Clinical View of Consciousness

Abstract

Consciousness changes with brain states, and as the brain is in a constant state of change, fluctuating between continuums of wakefulness–drowsiness–sleep cycles, one has to account for the many dimensions that consciousness takes.

The conscious brain must be constructed, the self, serving as the basis from which brain mechanisms lead to consciousness. Consciousness exists in a hierarchy of stages, each building upon and dependent on its predecessors. According to Damasio, the protoself is a nonconscious collection of representations of the multiple dimensions of the current state of the organism. Core consciousness arises when the brain generates a representation of the relationship between the organism (the self) and an environmental stimulus. The state following core consciousness is extended consciousness, the capacity to be aware of a large collection of entities and events and the ability to generate a sense of individual perspective or ownership. In agreement, Stern’s phases in the development of the sense of self map neatly into Damasio’s neuropsychological description. The emergent self that Stern describes is conceptualized by Damasio as the protoself. This brings an interesting parallel between the neural self and the psychoanalytical theories of self, which—as Freud himself believed—are rooted in biology.

We consider the very many altered states of consciousness that are part of a large behavioral repertoire of both physiological and pathological states of consciousness. For consciousness to exist, our brain must be capable of integrating information. Consciousness is lost when this is no longer possible, as in anesthesia, where there is a breakdown of connectivity and thus of integration of information. Studies that help us to better understand the most extreme states of impaired consciousness, persistent vegetative state, are discussed.

We describe a few clinical examples that demonstrate loss of awareness such as disconnection and neglect syndromes. The notion that consciousness can be fragmented is particularly apparent from the observation of patients with temporal lobe epilepsy in which patients may experience feelings of depersonalization together with multiple fragmentized sensory states. A loss of control of the normal boundaries between sleep and wake states results in a condition called narcolepsy. The memory impairment in Alzheimer’s disease eventually leads to a profound degradation of consciousness.