Posture used in fMRI-PET elicits reduced cortical activity and altered hemispheric asymmetry with respect to sitting position: An EEG resting state study

Horizontal body position is a posture typically adopted for sleeping or during brain imaging recording in both neuroscience experiments and diagnostic situations. Recent literature showed how this position and similar ones with head down are associated to reduced plasticity, impaired pain and emotional responses. The present study aimed at further understanding the decrease of cortical activity associated with horizontal body position by measuring high-frequency EEG bands \u2013 typically associated with high-level cognitive activation \u2013 in a resting state experimental condition. To this end, two groups of 16 female students were randomly assigned to either sitting control (SC) or 2-h horizontal Bed Rest condition (hBR) while EEG was recorded from 38 scalp recording sites. The hBR group underwent several body transitions, from sitting to supine, and from supine to sitting. Results revealed a clear effect of horizontal posture: the hBR group showed, compared to its baseline and to SC, reduced High-Beta and Gamma EEG band amplitudes throughout the 2-h of hBR condition. In addition, before and after the supine condition, hBR group as well as SC exhibited a greater left vs. right frontal activation in both EEG bands while, on the contrary, the supine position induced a bilateral and reduced activation in hBR participants. The cortical sources significantly more active in SC compared with hBR participants included the left Inferior Frontal Gyrus and left Insula. Results are discussed in relation to the differences among neuroimaging methods (e.g., fMRI, EEG, NIRS), which can be partially explained by posture-induced neural network changes

Brain plasticity in aphasic patients: Intra- and inter-hemispheric reorganisation of the whole linguistic network probed by N150 and N350 components

The present study examined linguistic plastic reorganization of language through Evoked Potentials in a group of 17 non-fluent aphasic patients who had suffered left perisylvian focal lesions, and showed a good linguistic recovery. Language reorganisation was probed with three linguistic tasks (Phonological, Semantic, Orthographic), the early word recognition potential (N150) and the later phonological-related component (N350). Results showed the typical left-lateralised posterior N150 in healthy controls (source: left Fusiform Gyrus), that was bilateral (Semantic) or right sided (Phonological task) in patients (sources: right Inferior/Middle Temporal and Fusiform Gyri). As regards N350, controls revealed different intra- and inter-hemispheric linguistic activation across linguistic tasks, whereas patients exhibited greater activity in left intact sites, anterior and posterior to the damaged area, in all tasks (sources: Superior Frontal Gyri). A comprehensive neurofunctional model is presented, describing how complete intra- and inter-hemispheric reorganisation of the linguistic networks occurs after aphasic damage in the strategically dominant left perisylvian linguistic centres

Effects of Multimodal Load on Spatial Monitoring as Revealed by ERPs

While the role of selective attention in filtering out irrelevant information has been extensively studied, its characteristics and neural underpinnings when multiple environmental stimuli have to be processed in parallel are much less known. Building upon a dual-task paradigm that induced spatial awareness deficits for contralesional hemispace in right hemisphere-damaged patients, we investigated the electrophysiological correlates of multimodal load during spatial monitoring in healthy participants. The position of appearance of briefly presented, lateralized targets had to be reported either in isolation (single task) or together with a concurrent task, visual or auditory, which recruited additional attentional resources (dual-task). This top-down manipulation of attentional load, without any change of the sensory stimulation, modulated the amplitude of the first positive ERP response (P1) and shifted its neural generators, with a suppression of the signal in the early visual areas during both visual and auditory dual tasks. Furthermore, later N2 contralateral components elicited by left targets were particularly influenced by the concurrent visual task and were related to increased activation of the supramarginal gyrus. These results suggest that the right hemisphere is particularly affected by load manipulations, and confirm its crucial role in subtending automatic orienting of spatial attention and in monitoring both hemispaces

Influence of Body Position on Cortical Pain-Related Somatosensory Processing: An ERP Study

Background: Despite the consistent information available on the physiological changes induced by head down bed rest, a condition which simulates space microgravity, our knowledge on the possible perceptual-cortical alterations is still poor. The present study investigated the effects of 2-h head-down bed rest on subjective and cortical responses elicited by electrical, pain-related somatosensory stimulation. Methodology/Principal Findings: Twenty male subjects were randomly assigned to two groups, head-down bed rest (BR) or sitting control condition. Starting from individual electrical thresholds, Somatosensory Evoked Potentials were elicited by electrical stimuli administered randomly to the left wrist and divided into four conditions: control painless condition, electrical pain threshold, 30 % above pain threshold, 30 % below pain threshold. Subjective pain ratings collected during the EEG session showed significantly reduced pain perception in BR compared to Control group. Statistical analysis on four electrode clusters and sLORETA source analysis revealed, in sitting controls, a P1 component (40–50 ms) in the right somatosensory cortex, whereas it was bilateral and differently located in BR group. Controls ’ N1 (80–90 ms) had widespread right hemisphere activation, involving also anterior cingulate, whereas BR group showed primary somatosensory cortex activation. The P2 (190–220 ms) was larger in left-central locations of Controls compared with BR group. Conclusions/Significance: Head-down bed rest was associated to an overall decrease of pain sensitivity and an altered pai

Complex Time-Dependent ERP Hemispheric Asymmetries during Word Matching in Phonological, Semantic and Orthographical Matching Judgment Tasks

