The effects of total sleep deprivation on semantic priming: event-related potential evidence for automatic and controlled processing strategies.

There is general consensus that performance on a number of cognitive tasks deteriorates following total sleep deprivation. At times, however, subjects manage to maintain performance. This may be because of an ability to switch cognitive strategies including the exertion of compensatory effort. The present study examines the effects of total sleep deprivation on a semantic word priming task. Word priming is unique because it can be carried out using different strategies involving either automatic, effortless or controlled, effortful processing. Twelve subjects were presented with word pairs, a prime and a target, that were either highly semantically associated (cat…dog), weakly associated (cow…barn) or unassociated (apple…road). In order to increase the probability of the use of controlled processing following normal sleep, the subject's task was to determine if the target word was semantically related to the prime. Furthermore, the time between the offset of the prime and the onset of the target was relatively long, permitting the use of an effortful, expectancy-predictive strategy. Event-related potentials (ERPs) were recorded from 64 electrode sites. After normal sleep, RTs were faster and accuracy higher to highly associated targets; this performance advantage was also maintained following sleep deprivation. A large negative deflection, the N400, was larger to weakly associated and unassociated targets in both sleep-deprived and normal conditions. The overall N400 was however larger in the normal sleep condition. Moreover, a long-lasting negative slow wave developed between the offset of the prime and the onset of the target. These physiological measures are consistent with the use of an effortful, predictive strategy following normal sleep but an automatic, effortless strategy following total sleep deprivation. A picture priming task was also run. This task benefits less from the use of a predictive strategy. Accordingly, in this task, ERPs following the target did not differ as a function of the amount of sleep.

Lexico-semantic access and audiovisual integration in the aging brain: Insights from mixed-effects regression analyses of event-related potentials.

We investigated how aging modulates lexico-semantic processes in the visual (seeing written items), auditory (hearing spoken items) and audiovisual (seeing written items while hearing congruent spoken items) modalities. Participants were young and older adults who performed a delayed lexical decision task (LDT) presented in blocks of visual, auditory, and audiovisual stimuli. Event-related potentials (ERPs) revealed differences between young and older adults despite older adults' ability to identify words and pseudowords as accurately as young adults. The observed differences included more focalized lexico-semantic access in the N400 time window in older relative to young adults, stronger re-instantiation and/or more widespread activity of the lexicality effect at the time of responding, and stronger multimodal integration for older relative to young adults. Our results offer new insights into how functional neural differences in older adults can result in efficient access to lexico-semantic representations across the lifespan.

Lexical access versus lexical decision processes for auditory, visual, and audiovisual items: Insights from behavioral and neural measures.

In two experiments, we investigated the relationship between lexical access processes, and processes that are specifically related to making lexical decisions. In Experiment 1, participants performed a standard lexical decision task in which they had to respond as quickly and as accurately as possible to visual (written), auditory (spoken) and audiovisual (written + spoken) items. In Experiment 2, a different group of participants performed the same task but were required to make responses after a delay. Linear mixed effect models on reaction times and single trial Event-Related Potentials (ERPs) revealed that ERP lexicality effects started earlier in the visual than auditory modality, and that effects were driven by the written input in the audiovisual modality. More negative ERP amplitudes predicted slower reaction times in all modalities in both experiments. However, these predictive amplitudes were mainly observed within the window of the lexicality effect in Experiment 1 (the speeded task), and shifted to post-response-probe time windows in Experiment 2 (the delayed task). The lexicality effects lasted longer in Experiment 1 than in Experiment 2, and in the delayed task, we additionally observed a "re-instantiation" of the lexicality effect related to the delayed response. Delaying the response in an otherwise identical lexical decision task thus allowed us to separate lexical access processes from processes specific to lexical decision.

Task switching and bilingualism in young and older adults: A behavioral and electrophysiological investigation.

