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Cognitive deficits are common in about one third of patients with amyotrophic lateral sclerosis, a neurological condition leading to progressive impairments in speech and movement abilities. To conduct cognitive tests in patients unable to speak or write a reliable and easy to administer eye-tracking paradigm was developed.
Amyotrophic lateral sclerosis (ALS) is a neurodegenerative disorder with pathological involvement of upper and lower motoneurons, subsequently leading to progressive loss of motor and speech abilities. In addition, cognitive functions are impaired in a subset of patients. To evaluate these potential deficits in severely physically impaired ALS patients, eye-tracking is a promising means to conduct cognitive tests. The present article focuses on how eye movements, an indirect means of communication for physically disabled patients, can be utilized to allow for detailed neuropsychological assessment. The requirements, in terms of oculomotor parameters that have to be met for sufficient eye-tracking in ALS patients are presented. The properties of stimuli, including type of neuropsychological tests and style of presentation, best suited to successfully assess cognitive functioning, are also described. Furthermore, recommendations regarding procedural requirements are provided. Overall, this methodology provides a reliable, easy to administer and fast approach for assessing cognitive deficits in patients who are unable to speak or write such as patients with severe ALS. The only confounding factor might be deficits in voluntary eye movement control in a subset of ALS patients.
Amyotrophic lateral sclerosis (ALS) is a fatal neurodegenerative disorder usually leading to death within 3 to 5 years. In the course of the pathology, patients present with progressive loss of respiratory and bulbar functioning as well as impairments in movement abilities1. It shares some clinical, pathological, and genetic features with frontotemporal dementia2 and it is well documented that about 30% of ALS patients exhibit cognitive deficits3. These deficits are most prominent in the domains of executive function, verbal fluency and language4 and have an influence on survival5, compliance6 and carer burden7. Thus, reliable neuropsychological assessment is crucial in this disease.
Advancing impairments in motor and speech abilities are, however, a limiting factor for thorough evaluation of cognitive abilities in later stages of the disease8. Here, oculomotor based approaches seem to be very promising, as basic eye movement control remains intact for a comparably long time during the course of ALS for the majority of patients9. Eye-tracking parameters itself have been used to gain information about the cognitive status of patients with ALS10 and also correlate with the sequential spreading pattern of ALS11. Eye movement as a means to control cognitive tests in the context of ALS has also been studied in previous works. One study has successfully demonstrated its usability in healthy controls using an oculomotor based version of the Trail-Making Test12, whereas another found it suitable to distinguish between healthy controls and ALS patients based on cognitive performance and to discriminate between cognitively more and less impaired patients13.
The research described here used an oculomotor based methodology to study cognitive impairments in ALS patients, specifically in the domain of executive functioning. Two well validated and commonly used neuropsychological tests were adapted to eye movement control: the Raven's coloured progressive matrices (CPM)14 and the D2-test15. The CPM is a non-verbal instrument used to measure executive and visuospatial abilities as well as fluid intelligence. The D2-test is also a non-verbal tool used to uncover executive dysfunction in the domains of selective and sustained attention and visual processing speed. Both are widely used clinical tools which have been successfully employed in previous studies assessing potential cognitive decline during the course of the disease16 and the neuropsychological status of ALS patients compared to healthy controls17.
The goal of this work was to show the requirements for successful evaluation of cognitive deficits in ALS independent of movement and speech disabilities using a reliable, eye-tracking based version of the CPM and the D2-test. Importantly, the method described here has the potential to be expanded to study other populations of patients with severe motor impairments.
The study was approved by the Ethics Committee of the University of Ulm (Statement No. 19/12) and the protocol described therefore follows their guidelines. All participants gave written informed consent.
1. Stimuli and Testing Environment
2. Running the Experiment
For the purpose of the research presented here, i.e., the development of a reliable oculomotor based neuropsychological assessment for ALS patients, in-house developed software stores the subject's choices of the CPM in a separate file, allowing for manual computation of the percentage of correct answers. For the D2-test, a record of the vertical eye movements is manually analyzed using a threshold of + 5° for detection of a relevant response. Recordings are assigne...
It is a challenging task to successfully assess the cognitive status of patients with ALS who are unable to speak and write. The use of videooculography systems provides a promising approach. The hereby presented technique is reliable in detecting cognitive deficits, which play a pivotal role in the context of carer burden and disease management20 in ALS patients. Also, the oculomotor versions of the CPM and the D2-test correlate significantly with their respective standard paper-pencil versions, but further s...
The authors declare that they have no competing financial interests.
The authors would like to thank Ralf Kühne for technical support. This work was funded by the Deutsche Forschungsgemeinschaft (DFG) and the Bundesministerium für Bildung und Forschung (BMBF #01GM1103A). This is an EU Joint Programme-Neurodegenerative Disease Research (JPND) project. The project is supported through the following organizations under the aegis of JPND-e.g., Germany, Bundesministerium für Bildung und Forschung (BMBF, FKZ), Sweden, Vetenskaprådet Sverige, Poland, Narodowe Centrum Badań i Rozwoju (NCBR).
Name | Company | Catalog Number | Comments |
EyeSeeCam | EyeSeeTec GmbH; 82256 Fürstenfeldbruck, Germany | Videooculography device |
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