further clinical evidence, the present state of
imaging technologies cannot provide alterna-
tive markers of awareness. While neuroimag-
ing studies hold the promise of elucidating
underlying differences between VS/PVS and
MCS patients, at present no techniques are
able to identify awareness in such patients
unambiguously.
Owen and colleagues
119
have subsequently
developed a new imaging framework to evalu-
ate volitional responses in VS and MCS pa-
tients that address the ambiguities of the meth-
ods used in the Menon study.
114
Applying
these new methods,
120
they identified unequiv-
ocal neuroimaging evidence of a patient re-
maining in VS at 5 months following a severe
traumatic brain injury being able to follow
commands to imagine various visual scenes. The
commands were associated with activation of
appropriate areas of the cerebral cortex, de-
spite lack of an external motor response. At the
time of examination the patient showed evi-
dence of brief visual fixation, a possible transi-
tional sign for evolution into MCS.
76
Another
examination 11 months later revealed visual
tracking to a mirror, another transitional sign,
but no evidence of object manipulation or be-
havioral manifestations of command following.
Figure 9–9 shows the main result of the study.
The imaging findings demonstrated preser-
vation of cognitive function for this particu-
lar patient that the clinical bedside examina-
tion failed to reveal, and indicated a cognitive
level at least consistent with MCS. It is im-
portant to recognize that command following
is a cardinal feature of MCS that does imply
Figure 9–8. (A) A magnetic resonance image (1.5T) from the same patient illustrated in Figure 9–7C reveals destruction
of the right basal ganglia and thalamus as well as severe damage to most of the cerebral cortex of the right hemisphere.
Additional areas of damage include the left posterior thalamus and posterior parietal cortex with moderately severe
atrophy of the rest of the left hemisphere. Resting fluorodeoxyglucose-positron emission tomography measurements of the
patient’s brain demonstrated a widespread and marked reduction in cerebral metabolism to less than 50% of normal
across most brain regions. Several isolated and relatively small regions in the left hemisphere, however, expressed higher
levels of metabolism (yellow color indicates values greater than 55% of normal). Magnetoencephalographic analysis of
responses to bilateral auditory stimulation (C, D) demonstrated a time-locked response in the high-frequency (20 to 50 Hz)
range restricted to the left hemisphere reduced in amplitude, coherence, and duration compared with normal controls.
194
Source localization of the time-varying magnetic field obtained from the averaged response identified sources in the left
(D) but not right (C) temporal lobe, consistent with preservation of a response from Heschl’s gyrus. (From Schiff et al.,
117
with permission.)
368
Plum and Posner’s Diagnosis of Stupor and Coma
communication. MCS patients may show con-
sistent evidence of command following with
visible motor responses that cannot be used to
establish communication. Neuroimaging stud-
ies in such MCS patients also show preserva-
tion of large-scale cerebral networks (see be-
low). As a result, it is unclear from the methods
used in the Owen study whether or not the
patient’s level of consciousness was consistent
with MCS or a higher level of recovery.
FUNCTIONAL IMAGING OF
MINIMALLY CONSCIOUS STATES
Only a few studies have examined brain activity
in MCS.
121
In five MCS patients,
15
O-PET
identified activation of auditory association
regions in the superior temporal gyrus not seen
in PVS patients.
122
In addition, stronger cor-
relation of the auditory cortical responses with
frontal cortical regions was observed in both
MCS patients and control subjects than in PVS
patients. Median nerve electrical stimulation
activated the entire pain network, similar to the
response in normal subjects
123
(see Figure 9–
6). These findings stress the need for analgesic
medications when MCS patients undergo pain-
ful procedures.
Multimodal imaging studies using functional
MRI activation paradigms and FDG-PET
in two MCS patients near emergence from
MCS uncovered unexpected evidence of widely
Figure 9–9. Command following in posttraumatic brain injury vegetative state (VS) at 5 months. A 23-year-old woman
with clinical examination consistent with VS, with the exception of brief periods of visual fixation, following severe
traumatic brain injury was asked to imagine playing tennis or walking throughout her own house. The regionally selective
brain activation patterns obtained from functional magnetic resonance imaging measurements for each condition were
identical to those of normal controls. (From Owen et al.,
120
with permission.)
Consciousness, Mechanisms Underlying Outcomes, and Ethical Considerations
369
preserved large-scale cerebral network re-
sponses
121
(Figure 9–10). Both patients suf-
fered sudden brain injuries (blunt trauma,
spontaneous intracerebral hemorrhage) leaving
them in MCS for longer than 18 months. The
acute phase of injury of each patient included
herniation to a midbrain level. This historical
feature is commonly associated with MCS and
other poor outcomes following traumatic brain
injuries as a result of focal infarction or indirect
(axonal shearing, ischemic) damage.
124
Neither
patient demonstrated consistent command fol-
lowing or functional communication (either ges-
tural or verbal) on repeated examinations. Both
patients, however, did demonstrate best re-
sponses that included command following or
occasional verbal output (single words).
Significant fluctuations in their responsive-
ness occurred across examinations. Figure
9–10 shows cortical activity for one patient and
one normal control associated with receptive
language comprehension during presentation
of 40-second narratives prerecorded by a fa-
miliar relative, presented as normal speech, and
also played as time reversed (backward). Brain
activations in response to normal speech are
shown in yellow. Selective responses to back-
ward presentations are shown in blue. Normal
speech generated robust activity in language-
related areas of the superior and middle tem-
poral gyri for both the control subject and the
MCS patient. In addition, the normal speech
stimuli produced brain activations in the MCS
patient’s brain in the inferior and middle frontal
Figure 9–10. Functional mag-
netic resonance imaging (MRI)
maps obtained during listening to
spoken narratives, in a minimally
conscious state patient (left) and
control subject (right) measured
by functional MRI. Yellow color
indicates response to spoken
narratives, blue color indicates
response to time-reversed narra-
tives, and red color indicates
regions of overlapping response to
both conditions. See text for de-
tails of paradigm. (Adapted from
Schiff et al.,
121
with permission.)
370
Plum and Posner’s Diagnosis of Stupor and Coma
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