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.

Functional imaging of cognition in an old-old population: A case for portable functional near-infrared spectroscopy

“…In these studies, older and young adults have demonstrated greater oxyhemoglobin concentration with greater working memory load, and greater bilateral activation in older adults [36]. In addition, a larger decline in performance as the working memory load increased resulted in greater bilateral activation [37]. However, individuals with mild cognitive impairment may produce decreased oxyhemoglobin concentrations.…”

Functional Near-Infrared Spectroscopy to Study Cerebral Hemodynamics in Older Adults During Cognitive and Motor Tasks: A Review

“…Of the 46 included articles, 13 included a mix of younger and older participants (Heilbronner and Münte, 2013;Ohsugi et al, 2013;Beurskens et al, 2014;Müller et al, 2014;Oboshi et al, 2014;Hernandez et al, 2016;Bierre et al, 2017;Mirelman et al, 2017;Rosso et al, 2017;Hawkins et al, 2018) whereas 29 included only older adults (Doi et al, 2013;Heinzel et al, 2013Heinzel et al, , 2015Niu et al, 2013;Clark et al, 2014;Vermeij et al, 2014;Dupuy et al, 2015;Holtzer et al, 2015Holtzer et al, , 2016Holtzer et al, , 2017aHoltzer et al, ,b, 2018aLaguë-Beauvais et al, 2015;Al-Yahya et al, 2016;Maidan et al, 2016Maidan et al, , 2017Mahoney et al, 2016;Nieuwhof et al, 2016;Osofundiya et al, 2016;Takeuchi et al, 2016;Uemura et al, 2016;Yeung et al, 2016a,b;Chen et al, 2017;Huppert et al, 2017;Verghese et al, 2017;Yap et al, 2017;Halliday et al, 2018;Katzorke et al, 2018;Lucas et al, 2018;Mori et al, 2018;Thumm et al, 2018). Moreover, 26 studies included only cognitively normal participants…”

“…Generally, VF tests ask the participants to produce the maximum number of words starting with a specific letter (phonemic) or belonging to a pre-specified semantic category (semantic). Three studies used N-back tests (Niu et al, 2013;Vermeij et al, 2014;Yeung et al, 2016b), which assess working memory function. N-back tasks are usually designed as conditions with increasing working-memory load: 0back (subject has to detect if the presented stimulus is the one described as target), 1-back (the subject has to remember if the presented stimulus was presented on the previous position) and 2-back conditions (the participant must be able to remember if the stimulus is the same presented 2 positions before).…”

“…Regarding the studies that assessed frontal hemodynamics in cognitively healthy older adults, two studies by Heinzel et al (2015) showed different activation patterns while performing VF tasks: one showed an increased activation and another found a decreased activation on bilateral inferior frontal junction in healthy older adults while middle frontal gyri and supramarginal gyri showed an increased activation (interpreted as compensatory mechanisms) (Heinzel et al, 2013). Cognitively healthy older adults showed an increased prefrontal activation while performing a working memory task with visual recognition (Oboshi et al, 2014) as well as with increasing working memory load during a N-back task (Vermeij et al, 2014). Studies using other executive function tests, found an increase in frontal lobe activation during executive function tasks (Heilbronner and Münte, 2013;Albinet et al, 2014;Müller et al, 2014;Bierre et al, 2017;Huppert et al, 2017).…”

Modulating perceptual complexity and load reveals degradation of the visual working memory network in ageing

“…Previous work has used fNIRS to explore the neural mechanisms that underlie age-related decline in working memory (Vermeij et al, 2016(Vermeij et al, , 2014(Vermeij et al, , 2012. However, these studies relied on recordings from two channels placed over the prefrontal cortex only and did not explore posterior cortical activity.…”