Complexity in relational processing predicts changes in functional brain network dynamics.

The ability to link variables is critical to many high-order cognitive functions, including reasoning. It has been proposed that limits in relating variables depend critically on relational complexity, defined formally as the number of variables to be related in solving a problem. In humans, the prefrontal cortex is known to be important for reasoning, but recent studies have suggested that such processes are likely to involve widespread functional brain networks. To test this hypothesis, we used functional magnetic resonance imaging and a classic measure of deductive reasoning to examine changes in brain networks as a function of relational complexity. As expected, behavioral performance declined as the number of variables to be related increased. Likewise, increments in relational complexity were associated with proportional enhancements in brain activity and task-based connectivity within and between 2 cognitive control networks: A cingulo-opercular network for maintaining task set, and a fronto-parietal network for implementing trial-by-trial control. Changes in effective connectivity as a function of increased relational complexity suggested a key role for the left dorsolateral prefrontal cortex in integrating and implementing task set in a trial-by-trial manner. Our findings show that limits in relational processing are manifested in the brain as complexity-dependent modulations of large-scale networks.

Estimating left atrial enlargement parameters from the electrocardiogram using wavelets.

BACKGROUND: The aim of this article was to examine the utility of using the P wave of the electrocardiogram to indicate left atrial enlargement measures determined from the echocardiogram and cardiac magnetic resonance. METHOD: Wavelet-based features extracted from the beat-averaged P wave were correlated to the left atrial diameter, left atrial area, and left atrial volume index measures from echocardiogram and cardiac magnetic resonance. RESULTS: Significant correlations were found between several of the wavelet features and the left atrial enlargement size measures (r > 0.5, P < .01). Left atrial diameter and left atrial area correlated best to the derived Z lead, and left atrial volume index correlated best to the derived X lead. CONCLUSIONS: The good correlations illustrate that it is feasible to estimate the size of the left atrium from the P wave using wavelet techniques.

The development of prospective memory across adolescence: an event-related potential analysis.

Prospective memory (PM) is an important cognitive function vital for day-to-day functioning. Although there has been extensive research into the decline of PM in older adulthood, little is known about its developmental trajectory throughout adolescence, a time of important brain maturation. In the present study, the development of PM was examined in 85 participants across the following groups: 12 to 13-year-olds (n = 19), 14 to 15-year-olds (n = 21), 16 to 17-year-olds (n = 19), and 18 to 19-year-olds (n = 26). A 30-cue (30 min) event-based PM task (with font-color stimuli as PM cues and a lexical-decision task as the ongoing task) was used while recording Event-Related Potentials (ERPs). The well-established neural correlates of PM, the N300 and parietal positivity, were examined across the age groups. In addition, hierarchical multiple regressions were used to examine the unique contribution of executive functioning measures (viz., the Self-Ordered Pointing Task [SOPT], the Stroop task, and Trail Making Test [TMT]) on the ERP components of PM (after controlling for age). First, the established components of ERPs associated with prospective remembering (i.e., N300 and parietal positivity) were detected for each age group. Second, although there were no significant age- group differences on the amplitude of the N300, the amplitude of the parietal positivity was found to be different between the 12 to 13-year-olds and 18 to 19-year-olds (viz., the 12 to 13-year-olds had the highest amplitude). Third, for the contribution of executive functioning measures on the amplitude of the ERP components of PM, the regression on the N300 was not significant, however, the SOPT beta weights were significant predictors of the amplitude of the parietal positivity. This relationship was found to be specific for the central and right electrode region. These findings are discussed within the context of brain development and executive functioning along with particular task demands, which may contribute to age-related PM differences across adolescence. Moreover, the findings suggest that cognitive processes associated with parietal positivity may continue to develop across adolescence.

Neural correlates of deductive reasoning: An ERP study with the Wason Selection Task.

