Reduced frontal cortex efficiency is associated with lower white matter integrity in aging.

Increased frontal cortex activation during cognitive task performance is common in aging but remains poorly understood. Here we explored patterns of age-related frontal brain activations under multiple task performance conditions and their relationship to white matter (WM) microstructure. Groups of younger (N = 28) and older (N = 33) participants completed a task-switching paradigm while functional magnetic resonance imaging (fMRI) was performed, and rested while diffusion tensor imaging was performed. Results from fMRI analyses indicated age-related increases in frontal brain activations under conditions of poorer performance in the older group (the nonswitch and switch conditions) and for a contrast in which behavioral performance was equated (older group nonswitch condition vs. younger group switch condition). Within the older adult group, higher frontal activation was associated with poorer behavioral performance under all task conditions. In 2 regions in right frontal cortex, blood oxygen level-dependent (BOLD) magnitudes were negatively correlated with WM integrity in tracts connecting these structures with other task-relevant frontoparietal and striatal regions. Our results link age-related declines in the efficiency of frontal cortex functioning with lower WM integrity in aging.

Neural correlates of cognitive style and flexible cognitive control.

Human abilities of flexible cognitive control are associated with appropriately regulating the amount of cognitive control required in response to contextual demands. In the context of conflicting situations, for instance, the amount of cognitive control increases according to the level of previously experienced conflict, resulting in optimized performance. We explored whether the amount of cognitive control in conflict resolution was related to individual differences in cognitive style that were determined with the Object-Spatial-Verbal cognitive style questionnaire. In this functional magnetic resonance imaging (fMRI) study, a version of the color-word Stroop task, which evokes conflict between color and verbal components, was employed to explore whether individual preferences for distracting information were related to the increases in neural conflict adaptation in cognitive control network regions. The behavioral data revealed that the more the verbal style was preferred, the greater the conflict adaptation effect was observed, especially when the current trial type was congruent. Consistent with the behavioral data, the imaging results demonstrated increased neural conflict adaptation effects in task-relevant network regions, including the left dorsolateral prefrontal cortex, left fusiform gyrus, and left precuneus, as the preference for verbal style increased. These results provide new evidence that flexible cognitive control is closely associated with individuals' preference of cognitive style.

Development of an auditory emotion recognition function using psychoacoustic parameters based on the International Affective Digitized Sounds.

The purpose of this study was to develop an auditory emotion recognition function that could determine the emotion caused by sounds coming from the environment in our daily life. For this purpose, sound stimuli from the International Affective Digitized Sounds (IADS-2), a standardized database of sounds intended to evoke emotion, were selected, and four psychoacoustic parameters (i.e., loudness, sharpness, roughness, and fluctuation strength) were extracted from the sounds. Also, by using an emotion adjective scale, 140 college students were tested to measure three basic emotions (happiness, sadness, and negativity). From this discriminant analysis to predict basic emotions from the psychoacoustic parameters of sound, a discriminant function with overall discriminant accuracy of 88.9% was produced from training data. In order to validate the discriminant function, the same four psychoacoustic parameters were extracted from 46 sound stimuli collected from another database and substituted into the discriminant function. The results showed that an overall discriminant accuracy of 63.04% was confirmed. Our findings provide the possibility that daily-life sounds, beyond voice and music, can be used in a human-machine interface.

Lifelong bilingualism maintains neural efficiency for cognitive control in aging.

Recent behavioral data have shown that lifelong bilingualism can maintain youthful cognitive control abilities in aging. Here, we provide the first direct evidence of a neural basis for the bilingual cognitive control boost in aging. Two experiments were conducted, using a perceptual task-switching paradigm, including a total of 110 participants. In Experiment 1, older adult bilinguals showed better perceptual switching performance than their monolingual peers. In Experiment 2, younger and older adult monolinguals and bilinguals completed the same perceptual task-switching experiment while functional magnetic resonance imaging (fMRI) was performed. Typical age-related performance reductions and fMRI activation increases were observed. However, like younger adults, bilingual older adults outperformed their monolingual peers while displaying decreased activation in left lateral frontal cortex and cingulate cortex. Critically, this attenuation of age-related over-recruitment associated with bilingualism was directly correlated with better task-switching performance. In addition, the lower blood oxygenation level-dependent response in frontal regions accounted for 82% of the variance in the bilingual task-switching reaction time advantage. These results suggest that lifelong bilingualism offsets age-related declines in the neural efficiency for cognitive control processes.

