Juan Silva-Pereyra

N400 during lexical decision tasks: a current source localization study

OBJECTIVE Our primary aim in the present study was to establish the anatomic and psychophysiological correlates of automatic and controlled semantic priming. METHODS Current sources were calculated on N400 component data from a previous study on lexical decision tasks [Clin Neurophysiol 1999;110:813] using the variable resolution electromagnetic tomography method (VARETA). In this study, two experiments were carried out, one using directly related pairs and the other one using mediated related pairs. Each experiment consisted of 3 tasks that required different levels of contribution from controlled processes. RESULTS Average source localization images showed the brain structures involved in lexical decision tasks. The automatic component of the N400 effect was related to activation of occipitotemporal and parahippocampal gyri and anterior temporal lobes bilaterally. The expectancy strategy was related to activation of the right posterior temporal and right frontal areas. The postlexical strategy was associated with activation of right frontal, anterior cingulate and bilateral superior parietal areas. CONCLUSIONS The findings indicated that the current sources of the N400 varied according to the relative contributions of automatic and controlled mechanisms. Moreover, the sources of the N400 effect depended on the type of strategy used.

Specific EEG frequencies at specific brain areas and performance.

In this study it was shown that in adults, the frequency characteristics of EEG preceding stimuli that were followed by incorrect responses were different from the characteristics of EEG preceding stimuli that were followed by correct responses. In the recording during three different tasks that explore different neuronal networks, higher values of current preceding incorrect performance in those areas directly related to the task were found in frequencies within the delta (1.56 and 3.12 Hz) and beta bands (13.26, 14.04, 14.82, 15.6, 17.16 and 17.94 Hz), suggesting that these frequencies signal inhibition. Frequencies within the alpha band (9.36 and 12.48 Hz) showed greater energy preceding correct responses in task-specific areas, supporting previous results observed in children.

Are poor readers semantically challenged? An event-related brain potential assessment

This study explores visual event-related potentials components in a group of poor readers (PRs) and control children who carried out figure and word categorization tasks. In both tasks, every child had to categorize between animal and non-animal stimuli in an odd-ball GO-GO paradigm. During the word categorization task, PRs presented longer reaction times, a poorer performance, longer and larger P2 amplitudes, and smaller amplitudes and longer P300 latencies than controls. There were no differences in the N400 component between groups. These results suggest that semantic processing underachievement in PRs may not be a semantic deficit per se, but the late reflection of an early word codification problem, deficient use of attentional resources and lack of target identification during reading.

Principal Component Analyses and Scalp Distribution of the Auditory P150–250 and N250–550 to Speech Contrasts in Mexican and American Infants

We report a Principal Component Analysis (PCA) and the scalp distribution of the normalized peak amplitude values for speech-related auditory Event-related Potentials (ERP) P150–250 and N250–550 in 7-, 11-, and 20-month-old American infants learning English and in 10–13-month-old Mexican infants learning Spanish. After assessing the infant auditory ERP P-N complex using PCA, we evaluated the topographic distribution of each of the discriminatory phases to native and non-native CV-syllabic contrasts used in Spanish and English. We found that the first two Principal Components for each contrast type across ages showing a maximization of differences between the P150–250 and the N250–550 waves, explain more than 70% of the variance. The scalp distributions of the P150–250 and N250–550 components also differed, the P150–250 showing a frontal and anterior temporal distribution, and the N250–550 a more posterior distribution. The older infants showed a broader distribution of responses, particularly for the N250–550. There were no differences in the topographies of the components between same-aged Mexican and American infants. We discuss the perceptual/linguistic functions that each component may reflect during development and across the two cultures.

Grammatical Processing without Semantics? An Event-related Brain Potential Study of Preschoolers using Jabberwocky Sentences

Behavioral studies have demonstrated that children develop a nearly adult-like grammar between 36 and 42 months, but few studies have addressed how the childs brain processes semantic versus syntactic information. In previous research, Silva-Pereyra and colleagues showed that distinct event-related potentials (ERPs) are elicited by semantic and syntactic violations in sentences in children as young as 30, 36, and 48 months, following the patterns displayed by adults. In the current study, we examined ERPs to syntactic phrase structure violations in real and jabberwocky sentences in 36-month-old children. Jabberwocky sentences are sentences in which content (open-class) words are replaced by pseudowords while function (closed-class) words are retained. Results showed that syntactically anomalous real sentences elicited two positive ERP effects: left-distributed effects from 500 to 750 msec and 1050 to 1300 msec, whereas syntactically anomalous jabberwocky sentences elicited two negative ERP effects: a left-distributed effect from 750 to 900 msec and a later broadly distributed effect from 950 to 1150 msec. The results indicate that when preschoolers process real English sentences, ERPs resembling the positive effects previously reported for adults are noted, although at longer latencies and with broader scalp distributions. However, when preschoolers process jabberwocky sentences with altered lexical-semantic content, a negative-going ERP component similar to one typically associated with the extraction of meaning is noted.

