M1 Levels of consciousness and coma

Topic

The level of consciousness is modeled as the product of two distinct components: thalamocortical activation originating from the ascending reticular activating system, and the cortical network's capacity for information integration—an extension of the effective connectivity previously used to describe the cortical network in another model.

Since the level of consciousness is the product of these two components, high thalamocortical activation without sufficient information integration capacity does not yield full consciousness; conversely, high information integration capacity without sufficient thalamocortical activation also fails to produce full consciousness. This dissociation between the two components of the level of consciousness is clinically observed in the vegetative state, where thalamocortical activation is present but information integration capacity is absent—in contrast to deep sleep, where information integration capacity is only partial and thalamocortical activation is low.

The Glasgow scale is modeled as a sigmoid function of the continuous level of consciousness: at very low levels of consciousness, the Glasgow scale changes little; at intermediate levels, it changes rapidly; and at very high levels, it again changes little as it approaches its maximum value. This sigmoid function is useful for mapping the model's continuous level of consciousness to clinical practice, where the Glasgow scale is used in a standardized manner.

Following an acute injury, the level of consciousness follows a dynamic pattern of deterioration and recovery over time. Global cerebral metabolism—an extension of the cerebral metabolic rate of oxygen previously defined in the neurovascular coupling model—decreases in proportion to this level of consciousness: the lower the level of consciousness, the lower the global cerebral metabolism. This proportional relationship between global cerebral metabolism and the level of consciousness forms the physiological basis for monitoring techniques used in intensive care. Overall, it is this very level of consciousness—resulting from thalamocortical activation and the cortical network's capacity for information integration—that determines both a person's Glasgow scale score and their global cerebral metabolism, and that follows its own dynamics of deterioration and recovery following an acute injury.

ID:4273