Decoding the neural impact of radical complexity in Chinese characters during working memory task

Readers of Chinese characters need to recognize how they are formed in order to identify them correctly. However, our understanding of the cognitive processing of characters in working memory is limited. In Experiment 1, using the character N-back task paradigm, electrophysiological data were recorded from 26 participants to investigate the effects of the visual feature of radicals on neural activity during the character recognition, updating and maintenance in the N-back task. Results showed that compound characters required longer response times than single-component characters. For the event-related potentials (ERPs), the compound character condition had more negative N2pc and lower P300 amplitudes than the single-component character condition. In Experiment 2, data from 26 participants were used to analyse the effect of the phonological feature of radicals on neural activity during the character recognition, updating and maintenance in the N-back task. Results showed that there was a larger P200 in the irregular character condition than in the regular character condition, but there was no difference between the regular and the irregular characters in the N2pc, P300 and slow wave (SW) components. The visual feature and the phonological feature of the radicals may have different effects on the character processing. This study reveals the neural effects of Chinese character radicals on cognitive processing in a working memory task and provides behavioural and electrophysiological evidence for a theoretical model of verbal working memory subprocesses.

Neural signatures for the n-back task with different loads: An event-related potential study

The n-back task is widely used in working memory (WM) research. However, it remains unclear how the electrophysiological correlates of WM processes, the P2, N2, P300, and negative slow wave (NSW), are affected by differences in load. Specifically, while previous work has examined the P300, less attention has been paid to the other components assessing the load of the n-back paradigm. The present study aims to investigate whether other sub-processes in WM (such as inhibitory control) are as sensitive to n-back load changes as the update process by observing changes in the above event-related potential (ERP) components. The results showed poorer behavioral performance with increasing WM load. Greater NSW and smaller P300 amplitudes were elicited by n-back task with a higher load compared to that with lower load. In contrast, there was no significant effect of the n-back load on the amplitudes of P2 and N2. These findings suggest that the updating process and the maintenance process are sensitive to the n-back load change. Therefore, changes in the updating and maintenance processes should be considered when using the n-back task to manipulate the WM load in experiments. The present study may contribute to the understanding of the complexity of WM loads. Additionally, a theoretical basis for follow-up research to explore ways of improving WM performance with high load is provided.

Event-Related Potentials as Markers of Efficacy for Combined Working Memory Training and Transcranial Direct Current Stimulation Regimens: A Proof-of-Concept Study

Our brains are often under pressure to process a continuous flow of information in a short time, therefore facing a constantly increasing demand for cognitive resources. Recent studies have highlighted that a lasting improvement of cognitive functions may be achieved by exploiting plasticity, i.e., the brain’s ability to adapt to the ever-changing cognitive demands imposed by the environment. Transcranial direct current stimulation (tDCS), when combined with cognitive training, can promote plasticity, amplify training gains and their maintenance over time. The availability of low-cost wearable devices has made these approaches more feasible, albeit the effectiveness of combined training regimens is still unclear. To quantify the effectiveness of such protocols, many researchers have focused on behavioral measures such as accuracy or reaction time. These variables only return a global, non-specific picture of the underlying cognitive process. Electrophysiology instead has the finer grained resolution required to shed new light on the time course of the events underpinning processes critical to cognitive control, and if and how these processes are modulated by concurrent tDCS. To the best of our knowledge, research in this direction is still very limited. We investigate the electrophysiological correlates of combined 3-day working memory training and non-invasive brain stimulation in young adults. We focus on event-related potentials (ERPs), instead of other features such as oscillations or connectivity, because components can be measured on as little as one electrode. ERP components are, therefore, well suited for use with home devices, usually equipped with a limited number of recording channels. We consider short-, mid-, and long-latency components typically elicited by working memory tasks and assess if and how the amplitude of these components are modulated by the combined training regimen. We found no significant effects of tDCS either behaviorally or in brain activity, as measured by ERPs. We concluded that either tDCS was ineffective (because of the specific protocol or the sample under consideration, i.e., young adults) or brain-related changes, if present, were too subtle. Therefore, we suggest that other measures of brain activity may be more appropriate/sensitive to training- and/or tDCS-induced modulations, such as network connectivity, especially in young adults.

