Online research in philosophy

Rolls presents a good integrative summary of the neural bases of emotions, adds new findings and insights, and takes a stance on controversial issues such as separate or distinct brain systems for processing emotion information and for planning and action. This commentary raises questions about his explanations of emotion activation, response to novelty, the evolution of emotions, and the phenomenal experience of emotions in human consciousness.

“Decortication” does not distinguish between removing all cerebral cortex, including three-layered allocortex or just six-layered neocortex. Functional decortication, by spreading depression, reversibly suppresses only neocortex, leaving minimal intentionality. Removal of all forebrain structures except a hypothalamic “island” blocks all intentional behaviors, leaving only tropisms. To what extent do Merker's examples retain allocortex, and how might such residues affect his interpretations? (Published Online May 1 2007).

In this commentary we discuss the possibility of subcortical consciousness and its implications for fetal anesthesia and analgesia. We review the neural development of structural and functional elements that may participate in conscious representation, with a particular focus on the experience of pain. (Published Online May 1 2007).

Seeking to unlock the secrets of consciousness, neuroscientists have been studying neural correlates of sensory awareness, such as meaningless randomly moving dots. But in the natural world of species' survival, “raw feelings” mediate conscious adaptive responses. Merker connects the brainstem with vigilance, orientating, and emotional consciousness. However, depending on the brain's phylogenetic level, raw feeling takes particular forms. (Published Online May 1 2007).

Merker's core idea, that the experience of being conscious reflects the interactions of actions, targets, and motivations in the upper brainstem, with cortex providing the content of the conscious experience, merits serious consideration. However, we have two areas of concern: first, that his definition of consciousness is so broad that it is difficult to find any organisms with a brain that could be non-conscious; second, that the focus on one cortical–subcortical system neglects other systems (e.g., basal forebrain and brainstem cholinergic systems and their cortical and thalamic target areas) which may be of at least equal significance. (Published Online May 1 2007).

A broad range of evidence regarding the functional organization of the vertebrate brain – spanning from comparative neurology to experimental psychology and neurophysiology to clinical data – is reviewed for its bearing on conceptions of the neural organization of consciousness. A novel principle relating target selection, action selection, and motivation to one another, as a means to optimize integration for action in real time, is introduced. With its help, the principal macrosystems of the vertebrate brain can be seen to form a centralized functional design in which an upper brain stem system organized for conscious function performs a penultimate step in action control. This upper brain stem system retained a key role throughout the evolutionary process by which an expanding forebrain – culminating in the cerebral cortex of mammals – came to serve as a medium for the elaboration of conscious contents. This highly conserved upper brainstem system, which extends from the roof of the midbrain to the basal diencephalon, integrates the massively parallel and distributed information capacity of the cerebral hemispheres into the limited-capacity, sequential mode of operation required for coherent behavior. It maintains special connective relations with cortical territories implicated in attentional and conscious functions, but is not rendered nonfunctional in the absence of cortical input. This helps explain the purposive, goal-directed behavior exhibited by mammals after experimental decortication, as well as the evidence that children born without a cortex are conscious. Taken together these circumstances suggest that brainstem mechanisms are integral to the constitution of the conscious state, and that an adequate account of neural mechanisms of conscious function cannot be confined to the thalamocortical complex alone. (Published Online May 1 2007) Key Words: action selection; anencephaly; central decision making; consciousness; control architectures; hydranencephaly; macrosystems; motivation; target selection; zona incerta.

To further illuminate the nature of conscious states, it may be progressive to integrate Merker's important contribution with what is known regarding (a) the temporal relation between conscious states and activation of the mesodiencephalic system; (b) the nature of the information (e.g., perceptual vs. premotor) involved in conscious integration; and (c) the neural correlates of olfactory consciousness. (Published Online May 1 2007).

Merker's approach allows the formulation of an evolutionary view of consciousness that abandons a dependence on structural homology – in this case, the presence of a cerebral cortex – in favor of functional concordance. In contrast to Merker, though, I maintain that the emergence of complex, dynamic interactions, such as those which occur between thalamus and cortex, was central to the appearance of consciousness. (Published Online May 1 2007).

My response addresses general commentary themes such as my neglect of the forebrain contribution to human consciousness, the bearing of blindsight on consciousness theory, the definition of wakefulness, the significance of emotion and pain perception for consciousness theory, and concerns regarding remnant cortex in children with hydranencephaly. Further specific topics, such as phenomenal and phylogenetic aspects of mesodiencephalic-thalamocortical relations, are also discussed. (Published Online May 1 2007).