lower than values from age-matched French
control subjects. Importantly, perception of
mental health and the presence of physical
pain correlated with the frequency of suicidal
thoughts (r ¼ –0.67 and 0.56, respectively,
p < 0.05), indicating the importance of proper
pain management in chronic locked-in patients
who are frequently undertreated. At present,
there are three European societies for locked-
in-patients with a membership exceeding 300
persons (http://alis-asso.fr/).
MECHANISMS UNDERLYING
OUTCOMES OF SEVERE BRAIN
INJURY: NEUROIMAGING
STUDIES AND CONCEPTUAL
FRAMEWORKS
The above discussion details the problems of
diagnostic accuracy and prognosis for disorders
of consciousness. At present, careful clinical
evaluations combined in some instances with
structural imaging criteria, or measurements
of early cortical sensory responses, remain
the foundation for decision making. Available
guidelines invariably indicate likelihoods of
death or VS as outcomes rather than providing
reliable indices of potential for functional re-
coveries with or without persistent disabilities.
In large part this is a consequence of the fact
that preserved brainstem function may only
herald PVS. Moreover, it is clear that in the
aggregate, the clinical neurologic examination
and assessments of structural brain integrity
provide only limited insight into the neuro-
physiologic mechanisms of coma, VS, or MCS.
This is because the functional impairment of
distributed neuronal populations of the cere-
bral cortex, basal ganglia, and thalamus under-
lying the conditions often cannot be adequately
assessed by these methods. Neuroimaging
techniques that can directly assess functional
changes within these cerebral networks hold
significant promise to ultimately improve diag-
nostic accuracy and understanding of the path-
ophysiology of the severely injured brain (see
99
for review).
Expanded use of neuroimaging techniques
for evaluating functional outcomes of patients
recovering from coma will likely have the
greatest impact on the category of severe dis-
ability. This broad category includes within its
limits patients who, while not permanently
unconscious, as in the chronic VS, may none-
theless never regain a capacity to communicate,
as well as other patients near the functional bor-
derline of independence in activities of daily
living. More than 20 years ago, the third edition
of Stupor and Coma commented that the overly
broad definition of severe disability needed sig-
Table 9–13 Functional Measurements
in a Cohort of Locked-in Patients
(N ¼ 44)
Variable
%
Cognitive Functioning
Level of attention
Good
86.0
Tends to sleep
9.0
Normally awake
2.3
Sleeps most of the time
2.3
Can pay attention >15 minutes
95.3
Can watch and follow a
film on TV
95.3
Can say what day it is
97.6
Can read
76.7
Has a visual deficit
14.0
Has memory problems
18.6
Emotions and Feelings
Mood state
Good
47.5
Bad
5.0
Depressed
12.5
Other
35.0
Is more sensitive since onset
85.0
Laughs or cries more easily
87.8
Sexuality
Has sexual desire
61.1
Can maintain sexual relations
30.0
Communication
Can emit sounds
78.0
Can communicate with or without
technical aid
65.8
Social Activities
Enjoys going out
73.2
Participates in social activities
14.3
Watches television normally
23.8
Participates in other family activities
61.9
Is accompanied out once or
twice a week
61.9
Meets with friends at least twice a
month
81.0
364
Plum and Posner’s Diagnosis of Stupor and Coma
nificant refinement. As discussed above, recent
efforts to define MCS are a step in this di-
rection. The significance of identifying the
physiologic mechanisms underlying different
functional outcomes within the category of
severe disability is that this knowledge will lead
to a better understanding of the necessary and
sufficient neurologic substrates to recover con-
sciousness and varying levels of cognitive capac-
ity. Just as the concept of brain death clarified
the concept of death, MCS and other future
subdivisions of the category of severe disability
will force us to consider the concept of con-
sciousness more precisely.
FUNCTIONAL IMAGING OF THE
PERSISTENT VEGETATIVE STATE
Levy and associates
100
provided the first exper-
imental evidence supporting the clinical hypo-
thesis that patients in VS were unconscious.
Using FDG-PET, seven patients in PVS were
compared to three patients in the locked-in
state and 18 normal subjects. In PVS patients,
cerebral metabolic rates were globally reduced
by 50% or more. Regional cerebral blood flow
measurements showed a similar but more vari-
able pattern of global reduction. Subsequent
studies have confirmed these findings, with an
average of less than 50% of normal metabo-
lic rates in most VS patients studied (reduced
further to 30% to 40% in cases of hypoxic-
ischemic etiology).
101–105
Comparable reduc-
tions are identified during generalized anes-
thesia
106,107
and in stage IV sleep in normal
individuals.
108
The small number of patients in
the locked-in state (three) in the Levy study
had a low average metabolic rate, but recent
quantitative FDG-PET studies have demon-
strated essentially normal resting metabolic
rates in the cerebrum, even acutely.
99
Cerebel-
lar metabolic rates were low, consistent with the
lack of motor outflow in the locked-in state.
98
More sensitive imaging techniques have
recently been applied to the evaluation of PVS
patients. They reveal a marked loss of distrib-
uted network processing in VS.
99,104,109
Ele-
mentary auditory and somatosensory stimuli
fail to produce brain activation outside of pri-
mary sensory cortices (Figure 9–6). The data
suggest multiple functional disconnections
along the auditory or somatosensory cortical
pathways and support the inference that the
residual cortical activity seen in PVS patients
does not reflect awareness. The findings are
consistent with evidence of early sensory pro-
cessing in PVS patients as measured by evoked
potential studies, but loss of later compo-
nents
39
; they suggest that VS/PVS correlates
with failure of sensory information to propa-
gate beyond the earliest stages of cortical
processing. Preliminary studies discussed be-
low indicate that MCS patients show wider
activation of cortical networks, findings that
may help ultimately distinguish the conditions
among patients with severe sensory and motor
impairments limiting behavioral assessments
(e.g., spastic contractions and blindness).
Atypical Behavioral Features in
the Persistent Vegetative State
Stereotyped behavior, typically limbic displays
of crying, smiling, or other emotional patterns
that are not related to environmental stimuli,
occur in some VS patients. Occasionally, other
fragments of behavior that may appear semi-
purposeful, or inconsistently related to envi-
ronmental stimuli, arise in VS/PVS patients.
Neuroimaging studies, including FDG-PET,
magnetoencephalography (MEG), and func-
tional MRI (fMRI), have identified residual
cerebral circuits underlying such isolated be-
havioral fragments.
105,110,117
One remarkable
patient studied had remained in the PVS for 20
years but infrequently expressed single words
(typically epithets) not related to environ-
mental stimulation (Figure 9–7C). Two other
patients in this group revealed similar isolated
metabolic activity that could be correlated with
unusual behavioral patterns.
105
These data
provide novel evidence for the modular orga-
nization of the brain and suggest that preser-
vation of residual cerebral activity following
severe brain injuries is not random. Regional
preservation of cerebral metabolic activity
likely reflects both preservation of anatomic
connectivity and endogenous neuronal firing
patterns of remnant but incomplete networks.
Further study of this patient showed that
islands of higher resting brain metabolism in-
cluded Heschl’s gyrus (Figure 9–8), Broca’s
area, Wernicke’s area, and the left anterior
basal ganglia (caudate nucleus, possibly puta-
men). Despite limited amounts of remaining
left thalamus identified by MRI that expressed
Consciousness, Mechanisms Underlying Outcomes, and Ethical Considerations
365