Despite converging agreement about the definition of<unk> , recent reports have raised concerns about the accuracy of diagnosis in some patients, and the extent to which, in a selection of cases, residual cognitive functions may remain undetected and patients are diagnosed as being in a<unk> . Objective assessment of residual cognitive function can be extremely difficult as motor responses may be minimal, inconsistent, and difficult to document in many patients, or may be undetectable in others because no cognitive output is possible. In recent years, a number of studies have demonstrated an important role for functional neuroimaging in the identification of residual cognitive function in<unk> ; this technology is providing new insights into cerebral activity in patients with severe brain damage. Such studies, when successful, may be particularly useful where there is concern about the accuracy of the diagnosis and the possibility that residual cognitive function has remained undetected. Diagnostic experiments Researchers have begun to use functional neuroimaging studies to study implicit cognitive processing in patients with a clinical diagnosis of<unk> . Activations in response to sensory stimuli with positron emission tomography (PET), functional magnetic resonance imaging (fMRI), and electrophysiological methods can provide information on the presence, degree, and location of any residual brain function. However, use of these techniques in people with severe brain damage is methodologically, clinically, and theoretically complex and needs careful quantitative analysis and interpretation. For example, PET studies have shown the identification of residual cognitive function in<unk> . That is, an external stimulation, such as a painful stimulus, still activates "primary" sensory cortices in these patients but these areas are functionally disconnected from "higher order" associative areas needed for awareness. These results show that parts of the cortex are indeed still functioning in<unk> " patients. In addition, other PET studies have revealed preserved and consistent responses in predicted regions of auditory cortex in response to intelligible speech stimuli. Moreover, a preliminary fMRI examination revealed partially intact responses to semantically ambiguous stimuli, which are known to tap higher aspects of speech comprehension. Furthermore, several studies have used PET to assess the central processing of noxious somatosensory stimuli in patients in<unk> . Noxious somatosensory stimulation activated midbrain, contralateral thalamus, and primary somatosensory cortex in each and every<unk>  patient, even in the absence of detectable cortical evoked potentials. In conclusion, somatosensory stimulation of<unk>  patients, at intensities that elicited pain in controls, resulted in increased neuronal activity in primary somatosensory cortex, even if resting brain metabolism was severely impaired. However, this activation of primary cortex seems to be isolated and dissociated from higher-order associative cortices. Also, there is evidence of partially functional cerebral regions in catastrophically injured brains. To study five patients in<unk>  with different behavioral features, researchers employed PET, MRI and magnetoencephalographic (MEG) responses to sensory stimulation. In three of the five patients, co-registered PET/MRI correlate areas of relatively preserved brain metabolism with isolated fragments of behavior. Two patients had suffered anoxic injuries and demonstrated marked decreases in overall cerebral metabolism to 30–40% of normal. Two other patients with non-anoxic, multifocal brain injuries demonstrated several isolated brain regions with higher metabolic rates, that ranged up to 50–80% of normal. Nevertheless, their global metabolic rates remained <50% of normal. MEG recordings from three<unk>  patients provide clear evidence for the absence, abnormality or reduction of evoked responses. Despite major abnormalities, however, these data also provide evidence for localized residual activity at the cortical level. Each patient partially preserved restricted sensory representations, as evidenced by slow evoked magnetic fields and gamma band activity. In two patients, these activations correlate with isolated behavioral patterns and metabolic activity. Remaining active regions identified in the three<unk>  patients with behavioral fragments appear to consist of segregated corticothalamic networks that retain connectivity and partial functional integrity. A single patient who suffered severe injury to the tegmental mesencephalon and paramedian thalamus showed widely preserved cortical metabolism, and a global average metabolic rate of 65% of normal. The relatively high preservation of cortical metabolism in this patient defines the first functional correlate of clinical–pathological reports associating permanent unconsciousness with structural damage to these regions. The specific patterns of preserved metabolic activity identified in these patients reflect novel evidence of the modular nature of individual functional networks that underlie conscious brain function. The variations in cerebral metabolism in chronic<unk>  patients indicate that some cerebral regions can retain partial function in catastrophically injured brains. Misdiagnoses<unk> stical<unk>  misdiagnosis is common. An example study with 40 patients in the United Kingdom reported 43% of their patients classified as<unk>  were believed so and another 33% had recovered whilst the study was underway. Some<unk>  cases may actually be a misdiagnosis of patients being in an undiagnosed minimally conscious<unk> . Since the exact diagnostic criteria of the minimally conscious<unk>  were only formulated in 2002, there may be chronic patients diagnosed as<unk>  before the secondary notion of the minimally conscious<unk>  became known. Whether or not there is any conscious awareness with a patient's<unk><unk>  is a prominent issue. Three completely different aspects of this should be distinguished. First, some patients can be conscious simply because they are misdiagnosed (see above). In fact, they are not in<unk><unk> s. Second, sometimes a patient was correctly diagnosed but is then examined during the early<unk> s of recovery. Third, perhaps some day the notion itself of<unk><unk> s will change so to include elements of conscious awareness. Inability to disentangle these three example cases causes confusion. An example of such confusion is the response to an experiment using functional magnetic resonance imaging which revealed that a woman diagnosed with<unk>  was able to activate predictable portions of her brain in response to the tester's requests that she imagine herself playing tennis or moving from room to room in her house. The brain activity in response to these instructions was indistinguishable from those of healthy patients. In 2010, Martin Monti and fellow researchers, working at the MRC Cognition and Brain Sciences Unit at the University of Cambridge, reported in an article in the New England Journal of Medicine that some patients in<unk> s responded to verbal instructions by displaying different patterns of brain activity on fMRI scans. Five out of a total of 54 diagnosed patients were apparently able to respond when instructed to think about one of two different physical activities. One of these five was also able to "answer" yes or no questions, again by imagining one of these two activities. It is unclear, however, whether the fact that portions of the patients' brains light up on fMRI could help these patients assume their own medical decision making. In November 2011, a publication in The Lancet presented bedside EEG apparatus and indicated that its signal could be used to detect awareness in three of 16 patients diagnosed in the<unk><unk> .
Persistent vegetative state
Emergence delirium
Excited delirium
Organic brain syndrome
Post-stroke depression
Diabetic coma
Vascular thalamic amnesia
Diencephalic syndrome