Rocío A. López Zunini

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.

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

Deficits in executive function are highly noticeable in Alzheimers 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.

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 subjects 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.

Implementation of a Brain Training Pilot Study For People With Mild Cognitive Impairment

Objective A pilot study to determine the feasibility of recruiting patients with MCI to test for cognitive interventions. Method Thirty patients with amnestic MCI were to be divided into two intervention arms and one control group. Participants went to local sites and completed brain training for one hour three times per week for nine weeks. Outcome measures were: recruitment, computer abilities, compliance, task performance, neuropsychological tests, and electroencephalography. Results After six months, only 20 participants had been recruited. Seventeen were allocated to one of the two intervention groups. Compliance was good and computer skills were not an obstacle. Participants improved their abilities in the modules, but there were no statistically significant changes on neuropsychological tests or EEG. Conclusions Recruitment of MCI participants for extensive cognitive intervention is challenging, but achievable. This pilot study was not powered to detect clinical changes. Future trials should consider recruitment criteria, intervention duration, scheduling, and study location.

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.

EEG/ERP: Within Episodic Assessment Framework for Cognition

This work explores the potential for electroencephalography (EEG)-based event-related potential (ERP) measurements to be included in the framework for episodic assessment. In current discrete clinical cognitive assessment methods used to diagnose mild cognitive impairment (MCI)/dementia, physicians see patients annually or biannually. They rely on patient’s history and clinical cognitive assessments to identify changes in memory or functional ability as indications of MCI/dementia in conjunction with exclusionary tests. They are limited in these discrete assessments by their accuracy and infrequent occurrence. The episodic assessment framework proposed will allow better ongoing information about the true well-being of the patient through assessment of memory and functional cognitive ability on a weekly or even daily basis between appointments. This paper identifies features of EEG/ERP measurements during Neuropsychological Behavioral Testing that could allow the future inclusion in the framework using now available consumer EEG devices. A pilot group of 32 participants (17 healthy, 15 MCI) was studied using a 1-back test, while their brain activity was measured using EEG. Features of the ERP thus generated were identified and measured. These ERP features and associated behavioral measurements from the 1-back test were analyzed to identify features both alone and in combination that allowed the correct classification of the participants using a repeated leave-one-out train and test method. A feature pair (1-back response time and CPz correlation) was identified that provides the best two-feature performance (1 false positive/1 false negative error) with a third feature (response required – Pz P1 to N1 latency) providing additional improvement. Given these results, it is possible that episodic ERP measurements may help with cognitive impairment diagnosis in the future.

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.

EVOKED RESPONSE POTENTIALS: WHICH FEATURES HELP DISTINGUISH MCI FROM HEALTHY CONTROLS?

and region-specific progression of neuropathology. Additionally, synaptic dysfunction is evident in early development of pathology. However, there is no consensus about the extent to which basal synaptic transmission (BST) and synaptic plasticity are affected in these models.Methods:We used extracellular field potential recordings to study BST, short-term plasticity (PTP, post-tetanic potentiation; PPF, paired-pulse facilitation) and long-term potentiation (LTP) at the Schaffer collateral-CA1 pyramidal cell synapses in young and old rTg4510 (2-3 and 6-7 month old) and old APP/ PS1 mice (8-10 month old). Results:We find that old but not young rTg4510 mice exhibit a correlated reduction in pre-synaptic fiber volley (FV) amplitude (w50%) and field excitatory post-synaptic potential (fEPSP) slope (w40%) compared to WT, consistent with hippocampal neurodegeneration. We also find that BST per se is not altered in this model, since fEPSP slope, controlled for FV amplitude, remained unchanged. In contrast, old APP/PS1 mice did not show reduced FV amplitude compared to WT, while fEPSP slope was reduced by w34%, suggesting a deficit in BST. PTP was reduced in old APP/PS1 mice compared to WT, but not in old rTg4510 mice. PPF was unchanged in old APP/PS1 compared to WT, but was reduced in old rTg4510 mice. LTP, induced with high-frequency stimulation, was reduced in old rTg4510 and APP/PS1 mice. Conclusions: Our data suggest that APP/PS1 mice show reduced BST. In rTg4510 mice, early onset of neurodegeneration may mask BST dysfunction. However, PPF was reduced in rTg4510 mice suggesting some pre-synaptic alteration in remaining neurons. In APP/PS1 mice LTP reduction may be due to induction deficits, since they exhibit both reduced BST and PTP. The basis of the LTP deficit in rTg4510 mice remains unclear.

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.