Factors influencing the role of cardiac autonomic regulation in the service of cognitive control.

Working from a model of neurovisceral integration, we examined whether adding response contingencies and motivational involvement would increase the need for cardiac autonomic regulation in maintaining effective cognitive control. Respiratory sinus arrhythmia (RSA) was recorded during variants of the Stroop color-word task. The Basic task involved "accepting" congruent items and "rejecting" words printed in incongruent colors (BLUE in red font); an added contingency involved rejecting a particular congruent word (e.g., RED in red font), or a congruent word repeated on an immediately subsequent trial. Motivation was increased by adding a financial incentive phase. Results indicate that pre-task RSA predicted accuracy best when response contingencies required the maintenance of a specific item in memory or on the Basic Stroop task when errors resulted in financial loss. Overall, RSA appeared to be most relevant to performance when the task encouraged a more proactive style of cognitive control, a control strategy thought to be more metabolically costly, and hence, more reliant on flexible cardiac autonomic regulation.

Cardiac workload and inhibitory control in younger and older adults.

Our goal was to investigate age differences in the role played by cardiovascular regulation in response control. We questioned whether pre-test respiratory sinus arrhythmia (RSA; an index of phasic vagal cardiac control) and/or rate pressure product (RPP; a measure of cardiac workload) were associated with error rate and/or error-related electrocortical responses (ERPs) during a Go/NoGo inhibitory control task across three levels of working memory load. ERPs, RSA and RPP were indirectly associated with performance in young adults. Within the older group, higher resting RPP was directly associated with NoGo errors at all levels of load, an association not seen in the younger group. Thus, for older adults, excessive hemodynamic demands at rest were more relevant than on-task electrocortical responses in the prediction of inhibitory control errors. These data support the relevance of autonomic regulation in understanding age-related change in higher-order neurocognitive function.

Autonomic regulation and maze-learning performance in older and younger adults.

There is growing evidence that centrally modulated autonomic regulation can influence performance on complex cognitive tasks but the specificity of these influences and the effects of age-related decline in these systems have not been determined. We recorded pre-task levels of respiratory sinus arrhythmia (RSA; an index of phasic vagal cardiac control) and rate pressure produce (RPP; an index of cardiac workload) to determine their relationship to performance on a cumulative maze learning task. Maze performance has been shown to reflect executive error monitoring capacity and non-executive visuo-motor processing speed. Error monitoring was predicted by RSA in both older and younger adults but by RPP only in the older group. Non-executive processes were unrelated to either measure. These data suggest that vagal regulation is more closely associated with executive than nonexecutive aspects of maze performance and that, in later life, pre-task levels of cardiac workload also influence executive control.

Age-related differences during simple working memory decisions: ERP indices of early recognition and compensation failure.

Imaging data has identified frontal cortical activation in older adults during simple recognition tasks that relates positively with performance and could, therefore, be considered compensatory. However, in a previous electrophysiological study involving a Sternberg task with proactive interference manipulations, we observed a frontal positive scalp potential between 400 and 500 ms that was unique to older adults and predictive of poorer performance. These results led us to ask whether unique frontal activation in older adults serves a compensatory role only during relatively simple tasks when stimulus familiarity provides an unambiguous basis for response selection. In the current study, we tested this hypothesis by having younger and older adults complete a verbal Sternberg task without interference manipulations. In younger adults, we observed an early posterior negativity (90-120 ms) that predicted performance accuracy. Older adults failed to show this early negativity but did produce the expected frontal positivity. However, the frontal positivity was again associated with poorer performance. These data support the view that younger adults are able to bias early target discrimination to benefit response selection whereas older adults rely on later controlled processes that are not always effective in buffering against normative age-related decline.

General proactive interference and the N450 response.