The role of the prefrontal cortex in semantic control for selecting weakly associated meanings in creative idea generation.

Although semantic control is known to play a critical role in selecting weakly associated representations for creative idea generation, direct evidence for this is still lacking. The current study aimed to reveal the role of brain regions, including the inferior frontal gyrus (IFG), medial frontal gyrus (MFG), and inferior parietal lobule (IPL), previously reported to be associated with creative idea generation. For this purpose, a functional MRI experiment with a newly developed category judgment task was conducted, which required participants to judge whether two words belonged to the same category. Importantly, weakly associated meanings were manipulated by the task condition, which required selecting an unused meaning of the homonym in a preceding semantic context. The results showed that the selection of a weakly associated meaning for a homonym was associated with an increased activation of the IFG and MFG and a decreased activation of the IPL. These results suggest that IFG and MFG contribute to semantic control processes recruited for the selection of weakly associated meanings and self-guided retrieval, whereas IPL appears to be unrelated to the control demand for creative idea generation.

Common and distinct mechanisms of cognitive flexibility in prefrontal cortex.

The human ability to flexibly alternate between tasks represents a central component of cognitive control. Neuroimaging studies have linked task switching with a diverse set of prefrontal cortex (PFC) regions, but the contributions of these regions to various forms of cognitive flexibility remain largely unknown. Here, subjects underwent functional brain imaging while they completed a paradigm that selectively induced stimulus, response, or cognitive set switches in the context of a single task decision performed on a common set of stimuli. Behavioral results indicated comparable reaction time costs associated with each switch type. Domain-general task-switching activation was observed in the inferior frontal junction and posterior parietal cortex, suggesting core roles for these regions in switching such as updating and representing task sets. In contrast, multiple domain-preferential PFC activations were observed across lateral and medial PFC, with progressively more rostral regions recruited as switches became increasingly abstract. Specifically, highly abstract cognitive set switches recruited anterior-PFC regions, moderately abstract response switches recruited mid-PFC regions, and highly constrained stimulus switches recruited posterior-PFC regions. These results demonstrate a functional organization across lateral and medial PFC according to the level of abstraction associated with acts of cognitive flexibility.

Cardiorespiratory fitness is positively correlated with cerebral white matter integrity in healthy seniors.

High cardiorespiratory fitness (CRF) is an important protective factor reducing the risk of cardiac-related disability and mortality. Recent research suggests that high CRF also has protective effects on the brain's macrostructure and functional response. However, little is known about the potential relationship between CRF and the brain's white matter (WM) microstructure. This study explored the relationship between a comprehensive measure of CRF (VO(2) peak, total time on treadmill, and 1-minute heart rate recovery) and multiple diffusion tensor imaging measures of WM integrity. Participants were 26 healthy community dwelling seniors between the ages of 60 and 69 (mean=64.79 years, SD=2.8). Results indicated a positive correlation between comprehensive CRF and fractional anisotropy (FA) in a large portion of the corpus callosum. Both VO(2) peak and total time on treadmill contributed significantly to explaining the variance in mean FA in this region. The CRF-FA relationship observed in the corpus callosum was primarily characterized by a negative correlation between CRF and radial diffusivity in the absence of CRF correlations with either axial diffusivity or mean diffusivity. Tractography results demonstrated that portions of the corpus callosum associated with CRF primarily involved those interconnecting frontal regions associated with high-level motor planning. These results suggest that high CRF may attenuate age-related myelin declines in portions of the corpus callosum that interconnect homologous premotor cortex regions involved in motor planning.

Domain general and domain preferential brain regions associated with different types of task switching: a meta-analysis.

