Claudio Zucca

Multimodal analysis of a sustained attention protocol: continuous performance test assessed with near infrared spectroscopy and EEG.

The aim of this work is to describe, using functional imaging techniques, the spatial and temporal distribution of neural activations ensuing from execution of cognitive functions and to find correlation in data coming from analysis modalities related to different physical properties. A 10-mm continuous performance test (CPT) was administered to a group of healthy subjects as measure of sustained attention. Images of electroencephalography (EEG) and of near infrared spectroscopy (NIRS) were recorded during the task. cerebral activations measure is obtained from the recording of quantities linked with electrical neural activity for the EEG and with change in blood oxygenation for the NIRS system. Good agreement was found between the two modalities, both showing higher activation in the middle upper frontal region and similar temporal trend. A further understanding of the superior central nervous system behavior can be achieved from combined use of both imaging modalities

Analysis of the dynamical behaviour of the EEG rhythms during a test of sustained attention

In clinical routine, the evaluation of sustained attention is often performed analyzing behavioral data collected during specific tests. It is not common to match such analyses with a detailed examination of the subjects simultaneous electroencephalographic (EEG) activity, and particularly its frequency content. In this study, 9 healthy volunteers underwent a modified Conners CPT test, while their EEG was contemporarily recorded. Spectral power was calculated for each of the recorded EEG signals, with particular attention to frequency bands that are traditionally reported in literature. Then compressed spectral array (CSA) sequence of spectra was plotted, and the analysis of the variability of the rhythms was carried out. Evaluation of the obtained results shows that the nine subjects shared a progressive backshift of alpha rhythm during the accomplishment of the CPT test. Moreover, beta and gamma activities were stronger in the right than in the left hemisphere. An intense and widespread decrease in EEG spectral power during test performing became visible in many subjects. Statistical analysis provided evidence that EEG activity correlates with the test behavioral results in many cerebral areas. For this reason, we encourage further investigations of the combined employment of tests and EEG recording during the clinical assessment of sustained attention performance.

Investigation of negative BOLD responses in human brain through NIRS technique. A visual stimulation study

Despite negative blood oxygenation level dependent (BOLD) responses to visual stimuli have recently gained considerable interest, the explanation for their underlying neuronal and vascular mechanisms is still controversial. In the present study, a multimodal experimental approach is presented to shed light on the negative BOLD phenomenon in the human brain. In particular, information from functional magnetic resonance imaging (fMRI) and near infrared spectroscopy (NIRS) was integrated to confirm and gain insight into the phenomenon of negative BOLD responses (NBRs) to unpatterned intermittent photic stimulation (IPS) in healthy subjects. Eight healthy subjects participated in the study. Consistent findings emerged from the activation analysis of fMRI and NIRS data and the comparison of BOLD and hemoglobin responses at the single channel level showed that NBRs are related to a decrease in oxyhemoglobin (HbO) combined with a lower increase in deoxyhemoglobin (HHb), corresponding to a decrease in total hemoglobin (THb) and estimated cerebral blood volume (CBV). The HbO and HHb variations were significant in at least one channel in six subjects out of eight (p<0.05). The NIRS technique allowed obtaining valuable information on the vascular determinants of the NBRs, since the discrimination between HbO, HHb and THb information provided a more comprehensive view of the negative BOLD phenomenon. The within and between subject heterogeneous BOLD-Hb temporal relations pave the way to further investigations into the neurovascular properties of NBRs.

Combined behavioral and EEG power analysis in DAI improve accuracy in the assessment of sustained attention deficit.

In clinical routine, the evaluation of sustained attention is often performed by analyzing the behavioral data collected during specific tests. Such analyses are rarely accompanied by a detailed examination of the subject’s simultaneous electroencephalographic (EEG) activity, and particularly its frequency content. In this study, a group of healthy volunteers and a group of patients affected by diffuse axonal injury (DAI) were tested while performing a modified version of the Conners’ continuous performance test. A comparative study was carried out between the behavioral and neuropsychological data obtained during the task, to investigate neural activation. Spectral power was calculated for each of the recorded EEG signals, taking account of the frequency bands traditionally considered in literature. Then a compressed spectral array sequence of spectra was plotted to put into evidence the temporal modifications in the signal power spectral density, and, finally, the analysis of the rhythm variability was carried out. Evaluation of the results thus obtained shows that the two groups registered very different cerebral activation dynamics during the ongoing attentional task. Moreover, DAI patients showed mild cortical activation in the prefrontal region, spread equally throughout both brain hemispheres, while controls showed strong predominant activation of the right prefrontal area. Our findings encourage further investigations of the combined employment of tests and EEG recordings during the clinical assessment of sustained attention performance.

