Parkinson’s disease, l-Dopa and “express” saccades: Superior colliculus dyskinesias?

Cluster analysis reveals distinct patterns of saccade impairment and their relation to cognitive profiles in Parkinson's disease

“…Deliberately including participants in on‐medication state, we aimed at revealing new insights into the relationship between saccade performance and dopamine replacement therapy given that the reported effects of levodopa on pro‐ and antisaccades (Cubizolle et al, 2014; Hood et al, 2007; Lu et al, 2019) varied in previous studies. According to the dopamine overdose hypothesis (Cools et al, 2019), these discrepancies might be due to differential effects of levodopa depending on individual intrinsic levels of dopamine in fronto‐striatal circuits (Cools et al, 2003).…”

Are patients with Parkinson’s disease blind to blindsight?

“…As volitional saccades, memory-guided saccades rely on a correct internal representation of the movement pattern and are accessed to recheck a visual stimulus (Terao et al , 2013). Dopaminergic treatment facilitates planed eye movements and also suppresses paradoxical fast ‘reflexive’ saccades, although the contrary, coined superior colliculus dyskinesia, has also been reported (Cubizolle et al , 2013). These findings support the concept that the superior colliculus, pivotal for ‘blindsight’ and instrumental for visuomotor coordination, is the dysfunctional ‘bottleneck of saccades’ in Parkinson’s disease (Terao et al , 2013): visually guided saccades are impaired due to increased inhibition of the superior colliculus through excessive basal ganglia output and memory-guided saccades are impaired due to dysfunctional frontal cortex—superior colliculus circuitries.…”

Medication adversely impacts visually-guided eye movements in Parkinson’s disease

“…Therefore, understanding the medication effect on eye movements can also provide insight into the medication effect on more complex limb movements. Previous studies report conflicting results for medication effects on VGS ( Cubizolle et al, 2014 ; Dec-Ćwiek et al, 2017 ; Gibson et al, 1987 ; Hood et al, 2007 ; Kitagawa et al, 1994 ; Lu et al, 2019 ; Michell et al, 2006 ; Müller et al, 1994 ; Rascol et al, 1989 ; Temel et al, 2009 ; van Stockum et al, 2012 ; Waldthaler et al, 2019 ; Yugeta et al, 2008 ). Understanding the medication effect on VGS is important because the visually-guided saccadic system is tightly related to visual attention ( Awh et al, 2006 ; Corbetta, 1998 ; Jonikaitis and Moore, 2019 ; Moore and Zirnsak, 2017 ), which needs to be shifted easily and rapidly during daily activities.…”