a very low metabolic rate, incompletely pre-
served MEG patterns of spontaneous and
evoked gamma-band responses were seen.
Taken together, these imaging data suggest the
modular sparing of cortical networks associ-
ated with language functions.
117
Nevertheless,
despite this patient, any verbal output suggests
function better than vegetative until proved
otherwise.
Another patient, a 26-year-old man, re-
mained in a behaviorally unremarkable VS for
6 years following a motor vehicle accident
(Figure 9–8A). MRI T1 images revealed bilat-
eral paramedian thalamic injury, severe bilat-
eral infarction of the tegmental mesencepha-
lon, and diffuse white matter injury. However,
nearly normal cerebral cortical metabolism was
measured by quantitative FDG-PET in the
brain. EEG showed diffuse low-voltage, low-
frequency activity that did not change with
arousal patterns correlating with the marked
loss of metabolic signal in the paramedian mes-
encephalon and thalami. Isolated damage to the
paramedianthalamusandmesencephalonalone
may cause PVS,
112,113
so that in this patient, the
preserved cortical metabolism may reflect mul-
tiple preserved but isolated networks that fail
to integrate because of the overwhelming in-
jury to the paramedian mesencephalon and
thalamus.
105
Neuroimaging of Isolated Cortical
Responses in Persistent Vegetative
State Patients
In a widely discussed Lancet paper, Menon
and colleagues
114
described selective cortical
activation patterns using a
15
O-PET subtrac-
tion paradigm in a 26-year-old woman de-
scribed as being in PVS 4 months following
an attack of ADEM. MRI studies of the pa-
tient’s brain showed evidence of both diffuse
cortical and subcortical (brainstem and tha-
lamic) lesions. Although the patient inconsis-
tently demonstrated visual tracking (leading to
some debate as to whether her condition at the
Figure 9–6. Somatosensory stimulation in the vegetative state. Top row: Brain activation patterns from normal subjects,
shown in red, that were elicited by noxious stimulation (super-threshold electrical stimulation experienced as ‘‘painful’’;
subtraction stimulation-rest). Bottom row: Brain activation patterns from the persistent vegetative state (PVS), again
shown in red, that were elicited by same noxious stimulation method (subtraction stimulation-rest). Blue regions indicate
areal differences in network activation showing region less active in patients than in controls (interaction [stimulation vs.
rest] Â [patient vs. control]). All regions of activation are projected onto transverse sections of a normalized brain mag-
netic resonance imaging (MRI) template in controls and on the mean MRI of the patients (distances are relative to the
bicommissural plane). (From Laureys et al.,
109
with permission.)
366
Plum and Posner’s Diagnosis of Stupor and Coma
time of study reflected PVS or MCS), no other
features of her examination were inconsistent
with the diagnosis of VS. Improvements in re-
sponsiveness unequivocally consistent with the
MCS level were noted by 6 months, with emer-
gence from MCS occurring some time after 8
months. As noted above, it is now generally
recognized that prognosis in ADEM includes
later recoveries at time periods 6 months or
longer after the injury. Thus, patients with
ADEM may harbor residual integrative capa-
cities despite a long convalescence. By con-
trast, similar clinical examination findings in
a patient 6 months following cardiac arrest
would not portend such a cerebral reserve.
The patient eventually made a full cognitive
recovery.
115
Imaging studies in this patient at 4
months, when described as being in PVS, dem-
onstrated selective activations of right occipital-
temporal regions (in a subtraction paradigm
comparing familiar faces and scrambled im-
ages). The investigators interpreted activa-
tion of the right fusiform gyrus and extrastriate
visual association areas as indicating a recov-
ery of minimal awareness without behavioral
manifestation. The findings in this patient,
however, point out a significant limitation of
brain imaging techniques in this clinical context
and have been extensively debated.
111,116
The selective identification of relatively com-
plex information processing associated with vi-
sual processing of faces as shown here may not
alone provide an index of recovery of cogni-
tive function or even potential for recovery.
Specific cortical responses to faces are obtain-
able in anesthetized animals
118
and, if found
in isolation of any other imaging evidence or
bedside demonstration of awareness, do not
guarantee that these patterns of activation
represent cognitive function per se. Without
Figure 9–7. An overview of coregistered magnetic resonance imaging and fluorodeoxyglucose-positron emission to-
mography (FDG-PET) images in five chronic persistent vegetative state (PVS) patients.
105
The PET data are normalized
by region and expressed on a color scale ranging from 35% to 100% of normal. The brackets segregate three patients who
suffered focal brain injuries due to trauma (A, B) or deep brain hemorrhage (C), and two patients in PVS due to anoxic
injuries (D, E). As seen in the marked difference in overall brain metabolism, patients in PVS following anoxic injuries
demonstrate global reductions of cerebral metabolism in all brain regions. Patient C is a 49-year-old woman who suffered
successive hemorrhages from a deep, central arteriovenous malformation of her brain. Despite a 20-year period of PVS,
this patient infrequently expressed isolated words (typically epithets) not related to environmental stimulation. (From
Schiff, et al.,
105
with permission.)
Consciousness, Mechanisms Underlying Outcomes, and Ethical Considerations
367