Language-induced asymmetry to single word reading has been well investigated in past research. Less known are the complex processes and related asymmetries occurring when a word is compared with the previous one, according to specific tasks. To this end, we used a paradigm based on 80 sequential word pair comparisons and three blocked tasks: phonological, semantic and orthographical matching judgment. Participants had to decide whether the target word (W2) did or did not match the prime word (W1), presented 2 sec before, according to the task. The event-related potentials (ERPs) evoked by W2 in 20 participants have been analyzed. The first negative wave, the Recognition Potential (RP), peaking at about 120 ms over parietal sites, showed greater amplitude at left sites in all tasks, thus revealing the typical left-lateralization. At frontal sites, only the phonological task showed left lateralization. The following N400 (300–450 ms) showed an interesting interaction: Match trials elicited greater left asymmetry on frontal regions to phonological than to semantic than to visual-perceptual tasks, whereas mismatch trials induced an inverted asymmetry, marked by greater amplitude over right frontal sites, regardless of the task. Concerning the late N400 (450–600 ms), phonological and semantic tasks showed an overlapping pattern, with left lateralization in match and right lateralization in mismatch conditions. Results point to complex task- and time-dependent hemispheric asymmetries in word matching

EEG delta band as a marker of brain damage in aphasic patients after recovery of language

In this study spectral delta percentage was used to assess both brain dysfunction/inhibition and functional linguistic impairment during different phases of word processing. To this aim, EEG delta amplitude was measured in 17 chronic non-fluent aphasic patients while engaged in three linguistic tasks: Orthographic, Phonological and Semantic. Average mapping of aphasics' structural lesion showed core damage in the left cortical-subcortical perisylvian areas. Delta amplitude was overall significantly higher in aphasics with respect to matched controls, a result in line with the view that diaschisis/cortical inhibition persists to some extent also in the chronic phase. Analysis of regions of interest revealed a peak of delta activity in left perilesional EEG sites, posterior to the core damage where residual suffering tissue probably projects its dysfunctional activity. Time course of word processing showed in patients greater delta percentage/inhibition in the first interval after word offset in correspondence of which verbal working memory is engaged. The significant interaction including group and task factors points to greater left posterior inhibition in aphasics across all tasks and left vs. right anterior relative disinhibition only during the Phonological task, whereas controls showed greater left vs. right disinhibition at anterior sites in all tasks. Delta band, in addition to its ability to reflect structural damage, was effective in the assessment of functional impairment as well as of linguistic reorganization of aphasics at hemispheric level with a spatial scalp distribution consistent with lesion map

Le asimmetrie dell'effetto Simon

Nel presente lavoro viene proposto un modello per spiegare le asimmetrie dell\u2019effetto Simon. Il modello si basa sull\u2019integrazione delle spiegazioni cognitive dell\u2019effetto Simon con le informazioni che la letteratura neurofisiologica fornisce riguardo alla lateralizzazione del processo di selezione della risposta. Da questo modello si ricavano delle previsioni sulle asimmetrie ed un esperimento \ue8 stato condotto per testarle. A model aimed at explaining asymmetries in the Simon effect is presented. It is based on neuropsychological and neurophysiological data about lateralization of processes related to the response selection stage. Predictions about asymmetries one should expect when subjects perform a Simon task by executing responses only with one hand are derived from the model, and an experiment is carried out to test these predictions. Data confirm the assumption that Simon effect asymmetries are due to the different hemispheric patterns of activation for response selection

Language-related gamma EEG frontal reduction is associated with positive symptoms in schizophrenia patients

OBJECTIVES: Frontal hypoactivation has been consistently found in schizophrenia. We hypothesized that patients' deficit is asymmetrical, i.e., centred over the left frontal locations, associated with loss of language-related asymmetry, and correlated with positive symptoms. METHOD: The amplitude of EEG gamma band (36-48Hz) was measured during the processing of three linguistic (Phonological vs. Semantic vs. Visuo-perceptual) tasks and used as index of activation/connectivity in 18 schizophrenia patients and 18 healthy participants. RESULTS: Healthy controls showed higher gamma in frontal sites, revealing a significantly greater left vs. right asymmetry in all linguistic tasks, whereas patients exhibited decreased and bilateral gamma amplitude (i.e., reduced activation/connectivity) in frontal regions. The patients' left hypofrontality during phonological processing was positively correlated with higher levels of Delusions (P1) and Hallucination (P3) PANSS subscales. A significantly greater left posterior gamma amplitude was found in patients compared with controls. CONCLUSION: Results suggest, in schizophrenia patients, a functional deficit of left frontal regions including Broca's area, a key site playing a fundamental hierarchical role between and within hemispheres which integrates many basic processes in linguistic and conceptual organization. The significant correlation between lack of the left anterior asymmetry and increased positive symptoms is in line with Crow's hypothesis postulating the aetiological role of disrupted linguistic frontal asymmetry on the onset of the key symptoms of schizophrenia

Cortical plasticity of language measured by EEG in a case of anomic aphasia

Aphasia is a neurological disorder caused by a left hemisphere damage which is generally followed by some degree of spontaneous or therapy induced language recovery. Identifying the mechanisms underlying this recovery is difficult, but determining the neural substrate of recovery and its relationship with specific aspects of word processing may provide cues for language intervention. This study explores the cortical dynamics of linguistic functions during the rehabilitation-induced recovery of language in a patient, CR, affected by anomic aphasia. To this aim we mapped the language-related cortical activity of CR by means of the slow cortical potentials before and after a rehabilitative training. Thus, the first EEG measure showed the dysfunctional cortical networks related to the anomic disease and the second EEG revealed the new cortical circuits underlying the functional recovery