Development of the brain’s organization of working memory in young schoolchildren

In 7–8 and 9–10-years old children, we studied event-related potentials (ERPs) during paired comparison of non-verbalizable visuospatial stimuli presented at an interval of 1.5–1.8 s. Age-related differences were found in the involvement of various cortical areas in the formation and retention of a short-term memory trace of the reference stimulus and during comparison of the short-term trace with the test stimulus presented. In both age groups, working memory was associated with an elevation of the amplitude of the sensory-specific N1 component in the visual cortical areas. Age-related differences in the processing of sensory-specific characteristics of a stimulus were the greatest in the ERPs to the test stimulus: at the age of 9–10, the N1 component amplitude was significantly increased in all caudal leads and, in the occipital and inferior temporal leads, this component was preceded by P1 component. At this age, we observed the early involvement of the inferior frontal cortex, which was not observed at the age of seven. The increase in positivity over that area was observed in the interval of 100–200 ms. Substantial differences between age groups were found in the late ERP component corresponding to cognitive processes. At the age of 7–8, the presentation of both the reference and test stimuli causes the increase in the amplitude of the slow positive complex (SPC) in the caudal liads with the maximum enhancement found in the interval of 300–800 ms in the parietal leads. At the age of 9–10, the SPC increase, much like in adults, was observed in ERP to the test stimulus only. At this age, adult-like specific changes in the late phases of ERPs were observed in the fronto-central regions at the different stages of working memory. They are the increases in the negative N400 wave in the ERP to the reference stimulus and the SPC to the test stimulus. These data show that, at the age of 9–10, the functional organization of working memory of the adult type is formed; however, the extent to which the frontal cortex, and its dorsal regions in particular, is involved into working memory processes does not meet yet a definitive level.     

Age-related specificity of the processing of visual information in the system of working memory

In adults and seven- to eight-year-old children, event-related potentials (ERPs) were analyzed during quiet observation and detailed paired comparison of visual stimuli. In both age groups, we showed the differences in the initial stages (component N1) of sensory analysis in these situations. In adults, an increase in the negativity during the initial stages of analysis was observed in the caudal and central areas of the cortex during presentation of standard and test stimuli. In the frontal areas of the cortex, an increase in the negative potential was observed only in ERPs induced by the test stimulus. In children, an increase in the negativity at the initial phases of analysis of stimuli in the situation of working memory, as compared to quiet observation, was confined to the caudal areas of the cortex. Differential curves that characterize analysis of standard and test stimuli showed age-related differences in the initial and late phases of information processing under the conditions of working memory. In adults, the differential curves that characterize analysis of the standard stimulus were represented by negative phases, and the curves related to the test stimulus, by positive phases. In children, late phases of analysis of the standard and test stimuli had smaller differences as compared to adults: the late positive wave was predominant in the responses to both standard and test stimulus in the caudal areas of the cortex. In the frontal areas, there was no considerable increase in the amplitude of the late positive wave in response to the test stimulus. This fact, together with the absence of enhancement of initial negativity in the frontal areas, which reflects analysis of the test stimulus, indicates that the prefrontal cortex plays a smaller role in the comparison of the memory trace with the current information in seven- to eight-year-old children. The data obtained suggest that the central executive of working memory is not sufficiently mature in children aged seven to eight years.     

Organization of selective attention during preparation for the recognition of global and local characteristics of a visual stimulus in children with different levels of maturity of the regulatory brain systems