The current study investigated behavioral and electrophysiological (event-related potential; ERP) differences associated with task switching in a sample of young and older monolingual and bilingual adults. ERPs associated with task preparation (switch and mixing positivity) and task execution processes (N2 and P3b) were investigated. Participants performed a cued letter-number task switching paradigm that included single task and mixed task blocks, while their electroencephalography was recorded. Behavioral results revealed smaller switch and mixing costs in bilinguals relative to monolinguals, in both young and older participants. There were no ERP differences in the effect size of the cue-locked mixing and switch positivities, nor the target-locked mixing and switch N2 and P3b components. However, overall larger target-locked N2 amplitudes were observed in bilinguals relative to monolinguals. In addition, bilingual older adults exhibited smaller P3b amplitudes than monolingual older adults. The smaller behavioral mixing and switch costs observed in bilinguals suggest that bilinguals exhibit superior sustained attention and faster task-set reconfiguration processes compared to monolinguals. The ERP measures provide evidence for differences in brain processes between monolinguals and bilinguals and a reliance on different processing strategies in bilingual compared to monolingual older adults.

N400 effects of semantic richness can be modulated by task demands.

Semantic richness is a multidimensional construct that can be defined as the amount of semantic information associated with a concept. OBJECTIVE: To investigate neurophysiological correlates of semantic richness information associated with words and its interaction with task demands. METHOD: Two different dimensions of semantic richness (number of associates and number of semantic neighbors) were investigated using event-related potentials (ERPs) in lexical decision (LDT) and semantic categorization tasks (SCT) using the same stimuli in 2 groups of participants (24 in each group). RESULTS: The amplitude of the N400 ERP component, which is associated with semantic processing, was smaller for words with a high number of associates (p = .003 at fronto-centro-parietal sites) or semantic neighbors (p < .03 at centro-parietal sites) than for words with a low number of associates or number of semantic neighbors, in the LDT but not the SCT. CONCLUSIONS: These results suggest that the effects of semantic richness vary with task demands and may be used in a top-down manner to accommodate the current context. (PsycINFO Database Record

Effects of Semantic Richness on Lexical Processing in Monolinguals and Bilinguals.

The effect of number of senses (NoS), a measure of semantic richness, was examined in monolingual English speakers (n = 17) and bilingual speakers of English and French (n = 18). Participants completed lexical decision tasks while EEG was recorded: monolinguals completed the task in English only, and bilinguals completed two lexical decision tasks, one in English and one in French. Effects of NoS were observed in both participant groups, with shorter response times and reduced N400 amplitudes to high relative to low NoS items. These effects were stronger in monolinguals than in bilinguals. Moreover, we found dissociations across languages in bilinguals, with stronger behavioral NoS effects in English and stronger event-related potential (ERP) NoS effects in French. This finding suggests that different aspects of linguistic performance may be stronger in each of a bilingual's two languages.

P300 amplitude alterations during inhibitory control in persons with Mild Cognitive Impairment.

Deficits in executive function are highly noticeable in Alzheimer's disease, and recent behavioral studies have shown that such deficits - particularly during inhibitory control - can also be found in persons with Mild Cognitive Impairment (MCI). Thus, the objective of this study was to investigate behavioral and electrophysiological correlates of inhibitory control in persons with MCI. A group of persons with MCI and a group healthy older adults performed a Go/NoGo task while electroencephalogram was recorded. Our results revealed that persons with MCI performed less accurately than healthy controls during the Go and NoGo conditions. In addition, we found reduced P300 amplitudes during Go and NoGo conditions relative to healthy older adults. Our results suggest that neurocognitive mechanisms associated with target detection and evaluation (Go P300) and response inhibition (NoGo P300) are compromised in persons with MCI.

Event-related potentials elicited during working memory are altered in mild cognitive impairment.

Persons with Mild Cognitive Impairment (MCI) can experience deficits in working memory. In the present study, we investigated working memory in persons with MCI and cognitively healthy older adults using event-related potentials (ERPs). Participants performed an n-back working memory task with baseline (0-back), low load (1-back), and high load (2-back) working memory conditions. MCI participants' performance was less accurate than that of healthy older adults in both the 1-back and 2-back conditions, and reaction times were longer in MCI than control participants in the 0-back, 1-back and 2-back conditions. ERP analyses revealed delayed P200 and N200 latencies and smaller P300 amplitudes in MCI relative to control participants in the 0-back, 1-back and 2-back conditions. Deterioration in working memory performance concomitant with marked electrophysiological alterations suggests that persons with MCI exhibit deficits in several cognitive processes that include early attention, stimulus discrimination and classification, and updating and manipulation of information held in working memory.

