Angélica Flores

Fronto-parietal networks activation during the contingent negative variation period.

The preparation for stimuli and responses in which the position and required finger to respond are cued, produces the preparatory activation of the specific neural resources that are going to be needed for the completion of the task. The focus of the present report is to evaluate if the fronto-parietal networks activated in fMRI studies during endogenous attention are also activated during the CNV period using EEG recording. The behavioural responses and 64 EEG channels were recorded during an S1-S2 paradigm similar to Posner central cue paradigms. The LORETA analysis based in the averaging of the z-LORETA values showed that the Brodmanns areas with the highest activation during the CNV period were in the medial and superior frontal areas, fronto-parietal lateral areas (including the premotor cortex) and extrastriate visual cortex. These results suggest that in addition to the previously described activation in premotor-motor, posterior sensory and superior and medial frontal areas, the activation of fronto-parietal networks is a main contributor to the CNV, indicating the endogenous attentional effort during the CNV period.

Wavelet analysis of the EEG during the neurocognitive evaluation of invalidly cued targets.

In a spatial central cueing paradigm, positions in the horizontal meridian were cued to evaluate the neurocognitive processing of validly (V) and invalidly cued (I) targets. ERPs were obtained from 20 EEG channel recordings. Complex Morlet wavelets were applied for computing event-related spectral power (ERSP) modulations and inter-trial phase coherence (ITC). P3a and P3b responses were increased in a statistically significant manner in I targets with regard to V targets. This increase seems to be generated only by phase resetting without enhancement of spectral power. Comparing ERSP modulations between I and V target trials we found a major effect centred in the alpha range. The following results were obtained for invalid condition in relation to valid condition: 6-12Hz ERSP decrease topographically widespread over the scalp, starting around 450 ms and peaking around 650 ms; 10-14Hz ERSP increase peaking around 200 ms at fronto-central electrodes; and 10-14Hz ERSP decrease occurring from 400 to 600 ms at posterior electrodes. Therefore, the invalidity effect indeed produces salient changes in the stimulus related and ongoing neuronal activity leading to a brain state of comparative higher activity both excitatory and inhibitory with respect to the validly cued target processing.

Development of preparatory activity indexed by the contingent negative variation in children

OBJECTIVES The present study investigated the effect of age on task-specific preparatory activation induced by a spatial cue using the central cue Posners paradigm. The behavioral responses and the contingent negative variation (CNV) generated between S1 (the warning stimulus) and S2 (the imperative stimulus) were compared between 16 healthy children (8-13 years old) and 17 healthy young adults (18-23 years old). METHODS The EEG was recorded from 20 scalp sites of the International 10-20 system. The complete trial period included a central directional cue that was on for 300 ms and an attentive waiting period lasting 1360 ms. Finally, a peripheral target appeared, subtending a visual angle of 4.56 degrees and situated 2.28 degrees eccentrically in the horizontal meridian. The early and late components of the CNV appearing in the period between cue and target were analyzed. RESULTS The CNV of children showed no contralateral cortical activation related to motor preparation. However, the young adults showed contralateral activation to the cue over motor areas. Both children and young adults showed cortical activation in posterior sensory areas, displaying a pattern of activation contralateral to the cue. Also, a positive parietal component appeared in children during the CNV period. CONCLUSIONS These results suggest that the motor preparation system in children is less mature than the sensory preparatory system. The children may have used strategies and brain areas different from those of the young adults to prepare for stimuli and responses.

P3a and P3b components associated to the neurocognitive evaluation of invalidly cued targets.

The present report focuses on evaluating the neurocognitive consequences of the correct or incorrect spatial prediction induced by a spatial cue. Positions in the vertical meridian were cued in order to evaluate the cognitive consequences in the processing of the validly (VC) or invalidly cued (IC) targets. The behavioural responses and the 64 EEG channel were recorded. The late endogenous event-related potential (ERP) induced by target stimuli in VC and IC targets were compared in voltage amplitude, voltage and current source density topographies. The P3a and a late positive complex, possibly P3b were increased in a statistically significant manner in the IC targets with regard to the VC targets. The previous result suggests that subjects prepare to accomplish the task upon specification of the cue, and when the IC target appeared it is treated as a low probability stimulus in a similar manner to deviant stimuli in odd-ball paradigms.

Evaluation of spatial validity–invalidity by the P300 component in children and young adults

The influence of cerebral maturity on the neurocognitive evaluation of target stimuli that have been cued by a spatial directional central cue, which, validly or invalidly, indicates the spatial position of the upcoming target has been investigated. ERPs and behavioural responses were recorded in 18 children and 20 young adults. P3a and P3b amplitudes were analyzed in the valid and invalid trials to assess possible differences between children and young adults. Young adults showed more activation in anterior (P3a) and posterior (P3b) areas in the invalid than the valid condition, whereas children only showed greater activation in P3b. This may be due to the later maturation of the frontal cortex than the more posterior sites. Children also showed a greater P3 component amplitude and a topography shifting to occipital sites, irrespective of the experimental condition.