Event-related potentials (ERPs) evoked by key stimuli informing a subject about the forthcoming recognition of the global or local level of a hierarchical test figure were analyzed in 7-year-old children with different levels of maturity of the regulatory brain systems. Differences in both the initial ERP components P1, N1, and P2 (which reflect the analysis of the sensory characteristics and significance of a key stimulus) and the late components N3, Pc, and Nc (which reflect the preparation for the recognition of a subsequent test figure) were found. It was shown that, in children with frontal-thalamic regulatory system immaturity (FTRSI), the amplitude of the ERP component N1 is decreased in the caudal areas. In children with an immature bottom-up activation system, a decrease in the amplitude of initial ERP components in the caudal areas was observed in a broader time interval in components P1, N1, and P2. As compared to the control groups of children, in children with immature frontal-thalamic structures, components N3, Pc, and Nc were different in both the caudal and precentral areas. In children with immature lower brainstem activation structures, the late ERP components were different, predominantly, in the parietal and temporo-parieto-occipital areas. Comparison of ERPs in response to global and local key stimuli in children of the control group demonstrated a clear-cut temporal and topographical organization in the period of preparation for subsequent recognition of a prescribed level of the test stimulus: the earlier preparation stages were associated with component N3 in the parietal and temporo-parieto-occipital areas, whereas later stages were associated with Pc changes in the frontal areas. In children with FTRSI, changes in the late components in the caudal areas were poorly expressed and their topographical organization (characteristic of the control group) was absent; the involvement of the frontal areas in the late stages of the key stimulus analysis was restricted. These findings may give grounds to suggest the significance of the frontal-thalamic system in the organization of the response to an expected stimulus. In children with immature lower brainstem activation structures, the type of the key stimulus was reflected in the late ERP components in a diffuse way.     

Functional Organization of the Brain during the Operation of Working Memory

Event-related potentials (ERPs) recorded from various cortical areas during matching of two consecutive pictures were analyzed. Reflecting the process of trace fixation, the ERP to the reference stimulus was characterized by an increase in components P150 and P300 in the occipital and temporo-parieto-occipital areas and components N300 and N400 in the precentral areas as compared with the ERP elicited by the warning stimulus. The ERP to the test stimulus, which reflected trace retrieval and matching with current information, was characterized by a generalized increase in the late positive complex in the interval 300–600 ms. Similarity and/or dissimilarity of the test and reference stimuli was reflected in the parameters of the ERP to the test stimulus. The results testify to the difference in functional and topographic organization of the brain cortex at the initial and late stages of operation of the working memory.     

Differences in semantic event-related potentials in learning-disabled, normal, and gifted children.

Cortical event-related potentials (ERP) were recorded over FZ, CZ, and PZ scalp sites in 15 learning-disabled (LD), 14 gifted (G), and 13 normal control (N) children of ages 8-12. The common stimulus consisted of nouns presented 80 percent of the time; the target stimulus of animal names presented 20 per cent of the time. ERPs were averaged over subjects from 180 msec pre-stimulus to 900 msec post-stimulus. Principal components analysis was used to determine if there were amplitude differences at different post-stimulus latencies as a function of condition. Differences in ERP's between groups (LD, gifted, and controls), scalp locations, and common versus target stimuli were analyzed by ANOVAs. P3, Late, P2, and N1 components represented by four factors were identified. Significant differences between G and LD and the N and LD groups were found target stimulus at all central locations for the P3 component. Differences were found centrally between G and LD, G and N, and N and LD groups for the P2 component centrally. Other differences were found for the N1 and late components. These differences could be interpreted as a deficit in either attentional mechanisms or information processing for the LD group.     

Temporal and topographic characteristics of evoked potentials in the conflict of two consecutive visual stimuli in a working memory task

Behavioral reactions and brain mechanisms involved in processing two matching or mismatching (conflicting) visual stimuli were studied in healthy subjects (mean age 22.57 ± 0.46 years). Line orientations (vertical, horizontal, or 45°) were used as stimuli and were presented with an interval of 1500–1800 ms. The reaction time was shown to increase in the case of a conflict of two orientations as compared with matching orientations. The reaction time depended on the orientation of the reference stimulus and was minimal when a vertical line was used as a reference. An increase in N2 negativity (time window 200–280 ms) in the frontal and parietal cortical areas was identified as an informative indicator of a conflict between the current orientation and the orientation stored in working memory. The dipole sources of N2 were localized to the prefrontal cortex (middle frontal gyrus, frontal pole, and pars orbitalis). The N2 amplitude was found to depend on the orientation of the first stimulus in a pair, being higher in the case of a 45° orientation. The visual areas were shown to play a role in detecting a conflict of two consecutive signals because the early sensory components increased in amplitude. The results implicate cortical structures, including the sensory-specific visual, parietal, and prefrontal areas, in comparing consecutive visual signals and detecting their conflict.     