The Relationship Between Socioeconomic Status and Scalp Event-Related Potentials: A Systematic Review

Several decades of behavioral research have established that variations in socioeconomic status (SES) are related to differences in cognitive performance. Neuroimaging and psychophysiological techniques have recently emerged as a method of choice to better understand the neurobiological processes underlying this phenomenon. Here we present a systematic review of a particular sub-domain of this field. Specifically, we used the PICOS approach to review studies investigating potential relationships between SES and scalp event-related brain potentials (ERP). This review found evidence that SES is related to amplitude variations in a diverse range of ERPs: P1, N1, N2, Error-Related Negativities (ERN), N400, auditory evoked potentials, negative difference waves (Nd), P3 and slow waves (SW). These ERPs include early, mid-latency and late potentials that reflect a broad range of cognitive processes (e.g., automatic attentional processes, overt attention, language, executive function, etc.). In this review, all SES effects on ERPs appeared to reflect an impairment or a less efficient form of task-related neural activity for low-SES compared to high-SES individuals. Overall, these results confirm that a wide variety of distinct neural processes with different functional meanings are sensitive to SES differences. The findings of this review also suggest that the relationship between SES and some ERP components may depend on the developmental stage of study participants. Results are further discussed in terms of the current limitations of this field and future avenues of research.

Neural measures of working memory in a bilateral change detection task

The change detection task is a widely used paradigm to examine visual working memory processes. Participants memorize a set of items and then, try to detect changes in the set after a retention period. The negative slow wave (NSW) and contralateral delay activity (CDA) are event-related potentials in the EEG signal that are commonly used in change detection tasks to track working memory load, as both increase with the number of items maintained in working memory (set size). While the CDA was argued to more purely reflect the memory-specific neural activity than the NSW, it also requires a lateralized design and attention shifts prior to memoranda onset, imposing more restrictions on the task than the NSW. The present study proposes a novel change detection task in which both CDA and NSW can be measured at the same time. Memory items were presented bilaterally, but their distribution in the left and right hemifield varied, inducing a target imbalance or "net load." NSW increased with set size, whereas CDA increased with net load. In addition, a multivariate linear classifier was able to decode the set size and net load from the EEG signal. CDA, NSW, and decoding accuracy predicted an individual's working memory capacity. In line with the notion of a bilateral advantage in working memory, accuracy, and CDA data suggest that participants tended to encode items relatively balanced. In sum, this novel change detection task offers a basis to make use of converging neural measures of working memory in a comprehensive paradigm.

Age-related changes in selection, recognition, updating and maintenance information in WM. An ERP study in children and adolescents

Possible age-related changes in different working memory (WM) subcomponents were assessed by analyzing the event-related-potentials associated with the n-back task. Two versions of the task (0- and 1-back) were administered to 168 subjects between 6 and 20 years of age. In both n-back tasks, lists of symbol-letter pairs were presented. Participants had to select the letter and decide whether it matched the target in memory. Selection-matching of the relevant item, as indexed by an N2pc component, was evident in all age groups, indicating early maturation of this ability. The decreasing amplitude of the P300 with age, coupled with the longer duration of the load effect in young children, suggests that WM updating requires greater processing resources at younger ages. The slow wave, present during the maintenance period, showed an inversion of polarity with age in anterior sites that could reflect age-related changes in the active maintenance of information in WM.

Processing differences between monolingual and bilingual young adults on an emotion n-back task

Bilingualism is associated with enhancement of executive control (EC) across the lifespan. Working memory and non-verbal emotion regulation both draw upon EC mechanisms so may also be affected by bilingualism, but these relationships are not fully understood. These relationships were explored using an n-back task with distracting emotional stimuli administered to young adults while continuous EEG was recorded. Monolinguals were faster but less accurate on the 2-back than bilinguals, and monolingual accuracy was more impeded by the presence of emotional stimuli than was that of bilinguals. The P300 event-related potential, a neural signature of working memory processing in the n-back, had smaller amplitudes in both groups on the 2-back than the 1-back, but attenuation in response to distracting emotional stimuli was greater for bilinguals than monolinguals. P300 latencies were also differentially affected by emotional stimuli in each group: Bilingual latencies were constant across emotions but monolingual latencies increased from neutral to angry conditions. In general, bilingual performance was less impacted by the emotional distraction than was that of the monolinguals. Additionally, bilinguals adjusted to the changing demands of the 1-back and 2-back conditions by recruiting neural networks to support different behavioral outcomes than monolinguals.