(2) In humans and other mammals, the main neural structures that have been postulated to produce HLC (e.g., Cotterill, 1997; Tononi and Edelman, 1998; Crick and Koch, 2003, 2005; Edelman, 2003;) include the claustrum, most or all of the neocortex, the dorsal thalamic specific sensory relay nuclei, the intralaminar nuclei, and the thalamic reticular nucleus.
The analysis (Cotterill, 2001) concludes that the attention mechanism involves the thalamic intralaminar nuclei and the nucleus reticularis thalami.
Within the thalamus, the intralaminar nuclei (Bogen, 1995; Purpura and Schiff, 1997; Ysbrand et al., 2002) are essential for maintaining a waking state in placental mammals, as is the rostral part of the reticular formation (Moruzzi and Magoun, 1949), which projects to them.
Lying deep to the main cortical layers in the lateral part of the cerebral hemisphere and receiving ascending input from the intralaminar nuclei, the claustrum might or might not be a good candidate for participation in the generation of consciousness in mammals.
These thalamic nuclei, along with the intralaminar nuclei and the thalamic reticular nucleus, which is discussed below, are thought to be essential for higher levels of consciousness (e.g., Steriade et al., 1996; Llinas et al., 1998, 2005; Steriade, 2006) In Figure 3, the main collothalamic pathways are shown as relays from the colliculi to the thalamus; the visual and somatosensory/multisensory pathways are shown as running together from the superior colliculus, and the main auditory pathway is shown as running from the inferior colliculus.
Here, the projections of the globus pallidus to the ventral anterior and ventral lateral (pars oralis) thalamic nuclei, VA and VLo, are shown, as are the globus pallidal projections to the intralaminar nuclei. The latter nuclei were discussed above, and in addition to their widespread cortical projections, they also project directly back to the striatum, completing a thalamo-striato-pallido-thalamic loop.