Memory-guided saccades in Parkinson’s disease: long delays can improve performance

Abstract

A recent study in control subjects suggested the existence of separate pathways for oculomotor spatial working memory tasks depending on whether the delay before movement execution is either short or long (>20 s). The long delay pathway might bypass brain areas commonly affected by Parkinson's disease (PD). This study aimed to assess spatial working memory in Parkinson's disease using short (3 s) and long (30 s) delays in a memory-guided saccade task. Fifteen mild-moderately affected PD subjects off-medication, and 15 age and sex-matched controls were tested (PD mean age 65.3; control 65.9). Subjects were tested in a darkened room using a horizontal LED bar to generate eye movements which were recorded using an infrared limbus tracker. Percentage error in amplitude of the primary saccade was analysed by repeated measures ANOVA. There was a significant interaction between the groups and their response to the short and long delay periods (P<0.02). PD subjects were more strongly impaired in the short delay than the long delay trials when compared with controls. Analysis of the percentage error in amplitude of the final eye position showed the same pattern but only in female subjects. This study provides the first evidence that the proposed parallel spatial memory pathway utilised in longer delay periods is relatively unimpaired in PD. In a broader sense, our results suggest there might be other alternative pathways to overcome deficits in functions impaired by PD.

Spatial and object working memory deficits in Parkinson's disease are due to impairment in different underlying processes.

“…The visual-object working memory deficit of PD patients seems to primarily reflect an inability to maintain information because their performance was normal after 1 s and 5 s delays but impaired after a 10 s delay. Maintenance of spatial information in working memory does not appear to be impaired because the magnitude of the patients’ deficit did not worsen as a function of the length of the delay period, which is consistent with previous findings (Fournet et al, 2000; Ketcham et al, 2003; LeHeron et al, 2005). Rather, the patients showed an equal impairment across the delay intervals and only when a high degree of specificity was required to judge whether locations were the same or different (i.e., when the non-match spatial locations were similar).…”

Impairment of voluntary saccades and facilitation of reflexive saccades do not co-occur in Parkinson’s disease

“…Characteristic deficits include hypometria (that is, the primary eye movement falls abnormally short of the target), prolonged latencies and increased error rates (unintended reflexive saccades) compared to controls. 4,[7][8][9][10][11][12][13][14][15] These observations are consistent with models of eye movement control such as the ''tonic inhibition model'', where the voluntary saccadic system is responsible for inhibitory control over reflexive components of the saccadic system. 16 Such models predict that impairment of the voluntary saccadic system is associated with disinhibition or facilitation of the reflexive saccadic system.…”

Cortical control of saccades in Parkinson disease and essential tremor

“…Helmchen et al (2003) and Trillenberg et al (2006) b Amador et al (2006), Armstrong et al (2002), Briand et al (1999), Crawford et al (1989), Crevits et al (2000), Chan et al (2005), Le Heron et al (2005) and Lueck et al (1990Lueck et al ( , 1992a …”

“…In contrast, many but not all studies using voluntary saccadic tasks (e.g. delayed response, memory-guided or anti saccade tasks) have found evidence of prolonged latencies, hypometria and impaired voluntary suppression of unwanted saccades in PD (Amador et al 2006;Armstrong et al 2002;Briand et al 1999;Crawford et al 1989;Crevits et al 2000;Chan et al 2005;Le Heron et al 2005;Lueck et al 1990Lueck et al , 1992a. Rieger et al (2008a) studied BOLD activation with functional magnetic resonance imaging (fMRI), while healthy participants and patients with PD performed horizontal voluntary saccades between peripheral visual targets or fixated centrally.…”