Radical Plasticity Thesis

While a detailed neuronal model of the dynamic core is lacking, a notable feature of the dynamic core hypothesis is the proposal of a quantitative measure of “neural complexity” (Tononi et al.1994), high values of which are suggested to accompany consciousness.According to the theory, distributed neural/cognitive models continually produce content in parallel, and conscious content is merely that content which has the biggest impact on the rest of the system.

Other automatically activated processors do not enter the global workspace. Any such global pattern can inhibit alternative activity patterns among workspace neurons, thus preventing the conscious processing of alternative stimuli (for example, during the so-called attentional blink).

The global neuronal workspace model predicts that conscious presence is a nonlinear function of stimulus salience; i.e., a gradual increase in stimulus visibility should be accompanied by a sudden transition of the neuronal workspace into a corresponding activity pattern (Dehaene et al. Wallace has advocated a network-theoretic modelling perspective on global workspace theory (Wallace 2005).

This metaphor emphasizes temporal aspects of the theory, in particular (i) there is no precise time at which particular content becomes ‘famous’ and (ii) fame can only be determined retrospectively.

According to Dennett, the only ‘hard problem’ of consciousness is acknowledging that there is nothing more to consciousness than mechanisms of conscious access and global influence.

Figure 1: A schematic of the neuronal global workspace.

A central global workspace, constituted by long-range cortico-cortical connections, assimilates other processes according to their salience. Dehaene, Changeux and colleagues have proposed a neuronal implementation of a global workspace architecture, the so-called ‘’neuronal global workspace’’ (see Figure and (Dehaene et al. In this model, sensory stimuli mobilize excitatory neurons with long-range cortico-cortical axons, leading to the genesis of a global activity pattern among workspace neurons.

The dynamic core hypothesis proposes that the neural mechanisms underlying consciousness consist of a functional cluster in the thalamocortical system, within which reentrant neuronal interactions yield a succession of differentiated yet unitary metastable states.

The boundaries of the dynamic core are suggested to shift over time, with some neuronal groups leaving and others being incorporated, these transitions occurring under the influence of internal and external signals (Edelman and Tononi 2000).

While the identification of correlations between aspects of brain activity and aspects of consciousness may constrain the specification of neurobiologically plausible models, such correlations do not by themselves provide explanatory links between neural activity and consciousness.

Models should also be distinguished from theories that do not propose any mechanistic implementation (e.g., Rosenthal’s ‘higher-order thought’ theories, Rosenthal 2005).

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