One of our highest evolved functions as human beings is our capacity to switch between multiple tasks effectively. A body of research has identified a distributed frontoparietal network of brain regions which contribute to task switching. However, relatively less is known about whether some brain regions may contribute to switching in a domain-general manner while others may be more preferential for different kinds of switching. To explore this issue, we conducted three meta-analyses focusing on different types of task switching frequently used in the literature (perceptual, response, and context switching), and created a conjunction map of these distinct switch types. A total of 36 switching studies with 562 activation coordinates were analyzed using the activation likelihood estimation method. Common areas associated with switching across switch type included the inferior frontal junction and posterior parietal cortex. In contrast, domain-preferential activation was observed for perceptual switching in the dorsal portion of the premotor cortex and for context switching in frontopolar cortex. Our results suggest that some regions within the frontoparietal network contribute to domain-general switching processes while others contribute to more domain-preferential processes, according to the type of task switch performed.

The role of the right prefrontal cortex in the retrieval of weak representations.

Although recent studies have shown the importance of control in creative problem solving, the neural mechanisms of control processes engaged in retrieval of weak representations, which is closely linked to creative problem solving, remain unclear. The current study aimed to examine the neural mechanisms associated with retrieval of weak representations using functional magnetic resonance imaging and their potential relationships with creativity task performance. For this purpose, participants performed an experimental task that enabled us to directly compare between retrieval of previously unattended-and-weak representations and attended-and-strong representations. Imaging results indicated that the right anterior dorsolateral prefrontal cortex (aDLPFC) was selectively engaged in retrieval of weak representations. Moreover, the right aDLPFC activations were positively correlated with individuals' creativity task performance but independent of attention-demanding task performance. We therefore suggest that the right aDLPFC plays a key role in retrieval of weak representations and may support creative problem solving.

A functional dissociation of conflict processing within anterior cingulate cortex.

Goal-directed behavior requires cognitive control to regulate the occurrence of conflict. The dorsal anterior cingulate cortex (dACC) has been suggested in detecting response conflict during various conflict tasks. Recent findings, however, have indicated not only that two distinct subregions of dACC are involved in conflict processing but also that the conflict occurs at both perceptual and response levels. In this study, we sought to examine whether perceptual and response conflicts are functionally dissociated in dACC. Thirteen healthy subjects performed a version of the Stroop task during functional magnetic resonance imaging (fMRI) scanning. We identified a functional dissociation of the caudal dACC (cdACC) and the rostral dACC (rdACC) in their responses to different sources of conflict. The cdACC was selectively engaged in perceptual conflict whereas the rdACC was more active in response conflict. Further, the dorsolateral prefrontal cortex (DLPFC) was coactivated not with cdACC but with rdACC. We suggest that cdACC plays an important role in regulative processing of perceptual conflict whereas rdACC is involved in detecting response conflict.

Dissociable neural correlates of spatial attention and response inhibition in spatially driven interference.

Neural mechanisms underlying response inhibition have been investigated using spatially driven interference tasks such as the arrow-word Stroop task. However, neural responses, which are observed in the arrow-word Stroop task, may reflect not only response inhibition, but spatial attention modulation as well due to the spatial properties of an arrow stimulus. The current study aimed to identify whether individual cortical regions associated with spatially driven interference contribute to either spatial attention modulation or response inhibition, or both. We therefore developed a new task that measures these two functions independently and then conducted a functional magnetic resonance imaging experiment. Our results indicate that the right inferior parietal lobule and precentral gyrus were engaged by the spatial attention modulation, while inhibition was closely associated with the bilateral inferior frontal gyri, aided by the left superior prefrontal gyrus and dorsal anterior cingulate cortex. The left inferior parietal lobule was associated with common processes engaged in allocating attentional resources. These findings provide new evidence that spatially driven interference may recruit distinct cortical regions involved in spatial attention modulation and/or response inhibition.

The role of frontopolar cortex in the individual differences in conflict adaptation.

