Abstract
Background: Multi-tasking is usually impaired in older people. In multi-tasking, a fixed order of sub-tasks can improve performance by promoting a time-structured preparation of sub-tasks. How proactive control prioritizes the pre-activation or inhibition of complex tasks in older people has received no sufficient clarification so far.Objective: To explore the effects of aging on neural proactive control mechanisms in a dual task.Methodology: To address this question, the psychological refractory period (PRP) paradigm was used. Two 2-alternative-forced-choice reaction tasks with a predefined order (T1 and T2) signaled by a cue had to be executed simultaneously or consecutively by young (mean age 25.1 years, n = 36) and old subjects (mean age 70.4 years, n = 118). Performance indices of dual-task preparation were used to assess the focused preparation of T1 and T2. To compare preparatory mechanisms at the neurophysiologic level, multi-channel electroencephalogram (EEG) was recorded and negative slow cortical potentials (SCPs) were analyzed as objective markers of the amount and localization of cortical pre-activation before sub-task presentation.Results: Dual-task performance was significantly slower in old adults. T1 performance was facilitated in both age groups, but T2 processing in old adults was not optimized by the temporal structure as efficiently as in young adults. Also, only young adults manifested a stable pattern of focused of negative slow-wave activity increase at medial frontal and right-hemisphere posterior regions, which was associated with a coordinated preparatory T1 pre-activation and T2 deferment, while old adults manifested a broad topographic distribution of negative SCPs associated with a pre-activation of sensory and motor processes.Conclusions: These observations demonstrate that the proactive preparation for dual tasking is altered with aging. It is suggested that in young adults, attention-based pre-activation of working memory and inhibitory networks in the right hemisphere synchronizes the simultaneous preparation of the two sub-tasks, whereas in old adults, sensory and motor networks appear to be non-specifically pre-activated for subsequent deferred mode of processing.
Highlights
Typical everyday tasks consist of a sequence of multiple subtasks
In the psychological refractory period (PRP) paradigm, participants execute two subtasks (T1 to be performed first and T2 to be performed second) which are separated by different temporal intervals (e.g., Pashler and Johnston, 1989; De Jong, 1995; Luria and Meiran, 2003)
In the two age groups, R2 responses were faster than R1 responses in the SOA750 condition as indexed by negative Preparation of T2 (PT2) values (Figure 2C), R2 speeding was significantly more expressed in young subjects [Age, F(1/152) = 41.2, p < 0.0001, ηp2 = 0.202] due to R2 speeding in only about half of old participants (χ2 = 22.8, p < 0.001)
Summary
Typical everyday tasks consist of a sequence of multiple subtasks. multi-tasking has as a rule detrimental effects on behavior (e.g., May and Elder, 2018), there is evidence that the temporal organization of sub-tasks in a goal-directed order is a key element of successful performance. Despite indications that top-down cognitive control networks subserving both proactive and reactive adaptive strategies (Braver, 2012) are critically involved in dual-task costs (e.g., Pashler and Johnston, 1989; Logan and Gordon, 2001; Tombu and Jolicsur, 2003; Worringer et al, 2019, for review), the specific role of proactive neurocognitive mechanisms in preparing dual-task performance has only recently been focused on (Steinhauser and Steinhauser, 2018) Addressing this question is of particular relevance for conditions with altered control or compromised cognitive reserve such as aging (Karayanidis et al, 2011; Robertson, 2014; Gajewski et al, 2020a). How proactive control prioritizes the pre-activation or inhibition of complex tasks in older people has received no sufficient clarification so far
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