The Wason Selection Task (WST) is a well-known test of reasoning in which one turns over cards to test a rule about the two faces. Modifications were made to the WST to enable more direct and analytical investigation of reasoning processes. The modifications included extensive training to reduce variations in task interpretation, isolation of working memory in the decision phase, a separate rule for each card and variations in the form of the rule (number-letter as well as letter-number), separate scoring for each card, and inclusion of control cards that could be recognized by features without relational processing. The cognitive complexity of each card was also analyzed to enable investigation of this factor. Behavioral and event-related potential data were recorded. Negative cards differed from positive cards and control cards were differentiated from cards involved in inferences. The N2 component differentiated the negative conditions (not-P, not-Q cards) from the positive conditions (P, Q cards). The P3 component was largest for control and P cards (the simpler conditions). The late slow wave tended to show more sustained processing of not-P, not-Q and Q cards and was little influenced by the simpler control and P cards. Effects were interpreted in terms of cognitive complexity. In particular, the negative conditions had a larger N2 response than the positive conditions, reflecting greater cognitive complexity of the former and their sustained processing.

Wavelet coherence of EEG signals for a visual oddball task.

Neural co-activation in frontal and central cortex was examined during a visual oddball task using wavelet coherence. EEG was recorded during a visual oddball task, presented to 12 participants with a random mix of 15% oddball targets and 85% frequent non-target letters over 265 trials. Wavelet coherence of individual trials was shown to distinguish frequent and oddball trials. Averaged wavelet coherence showed significant differences: oddball targets showed higher delta-theta activity whereas frequent background stimuli showed higher gamma activity. Increased gamma coherence appeared to be related to expectation of the targets with our analysis showing an R(2) of 0.935 for the relationship between averaged sections of gamma coherence and the number of intervening (frequent) trials since the last oddball.

Effects of cue frequency and repetition on prospective memory: an ERP investigation.

Prospective memory involves the formation and completion of delayed intentions and is essential for independent living. In this study (n = 33), event-related potentials (ERPs) were used to systematically evaluate the effects of PM cue frequency (10% versus 30%) and PM cue repetition (high versus low) on ERP modulations. PM cues elicited prospective positivity and frontal positivity but not N300, perhaps due to the semantic nature of the task. Results of this study revealed an interesting interaction between PM cue frequency and PM cue repetition for prospective positivity and frontal positivity, highlighting the importance of taking both factors into account when designing future studies.

An object cue is more effective than a word in ERP-based detection of deception.

Recent studies of deception have used a form of the guilty knowledge test along with the oddball P300 event-related potential (ERP) to uncover hidden memories. These studies typically have used words as the cuing stimuli. In the present study, a mock crime was enacted by participants to prime their episodic memory and different memory cue types (Words, Pictures of Objects and Faces) were created to investigate their relative efficacy in identifying guilt. A peak-to peak (p-p) P300 response was computed for rare known non-guilty item (target), rare guilty knowledge item (probe) and frequently presented unknown items (irrelevant). Difference in this P300 measure between the probe and irrelevant was the key dependent variable. Object cues were found to be the most effective, particularly at the parietal site. A bootstrap procedure commonly used to detect deception in individual participants by comparing their probe and irrelevant P300 p-p showed the object cues to provide the best discrimination. Furthermore, using all three of the cue types together provided high detection accuracy (94%). These results confirm prior findings on the utility of ERPs for detecting deception. More importantly, they provide support for the hypothesis that direct cueing with a picture of the crime object may be more effective than using a word (consistent with the picture superiority effect reported in the literature). Finally, a face cue (e.g., crime victim) may also provide a useful probe for detection of guilty knowledge but this stimulus form needs to be chosen with due caution.

Neurophysiological indices of perceptual object priming in the absence of explicit recognition memory.

The aim of this study was to identify ERP correlates of perceptual object priming that are insensitive to factors affecting explicit, episodic memory. EEG was recorded from 21 participants while they performed a visual object recognition test on a combination of unstudied items and old items that were previously encountered during either a 'deep' or 'shallow' levels-of-processing (LOP) study task. The results demonstrated a midline P150 old/new effect which was sensitive only to objects' old/new status and not to the accuracy of recognition responses to old items, or to the LOP manipulation. Similar outcomes were observed for the subsequent P200 and N400 effects, the former of which had a parietal scalp maximum and the latter, a broadly distributed topography. In addition an LPC old/new effect typical of those reported in past ERP recognition studies was observed. These outcomes support the proposal that the P150 effect is reflective of perceptual object priming and moreover, provide novel evidence that this and the P200 effect are independent of explicit recognition memory process(es).