Developmental changes in the mechanisms of image classification in young schoolchildren with different cognitive styles

Testing of 7- to 8- and 9- to 10-year-old children with the matching familiar figures test revealed groups of children differing in the time and accuracy of the reaction of choice from several alternatives. Classification of simple images and images with additional information congruous with the main discriminative character improved with age in children without evident signs of reflectivity or impulsivity (the main group) and in reflective children. No significant improvement was revealed in impulsive children. Developmental changes in the event-related potentials during image classification differed in character and location in children with different styles of cognitive activity. In the children of the main group and in the reflective children, the developmental changes consisted of an increase in the amplitude of the late positive complex predominantly in the caudal areas of both brain hemispheres. In the impulsive children, in the age period from 7–8 to 9–10 years, the late negative component N350 became more distinct, especially in the left hemisphere, and substantial reorganization of the involvement of the frontal areas in the classification process took place. The opposite electrophysiological changes in children with different cognitive styles testify to different developmental changes in the mechanisms of visual recognition.Translated from Fiziologiya Cheloveka, Vol. 31, No. 1, 2005, pp. 15–23.Original Russian Text Copyright © 2005 by Beteleva, Petrenko.     

Mechanisms of selective attention in adults and children as reflected by evoked potentials to warning stimuli

Components of evoked potentials to stimuli differing in size and warning about the necessity of subsequent recognition of an image at the global or local level were analyzed to identify the specific features of selective attention in adults and seven-year-old children. In both age groups, components were found that were related to selective attention aimed at processing a warning stimulus (the P1, N1, and P2 components) and producing a response to the subsequent test stimulus. Both age groups exhibited similar dependences of changes in the P1 component (40–110 and 110–220 ms in the adults and children, respectively) on the type of the warning stimulus. The children displayed a greater increase in the amplitude of the P1 component of the response to the global versus the local key than the adults did. The P1 component is suggested to reflect not only the sensory features of the stimulus but also the selective attention associated with its sensory processing. The amplitude of the P2 component of the response to the global key (190–240 and 330–410 ms in the adults and children, respectively) was higher in both age groups. This component is believed to indicate evaluation of the signal importance of the warning stimulus. In the adults, late components of event-related potentials (ERPs), i.e., P3-N3 (300–450 ms), were associated with the global or local level of recognition of a test hierarchical stimulus that was presented after the key, with the greatest differences in the central and posterior associative areas of the right hemisphere and in the frontocentral areas of the left hemisphere. In the children, the N3 component (530–600 ms) in the left parietal area, as well as the late ERP phases, i.e., Ps (680–950 ms) and Ns (1030–1130 ms), during which the frontal cortical areas are involved in preparing the subsequent response, was shown to depend on the type of the warning stimulus.     

Functional organization of working memory in seven- to eight-year-old children

Event-related potentials (ERPs) were analyzed during the operation of working memory (WM) using short-term traces of visuospatial and letter stimuli. A comparison of the two stimuli presented at an interval of about 1500 ms showed differences in the degree and mode of the involvement of the cortical areas during the formation and retention of a short-term memory trace (the first stimulus in the pair) and its comparison with the current information (the second stimulus in the pair). At the stage of trace formation, a significant increase was observed in the amplitudes of the components of the ERPs generated during the analysis and processing of sensory-specific information: visuospatial stimuli caused an increase in the N200 component in the O ₁, O ₂, T ₅, T ₆, P ₃, and P ₄ derivations; and letter stimuli caused an increase in the P200 component in the F ₃, F ₄, F ₇, F ₈, C ₃, C ₄, P ₃, P ₄, T ₃, and T ₄ derivations. The amplitude of the slow positive complex (SPC) significantly increased in the caudal cortical areas, which is not true for adults at this stage of the operation of WM. During a comparison of short-term memory traces with current information, the SPC amplitude significantly increased in the caudal cortical areas in seven- to eight-year-old children; the prefrontal cortex was not involved at this stage of the operation of WM. These findings testify to the insufficient maturity of the central executive of WM at an age of seven to eight years.     

