1. Evolutionary Perspectives. From an evolutionary perspective, consciousness could only have been selected for its adaptive advantages in maintaining life and fostering procreation. Most agree that the conscious mind evolved from unconscious brain dynamics. Thus, basic evolutionary perspectives on both the adaptive functions and the neural interactions underlying consciousness seem a safe organizing assumption for theory building and hypothesis testing. This would include assuming Darwinian mechanisms for how neurons and neuronal groups are selected for the functional network integration(s) that subserve consciousness (Edelman, 1987). Thus, salience-related competition within attention, and competition between potential working memories and other content determines what potentially gains access to consciousness generating neuronal work spaces. Most empirical work and theory have emphasized the crucial roles played by multiple reticular systems, and/or by thalamocortical connectivities (and to a lesser extent, paralimbic/heteromodal cortices). However, more specific details regarding how these two major component systems (the highly distributed and extended reticular structures, reviewed in detail in this chapter, and the thalamocortical mantle) interact are still poorly mapped. How the brain segues effortlessly and seamlessly through a succession of these transient (and fraction-of-a-second) functional integrations of widespread regions from conscious moment to conscious moment also remains poorly understood (see item 2).
2. Neurodynamic Perspectives and Functional Integration. The clinical data suggest that consciousness must be conceptualized as a graded, recursive, and hierarchically organized phenomenon, with various core aspects interacting with extended cognitive aspects. Core aspects include wakefulness, attentional functions, sensory content, salience, affective motivation, and agency. These core components permit cognitive extensions in extended working memories, language, and a host of higher cognitive-cortical functions that allow us an extraordinary richness and vast differentiation of conscious content. Although we have modeled consciousness in terms of these complex functional envelopes (attentional function, intention or directed activity, emotion, basic sensory content), these are clearly interdependent and seamlessly integrated aspects of consciousness, slices of the consciousness pie. Each of these functional domains represents a formidable neuroscientific problem in itself, and each requires widely distributed neural networks that are hard to study empirically. Global neurodynamical perspectives are essential to this task of mapping this functional integration, and neuroanatomy alone is certainly insufficient. An important focal point for future research and theory would be to explain neurodynamically how lesser lesions of multiple reticular activating system components can generate delirium or akinetic mutism, while more massive lesions of these very same systems yield coma or persistent vegetative state.
3. Anatomical Perspectives and the Medioventral/Dorsolateral Distinction. This is a perspective fully complementary to the neurodynamical. Neurodynamic perspectives uninformed by the functional neuroanatomy of consciousness run the risk of falling into a vague equipotentiality that does not adequately integrate the lesion correlate data summarized here. Indeed, understanding the organization of global neurodynamics will require untangling how the contributions of many distributed neuronal populations are hardly equal in consciousness (or that contributions from some populations are clearly more equal than others!). Global neurodynamic formulations have to incorporate evidence that virtually all the structures that appear essential to conscious states (with the exception of heteromodal systems in cortex) are midline systems. This finding is consistent with classical principles of functional neuroanatomy in which medial and ventral systems are earlier developing and more tied to homeostatic and emotional regulation, while anatomical systems situated more dorsolaterally are later developing and more tied to cognitive functions. Consistent with this midline-ventral hegemony for consciousness, even extensive lesions of the heteromodal systems in prefrontal and parietal lobes can only generate one of the lesser disorders of consciousness (HKM, or delirium, and never coma, PVS or AKM). Although we have emphasized that there are many disparate systems in these ventral mesodiencephalic regions, jointly they appear to provide the most crucial foundations for the functional integration of the brain in conscious states.
4. Neurodevelopmental Perspectives. The above considerations suggest that we will make considerably more progress if we can understand how consciousness unfolds from its earliest beginnings in a presumably primary affective form, in humans and in other mammals, and then develops into more complex, cognitive-extended forms with the help of symbolic language acquisition. Neu-rodevelopmental research into the fundamental mechanisms of consciousness in infants is understandably modest for obvious epistemological/ethical reasons, as much of the current neuroscientific work focuses on neural correlates of higher conscious and cognitive activity in adult brains. This suggests that basic research will have to refocus attention on basic neural processes taking place in the first year of life, as core component processes must be brought on-line to operate in an integrated fashion very early in neurodevelopment. Such research into early development will also likely pay dividends clinically in terms of an increased ability to understand and treat disorders of consciousness, such as coma and persistent vegetative state, but also lesser forms of akinetic mutism, autism, and schizophrenia. We suspect that the substrates for the early orienting/affective responses of the infant in its interactions with a caretaker potentially outline the most fundamental constituent neural processes for a primitive or core consciousness. These considerations suggest that consciousness first develops within the milieu of a primary attachment to mother/parenting figures, and in the context of affectively guided orienting toward and interacting with a primary caregiver.
To more fully understand the nature of conscious processes would pay enormous dividends to all areas of psychiatry, illuminating many of the still well-hidden secrets within the mind-brain realms from where emotional distress arises. Such an understanding of functional neural integration in the brain would also no doubt open many new mysteries and questions. A special focus on early neurodevelopmental processes will also have crucially important implications for psychiatry (Schore, 2001), as the affective climate of early life must have a profound effect on the developing brain, substantially increasing or reducing an epigenetic vulnerability in later life to many psychiatric conditions. There is already abundant evidence from preclinical studies that positive social interactions have robust and life-long benefits for the neuroemo-tional resilience of young animals (Meaney, 2001). Such an understanding of early neurodevelopmental processes will eventually help clarify positive and negative risk factors for most if not virtually all Axis I and Axis II disorders. It may also herald many new ways to intervene positively in developmental programs that will help prevent future psychiatric problems while also giving us lasting insights into the nature of the emotional aspects of human consciousness. However, these fundamental neu-rodevelopmental questions are uncharted territories where an enormous amount of research remains to be done, and such neurodevelopmental-affective perspectives on investigating consciousness are certainly not the dominant heuristic in current consciousness studies.
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