Eye-tracking Working Memory Training in School-aged Children and Youth With Severe Cerebral Palsy

Working memory (WM) is one of the core executive functions (EF) which encompass higher-order cognitive abilities, critical for optimal daily-life functioning. WM is defined as our ability to temporarily store information that is no longer perceptually present, allowing us to manipulate it for meaningful goal-directed behaviors, such as decision-making, problem-solving and reasoning. WM includes verbal WM and (nonverbal) visuospatial WM, two main components defined by content. Verbal WM is responsible for temporarily storing verbal information such as letters, words, numbers or nameable objects, and is a strong predictor of language development and reading comprehension. Visuo-spatial WM is a fundamental component of the eye movement system, visual perceptual functioning and it is a strong predictor of arithmetic performance. WM is related to active long-term memory aiding the retrieval of stored information from past experiences to successfully execute the task at present. WM is practically involved in most (if not all) daily-life activities, from simple tasks like remembering a phone number or following instructions, to highly complex tasks associated with learning, academic achievements in literacy, numeracy and science, or language comprehension.

One of the central limitations of human cognition is the restricted WM capacity, i.e., the amount and duration of information that can be stored and manipulated at once. Low WM capacity affects approximately 15% of all children, from which over 80% are at very high risk of educational underachievement. In terms of its neural basis, prior work consistently put forward an important role of fronto-parietal networks in WM performance with some variation depending on stimulus type. In typically developing (TD) people, WM continues developing throughout childhood and peaks in adolescence along with a number of structural maturational processes in the brain. Significant WM deficits have been described in an array of neurodevelopmental disorders.

Cerebral palsy (CP) is the most common cause of severe physical disability in childhood with a prevalence of 1.6-3.4 per 1000 livebirths. It comprises a group of developmental impairments of movement and posture attributed to nonprogressive lesions in the developing fetal or infant brain. CP is categorized into spastic, dyskinetic, ataxic and mixed forms, and functioning of individuals ranges from mild to severe levels of limitations. In CP, 41% of all people are not able to walk independently, 23% are unable to handle objects using their hands, and 32% are nonverbal. The motor impairments are frequently accompanied by impairments of cognition and behaviour. EF in CP are underreported to date, particularly in the non-ambulant and non-verbal cases of CP where these impairments tend to be overlooked due to challenges in finding appropriate assessment tools that do not rely on motor and verbal skills. Namely, only 36.8% of children with severe motor impairments in CP have their cognitive functioning assessed, compared to 96.5% of children with mild CP. Both verbal and visuospatial WM deficits seem to be present in all forms of CP and more so as severity of functional limitations increases. In CP, WM deficits are associated to impaired reading comprehension and arithmetic difficulties. Learning difficulties are present in around 40% and visual-perceptual impairments in 40-50% of all people with CP.

In addition to central neural alterations, children with CP also show altered functioning of the autonomic nervous system (ANS), as evidenced by inherent reduced heart rate variability (HRV). In TD population, higher performance of WM (and EFs in general) is strongly associated with increased HRV, an established marker of parasympathetic ANS drive (facilitating 'rest and digest'). This suggests that HRV also forms an important marker indexing effective cognitive function. In TD, increased HRV is accompanied by increased resting-state functional brain connectivity. Investigations into the relative contribution of HRV differences in CP and their relation to EF deficiencies and to core functional connectivity networks previously identified as related to WM have not been addressed in any prior study.

People with CP with severe motor impairments benefit from eye-tracking technology as an access method to assistive and alternative communication devices (AAC) and to computers for education and leisure. Eye movements are tracked by an infrared sensor and translated to cursor movements on the screen by which children can navigate and select icons of interest. Nonverbal children with CP have significantly impaired language comprehension, especially prominent in spastic CP. Eye-tracking technology leads to increased communication outcomes, and it has a positive impact on quality of life through increased activity levels, participation levels, self-efficacy, and self-esteem. With its undeniable benefits in mind, the use of AAC puts large demands on WM. For example, to express wants and needs, these children need to remember the symbol of interest, all the while navigating through an array of symbols not all of which are simultaneously present, remembering the most efficient path, inhibiting possible distractions and finally locating and selecting the target symbol. The use of AAC systems can be a real challenge for children with low WM capacity, likely leading to technology discontinuance, and loss of opportunities and benefits. People with CP also show lower quality of eye movements compared to TD people, however, eye movement accuracy can be improved through intensive eye-tracking training. In addition, eye-tracking methods have been previously used to successfully index WM, a method which has not yet been investigated in people with CP, but may hold important clinical implications.