Giuseppe A. Chiarenza

Principal component analysis for reduction of ocular artefacts in event-related potentials of normal and dyslexic children

OBJECTIVE The aim of this study was to reduce ocular artefacts in single trial event-related potentials (ERPs) recorded in normal and in dyslexic children. METHODS ERPs were recorded during passive and active reading of centrally presented alphabetic letters and non alphabetic symbols. EEG was recorded from 10 EEG locations using the 10-20 system. Diagonal EOG from the right eye was also recorded. Principal component analysis (PCA) was applied in order to reduce ocular artefacts: the first or the second principal component (PC) was subtracted when the correlation coefficient between the component and EOG was greater or equal to 0.9 or 0.95, respectively. Performance of the method was tested on simulated and real data, on both single and averaged trials, varying EOG amplitude and artefact transmission characteristics. RESULTS Applying the method to real recordings from normal and dyslexic children, we obtained a significant increase in the number of useful trials. In normal children we retrieved 41.0% of the rejected trials in passive and 39.1% in active reading. In dyslexic children 36.7 and 32.2% of the rejected trials in passive and active reading could be included in the respective averages. CONCLUSIONS The method allows an increase in the number of trials suitable for averaging, a great improvement in ERP quality and a reduction in the recording time.

Dynamic time warping in the analysis of event-related potentials

The aim of this article is to compute reliable templates of event-related potentials (ERPs) for homogeneous groups of subjects and to automatically quantify the morphological characteristics of the ERPs. We developed a method based on dynamic time warping (DTW). The method was applied to ERPs recorded from normal and dyslexic children during two reading tasks. We found that characteristic latency and amplitude changes of ERP components are due to task and pathology. Our results support the idea that dyslexia involves different and complex cerebral functions aside from the language system. This mathematical approach provides reproducible analysis criteria that are crucial for the reliability of ERP analysis.

Sex and ear differences of brain-stem acoustic evoked potentials in a sample of normal full-term newborns. Normative study

The present paper reports a normative study of the BAEPs recorded from 80 normal full-term newborns by using a rarefaction click at 70, 60, 40, 20 dB HL. Positive, negative peaks and the relative amplitudes were measured. Means, standard deviations and 95% and 99% confidence limits were calculated for each component, for positive and negative IPLs and amplitude ratios. A normality test distribution showed that each component had normal distribution except for wave PIII at 70 dB and at 60 dB HL because of its index of kurtosis and for IPLs PII-PIII and NII-NIII at 70 and 60 dB HL. MLRA was performed and significant statistical differences were found for sex, ears and intensities. Females had the latencies of waves PIII, PIV, PV, NII and NIV shorter than males. The BAEPs obtained from the left ear had shorter latencies for positive and negative peaks. Latencies, amplitude and morphology of the BAEPs vary with variations of the intensity. The IPLs PII-PV, PIII-PV and PIV-PV were not affected by changes of intensity.

Brain activity associated with skilled finger movements: Multichannel magnetic recordings

SummaryWe recorded with a 24-channel SQUID magnetometer cerebral activity preceding and following self-paced voluntary ‘skilled’ movements in four healthy adults. The subject pressed buttons successively with the right index and middle fingers aiming at a time difference of 40–60 ms; on-line feedback on performance was given after each movement. Slow magnetic readiness fields (RFs) preceded the movements by 0.5 s and culminated about 20 ms after the electromyogram (EMG) onset. Movement-evoked fields, MEFs, opposite in polarity to RFs, were observed 90–120 ms after the EMG onset. They were followed by an additional ‘skilled-performance field’, SPF, 400–500 ms after the EMG onset. The source locations of RF, MEF, and SPF were within 2 cm from sources of the somatosensory evoked responses, which were situated in the posterior wall of the Rolandic fissure; the sources of MEF were closest to the midline. Neural generators of these deflections and of the corresponding electric potentials are discussed.

Dynamic time warping in the study of ERPs in dyslexic children

Aim of this paper is to compute a normal ERP pattern (template) and to quantify the morphological characteristics of ERPs. ERPs were recorded from normal and dyslexic children in a passive and in an active condition. Dynamic time warping (DTW) was used to align the averaged ERPs of normal subjects. After the computation of the templates, individual averaged ERPs were aligned with the corresponding template, in order to automates the identification of the relevant ERPs components. The latencies of these components in normal and dyslexic subjects were compared in the two different conditions. ERPs components of dyslexic children were always delayed in respect to normal children. Statistically significant latency differences were noticed both in the short-latency waves, related to attention mechanisms, and in the long-latency waves, presumably related to memory processes. P1 latency in T4 differed in the two groups of children in both tasks, with p<0.05. Morphological differences between the ERPs of normal and dyslexic children were also noticed in the right hemisphere: N2 latency in T4 differed in the two groups of children with p<0.05. This result suggests that dyslexia is associated with more general disruptions of the cerebral functions than that confined to the classical linguistic areas.

