The functional logic of an orienting super-hub in the roof of the midbrain - Bjorn Merker

The roof - or tectum - of the vertebrate midbrain houses a complex neural machinery, called the superior colliculus in mammals, whose functional role has not been definitively settled despite almost two centuries of empirical studies. Over time, the interpretation of its functional role has advanced from that of implementing a simple "visual grasp reflex" to ever more sophisticated operations such as target selection and priority mapping for orienting gaze shifts. This "upgrading" of its functional role has been driven by the results of the ever more sophisticated experimental paradigms by which it has been allowed to give evidence of its operations. Conceptions of the potential functional sophistication of this midbrain structure therefore seem to be catching up with and starting to match the evidence for structural complexity that has long been known to reside in the midbrain roof on anatomical grounds. This might mean that we finally are approaching something resembling an asymptote in the functional interpretation of the role of this structure in the brain's over-all functional division of labor. By outlining how a specific conjecture regarding its key function aligns with current evidence regarding collicular connectivity, intrinsic circuitry and functional competences, I will place my bet on what that asymptote is pointing to.

Suggested reading:

Merker, B. (2013). The efference cascade, consciousness, and its self: Naturalizing the first person pivot of action control. Frontiers in Psychology 4, article 501: 1-20.

Anatomy:
- Isa T and Hall WC (2009). Exploring the superior colliculus in vitro. Journal of Neurophysiol 102: 2581–2593. doi:10.1152/jn.00498.2009.
- May PJ (2006). The mammalian superior colliculus: laminar structure and connections. Progress in Brain Research 151: 321–378.
- Sparks D and Hartwich-Young R (1989). The deep layers of the superior colliculus. In RH Wurtz and ME Goldberg (Eds.), The neurobiology of saccadic eye movements, pp. 213–255. Amsterdam: Elsevier.

Some functional issues:
- Fecteau JH and Munoz DP (2006): Salience, relevance, and firing: a priority map for target selection. Trends in Cognitive Sciences 10: 382–390. doi:10.1016/j.tics.2006.06.011
- Lovejoy LP and Krauzlis RJ (2010). Inactivation of primate superior colliculus impairs covert selection of signals for perceptual judgments. Nature Neuroscience 13: 261–267.
- Sparks DL (1999). Conceptual issues related to the role of the superior colliculus in the control of gaze. Current Opinion in Neurobiology 9: 698–707.