Increased Brain Activation During the Processing of Spatially Invalidly Cued Targets

In a spatial central cue Posner´s paradigm, positions in the vertical meridian were cued in order to evaluate the neuro-cognitive consequences in the processing of validly cued (VC) and invalidly cued (IC) targets. Sixty-four EEG channels were recorded and analyzed showing that IC targets produced an enhanced P3 component with respect to VC targets. With the purpose of reinforcing the idea of increased activation during IC targets and to define the areas in which the increased activation would occur, source localization was applied to the ERPs. LORETA and single dipole localization showed that the early P3 presented a localization in the dorsal part of the anterior cingulate cortex (dACC), while the late P3 was fitted by single dipole more posterior than the early P3, and LORETA added a source in the parahippocampal gyrus in addition to the already activated dACC. LORETA results also showed a differential activation of the inferior frontal gyrus when IC targets were processed. The previous results suggest that subjects prepare to accomplish the task upon specification of the cue. Therefore, when the IC target appears, it induces the activation of the frontal cortex including areas related to the conflict monitoring system and to the processing of unexpected events. The IC targets also induce the revision of internal models about the task, possibly by activation of the temporo-mesial surface. All the obtained current source differences indicate that a higher brain activation during IC trials with respect to VC trials occurs.

Alpha reduction and event-related potentials, theta and gamma increase linked to letter selection

We examined evoked and induced modulations in theta, alpha and gamma oscillations, and also the P2 and late positive component of event-related potentials, during a visual discrimination task with target and nontarget letters. Results for target letters showed a decrease in the amplitude of alpha-band (10–11 Hz) activity and an increase in theta (4–7 Hz) and gamma (40–44 Hz) activities around 350 ms after stimulation. P2 and late positive component presented a higher amplitude to target than to repeated nontarget letters. Alpha reduction was inversely related to theta and late positive component increase. Moreover, gamma oscillation amplitude was directly related to theta amplitude. The findings suggest the importance of occipitoparietal alpha reduction for the development of task-related neuronal activity.

Preparatory activity and evaluation of spatial validity–invalidity indexed by ERPs in children and young adults

matter centered at the anterior cingulate cortex were determined using LC model. Participants completed 9 subtests of the California Computerized Assessment Package (CalCAP) to assess reaction time, working-memory, and attention. Correlations between age, imaging, and cognitive measures were determined (p < 0.05 significance). The medial-orbital-frontal cortex thinned with age (r = −0.37). Improved CalCAP performance on 2 subtests (r > 0.34) and higher n-acetyl-aspartate (NAA) levels (r = −0.32) were associated with this thinning. The superior-frontal cortex also thinned with age (r = -0.45) with corresponding improved performance on 4 subtests (r > 0.33) and higher glutamate + glutamine (GLX) levels. The superior-frontal cortex volume also decreased with age (r = −0.42) and was associated with improved performance on 8 subtests (r > 0.30). Smaller volumes of the frontal pole were observed in older participants (r = −0.31), which correlated with improved performance on 1 test (r = 0.31). Smaller volumes in the medialorbital-frontal cortex correlated with improved performance on 4 subtests (r > 0.35) and higher NAA levels (r = −0.31). These results emphasize that the frontal cortex is still developing into the 3rd decade of life. In addition, our data suggest that cortical pruning (thinning and volume reductions) during periadolescent brain development is associated with increasing concentrations of neuronal markers (NAA and GLX), and improved performance on higher cognitive functions, possibly due to more compact and efficient neuronal function and enhanced neuronal integrity.

Co-maturation of P300 component and delta band

matter centered at the anterior cingulate cortex were determined using LC model. Participants completed 9 subtests of the California Computerized Assessment Package (CalCAP) to assess reaction time, working-memory, and attention. Correlations between age, imaging, and cognitive measures were determined (p < 0.05 significance). The medial-orbital-frontal cortex thinned with age (r = −0.37). Improved CalCAP performance on 2 subtests (r > 0.34) and higher n-acetyl-aspartate (NAA) levels (r = −0.32) were associated with this thinning. The superior-frontal cortex also thinned with age (r = -0.45) with corresponding improved performance on 4 subtests (r > 0.33) and higher glutamate + glutamine (GLX) levels. The superior-frontal cortex volume also decreased with age (r = −0.42) and was associated with improved performance on 8 subtests (r > 0.30). Smaller volumes of the frontal pole were observed in older participants (r = −0.31), which correlated with improved performance on 1 test (r = 0.31). Smaller volumes in the medialorbital-frontal cortex correlated with improved performance on 4 subtests (r > 0.35) and higher NAA levels (r = −0.31). These results emphasize that the frontal cortex is still developing into the 3rd decade of life. In addition, our data suggest that cortical pruning (thinning and volume reductions) during periadolescent brain development is associated with increasing concentrations of neuronal markers (NAA and GLX), and improved performance on higher cognitive functions, possibly due to more compact and efficient neuronal function and enhanced neuronal integrity.