It is well known that performance on a trial is flexibly modulated by preceding trial congruency in tasks that require cognitive control, such as the Stroop task, referred to as the conflict adaptation effect (CAE). The CAE indicates that conflict on the preceding trial leads to enhanced cognitive control, leading to more efficient regulation of current conflict. The present study aimed to identify neural mechanisms implicated in individual differences in CAEs. The participants performed a version of the color-word Stroop task during a functional magnetic resonance imaging (fMRI) experiment and were divided into two groups according to the magnitude of behavioral CAE: one exhibiting the CAE only in congruent trials and the other in both congruent and incongruent trials. The imaging results showed different activations in the pre-supplementary motor area for the Stroop effect between groups. Importantly, group differences in activation for the preceding trials were observed in several prefrontal regions including the bilateral frontopolar, dorsolateral prefrontal, and rostro-dorsal cingulate cortices. More interestingly, analyses of the preceding trials suggest that the frontopolar cortex is involved in conflict resolution through higher-order cognitive control strategies that are closely associated with subsequent conflict. The current study provides new evidence of the role of the frontopolar cortex in conflict adaptation.

The role of the frontopolar cortex in manipulation of integrated information in working memory.

Cognitive operations often require integration of information. Previous studies have shown that, integration of information in working memory recruits frontopolar cortex (FPC). In this fMRI study, we sought to reveal neural mechanisms of FPC underlying the integration of information during arithmetic tasks. We compared a condition requiring manipulation of two features of an item held in working memory with manipulation of one feature. The results showed that, FPC was equally recruited in both conditions, while dorsolateral prefrontal cortex (DLPFC) tended to be more activated when manipulating two features. We suggest that, FPC plays an integrative role and is recruited by the production of representations in accordance with task constraints, whereas DLPFC appears to be sensitive to processing demands induced by the manipulation of information.

Conflict adaptation in prefrontal cortex: now you see it, now you don't.

Daily life requires people to monitor and resolve conflict arising from distracting information irrelevant to current goals. The highly influential conflict monitoring theory (CMT) holds that the anterior cingulate cortex (ACC) detects conflict and subsequently triggers the dorsolateral prefrontal cortex (DLPFC) to regulate that conflict. Multiple lines of evidence have provided support for CMT. For example, performance is faster on incongruent trials that follow other incongruent trials (iI), and is accompanied by reduced ACC and increased DLPFC activation (the conflict adaptation effect). In this fMRI study, we explored whether ACC-DLPFC conflict signaling can result in behavioral adjustments beyond on-line contexts. Participants completed a modified version of the Stroop conflict adaptation paradigm which tested for conflict adaptation effects on the current (N) trial associated with not only the immediately preceding (N - 1) trial, but also 2-back (N - 2) trials. Results demonstrated evidence for direct relationships between ACC activity on N - 2 trials and both N trial DLPFC activity and behavioral adjustment when intervening trials were congruent (i.e., icI). In contrast, when N - 1 trials were incongruent (i.e., iiI), ACC-DLPFC signaling failed and conflict adaptation was absent. These results provide new evidence demonstrating that the conflict monitor-controller maintains previously experienced conflict in the service of subsequent behavioral adjustment. However, the processing of multiple, temporally proximal conflict signals takes a toll on the working memory (WM) system, which appears to require resetting in order to adapt our behavior to frequently changing environmental demands.

Task-dependent response conflict monitoring and cognitive control in anterior cingulate and dorsolateral prefrontal cortices.

Previous experience affects our behavior in terms of adjustments. It has been suggested that the conflict monitor-controller system implemented in the prefrontal cortex plays a critical role in such adjustments. Previous studies suggested that there exists multiple conflict monitor-controller systems associated with the level of information (i.e., stimulus and response levels). In this study, we sought to test whether different types of conflicts occur at the same information processing level (i.e., response level) are independently processed. For this purpose, we designed a task paradigm to measure two different types of response conflicts using color-based and location-based conflict stimuli and measured the conflict adaptation effects associated with the two types of conflicts either independently (i.e., single conflict conditions) or simultaneously (i.e., a double-conflict condition). The behavioral results demonstrated that performance on current incongruent trials was faster only when the preceding trial was the same type of response conflict regardless of whether they included a single- or double-conflict. Imaging data also showed that anterior cingulate and dorsolateral prefrontal cortices operate in a task-specific manner. These findings suggest that there may be multiple monitor-controller loops for color-based and location-based conflicts even at the same response level. Importantly, our results suggest that double-conflict processing is qualitatively different from single-conflict processing although double-conflict shares the same sources of conflict with two single-conflict conditions.