Role of the Frontal Cortical Areas in the Analysis of Visual Stimuli at Conscious and Unconscious Levels

Event-related potentials (ERP) in response to complex target stimuli, which consisted of a central recognizable picture and a lateral masked image (analyzed at the unconscious level) were recorded in adult subjects and seven-year-old children. ERP components N200, N300, and P400/N400 had different topography and were differently pronounced in adults and children. In adult subjects, the N200 component that reflects the processing of a sensory stimulus was recorded in the temporo-parieto-occipital and occipital areas. In children, N200 was recorded in the caudal regions and the frontal areas of the cortex. Analysis of different waveforms obtained by subtraction of the ERP to the central stimulus from the ERP to the complex stimulus showed that unconscious stimulus processing in adult subjects is not reflected in the ERP structure. In children, an unconsciously processed image incorporated into a complex stimulus evokes processing negativity in the occipital and frontal cortical areas. Comparison of ERP in groups of children divided by their reflectivity/impulsivity showed that, predominantly, the left frontal area is involved in image analysis at the unconscious level in reflective children and, predominantly, the right frontal area participates in unconscious image analysis in impulsive children. It is suggested that the perfection of the visual recognition of a target stimulus, which contains additional unconsciously processed information, consists in growth of the involvement of the left-hemispheric mechanisms (with respective growth of significance of the left-hemispheric mechanisms) and in a decrease in the role of the frontal areas in analysis of sensory information.     

Amplitude modulation of steady-state visual evoked potentials by event-related potentials in a working memory task

Previous studies have shown that the amplitude and phase of the steady-state visual-evoked potential (SSVEP) can be influenced by a cognitive task, yet the mechanism of this influence has not been understood. As the event-related potential (ERP) is the direct neural electric response to a cognitive task, studying the relationship between the SSVEP and ERP would be meaningful in understanding this underlying mechanism. In this work, the traditional average method was applied to extract the ERP directly, following the stimulus of a working memory task, while a technique named steady-state probe topography was utilized to estimate the SSVEP under the simultaneous stimulus of an 8.3-Hz flicker and a working memory task; a comparison between the ERP and SSVEP was completed. The results show that the ERP can modulate the SSVEP amplitude, and for regions where both SSVEP and ERP are strong, the modulation depth is large.     

Neurophysiological mechanisms of recognition fragmented images in 5 to 6-year-old children

Behavioral indices and ERP parameters were analyzed in 5-6 years old children who were shown a previously unseen set of fragmented drawings of familiar objects. Within this set, each object was represented by a series of drawings of different degree of fragmentation. It is found that children of 5-6, when compared to 7-8 years old children, are capable to recognize less fragmented drawings. In these children, no increase was found in N350-400 prefrontal negativity and late positive complex, otherwise a typical feature of mature recognition involving executive control. A comparison of ERP for recognized vs. unrecognized stimuli showed a significant increase in P300 and N400 amplitude over the right occipital area. A key feature of children of this age is a lack of significant difference between ERP to recognized vs. unrecognized stimuli over extrastriatal cortex (T5/T6) which is the crucial structure for recognition of fragmented objects via integration of their sensory features. The data we obtained suggest that both executive control immaturity and insufficient involvement of the ventral visual system constitute a specifics of recognition in children of 5-6.     

Ontogenetic characteristics of the development of slow negative and positive potentials during the performance of a visual perceptive task

In age aspect, topography and parameters were studied of late EPs and slow negative components (CNV) to successively presented visual stimuli: the preliminary signal and two compared contour images. Age characteristics of development of the frontal negativity N450 and the late positive complex (LPC) were revealed. in children 7 and 10 years old, the component N450 was present in response both to the preliminary and the first stimulus in the compared pair; LPC was recorded to all three presented visual stimuli. In 17 years old subjects and in adults, selectivity of N450 formation in the EP to the first of the compared stimuli and LPC to the second (imperative) stimulus correlates with involvement of rostral brain areas--central in youths, central and frontal ones in adults--both in the process of waiting (CNV) and evaluation of coming information (LPC).     

Event-related potentials associated with a shift in the strategy of visual perception during recognition of a hierarchical stimulus

Recording of event-related potentials (ERPs) was used to study the brain mechanisms of shifting the strategy of recognition of the global and local levels of a hierarchical image by adult subjects. A shift in the strategy of visual recognition results in substantial changes in ERP parameters in the caudal and frontocentral cortical areas. The activation effect of the switchover from one recognition strategy to another is associated with an increase in the amplitude of early ERP components (C1, P100, and N150) of the caudal cortical areas. Changes in the late ERP components associated with processing of significant information features during the shift in the recognition strategy are observed in the frontal areas within the interval 388–579 ms, with the amplitude of components N300 and N400 increasing.     