A Behavioral and Electrophysiological Investigation of the Effect of Bilingualism on Lexical Ambiguity Resolution in Young Adults.

Previous research suggests that bilinguals demonstrate superior cognitive control processes than monolinguals. The goal of the current investigation was to examine whether this "bilingual advantage" is observed in a language processing task that requires inhibition, i.e., lexical ambiguity processing. Monolingual and bilingual participants read sentences that biased the reading of a terminal homonym toward the subordinate or dominant reading (e.g., The doctor asked her to step onto the scale.). A relatedness judgment was made on target words that were related to the contextually appropriate (e.g., balance) or inappropriate meaning (e.g., skin), or unrelated to either meaning (e.g., shoe) while electrophysiological recording took place. The results revealed subtle processing differences between monolinguals and bilinguals that were evident in electrophysiological measures, but not in behavioral measures. These findings suggest that monolinguals rely on context to access the contextually appropriate meaning of a homonym to a greater extent than bilinguals, while bilinguals demonstrate simultaneous activation of both meanings.

ERP measures of semantic richness: the case of multiple senses.

Semantic richness refers to the amount of semantic information that a lexical item possesses. An important measure of semantic richness is the number of related senses that a word has (e.g., TABLE meaning a piece of furniture, a table of contents, to lay aside for future discussion, etc.). We measured electrophysiological response to lexical items with many and few related senses in monolingual English-speaking young adults. Participants performed lexical decision on each item. Overall, high-sense words elicited shorter response latencies and smaller N400 amplitudes than low-sense words. These results constitute further evidence of the importance of semantic richness in lexical processing, and provide evidence that processing of multiple related senses begins as early as 200 milliseconds after stimulus onset.

Alterations in resting-state activity relate to performance in a verbal recognition task.

In the brain, resting-state activity refers to non-random patterns of intrinsic activity occurring when participants are not actively engaged in a task. We monitored resting-state activity using electroencephalogram (EEG) both before and after a verbal recognition task. We show a strong positive correlation between accuracy in verbal recognition and pre-task resting-state alpha power at posterior sites. We further characterized this effect by examining resting-state post-task activity. We found marked alterations in resting-state alpha power when comparing pre- and post-task periods, with more pronounced alterations in participants that attained higher task accuracy. These findings support a dynamical view of cognitive processes where patterns of ongoing brain activity can facilitate -or interfere- with optimal task performance.

Differences in verbal memory retrieval in breast cancer chemotherapy patients compared to healthy controls: a prospective fMRI study.

Cognitive complaints by breast cancer survivors receiving chemotherapy have led to an increasing interest in elucidating the possible causes of such impairment. Although a number of neuroimaging studies have been conducted, only a handful of them have taken into account cognitive status pre-chemotherapy. The current study included pre-chemotherapy and post-chemotherapy assessment. In addition, various factors such as depression, anxiety, fatigue and days since surgery were considered during analyses. Breast cancer patients performed an fMRI verbal recall task before and an average of 1 month after chemotherapy. Well matched controls also performed the task with a similar timeline. Pre-chemotherapy analyses revealed that patients activated the anterior cingulate less than controls during memory retrieval when anxiety and fatigue scores were added as covariates during group comparisons. In addition, there were also changes in brain activation from pre- to post-chemotherapy in patients but not in controls. Post-chemotherapy, patients had less activation in the bilateral insula, the left inferior orbitofrontal cortex and the left middle temporal gyrus. Finally, patients also showed significantly less activation when compared to controls. Brain regions included: the right middle and superior temporal gyrus, the right medial frontal gyrus, the right inferior orbitofrontal cortex, the left insula and left superior temporal pole. Importantly, depression, anxiety, and particularly fatigue accounted for some of brain activation differences. Our results suggest that chemotherapy in part plays a role in brain activation differences and it also highlights the importance of rigorously controlling for confounding variables. Only by controlling such factors can we understand the role that chemotherapy may play on cognition.