Книги по МРТ КТ на английском языке / PLUM AND POSNER S DIAGNOSIS OF STUPOR AND COM
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Plum and Posner’s Diagnosis of Stupor and Coma |
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The very low overall resting cerebral met- |
arousal systems.145,146 Even incomplete in- |
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abolic rates in MCS patients generally in- |
juries to these networks may produce unique |
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clude the posterior and ventroanterior cingu- |
deficits in maintaining adequate cerebral ac- |
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late regions associated by Raichle with self- |
tivation and patterns of brain dynamics neces- |
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awareness. This may account for the failure to |
sary to establish, maintain, and complete com- |
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engage functional network activation with pre- |
plex behaviors. |
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sentation of time-reversed narratives (Figure |
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9–10). Specifically, a lack of a metabolically ex- |
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pensive ongoing self and environmental mon- |
The Potential Role of Regionally |
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itoring process may leave the MCS brain stim- |
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Selective Injuries Producing |
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ulus bound and limited to activations provoked |
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Widespread Effects on |
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by extremely salient events. This interpretation |
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is supported by direct comparisons of changes |
Brain Function |
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in cerebral metabolism, functional MRI signal |
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activation, and neuronal activity that indicate |
At least three different mechanisms may lead |
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a linear correlation of these measures.142,143 |
to marked alteration of integrative brain ac- |
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The dissociation of low resting cerebral me- |
tivity following relatively focal or regionally |
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tabolism and recruitable cerebral networks in |
restricted brain lesions: (1) a form of passive |
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MCS invites speculation that patients who re- |
inhibition of a brain area following deaffer- |
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main near the border of emergence from MCS |
entation of remote but strongly connected ar- |
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(see red line in Figure 9–1) may show fluctu- |
eas, (2) active inhibitory phenomena resulting |
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ation of recruitment of these large-scale net- |
from altered connectivity and neuronal func- |
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works under varying internal conditions of |
tion following injury, and (3) persistent or par- |
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arousal and appearance of environmentally sa- |
oxysmal functional activity producing excess |
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lient stimuli, leading to the occasional surpris- |
excitation of distributed neuronal networks.121 |
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ingly high level of response. |
Whether such processes underlie partially re- |
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A further consideration is whether injuries |
versible impairment of cognitive function in |
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incurred by compression of the thalamus and |
severely disabled patients is unknown. It is |
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brainstem during acute herniation may un- |
likely, however, that transient changes in dis- |
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derlie the chronically low metabolic rates in |
tributed network function underlie the wide |
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patients remaining in MCS despite connected |
fluctuations in cognitive performance in some |
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and recruitable cerebral networks (both MCS |
MCS patients and patients who emerge from |
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patients studied121 had herniated with mid- |
MCS. These phenomena are well known but |
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brain signs of third nerve palsies during the |
not frequently described in the medical liter- |
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acute phase of their injuries). As discussed in |
ature.91,127 We briefly discuss potentially rel- |
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Chapter 1, the paramedian mesencephalon and |
evant sources of variations of brain dynamics |
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thalamus contain several interconnected brain |
within the wakeful state of the injured brain. |
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systems that interact closely with the brain- |
A relatively common finding following focal |
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stem arousal systems. Although these struc- |
ischemia or traumatic brain injury is a reduc- |
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tures were originally identified as the primary |
tion in cerebral metabolism in brain regions |
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arousal systems, the thalamic intralaminar nu- |
remote from the site of injury. This transsy- |
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clei (ILN) (and paralaminar regions of the |
naptic (or ‘‘crossed’’) down-regulation of dis- |
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thalamus rich in neurons that preferentially |
tant neuronal populations results from the loss |
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project to layer I of the cerebral cortex), the |
of excitatory inputs from the damaged re- |
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mesencephalic reticular formation (MRF), |
gions.147 The clinical significance of these |
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and their connections with the thalamic retic- |
changes is unclear, although electrophysiologic |
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ular nucleus appear to play a key role linking |
correlates have been identified. A recent study |
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arousal states to the control of moment-to- |
by Gold and Lauritzen148 showed that al- |
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moment intention or attentional gating (re- |
though changes in blood flow may be modest |
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viewed in 144). These structures are well posi- |
in remote cortical regions, the transsynaptic |
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tioned to control interactions of the cerebral |
down-regulation produces dramatic decreases |
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cortex, basal ganglia, and thalamus through |
in neuronal firing rates (e.g., a neuronal firing |
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their patterns of innervation within the cortex |
rate decreased by 80% with only a 20% re- |
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as well as rich innervation from the brainstem |
duction in regional blood flow). Thus, stable |