The vestibulo-ocular reflex (VOR) can occur in total darkness, which means that it is independent of visual sensation putting it under efference-copy control, a control whose vital circuitry resides in the cerebellum (see VOR circuitry, Fig. 1; as well see: Bell et al. 1997; De Zeeuw 2021; Fukutomi and Carlson 2020; Loyola et al. 2019; Shadmehr 2020; Tehovnik et al. 2021; Wang et al. 2023). VOR occurs in all vertebrates, all of which have a cerebellum, as well as a telencephalon. Remember, a dysfunctional VOR prevents one from reading this text and one’s visual surround would be in a continuous spin, a spin that is only stoppable by closing one’s eyes. In total darkness, VOR gain cannot be changed: i.e., measured as the extent of head displacement (in degrees of rotation) as compared to the extent of eye displacement (in degrees of rotation, but in the opposite direction to that of the head). Normally, VOR gain between head and eye is set at a ratio of 1:1. Prisms are used to alter this gain by using minimizing or magnifying lenses that through visual experience resets the gain, for example, toward a ratio of 2:1 or 1:2, respectively (Lisberger, Miles, Zee et al. 1984). Damage to the cerebellum abolishes VOR gain adaptation to prisms (Lisberger, Miles, Zee et al. 1984), as it does to prism adaptation in general (Thach et al. 1992). We suspect that an intact neocortex is also necessary to change the gain values (as alluded to by the work of: Held and Hein 1958; Schiller and Tehovnik 2015; Schiller et al. 1980; Tehovnik et al. 2021; Ventre-Dominey et al. 2014). Specifically, all learning of visuomotor tasks depends on an intact neocortex, since subcortical pathways on their own are not sufficient for this learning (Schiller and Tehovnik 2015; Tehovnik et al. 2021). The neocortical areas critical for this modification may be MT/MST (see Ventre-Dominey 2014), but the vestibulo-ocular signal is highly distributed in neocortex containing VOR-related neurons in the parietal, temporal, and frontal cortices (see Fig. 2). Whether disabling the entire vestibular network (bilaterally) is necessary to abolish VOR adaptation will require further study.
Thus, much like classical conditioning (Pavlov 1927; Takahara et al. 2003), any change in VOR likely depends on both the cerebellum and neocortex, which further ascertains that these structures (containing over 95% of the neurons in the brain, Herculano-Houzel 2009) must be studied as a functional unit [e.g., the wonderful work of Hasanbegović (2024) unifies the two structures; shortly reading Hasanbegović’s PhD thesis will become mandatory for investigators wanting to deduce the relationship between automaticity and consciousness, as information is transferred and stored during bouts of new learning (Tehovnik, Hasanbegović, Chen 2024)].
Figure 1: Circuitry for the vestibulo-ocular reflex (Wikipedia, Dec 23, 2023): (https://en.wikipedia.org/wiki/Vestibulo%E2%80%93ocular_reflex#:~:text=The%20VOR%20does%20not%20depend,also%20added%20to%20the%20movement)
Figure 2: Many sites in neocortex (up to eight) contain neurons that are modulated by VOR. From Ventre-Dominey (2014, Fig. 1).
- Badges
- Science topic