One problem with the hierarchy model, though, is that the brain does not use layers as cleanly separated as in software. So, it's quite possible that after exiting the thalamaus and entering area MT or the amygdala, the signal goes on to "higher" regions such as the prefrontal cortex. So even though it's reaching the region, it's still insufficient. It could be because it's not stimulating enough neurons, but it's also possible that there's some qualitative difference as well.
For example, sheer numbers of neurons don't guarantee awareness. The cerebellum has half the total number of neurons in the brain, but they're arranged in a very repetitive manner and seem to have nothing to do with awareness. If you had your cerebellum removed (say, for cancer), you would have difficulty with fine motor control, but not much else. It wouldn't alter your awareness, even though you've just lost half your brain's neurons. If you believe the information integration theorists, what matters is heterogeneity and interconnectivity, rather than mere numbers.