Brain organization of the recognition of fragmented images in subjects who show different levels of task performance success

We studied the behavioral and EEG changes in healthy adults during recognition of fragmented images presented in a series beginning with a low fragmentation level up to a complete figure. Our sample was divided into two groups according to the recognition success. The first group made few mistakes. The other group made significantly more mistakes compared to the first group; this group had a shorter reaction time and a lower recognition threshold (i.e., the fragmentation level at which the object became recognizable). The ERP analysis showed the statistical dependence between the recognition success and the involvement of the frontal and caudal cortical areas. Compared to the second group, in the first one, we found no significant association between the recognition process and either early or late ERP components in the dorsolateral prefrontal cortex and found an increase of sensory-specific components P1 and P2 in the caudal areas. These results support the hypothesis on the impact of the prefrontal cortex on the successfulness of recognition of fragmented images.     

Differences in semantic event-related potentials in learning-disabled,normal, and gifted children

Cortical event-related potentials (ERP) were recorded over FZ, CZ, and PZ scalp sites in 15 learning-disabled (LD), 14 gifted (G), and 13 normal control (N) children of ages 8–12. The common stimulus consisted of nouns presented 80 percent of the time; the target stimulus of animal names presented 20 per cent of the time. ERPs were averaged over subjects from 180 msec pre-stimulus to 900 msec post-stimulus. Principal components analysis was used to determine if there were amplitude differences at different post-stimulus latencies as a function of condition. Differences in ERP's between groups (LD, gifted, and controls), scalp locations, and common versus target stimuli were analyzed by ANOVAs. P ₃ , Late, P ₂ , and N ₁ components represented by four factors were identified. Significant differences between G and LD and the N and LD groups were found target stimulus at all central locations for the P ₃ component. Differences were found centrally between G and LD, G and N, and N and LD groups for the P ₂ component centrally. Other differences were found for the N ₁ and late components. These differences could be interpreted as a deficit in either attentional mechanisms or information processing for the LD group.     

Event-related potentials at different stages of the operation of visual working memory

Trace fixation and comparison with incoming information was studied using event-related potentials (ERPs) recorded from various cortical areas during passive viewing and matching of two consecutive pictures. Visual stimuli differing in the spatial location of elements (4 × 4 square patterns with random positions of 4 black and 12 white squares) and phonological stimuli (differently written letters) were used. Trace fixation was studied by comparing the ERPs generated in response to the first (reference) stimulus in the pair with those generated during passive viewing. Sensory analysis of the reference stimuli was observed in the time interval 128–196 ms. For the patterns presented, it was reflected by an increased amplitude of the N1 component in the caudal areas as compared with passive viewing. The phonological stimuli produced a higher amplitude of a positive wave in the frontotemporal area in the same time interval. Processing of subsequent information to be stored in memory was observed in the interval 232–452 ms. Processing of patterns was reflected by a decreased positivity, most pronounced in the left temporo-parieto-occipital area. Comparison of a trace with incoming information was studied by comparing the ERPs generated in response to the first (reference) and second (test) stimuli. The number of cortical areas involved in the sensory analysis of the test stimuli was larger than the number involved in the analysis of the reference stimuli. Comparison of the new information with the trace was reflected by an increased amplitude of the late positive wave (components P3, Pc, and Pc-Nc) in the frontocentral and caudal cortical areas. The topographic changes in the late positive components depended on the type of stimulus.     

