Title: Working memory in children with epilepsy: an event-related potentials study
Other Titles: Werkgeheugen bij kinderen met epilepsie: een "event-related potentials (ERP)" onderzoek
Authors: Myatchin, Ivan; S0110167
Issue Date: 11-Sep-2013
Abstract: There are approximately 10 million children suffering from epilepsy worldwide, with additionally 1,4 million children up to 15 years old developing epilepsy annually. Except seizures, epilepsy also includes a number of other aspects: behavioral and psychological problems, cognitive disability, psychiatric and other neurologic problems, and even suddendeath. Among those comorbidities, cognitive impairment is very common in childhood epilepsy as 20-30% patients have mental retardation with IQ In human cognition, working memory constitutes an importantpart as it lies at the basis of complex higher cognitive functions likereading, language comprehension, mathematical abilities, spatial processing, planning, and other executive functions. In a number of studies, working memory impairments in childhood epilepsy have already been shown. However, event-related potentials (ERP) studies are lacking inresearch on WM functioning in childhood epilepsy. ERP is a non-invasivetechnique with high temporal resolution, which is able to provide a neurophysiological “index” of the patients’ cognitive functioning. Therefore we set up this project to study the effect of childhood epilepsy on the development of working memory using a combined approach of neuropsychology and ERP methodology. We aimed to show that epilepsy can disturb working memory functioning in children with epilepsy. Firs t, westudied electrophysiological patterns of visuo-spatial working memory development in a group of healthy and normally developing children in theage range of 6 to 16 years old. An n-backmatching paradigm was used to measure the electrophysiological patterns of working memory development . Behaviorally, children made fewer errors and reacted faster as they got older. ERP analysis showed clear developmental changes: shortening of peak latencies and lowering of peak amplitudes with age, although this was not uniform across the peaks. ‘Exogenous’ components (N150, P250) showed shortening of the latency and lowering of the amplitude with age. On the contrary, ‘endogenous’ components (N400, P450) did not always follow this principle. Our results show that in normal children different ERP components follow different developmental trajectories with the endogenous components developing later. When the fronto-parietal visuo-spatial working memory network is already active, not all its “nodes” are equally mature, so that a child is able to perform in a working memory task, but this performance is not yet perfect. In a next step, visual and visuo-spatial working memory was studied in two groups of normally developing children with well-controlled epilepsy using 1- and 2-backmatching tasks. Children with epilepsy performed equally well on the easy BM1 task but made significantly more omission errors during the more difficult BM2 task. At the electrophysiological level we found in the epilepsy group significantly increased ERP amplitudes over frontal and central regions during the late processing stages (in the time intervals 250-425 msec and 300-500 msec post stimulus). Our findings therefore indicate that even during an easy working memory task children with epilepsy have to develop more effort to achieve normal results. This is a reflection of an adequate compensatory mechanism: increased activity of morphologically normal working memory neuronal circuits in patients with normalintelligence in order to overcome the decrease in neurocognitive efficiency caused by the epilepsy and to achieve the same level of performanceas control non-epileptic children. Increasing of task demands leads to exhaustion of this compensatory mechanism: in a difficult task a larger amplitude difference was seen and this was still not sufficient to preserve performance at the level of non-epileptic controls. Next weexamined whether those findings are specific for children with epilepsy, or whether it is a more general phenomenon related to frontal dysfunction rather than to a particular pathology. We selected a ‘patient control’ group consisting of children with attention-deficit/hyperactivity disorder (ADHD). This disease is known with frontal functions disturbances and in particular with working memory problems. The same 1- and 2-backmatching visuo-spatial working memory tasks were applied to the ADHD and the control group. We did not find any time intervals of significant ERP amplitude difference between ADHD patients and controls, which proves that the ERP amplitude increase during the late processing stages of working memory is specific for epilepsy. Our studies confirm the role of the epilepsy in the development of WM disturbances in childhood epilepsy and stresses the importance of addressing the cognitive problems in children with epilepsy. In order to prevent or correct cognitive dysfunctions in these children, one should theoretically target the epilepticprocess itself, and not only the seizures.
Publication status: published
KU Leuven publication type: TH
Appears in Collections:Section Child - Miscellaneous (-)
Organ Systems (+)

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