The neural basis of task-switching in working memory: effects of performance and aging.

“Scaffolding”

“Such additional activations in complementary PFC regions might reflect compensatory activity, possibly due to the engagement of general-purpose mechanisms to assist in resolving difficult task demand”

“Shifting attention has been typically discussed as a unitary construct, alternately called attention switching, task switching, or attention shifting (Corbetta et al., 1993; Smith et al., 2001).”

“In a few studies, older subjects exhibited less left ventral PFC activity [3/9 studies; Grady et al., 1998; Jonides et al., 2000; Smith et al., 2001] and less right ventral PFC activity [2/9 studies; Grady et al.”

“The positive correlations we observed may seem counterintuitive, as activation of inhibitory mechanisms that prevent interference might be expected to produce low behavioral interference scores, but they are consistent with similar individual differences effects in task switching (Smith et al., 2001; Wager, 2003).”

“However, other studies have not demonstrated any additional prefrontal activity during dual-task performance (Adcock et al., 2000; Bunge et al., 2000; Klingberg, 1998; Smith et al., 2001).”

“Smith et al. (2001) compared brain activations due to the operation-span task with each of the component tasks alone.”

“Previous neuroimaging research indicated that performance in complex span tasks such as the one used here actively recruited the left dorsolateral prefrontal cortex, an area linked with executive processes, but not when either the span or arithmetic tasks were performed in isolation [48].”

“D 2002 Massachusetts Institute of Technology Journal of Cognitive Neuroscience 14:8, pp. 1184 – 1199 conditions (see also Smith et al., 2001 ).”

“These investigations have examined episodic memory [10–12,26,33,46,48,67], working memory [32,51,64,66], attention [5,39,47], and executive functioning [71].”

“In addition, there are reports of increased activity in dorsolateral prefrontal cortex in young adults for words that are later forgotten (Otten and Rugg, 2001b), and during verbal memory tasks in those young adults who perform more poorly on the task (Smith et al., 2001).”

“In some reports, lower prefrontal activation has been linked to better behavioral performance (Smith et al., 2001).”

“Furthermore, in a study which compared performance on a dual-task with performance on either task alone (Smith et al., 2001) it was found that both older subjects and young poor performers activated the left PFC during a demanding dual-task, whereas young good performers did not.”

“Also consistent with this account, PFC regions were differentially engaged by younger adults with limited cognitive resources (Smith et al., 2001).”

“For example, prior research has shown that the FPN is extensively activated during complex working memory span tasks compared to baseline tasks (Bunge et al., 2000; Chein et al., 2011; Faraco et al., 2011; Kondo et al., 2004; Osaka et al., 2003; Smith et al., 2001).”

“Using PET, Smith et al. (2001) found activation in the left PFC during operation span task.”

“In a previous study of the ageing effect on dual tasks, Smith et al. (2001) found that the left prefrontal cortex only activated in the dual task in aged subjects.”

“Bunge, Klingberg , Jacobsen, and Gabrieli (2000) and Smith et al. (2001) found increased lateral PFC and parietal activation in dual-task WM tasks (analogous to complex span tasks).”

“Neuroimaging studies have demonstrated that the anterior cingulate cortex (ACC) and dorsolateral prefrontal cortex (DLPFC) are neural bases of the central executive for dual-task performance (Bunge et al., 2000; D’Esposito et al., 1995; Smith et al., 2001) and Stroop task performance (Bush et al.”

“At first glance, one might suppose that performance deficits in older adults in mixed trial blocks could be obtained as a result of deficits in task switching (e.g., Kramer, Sowon, & Gopher, 1999; Smith et al., 2001).”

“Smith and colleagues likewise found no prefrontal regions that were active only during performance of a dual task in young subjects who performed the tasks well (Smith et al., 2001).”

“Of note, older adults have been shown to exhibit impaired task-switching abilities (17, 18), which may be a consequence of any of these possibilities.”

“Successful performance is an influential factor on brain activation detected with functional imaging [9, 28, 49, 50].”

“Smith et al. (2001) compared brain activities of good performers with those of poor performers using the operation span task.”

