
et al. 2013a; 2013b; Bendsten 2013).
A recent meta-analysis of command-following studies suggests that approximately 15% of
patients who would be regarded as VS on the basis of current clinical assessment schedules
appear to be capable of covert command-following—that is, they produce sustained, region-
appropriate neural activity in response to commands (Kondziella et al. 2016). The philosophically
interesting questions are whether these neural responses ground an ascription of consciousness
to these patients and, if so, how that ascription is to be justified.