Goal or near miss! Movement potential differences between adults and children in skilled performance

In this study, the performances and the movement-related brain macropotentials of a group of adults and 10-year-old children were analyzed to test whether and how they were correlated to the success or failure in the performance. Bereitschaftspotential (BP), motor cortex potential (MCP) and skilled performance positivity (SPP) related to preparation, execution and evaluation of performance respectively showed a significant relationship to the performance outcome. The BP area in the left precentral decreased significantly with increasing performance time. The amplitude of the MCP was maximum during target performances and decreased with increasing range of error of performance. There was a difference in trend between adults and children in the SPP latency. During target performances, SPP latency in Pz was maximum in children and minimum in adults. In children, the SPP amplitude was greater in frontal and precentral areas during target performance and decreased with increasing inaccuracy of performance. This trend was not evident in adults. The results seem to indicate that the SPP latency does not seem to depend on the performance time but on the evaluation of information conveyed by the stimulus. How this evaluation takes place seems to be different in children and adults; this evaluation process is also reflected in the SPP amplitude of children during target performances. For the adults who have already developed formal thinking, the probability that any outcome is possible exists and so the significant relationship between SPP amplitude and performance is not seen.

Automated identification of ERP peaks through Dynamic Time Warping: an application to developmental dyslexia.

OBJECTIVE This article proposes a method to automatically identify and label event-related potential (ERP) components with high accuracy and precision. METHODS We present a framework, referred to as peak-picking Dynamic Time Warping (ppDTW), where a priori knowledge about the ERPs under investigation is used to define a reference signal. We developed a combination of peak-picking and Dynamic Time Warping (DTW) that makes the temporal intervals for peak-picking adaptive on the basis of the morphology of the data. We tested the procedure on experimental data recorded from a control group and from children diagnosed with developmental dyslexia. RESULTS We compared our results with the traditional peak-picking. We demonstrated that our method achieves better performance than peak-picking, with an overall precision, recall and F-score of 93%, 86% and 89%, respectively, versus 93%, 80% and 85% achieved by peak-picking. CONCLUSION We showed that our hybrid method outperforms peak-picking, when dealing with data involving several peaks of interest. SIGNIFICANCE The proposed method can reliably identify and label ERP components in challenging event-related recordings, thus assisting the clinician in an objective assessment of amplitudes and latencies of peaks of clinical interest.

The psychophysiology of reading

Early identification of dyslexia would be fundamental to prevent the negative consequences of delayed treatment in the social, psychological and occupational domains. Movement-related potentials of dyslexic children are characterized by inadequate ability to program movements and reduced capacity to evaluate their performance and to correct their errors. Reading-related potentials recorded during different reading conditions elicit a series of positive and negative components with specific functional meaning and with a characteristic spatial-temporal pattern. These reading-related potentials, when analyzed with sLORETA, show significantly different patterns of activation when comparing self-paced reading aloud to passive viewing of single letters. Comparison of fMRI and sLORETA during both tasks showed that the cortical region with the widest inter-modality similarities is the middle-superior temporal lobe during self-paced reading aloud. Neuropsychological studies have shown the existence of clinical subtypes of dyslexia; these studies have been confirmed by the results of ICA applied to the EEG. Dyslexia can be defined as a disorder of programming and integrating ideokinetic elements, associated with a deficiency in the fast processing and integration of sensory information, with reduced efficiency of error systems analysis. Each of these phenomena occurs at different levels of the central nervous system and at different times.

Reading aloud: A psychophysiological investigation in children

This study investigated the electrophysiological responses to single-letter reading in children (reading-related potentials) and explored the morphological differences between covert and overt reading conditions. Sixty-five healthy children (6-13 years) participated in this study. Reading-related potentials were recorded during visual stimulation with single Italian alphabetic letters. Stimuli were displayed for 5 ms either automatically at a randomly jittered time lag or upon voluntary self-paced button press by children. In the covert conditions, children had to passively look at single letters, while in the overt conditions children were required to read aloud the letters. Electromyographic activity of the forearm and lips was additionally recorded during all tasks. Superimposition of reading-related potentials with the electromyographic activity of forearm and lips during self-paced reading aloud allowed to segregate the reading-related components into four periods: preparatory, pre-lexical, lexical and post-lexical. Reading-related potentials of the preparatory period can be related to preparation/intention to read, those of the pre-lexical period to visual-perceptual processes, those of the lexical period to the external/internal reafferent activity and those of the post-lexical period to the feedback processes following task completion. Analysis of variance showed a significant interaction of reading-related components with electrode locations and task conditions in all periods. The systematic characterization of the neurophysiological correlates of the elementary association between letters and sounds is helpful to highlight the neurobiological and functional basis of reading in healthy as well as impaired readers, for possibly developing neurophysiologically grounded rehabilitation therapies and further improving the explanatory models of dyslexia.

Analysis of single trial movement-related brain macropotential

A parametric method of identification of movement-related brain macropotentials on a single trial basis through an ARX (autoregressive with exogenous inputs) algorithm is presented. The basic estimation of the information contained in the single trial is taken from an average carried out on a sufficient number of trials, while the noise sources, EEG and EOG are characterized as exogenous inputs in the model. The simulations as well as the experimental results confirm the capability of the model to drastically improve the signal/noise ratio in each single trial and to satisfactorily identify the contributions of signal and noise in the overall recording. This way, using the same algorithm, a particularly efficient reduction of ocular artifacts is also achieved. The movement-related brain macropotentials recorded in three subjects show a high degree of variability from trial and this effect seems to be related to programming processes and evaluation of errors.