Implicit motor learning is impaired in strabismic adults

Abstract

Binocular vision disorders (BVD) are quite common in subjects with cerebellar dysfunctions. Also individuals with strabismus often suffer from many motor deficits, such as impaired body balance and walking. It is known that the cerebellum is necessary to maintain proper body posture but also to learn motor skills. It is conceivable that subjects with BVD would also have deficits in procedural (implicit) motor learning, one of the primary cerebellar functions. The primary aim of this study was to explore motor learning abilities in subjects with BVD (strabismic group, SG). Modified versions of a single reaction time task were used in the scheme proposed by Molinari et al. in 1997. A set of three different tasks (Experiment 1) were performed under dominant eye viewing to investigate (a) procedural (implicit) motor learning, (b) declarative (explicit) learning, and (c) simple stimulus-response associative learning. Because each task examined different aspects of motor learning abilities, it could be revealed which motor learning pathway is impaired in SG. Results showed that the SG had slower reaction times in all three tasks and demonstrated poor implicit motor learning ability compared to controls. To verify if these results were caused by reduced binocular vision or cerebellar deficits, per se, a nonstrabismic binocular anomalies group (NSG) was introduced, and all the same tests were performed (Experiment 2). These results revealed that there were no differences between the NSG and the control group with good binocularity. To conclude, the poor procedural learning ability and slower reaction times in strabismic subjects should not be explained as an effect of incomplete binocular vision that influences the maturity of the visual cortex and transformation of visual information into a motor program because binocular anomaly individuals without strabismus have motor learning abilities close to the controls. Some cerebellar deficits appear to be the origin of observed anomalies.

Not only amblyopic but also dominant eye in subjects with strabismus show increased saccadic latency

“…Due to the small sample available, we did not distinguish between binocular and nonbinocular subjects, but it is important to note that most of our anisometropic amblyopes had stereopsis, and most of our strabismic amblyopes were nonbinocular observers and manifested deeper amblyopia as compared to the anisometropic group from our previous research (Perdziak et al, 2014). It is commonly known that the lack of binocular vision affects not only visual but also a variety of other functions related to visuomotor coordination (Grant & Moseley, 2011;Suttle, Melmoth, Finlay, Sloper, & Grant, 2011) and motor control abilities (Przekoracka-Krawczyk, Nawrot, Czaińska, & Michalak, 2014;Przekoracka-Krawczyk, Nawrot, Kopyciuk, & Naskręcki, 2015). It was found that nonbinocular subjects (usually strabismic amblyopes) tend to have poorer optotype and Vernier acuity than those with residual binocular function (usually anisometropic amblyopes;McKee et al, 2003).…”

Deficient vergence prism adaptation in subjects with decompensated heterophoria

“…This, in turn, could be reflected by low adaptation rate and inability to fully reduce fixation disparity. The idea that the cerebellum may be involved in controlling VPA and other oculomotor deficits was also suggested in other studies which demonstrated impaired ability of implicit motor learning (one of the fundamental cerebellar functions) in subjects with binocular problems [56] and dyslexia [40], poor body balance control in adults [57] and children [58] with strabismus or changes in walking strategies applied by patients with strabismus [59]. All of these functions depend, at least to some extent, on cerebellar control.…”

Test–retest of a phoria adaptation stimulus-induced functional MRI experiment

“…Several investigations have reported dyslexic readers with deficits in vergence and other oculomotor function (Bucci, Brémond-Gignac, & Kapoula, 2008;Bucci, Nassibi, Gérard, Bui-Quoc, & Seassau, 2012;Kapoula & Bucci, 2007;Legrand, Bui-Quoc, Doré-Mazars, Lemoine, Gérard, & Bucci, 2012;Przekoracka-Krawczyk, Brenk-Krakowska, Nawrot, Rusiak, & Naskręcki, 2017). In addition, studies on strabismic patients also suggest dysfunction in the cerebellum (Gaertner, Creux, Espinasse-Berrod, Orssaud, Dufier, & Kapoula, 2013;Przekoracka-Krawczyk, Nawrot, Kopyciuk, & Naskrȩcki, 2015). Collectively, these lines of research indicate that the cerebellum is part of the neural circuit needed to mediate vergence eye movement function.…”

“…Previous clinical studies have demonstrated that phoria adaptation is reduced in patients with binocular dysfunction such as convergence insufficiency (Brautaset & Jennings, 2005a;Brautaset & Jennings, 2006;Henson & North, 1980;North & Henson, 1981;Schor & Horner, 1989;Sreenivasan & Bobier, 2014), exotropia (Kiyak Yilmaz, Kose, Yilmaz, & Uretmen, 2015;Zahavi, Friling, Ron, Ehrenberg, Nahum, & Snir, 2019), convergence excess esotropia (Garretty, 2018;Wygnanski-Jaffe, Trotter, Watts, Kraft, & Abdolell, 2003), and decompensated heterophoria (Przekoracka-Krawczyk, Michalak, & Pyżalska, 2019). In addition, there is evidence that therapeutic interventions such as vision therapy (Brautaset & Jennings, 2006) or surgery (Akbari, Mehrabi Bahar, Mirmohammadsadeghi, Bayat, & Masoumi, 2018;Garretty, 2018) may lead to an improvement in phoria adaptation in some patients.…”