Prosomeric classification of retinorecipient centers: a new causal scenario.

The retina is known to target many superficial areas in the brain. These have always been studied under the tenets of the classic columnar brain model, which was not designed to produce causal explanations, being functionally oriented. This has led over the years to a remarkable absence of understanding or even hypothetical thinking about why the optic tract takes its precise course, why there are so many retinal targets (some of them at surprising sites), what mechanism places each one of them exactly at its standard position, which processes specify spatial aspects of retinotopy and differential physiological properties within the visual system, and so on, including questions about conserved and changing evolutionary aspects of the visual structures. The author posits that the origin of the current causally uninformative state of the field is the columnar model, which worked as a subliminal or cryptic dogma that disregards the molecular developmental advances accruing during the last 40 years, and in general distracts the attention of neuroscientists from causal approaches. There is now an alternative brain model, known as the prosomeric model, that does not have these problems. The author aims to show that once the data on retinal projections are mapped and analyzed within the prosomeric model the scenario changes drastically and multiple opportunities for formulating hypotheses for causal explanation of any aspects about the visual projections become apparent (emphasis is made on mouse and rabbit data, but any set of data on retinal projections in vertebrates can be used, as shown in some examples).