Second half of the above:
From:
Evolution of Consciousness: Phylogeny, Ontogeny, and Emergence from General Anesthesia - In the Light of Evolution - NCBI Bookshelf
"Thalamocortical oscillations have been posited to be of critical importance to consciousness because they help integrate functionally diverse and spatially distinct cognitive modules in the cortex (
Saalmann et al., 2012;
Schmid et al., 2012). The interplay of segregation and integration is a fundamental focus of the integrated information theory of consciousness (
Tononi, 2004,
2012). The capacity of the thalamocortical system to achieve both integration and differentiation is reflected in higher levels of Phi, a proposed metric for consciousness (
Tononi, 2004). Phi reflects the amount of information generated by an integrated system beyond the information contained within the components of the system. In principle, this measure captures the emergent property of the system (consciousness) that cannot be causally reduced to individual subsystems (particular brain regions). Phi is predicted to decrease during sleep and seizures; preliminary evidence suggests it also decreases during anesthesia (
Lee et al., 2009b), possibly due to impaired long-range coupling of neural spike activity (
Lewis et al., 2012). Although the integrated information theory of consciousness has yet to be definitively demonstrated, it is a guiding paradigm that can inform the evolution of consciousness from the network perspective. Creatures with brain network systems that are capable of generating high values of Phi are more likely to be conscious (
Edlund et al., 2011).
Third, widespread brain activity appears correlated with conscious activity. Sensory input spreads quickly from sensory cortex to parietal, temporal, and prefrontal areas (
Dehaene et al., 2003). This spread of cortical activity is also associated with recurrent local feedback occurring along the way, followed shortly thereafter by long-range feedback from anterior to posterior structures (
Lamme, 2006). These long-range connections are thought to be important for the experiential aspects of consciousness (i.e., awareness) (
Singer, 1993) and appear to be preferentially suppressed during general anesthesia (
Lewis et al., 2012;
Schröter et al., 2012). In particular, there is strong evidence that networks across the frontal and parietal cortices are associated with awareness across multiple sensory modalities (
Gaillard et al., 2006;
Fahrenfort et al., 2008;
Blumenfeld, 2012). The lateral frontoparietal network plays a role in mediating consciousness of the environment, whereas the medial frontoparietal network plays a role in mediating internal conscious states such as dreaming and internally directed attention (
Boly et al., 2007;
Denton et al., 2009). It is becoming increasingly clear that the directionality of corticocortical network communication is relevant to conscious processing. Information processing from the caudal to rostral direction (feedforward) is associated with sensory processing that can occur in the absence of consciousness (e.g., general anesthesia, priming) (
Imas et al., 2005;
Gaillard et al., 2007). In contrast, information processing in the rostral-to-caudal direction (feedback or cortical reafference) is thought to be associated with experience itself and is preferentially inhibited by general anesthetics (
Imas et al., 2005;
Lee et al., 2009a;
Ku et al., 2011).
The neocortical view of consciousness originates, in part, from early morphologic examination of brain differences across species that suggested the capacities of consciousness increased as brains evolved from more primitive reptilian organization, to mammalian (or, with a limbic system, paleomammalian), and then neo-mammalian organization, characterized by an intricately folded neocortex. This conceptualization of brain evolution occurring in stages during which more “advanced” brains—along with their expanded behavioral repertoire—were built on the structure of earlier forms was popularized by Maclean as “the triune brain” (
Maclean, 1990). Importantly, this view of brain evolution is now largely considered erroneous (
Emery and Clayton, 2005;
Jarvis et al., 2005). It did offer an easy conceptualization for relating brain structure with function and suggested evolutionary time points for when various behaviors would have emerged. Newer findings, however, strongly refute the model of a triune brain, especially the concept of a later-developing neocortex (
Fig. 3.1) (
Emery and Clayton, 2005). As it turns out, a precursor of the neocortex was actually present in the earliest evolving vertebrates, a claim based on some aspects of connectivity and homology of early transcription factor expression (
Striedter, 2005). The basic structural pattern of a brainstem, midbrain, and forebrain did not need to be completely reinvented as each new species emerged. Rather, as various ecological niches were exploited by various creatures, those brain regions best suited for enhancing survival in the local environment were emphasized for further development (
Emery and Clayton, 2005).
FIGURE 3.1
Theories of brain evolution. Ancient brain structure evolution theory of Scala Naturae showing brain development proceeding from simple to more complicated with the addition of new brain regions as evolution progressed. This erroneous view is compared
(more...)."