Cerebral processing in the minimally conscious state

The minimally conscious state (MCS) is considered a transitional phase in the partial recovery of self- awareness or environmental-awareness from the vegetative state (VS). This recognition highlights the crucial role of pathophysiology in elucidating the generation of consciousness in these cases. [1] The patient described by Laureys et al showed context-dependent higher-order auditory processing. The authors previously reported that in the VS, auditory stimulation activates primary auditory cortices but not higher-order associative areas from which they have been disconnected. Their work revealed that functional connectivity between primary and higher-order associative cortices areas can be partially preserved in MCS although disconnected in VS. [2] In the original description of the apallic syndrome, extensive bilateral damage to the cerebral cortex was considered the primary pathological finding. However, recent publications have shown that VS results from a complex combination of discrete cortical and subcortical damage. In addition, consciousness requires sufficient thalamocortical and intercortical connections, as demonstrated by the identification of isolated functional activity in diverse parts of the cortex that does not provide awareness of self and the environment. [3,4] Patients in VS provide the only circumstance in which there is an apparent dissociation of both components of consciousness. The subjective dimension of awareness is impossible to test because it involves “internal awareness” or a state of mind that cannot be measured in an individual existing in apparent disconnection from the environment. [3] Despite limitations in measuring this phenomenon physiologically, subjective awareness might continue in some VS cases. [3] The development of rehabilitation techniques for VS patients and others suffering long-lasting effects of brain injury is challenging. The multisensory stimulation approach, the use of deep brain stimulation and the implementation of prosthetics to treat cognitive disabilities have provided new hope for cognitive rehabilitation from VS. [3,5] Beyond these advances, the use of neural stem cells is another hope. Laureys et al have demonstrated partial recovery in a patient who earlier had been in a persistent vegetative state. As these authors have emphasized, “MCS may be a transitional state on the route to further recovery, just like the patient’s vegetative state was a transitional state earlier in his course”. Neuroimaging could provide a powerful tool to follow up cognitive recovery in patients with PVS or MCS. References 1. Giacino JT, Ashwal S, Childs N, et al. The minimally conscious state: Definition and diagnostic criteria. Neurology 200258:349-353. 2.Laureys S, Faymonville ME, Degueldre C, et al. Auditory processing in the vegetative state. Brain. 2000; 123: 1589–1601 3.Machado C. Consciousness as a definition of death: Its appeal and complexity. Clinical Electroencephalography 1999;30:156-164. 4.Kinney HC, Korein J, Panigraphy A, Dikkes P, Goode R. Neuropathologic findings in the brain of Karen Ann Quinlan: The role of the thalamus in the persistent vegetative state. N Engl J Med 1994;330:1469-1475. 5.Schiff ND, Plum F, Rezai AR. Developing prosthetics to treat cognitive disabilities resulting from acquired brain injuries. Neurol Res 2002;24(2):116-24.

References

1. Giacino JT, Ashwal S, Childs N, et al. The minimally conscious state: Definition and diagnostic criteria. Neurology 200258:349-353.

2.Laureys S, Faymonville ME, Degueldre C, et al. Auditory processing in the vegetative state. Brain. 2000; 123: 1589–1601

3.Machado C. Consciousness as a definition of death: Its appeal and complexity. Clinical Electroencephalography 1999;30:156-164.

4.Kinney HC, Korein J, Panigraphy A, Dikkes P, Goode R. Neuropathologic findings in the brain of Karen Ann Quinlan: The role of the thalamus in the persistent vegetative state. N Engl J Med 1994;330:1469-1475.

5.Schiff ND, Plum F, Rezai AR. Developing prosthetics to treat cognitive disabilities resulting from acquired brain injuries. Neurol Res 2002;24(2):116-24.