“One of the few labs to administer CWMS in an imaging environment (Smith et al., 2001) noted this juxtaposition: “…by and large the WM tasks used in neuroimaging are not the kinds of tasks that correlate with higher-level cognition.”

“Right parietal cortex was not recruited during WM studies of letters and numbers in seniors (Reuter-Lorenz et al., 2000; Smith et al., 2001 ).”

“…tasks, age-related bi-hemispheric activation versus the hemispheric asymmetry of the young has been interpreted as a compensatory mechanism similar to what happens for the execution of simple motor tasks (Babiloni et al., 2000; Reuter- Lorenz et al., 2000; Smith et al., 2001; Mattay et al., 2002).”

“Looking at the load-dependent activation patterns for each performance group separately, a comparable activation pattern was observed in the three prefrontal VOIs (DLPFC, IFG, and sf): Whereas the low-performing group showed an activation increase, the high-performing group showed the inverted U-shaped pattern.”

“Neuroimaging shows that older adults recruit areas of prefrontal cortex during executive function tasks (Smith et al., 2001) and that older adults with greater computer experience show greater brain activation in frontal regions during an Internet searching task (Small et al., 2009).”

“An interesting parallel to these findings is a study by Smith et al. (2001) involving task-switching in working memory.”

“[54], in which only subjects with the lower dual-task performance recruited the left dorsolateral prefrontal cortex.”

“Understanding age-related changes in working memory (WM) (Smith et al., 2001; Hartley, 1992; Dobbs & Rule, 1989) is critical, given the importance of their contribution to cognitive decline in old age (Oberauer, 2005; Salthouse & Ferrer-Caja, 2003).”

“It should be noted, however, that task switching has been shown to engage other cortical areas besides prefrontal cortex (Kimberg et al., 2000; Smith et al., 2001).”

“These abilities govern problem solving, utilizing environmental feedback and adaptation, all of which are considered to be mediated primarily by the prefrontal cortices [44,58,59,66,76,78].”

“Other work associates dorsolateral prefrontal cortex with the strategic manipulation of information that is being held in working memory ( Smith et al., 1999, 2001 ) and with task switching (Paulus et al., 2001; Rowe and Passingham 2001; Savage et al., 2001; Seger et al., 2000a) in healthy subjects.”

“This is in line with studies that have shown a differential detriment to older adults with increased task difficulty (Erickson et al, 2007; Prakash et al., 2009; Smith et al., 2001).”

“…other studies indicating that high cognitive load might eventually result in reaching a resource ceiling in older adults, which is reflected in performance decline associated with hypoactivation of neural networks (Cappell et al., 2010; Mattay et al., 2006; Rypma et al., 2007; Smith et al., 2001).”

“, poor performing young or elderly subjects (Smith et al., 2001).”

“Also, deactivation with transcranial magnetic stimulation of the left but not the right BA 37 inhibits object naming (Stewart et al., 2001) and Smith et al. (2001) reported left but not right differences in BA 37/19 between good and poor performers on a task-switching test.”

“For example, decreased activation has been reported in both older adults (Smith et al., 2001) and sleep deprived young adults (Drummond et al., 1999; Thomas et al., 2000) during arithmetic working memory tasks.”

“, 2002, 2006; Wu and Hallett, 2008), while others found no evidence that there are any areas related to dual-task performance (Adcock et al., 2000; Bunge et al., 2000; Jiang, 2004; Klingberg, 1998; Smith et al., 2001), or found”

“…level, age-related overrecruitment of brain regions often accompanies more complex and demanding task conditions, such as dual versus single tasks (Smith et al., 2001), source versus item memory retrieval (Morcom et al., 2007), or high versus low selection demands in word generation tasks…”

“... have shown that complex span tasks can be dissociated from simple span tasks (i.e., serial recall tasks without additional processing demand) by factor analysis (Cantor, Engle, & Hamilton, 1991; Conway, Cowan, Bunting, Therriault, & Minkoff, 2002; Engle, Tuholski, Laughlin, & Conway, 1999; Kail & Hall, 2001; Obera…”

“, 1997), and executive function (Smith et al., 2001) suggest that older adults tend to activate more brain regions than their younger counterparts, coinciding with the hemispheric asymmetry reduction in older adults model, which suggests that older adults attempt to compensate for cortical networks that have become le…”

“Successful performance is an influential factor in brain activation as measured by functional imaging [36,37].”

