title: An exploratory study of the effects of spatial working-memory load on prefrontal activation in low- and high-performing elderly.
abstract: Older adults show more bilateral prefrontal activation during cognitive performance than younger adults, who typically show unilateral activation. This over-recruitment has been interpreted as compensation for declining structure and function of the brain. Here we examined how the relationship between behavioral performance and prefrontal activation is modulated by different levels of working-memory load. Eighteen healthy older adults (70.8 ± 5.0 years; MMSE 29.3 ± 0.9) performed a spatial working-memory task (n-back). Oxygenated ([O2Hb]) and deoxygenated ([HHb]) hemoglobin concentration changes were registered by two functional Near-Infrared Spectroscopy (fNIRS) channels located over the left and right prefrontal cortex. Increased working-memory load resulted in worse performance compared to the control condition. [O2Hb] increased with rising working-memory load in both fNIRS channels. Based on the performance in the high working-memory load condition, the group was divided into low and high performers. A significant interaction effect of performance level and hemisphere on [O2Hb] increase was found, indicating that high performers were better able to keep the right prefrontal cortex engaged under high cognitive demand. Furthermore, in the low performers group, individuals with a larger decline in task performance from the control to the high working-memory load condition had a larger bilateral increase of [O2Hb]. The high performers did not show a correlation between performance decline and working-memory load related prefrontal activation changes. Thus, additional bilateral prefrontal activation in low performers did not necessarily result in better cognitive performance. Our study showed that bilateral prefrontal activation may not always be successfully compensatory. Individual behavioral performance should be taken into account to be able to distinguish successful and unsuccessful compensation or declined neural efficiency.
authors.affiliation: Donders Institute for Brain, Cognition and Behaviour, Radboud University Nijmegen Nijmegen, Netherlands ; Department of Geriatric Medicine, Radboud University Medical Center Nijmegen, Netherlands.
authors.forename: Anouk
authors.initials: A
authors.lastname: Vermeij
authors.affiliation: Department of Geriatric Medicine, Radboud University Medical Center Nijmegen, Netherlands.
authors.forename: Arenda H E A
authors.initials: AH
authors.lastname: van Beek
authors.affiliation: Department of Psychiatry and Neuropsychology, Maastricht University Maastricht, Netherlands.
authors.forename: Babette L R
authors.initials: BL
authors.lastname: Reijs
authors.affiliation: Donders Institute for Brain, Cognition and Behaviour, Radboud University Nijmegen Nijmegen, Netherlands ; Department of Geriatric Medicine, Radboud University Medical Center Nijmegen, Netherlands.
authors.forename: Jurgen A H R
authors.initials: JA
authors.lastname: Claassen
authors.affiliation: Donders Institute for Brain, Cognition and Behaviour, Radboud University Nijmegen Nijmegen, Netherlands ; Department of Geriatric Medicine, Radboud University Medical Center Nijmegen, Netherlands ; Department of Medical Psychology, Radboud University Medical Center Nijmegen, Netherlands.
authors.forename: Roy P C
authors.initials: RP
authors.lastname: Kessels
keywords: BOLD; CRUNCH; HAROLD; cognitive aging; functional near-infrared spectroscopy; n-back; prefrontal cortex; working memory