The optic tectum and pretectum of mammals mediate blindsight by establishing a connection between the retina and extrastriate cortex and by permitting an orientation response to punctate and large-tunnel-like targets of high contrast, > 95% (Tehovnik, Patel, Tolias et al. 2021); incidentally, a suggestion was made by Schmidt et al. (2010) that the lateral geniculate nucleus (in primates) also participates in blindsight but there are serious methodological shortcomings with the study (see Footnote 1).
When transitioning across the vertebrate line going from fishes to mammals, it is noteworthy that the relative size of the optic tectum/pretectum decreases with a maximal diminution found in mammals (see Fig. 1). Furthermore, and consistent with the foregoing, both the telencephalon and cerebellar cortices undergo an increase in size relative to the optic tectum/pretectum. As we have argued, the role of the neocortex in the mediation of behavior is to store declarative, conscious information, whereas the role of the cerebellum is to store executable code for the expression of over-learned declarative, conscious routines (Tehovnik, Hasanbegović, Chen 2024): e.g., fluent language expression by humans, digging/next building by rodents, migration by birds, predatory attack by reptiles (e.g., venomous snakes), escape behavior by amphibians (avoiding a visual loom), and immobility by fishes (e.g., freezing behavior). These are some examples of automatic behaviors that are routinely expressed by vertebrates. Readers should be able to establish their own favorite list of automatic behaviors as triggered by a specific behavioral context, both--the behavior and the context--associated by declarative, conscious learning. We now need to determine the information storge capacity of the telencephalon and cerebellum for all vertebrates. The best storage estimates have been made for humans: 1.6 x 10^14 bits for the telencephalon and 2.8 x 10^14 bits for the cerebellum (Tehovnik, Hasabegović, Chen 2024). To make similar estimates for the remaining vertebrates, we just need to determine the number of neurons and synapses per neurons for the telencephalon and cerebellum. This should indicate the capacity of declarative conscious information storage versus executable information storage from fishes to humans. Christof Koch (2013) will now have a way to quantify consciousness across the vertebrate line.
Figure 1: Shown are the relative size relationships across the vertebrate line (from fishes to mammals) for the optic lobe (i.e., tectum and pretectum), the cerebrum (also called the telencephalon or the neocortex), and the cerebellum.
Footnote 1: Schmidt et al. (2010) have proposed that projections via the lateral geniculate nucleus (LGN) to extrastriate cortex of monkeys are sufficient to maintain blindsight (Schmidt et al. 2010), but in the study unilateral inactivation was performed in the LGN (of V1 damaged animals) which induces a position habit such that saccades occur preferentially into the field ipsilateral to the LGN lesion, i.e., the intact field. Bilateral lesions of the LGN would have been the better way to do this experiment. Also, the fMRI signal strength of extrastriate cortex to visual presentations was minimally different for the V1-only-lesion condition and the V1-LGN-lesion condition, and often not significant. These experiments need to be redone before being accepted.
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