“Compared with enumerating animal names, backward counting out loud from 50 is a simple and automatic mental arithmetic task requiring low attention involvement in a sample of healthy young University students [10–12,18,19].”

“In linewith previous studies, thesefindings suggest a general slowing of RT in older adults, along with a larger age-related deficit in task-switching (e.g., Andrés et al., 2008; Bugg et al., 2007; Davidson et al., 2003; Smith et al., 2001; Verhaeghen and De Meersman, 1998).”

“Non-linguistic studies of planning and switching implicate dorsolateral prefrontal cortex (dlPFC) (Braver and Bongiolatti, 2002; Paulus et al., 2001; Rowe and Passingham, 2001; Savage et al., 2001; Seger et al., 2000; Smith et al., 2001; Sylvester et al., 2003).”

“Age differences in inhibitory control, task switching, and interference suppression in WM tasks have been related to age differences in measures of frontal lobe integrity, as measured by functional (Jonides et al., 2000; Smith et al., 2001) and structural MRI (Raz, Gunning-Dixon, Head, Dupuis, & Acker, 1998).”

“Brain-imaging studies have also suggested that the central executive system is located in both DLPFC and anterior cingulate cortex (ACC) (Bunge et al., 2000; D’Esposito et al., 1995; M. Osaka et al., 2003; N. Osaka et al., 2004; Smith et al., 2001; Smith & Jonides, 1999).”

“A math equation verification task based on the operation span task (Turner & Engle, 1989) was adapted from Smith et al. (2001).”

“Second, observations of less activation in older adults are found in several studies, and this pattern of less activation is most consistent for left VLPFC (e.g., Grady et al., 1998; Jonides et al., 2000; Smith et al., 2001).”

“Firstly, counting involves working memory,(19) and in contrast to some other popular tasks such as naming objects/animals, is more directly related to executive function.(20,21) Secondly, since counting is a rhythmic task, it may substantially interfere with rhythmic tasks of a different frequency such as walking or r…”

“Also, Smith et al. [ 81 ] indicated that no supplementary foci of activation were found in a group of participants performing well in the dual task.”

“Notably, when the same dual task was performed by good and poor performers (i.e., those who showed a weak and strong dual-task interference effect, respectively), dual-task-specific activation in the DLPFC was observed only in the poor performers (Smith et al., 2001).”

“, 2000), shifting of attention for task management (Kondo et al., 2004a,b; Smith et al., 2001), and error detection (Gehring and Knight, 2000; Swick and Turken, 2002).”

“, 2006, 2002), others concluded that there are no specific neural correlates of dual-task performance (Adcock et al., 2000; Bunge et al., 2000; Jiang et al., 2004; Klingberg, 1998; Smith et al., 2001), and sometimes even reduced neural activity associated with dual-task performance was reported (Jaeggi et al.”

“These types of divided attention effects are the hallmark of complex WM span tasks, and are well-established to engage DLPFC regions (e.g., DiPisapia et al., 2007; Iidaka, Anderson, Kapur, Cabeza, and Craik, 2000; Smith et al., 2001).”

“A number of studies by now indicate that strategic organization and strategy-shifting processes are mediated by dorsolateral PFC (Bor et al., 2003; Prabhakaran et al., 1997, 2001; Smith et al., 2001; Jenkins et al., 1994; Deiber et al., 1991).”

“recall, cued recall, recognition) have been conducted, they potentially suggest a common recruitment of lateral prefrontal cortex, anterior cingulate and posterior parietal cingulate areas during task performance (Bunge et al., 2000; Chein et al., 2011; Kondo et al., 2004; Osaka & Osaka, 2002; Osaka et al., 2004; Smit…”

“Conversely, increased activation of the same control areas in younger adults related to worse cognitive performance, suggesting that recruitment of the same control regions in younger adults, at least at this level of demand, reflects less efficient neural functioning (e.g., Park & Reuter-Lorenz, 2009; Reuter-Lorenz &…”

“switching performance in older adults reflect a lower flexibility in allocating the fewer available resources to the relevant task at hand (Smith et al., 2001).”