Socioeconomic status is positively correlated with frontal white matter integrity in aging.

Socioeconomic status (SES) is an important reserve variable which has been shown to benefit the aging brain's macrostructure. However, it remains unknown whether SES affects age-related changes in the brain's white matter (WM) microstructure. Here, we used diffusion tensor imaging to explore the relationship between SES and three components of the diffusion tensor [fractional anisotropy (FA), axial diffusivity, and radial diffusivity (DR)]. Participants were 40 (16 male) cognitively normal young adults (mean age = 33.3 years, SD = 4.27) and 44 (19 male) cognitively normal community dwelling seniors (mean age = 66.2 years, SD = 7.5). Age-related FA declines were observed across a large portion of the WM skeleton. However, seniors with high SES showed lower age-related WM integrity declines in three frontal tracts: the right anterior corona radiata and bilateral portions of WM underlying the superior frontal gyri (SFG-WM). Positive SES-FA correlations were primarily driven by negative DR-SES correlations, suggesting that SES may buffer age-related declines in myelin. The functional significance of high SES in these frontal tracts was demonstrated through positive correlations with working memory performance. Possible mechanisms through which SES may attenuate the effects of age on frontal WM integrity are discussed.

Conflict adjustment through domain-specific multiple cognitive control mechanisms.

Cognitive control is required to regulate conflict between relevant and irrelevant information. Although previous neuroimaging studies have focused on response conflict, recent studies suggested that distinct neural networks are recruited in regulating perceptual conflict. The aim of the current study was to distinguish between brain areas involved in detecting and regulating perceptual conflict using a conflict adjustment paradigm. The Stroop color-matching task was combined with an arrow version of the Stroop task in order to independently manipulate perceptual and response conflicts. Behavioral results showed that post-conflict adjustment for perceptual and response conflicts were independent from each other. Imaging results demonstrated that the caudal portion of the dorsal cingulate cortex (cdACC) was selectively associated with the occurrence of perceptual conflict, whereas the left dorsal portion of the premotor cortex (pre-PMd) was selectively associated with both preceding and current perceptual conflict trials. Furthermore, the rostral portion of the dorsal cingulate cortex (rdACC) was selectively linked with response conflict, whereas the left dorsolateral prefrontal cortex (DLPFC) was selectively involved in both preceding and current response conflict trials. We suggest that cdACC is involved in detecting perceptual conflict and left pre-PMd is involved in regulating perceptual conflict, which is analogous to the recruitment of rdACC and left DLPFC in control processes for response conflict. Our findings provide support for the hypothesis that multiple independent monitor-controller loops are implemented in the frontal cognitive control system.

Common and distinct neural mechanisms of attentional switching and response conflict.

The human capacities for overcoming prepotent actions and flexibly switching between tasks represent cornerstones of cognitive control. Functional neuroimaging has implicated a diverse set of brain regions contributing to each of these cognitive control processes. However, the extent to which attentional switching and response conflict draw on shared or distinct neural mechanisms remains unclear. The current study examined the neural correlates of response conflict and attentional switching using event-related functional magnetic resonance imaging (fMRI) and a fully randomized 2×2 design. We manipulated an arrow-word version of the Stroop task to measure conflict and switching in the context of a single task decision, in response to a common set of stimuli. Under these common conditions, both behavioral and imaging data showed significant main effects of conflict and switching but no interaction. However, conjunction analyses identified frontal regions involved in both switching and response conflict, including the dorsal anterior cingulate cortex (dACC) and left inferior frontal junction. In addition, connectivity analyses demonstrated task-dependent functional connectivity patterns between dACC and inferior temporal cortex for attentional switching and between dACC and posterior parietal cortex for response conflict. These results suggest that the brain makes use of shared frontal regions, but can dynamically modulate the connectivity patterns of some of those regions, to deal with attentional switching and response conflict.