Strategic repetition of verbal stimuli can effectively produce proactive interference (PI) effects in the Sternberg working memory task. Unique fronto-cortical activation to PI-eliciting letter probes has been interpreted as reflecting brain responses to PI. However, the use of only a small set of stimuli (e.g., letters and digits) requires constant repetition of stimuli in both PI and baseline trials, potentially creating a general PI effect in all conditions. We used event-related potentials to examine general PI effects by contrasting the interference-related frontal N450 response in two Sternberg tasks using a small versus large set size. We found that the N450 response differed significantly from baseline during the small set-size task only for response-conflict PI trials but not when PI was created solely from stimulus repetition. During the large set-size task N450 responses in both the familiarity-based and response-conflict PI conditions differed from baseline but not from each other. We conclude that the general stimulus repetition inherent in small set-size conditions can mask effects of familiarity-based PI and complicate the interpretation of any associated neural response.

Aging and electrocortical response to error feedback during a spatial learning task.

Event-related potentials were collected as older and younger adults responded to error feedback in an adaptation of the Groton Maze Learning Test, an age-sensitive measure of spatial learning and executive skills expected to maximally involve anterior cingulate cortex (ACC). Older adults made more errors and produced smaller feedback-related negativities (FRNs) than young controls. LORETA source localization revealed that, for young adults, neural activation associated with the FRN was focused in ACC and was stronger to negative feedback. Older adults responded with less intense and less differentiated ACC activation, but FRN amplitudes did relate to error rate for the most difficult mazes. The feedback P3 was sensitive to negative feedback but played no role in the prediction of error for either group. These data reflect the selective age-related decline of ACC response but also its continued contribution to performance monitoring in aging.

Age differences in target detection and interference resolution in working memory: an event-related potential study.

There is growing consensus that a decline in attentional control is a core aspect of cognitive aging. We used event-related potentials to examine the time course of attentional control in older and younger adults as they attempted to resolve familiarity-based and response-based interference during a working memory task. Accuracy was high for both groups but their neural response to targets and to distracters was markedly different. Young adults' early target selection was evident by 300 msec in a differentiated P3a and they responded to interference by generating a medial frontal negativity (MFN) to distracters by 450 msec that was largest when the need for interference resolution was greatest. Dipole source analyses revealed a temporal coactivation of the inferior frontal and anterior cingulate cortex in younger adults, suggesting that these regions may interact during interference resolution. Older adults did not show the early target-selective P3a effect and failed to subsequently produce the MFN in response to distracting stimuli. In fact, older adults showed a large frontal positivity in place of the MFN but, rather than serve a compensatory role, this frontal activation was associated with poorer behavioral performance. These data suggest that aging interferes with a dynamic interplay of early target selection followed by later suppression of distracter-related neural activity--a process central to the efficient control of attention.

Anomaly detection in the right hemisphere: The influence of visuospatial factors.

Previous research with both brain-damaged and neurologically intact populations has demonstrated that the right cerebral hemisphere (RH) is superior to the left cerebral hemisphere (LH) at detecting anomalies (or incongruities) in objects (Ramachandran, 1995; Smith, Tays, Dixon, & Bulman-Fleming, 2002). The current research assesses whether the RH advantage for anomaly detection is due to the RH superiority for visuospatial skills or is a distinct cognitive process. Sixty undergraduate participants completed tasks assessing anomaly detection, mental rotation, and global and local perceptual abilities. The results demonstrate that anomaly detection is negatively correlated with mental rotation. These findings suggest that anomaly detection is not simply a function of visuospatial skills.

The right hemisphere as an anomaly detector: evidence from visual perception.

V. S. Ramachandran (1998) has suggested that the right hemisphere, which tends to be specialized for the analysis of global-level information, serves as an anomaly detector. Its role is to judge whether a given percept is possible and whether there are elements of that percept that seem incongruent with the other elements. In contrast, the left hemisphere tends to create a "story" to make sense of the incongruities. In the current study, pictures of possible or impossible objects were displayed for brief exposure durations to either the left visual field/right hemisphere or to the right visual field/left hemisphere). The results provide tentative support for the work of Ramachandran. In male participants, the right hemisphere was superior to the left in detecting impossible objects.