Consciousness

Abstract

Consciousness is topical, for reasons including its renewed respectability among psychologists, rapid progress in the neuroscience of perception, memory and action, advances in artificial intelligence and dissatisfaction with the dualistic separation of mind and body. Consciousness is an ambiguous term. It can refer to (i) the waking state; (ii) experience; and (iii) the possession of any mental state. Self-consciousness is equally ambiguous, with senses including (i) proneness to embarrassment in social settings; (ii) the ability to detect our own sensations and recall our recent actions; (iii) self-recognition; (iv) the awareness of awareness; and (v) self-knowledge in the broadest sense. The understanding of states of consciousness has been transformed by the delineation of their electrical correlates, of structures in brainstem and diencephalon which regulate the sleep-wake cycle, and of these structures' cellular physiology and regional pharmacology. Clinical studies have defined pathologies of wakefulness: coma, the persistent vegetative state, the 'locked-in' syndrome, akinetic mutism and brain death. Interest in the neural basis of perceptual awareness has focused on vision. Increasingly detailed neuronal correlates of real and illusory visual experience are being defined. Experiments exploiting circumstances in which visual experience changes while external stimulation is held constant are tightening the experimental link between consciousness and its neural correlates. Work on unconscious neural processes provides a complementary approach. 'Unperceived' stimuli have detectable effects on neural events and subsequent action in a range of circumstances: blindsight provides the classical example. Other areas of cognitive neuroscience also promise experimental insights into consciousness, in particular the distinctions between implicit and explicit memory and deliberate and automatic action. Overarching scientific theories of consciousness include neurobiological accounts which specify anatomical or physiological mechanisms for awareness, theories focusing on the role played by conscious processes in information processing and theories envisaging the functions of consciousness in a social context. Whether scientific observation and theory will yield a complete account of consciousness remains a live issue. Physicalism, functionalism, property dualism and dual aspect theories attempt to do justice to three central, but controversial, intuitions about experience: that it is a robust phenomenon which calls for explanation, that it is intimately related to the activity of the brain and that it has an important influence on behaviour.

Functional neuroanatomy of disorders of consciousness

“…Despite ongoing efforts, no universal definition of the term has been agreed on [1,2]. For practical and didactic purposes, consciousness is often described as having two main components: awareness and wakefulness [3].…”

From affective blindsight to emotional consciousness

“…Because homeostatic processes provide the sense of invariance that accompanies every subjective experience, they constitute a neurobiological mechanism for the invariance of the sense of self and the continuity of our first-person experience of the world (Damasio, 1999;Park & Tallon-Baudry, 2014;Tsuchiya & Adolphs, 2007). Accordingly, basic aspects of the physiological reactions to emotional stimuli, including reactions to stimuli that are not consciously perceived, overlap with physiological responses related to corrections of homeostatic imbalance and thought to be necessary for the general level of consciousness (Damasio, 1999;Damasio & Carvalho, 2013;Zeman, 2001). It is no coincidence that these emotional responses are controlled by neural structures in the brainstem that also control the level of consciousness.…”

Brain Function in the Vegetative State

“…Among these activities, 40 Hz oscillations seem to be deeply, although not exclusively, involved in conscious experience. 34,35 Thus, thalamic nuclei seem critical for the maintenance of human awareness.…”

“…5 Thus, despite an altered resting metabolism, primary sensory cortices still activate during external stimulation, whereas hierarchically higher-order downstream multimodal association areas do not. In the absence of a generally accepted neural correlate of consciousness, 35 it is difficult to make definite judgments about conscious perception in VS patients. However, the cascade of functional disconnections along the sensory cortical pathways, from primary areas to multimodal and limbic areas, suggests that the observed activation of primary sensory cortex subsists as an island, dissociated from higher-order cortices that would be necessary to produce awareness.…”