Poor reading skills may involve a failure to focus attention

A source localization analysis was carried out to provide brain functional and structural assessments of individuals with poor reading skills. Standardized low-resolution brain electromagnetic tomography was used to locate sources of P2 and P3 event-related potential components in normal readers and in poor reader children performing a cued continuous performance task. Cue-elicited P2 sources in the right superior parietal gyrus were smaller in 37 poor readers than in 40 normal readers. Poor readers showed a higher P3 activation in response to a false target in frontal and frontorbital regions than normal readers. These results suggest that reading disabilities may be attributed to failures in attentional focalization for incoming stimuli.

Phonological processing in Parkinson's disease: a neuropsychological assessment.

Patients with Parkinson’s disease (PD) have cognitive deficits that cause functional impairments across several domains, including language. There is experimental evidence that basal ganglia and frontostriatal circuits are implicated in phonological processing, which leads to the hypothesis that a dysfunction of these circuits could be expressed behaviorally as phonological deficiencies in patients with PD. Using neuropsychological assessments, the present study aimed to explore the phonological processing abilities of patients in the initial stages of PD while controlling for other cognitive processes. The results showed lower scores in patients with PD on phonological tests with respect to a control group and these differences were independent of processes such as attention/working memory, long-term memory, thinking, and verbal language comprehension. However, there was an association between phonological skills and reading comprehension abilities. This finding implies a specific phonological deficit in terms of word reading.

Brain potentials in response to native and non‐native speech contrasts in 11‐month‐old American infants

Behavioral studies show that 6‐ to 8‐month‐old infants discriminate both native and non‐native phonetic differences, but that by 10–12 months of age, infants’ perceptual sensitivities decline to many non‐native contrasts. Kuhl et al. (1997) and Tsao et al. (2000) have also shown an enhancement in sensitivity to native contrasts, which was also shown by Cheour et al. (1998) using electrophysiological methods. Using both behavior and ERPs, Rivera‐Gaxiola et al. (2000) reported MMNs in native English speaking adults for a non‐native contrast that the same adults did not overtly discriminate. We here report auditory ERPs to native and non‐native VOT contrasts in 11‐month‐old monolingual American infants (N=16). Stimuli were presented as a double‐oddball paradigm. Continuous EEG was recorded using electrocaps. ERPs were obtained off‐line using standard methods. The results show that 11‐month‐olds display differential brain activity for native and non‐native contrasts. A clear, widely distributed phonetic MMN c...

Two Different Populations within the Healthy Elderly: Lack of Conflict Detection in Those at Risk of Cognitive Decline

During healthy aging, inhibitory processing is affected at the sensorial, perceptual, and cognitive levels. The assessment of event-related potentials (ERPs) during the Stroop task has been used to study age-related decline in the efficiency of inhibitory processes. Studies using ERPs have found that the P300 amplitude increases and the N500 amplitude is attenuated in healthy elderly adults compared to those in young adults. On the other hand, it has been reported that theta excess in resting EEG with eyes closed is a good predictor of cognitive decline during aging 7 years later, while a normal EEG increases the probability of not developing cognitive decline. The behavioral and ERP responses during a Counting-Stroop task were compared between 22 healthy elderly subjects with normal EEG (Normal-EEG group) and 22 healthy elderly subjects with an excess of EEG theta activity (Theta-EEG group). Behaviorally, the Normal-EEG group showed a higher behavioral interference effect than the Theta-EEG group. ERP patterns were different between the groups, and two facts are highlighted: (a) the P300 amplitude was higher in the Theta-EEG group, with both groups showing a P300 effect in almost all electrodes, and (b) the Theta-EEG group did not show an N500 effect. These results suggest that the diminishment in inhibitory control observed in the Theta-EEG group may be compensated by different processes in earlier stages, which would allow them to perform the task with similar efficiency to that of participants with a normal EEG. This study is the first to show that healthy elderly subjects with an excess of theta EEG activity not only are at risk of developing cognitive decline but already have a cognitive impairment.

Preattentive language effects in bilinguals.

Event related potentials (ERPs) were recorded from Spanish‐English bilinguals (N=11) to test if their pre‐attentive speech discrimination changes depending on the language they are using at the moment. ERPs were recorded in two language contexts (i.e., participants silently read magazines in the language of interest). Two speech contrast conditions were recorded in each language context. In the unique to English condition, the speech sounds represented two different sounds for the English language, but represented the same sound for the Spanish language. In the unique to Spanish condition, the speech sounds represented two different sounds for the Spanish language, but represented the same sounds for the English language. We expected that bilinguals in the unique to English condition would pre‐attentively discriminate the sound during the English language context, but not during the Spanish language context. The opposite was expected for the unique to Spanish condition. A monolingual control group (N=9) w...