Authors :
Presenting Author: Hue Mun Au Yong, PhD, MBBS, BMedSc – Royal Melbourne Hospital, Alfred Hospital, Monash University
Meaghan Clough, PhD – Monash University; Piero Perucca, MD, PhD, FRACP – Austin Health; Charles Malpas, PhD – The University of Melbourne; Patrick Kwan, MD, PhD, FRACP – Monash University; Terence O'Brien, MD, PhD, FRACP – Monash University; Joanne Fielding, PhD – Monash University
Rationale: Executive dysfunction such as working memory and inhibitory control impairments are common in people with focal epilepsy and are associated with poor academic and vocational performance. In this study, we used an oculomotor paradigm, namely the memory-guided saccade task, to evaluate visuospatial working memory and inhibition in adults with focal drug-resistant epilepsy (DRE). Oculomotor (OM) performance was evaluated in comparison to neurologically healthy controls, and between DRE subgroups based on epilepsy laterality (right vs. left hemisphere) and localization of epileptogenic zone (temporal vs. frontal lobe).
Methods: Adults with focal DRE were recruited from two tertiary epilepsy centres in Melbourne, Australia. A memory-guided saccade task (Figure 1) was performed by 64 adults with focal DRE and 23 neurologically healthy controls. Horizontal eye movements were recorded using an EyeLink
® 1000 dark pupil video-oculography system. Saccade latency, absolute position error, and anticipatory error rate were measured. Absolute position error (%) was calculated using the formula: (Final eye position amplitude – target amplitude)/target amplitude x 100. General linear mixed model (GLMM) analyses were performed to compare OM performance between adults with focal DRE with healthy controls and between DRE subgroups.
Results: Adults with focal DRE had longer saccade latencies (mean difference = 75.52ms, 95%CI = 34.69–116.35) and higher rates of anticipatory errors (mean difference = 7.06%, 95%CI = 0.05–14.07) compared to healthy controls. Adults with right hemispheric epilepsy demonstrated significantly larger absolute position errors compared to healthy controls (mean difference = 19.26%, 95%CI = 2.64–35.87) and adults with left hemispheric epilepsy (mean difference = 16.79%, 95%CI = 1.90–31.69); while adults with frontal lobe epilepsy (FLE) demonstrated significantly larger absolute position errors compared to healthy controls (mean difference = 21.06%, 95%CI = 4.35–37.76) and adults with temporal lobe epilepsy (mean difference = 20.39%, 95%CI = 5.48–35.31). Patients with right FLE exhibited the largest absolute position errors (55.92%, 95%CI = 34.53–77.32), longest latency (527.60ms, 95%CI = 458.33–596.87), and highest anticipatory error rate (31.28%, 95%CI = 20.21–42.36) amongst all DRE subgroups.
Conclusions: In summary, adults with focal DRE demonstrated impaired visuospatial working memory performance, reflected in slower oculomotor response times (longer saccade latencies) and inhibitory failure (increased anticipatory error rate) compared to healthy controls. Adults with right FLE performed poorer than all other DRE groups across all parameters of the memory-guided saccade task, reflecting the right hemispheric dominance of visuospatial working memory control and prefrontal executive dysfunction impacting on working memory, attention, and inhibitory control processes. This study showed that OM paradigm has the clinical potential to evaluate and monitor executive dysfunction in adults with focal DRE.
Funding: HMAY was supported by the Research Training Program (RTP) Scholarship provided by the Australian Government.