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Abstract:
The appearence of apparently organized behavior and
wakefulness in the persistent vegetative state is a disturbing and
potentially confounding observation. Therefore a better
understanding of the correlation between expressed behavior and
underlying brain function is required. Clinical characterization
were implemented in five patients in persistent vegetative state (6
months to 20 years duration). Isolated behavioral patterns were
correlated with data obtained from functional brain imaging with
magnetoencephalography (MEG) and positron emission tomography
(PET). In addition, functional data was overlayed on magnetic
resonance images (MRI). Three patients showed dissociations between
fractionally coordinated behaviors and quantitative brain function.
Patient 1 spoke infrequently, single understandable words and
demonstrated preserved islands of functional metabolism in the left
hemisphere as well as some preserved gamma-band oscillations with a
reduced and incomplete reset during early sensory processing in the
left hemisphere only. Patient 2 exhibited fragments of fixed
coordinated movement patterns accompanied by globally reduced brain
metabolism with partial preservation of metabolism in several
connected cortical and subcortical areas involved in movement.
Patient 3 demonstrated behavioral arousal responses to
somatosensory stimulation and prosodic stimuli. MEG data indicated
evidence of abnormal evoked field components and a reduced and
incomplete reset in gamma-band activity during early sensory
processing. Baseline brain metabolism in these three patients
demonstrated 50-60% reductions of global metabolism, consistent
with previous PET results in vegetative patients. These findings
suggest that global integration of modular functions characterizes
the normal human brain but unconscious persons may express
partially preserved modules of activity, sufficient to produce
isolated behavioral patterns such as spoken words.
Support: Charles A. Dana Foundation, Annie Laurie Aitken
Charitable Trust, NIH Clinical Research Center.
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