Event-related Potential Study of Novelty Processing Abnormalities in Autism

To better understand visual processing abnormalities in autism we studied the attention orienting related frontal event potentials (ERP) and the sustained attention related centro-parietal ERPs in a three stimulus oddball experiment. The three stimulus oddball paradigm was aimed to test the hypothesis that individuals with autism abnormally orient their attention to novel distracters as compared to controls. A dense-array 128 channel EGI electroencephalographic (EEG) system was used on 11 high-functioning children and young adults with autism spectrum disorder (ASD) and 11 age-matched, typically developing control subjects. Patients with ASD showed slower reaction times but did not differ in response accuracy. At the anterior (frontal) topography the ASD group showed significantly higher amplitudes and longer latencies of early ERP components (e.g., P100, N100) to novel distracter stimuli in both hemispheres. The ASD group also showed prolonged latencies of late ERP components (e.g., P2a, N200, P3a) to novel distracter stimuli in both hemispheres. However, differences were more profound in the right hemisphere for both early and late ERP components. Our results indicate augmented and prolonged early frontal potentials and a delayed P3a component to novel stimuli, which suggest low selectivity in pre-processing and later-stage under-activation of integrative regions in the prefrontal cortices. Also, at the posterior (centro-parietal) topography the ASD group showed significantly prolonged N100 latencies and reduced amplitudes of the N2b component to target stimuli. In addition, the latency of the P3b component was prolonged to novel distracters in the ASD group. In general, the autistic group showed prolonged latencies to novel stimuli especially in the right hemisphere. These results suggest that individuals with autism over-process information needed for the successful differentiation of target and novel stimuli. We propose the potential application of ERP evaluations in a novelty task as outcome measurements in the biobehavioral treatment (e.g., EEG biofeedback, TMS) of autism.     

Functional brain organization of global and local visual perception: an ERP study

Adult subjects were asked to recognize a hierarchical visual stimulus (a letter) while their attention was drawn to either the global or local level of the stimulus. Event-related potentials (ERP) and psychophysical indices (reaction time and percentage of correct responses) were measured. An analysis of psychophysical indices showed the global level precedence effect, i.e., the increase in a small letter recognition time when this letter is a part of incongruent stimulus. An analysis of ERP components showed level-related (global vs. local) differences in the timing and topography of the brain organization of perceptual processing and regulatory mechanisms of attention. Visual recognition at the local level was accompanied by (1) stronger activation of the visual associative areas (Pz and T6) at the stage of sensory features analysis (P1 ERP component), (2) involvement mainly of inferior temporal cortices of the right hemisphere (T6) at the stage of sensory categorization (P2 ERP component), and (3) involvement of prefrontal cortex of the right hemisphere at the stage of the selection of the relevant features of the target (N2 ERP component). Visual recognition at the global level was accompanied by (1) pronounced involvement of mechanisms of early sensory selection (N1 ERP component), (2) prevailing activation of parietal cortex of the right hemisphere (P4) at the stage of sensory categorization (P2 ERP component) as well as at the stage of the target stimulus identification (P3 ERP component). It is suggested that perception at the global level of the hierarchical stimulus is related primarily to the analysis of the spatial features of the stimulus in the dorsal visual system whereas the perception at the local level primarily involves an analysis of the object-related features in the ventral visual system.     

Can You Catch a Liar? How Negative Emotions Affect Brain Responses when Lying or Telling the Truth

The capacity to deceive others is a complex mental skill that requires the ability to suppress truthful information. The polygraph is widely used in countries such as the USA to detect deception. However, little is known about the effects of emotional processes (such as the fear of being found guilty despite being innocent) on the physiological responses that are used to detect lies. The aim of this study was to investigate the time course and neural correlates of untruthful behavior by analyzing electrocortical indexes in response to visually presented neutral and affective questions. Affective questions included sexual, shameful or disgusting topics. A total of 296 questions that were inherently true or false were presented to 25 subjects while ERPs were recorded from 128 scalp sites. Subjects were asked to lie on half of the questions and to answer truthfully on the remaining half. Behavioral and ERP responses indicated an increased need for executive control functions, namely working memory, inhibition and task switching processes, during deceptive responses. Deceptive responses also elicited a more negative N400 over the prefrontal areas and a smaller late positivity (LP 550–750 ms) over the prefrontal and frontal areas. However, a reduction in LP amplitude was also elicited by truthful affective responses. The failure to observe a difference in LP responses across conditions likely results from emotional interference. A swLORETA inverse solution was computed on the N400 amplitude (300–400 ms) for the dishonest – honest contrast. These results showed the activation of the superior, medial, middle and inferior frontal gyri (BA9, 11, 47) and the anterior cingulate cortex during deceptive responses. Our results conclude that the N400 amplitude is a reliable neural marker of deception.