Constructing fMRI connectivity networks: A whole brain functional parcellation method for node definition

BACKGROUNDnFunctional Magnetic Resonance Imaging (fMRI) is used for exploring brain functionality, and recently it was applied for mapping the brain connection patterns. To give a meaningful neurobiological interpretation to the connectivity network, it is fundamental to properly define the network framework. In particular, the choice of the network nodes may affect the final connectivity results and the consequent interpretation.nnnNEW METHODnWe introduce a novel method for the intra subject topological characterization of the nodes of fMRI brain networks, based on a whole brain parcellation scheme. The proposed whole brain parcellation algorithm divides the brain into clusters that are homogeneous from the anatomical and functional point of view, each of which constitutes a node. The functional parcellation described is based on the Tononis cluster index, which measures instantaneous correlation in terms of intrinsic and extrinsic statistical dependencies.nnnRESULTSnThe method performance and reliability were first tested on simulated data, then on a real fMRI dataset acquired on healthy subjects during visual stimulation. Finally, the proposed algorithm was applied to epileptic patients fMRI data recorded during seizures, to verify its usefulness as preparatory step for effective connectivity analysis. For each patient, the nodes of the network involved in ictal activity were defined according to the proposed parcellation scheme and Granger Causality Analysis (GCA) was applied to infer effective connectivity.nnnCONCLUSIONSnWe showed that the algorithm 1) performed well on simulated data, 2) was able to produce reliable inter subjects results and 3) led to a detailed definition of the effective connectivity pattern.

EEG-based index for engagement level monitoring during sustained attention.

This paper investigates the relation between mental engagement level and sustained attention in 9 healthy adults performing a Conners “not-X” continuous performance test (CPT), while their electroencephalographic (EEG) activity was simultaneously acquired. Spectral powers were estimated and extracted in the classical EEG frequency bands. The engagement index (β/α) was calculated employing four different cortical montages suggested by the literature. Results show the efficacy of the estimated measures in detecting changes in mental state and its correlation with subject reaction times throughout the test. Moreover, the influence of the recording sites was proved underling the role of frontal cortex in maintaining a constant sustained attention level.

Coupling of fMRI and NIRS measurements in the study of negative BOLD response to intermittent photic stimulation

Functional Magnetic Resonance Imaging (fMRI) in combination with Near Infrared Spectroscopy (NIRS) is finding widespread use in the analysis of brain function. While most of the studies deal with the detection of positive responses, here we focus on negative responses to visual stimulation. In a group fMRI study on Intermittent Photic Stimulation (IPS) we detected a sustained Negative BOLD Response (NBR) in the extrastriate visual cortex. To confirm and better characterize NBR, we repeated the same protocol during NIRS recordings. In this paper we show fMRI results and demonstrate the NBR on the basis of NIRS findings.

Investigation of the electrophysiological correlates of negative BOLD response during intermittent photic stimulation: An EEG-fMRI study.

Although the occurrence of concomitant positive BOLD responses (PBRs) and negative BOLD responses (NBRs) to visual stimuli is increasingly investigated in neuroscience, it still lacks a definite explanation. Multimodal imaging represents a powerful tool to study the determinants of negative BOLD responses: the integration of functional Magnetic Resonance Imaging (fMRI) and electroencephalographic (EEG) recordings is especially useful, since it can give information on the neurovascular coupling underlying this complex phenomenon. In the present study, the brain response to intermittent photic stimulation (IPS) was investigated in a group of healthy subjects using simultaneous EEG‐fMRI, with the main objective to study the electrophysiological mechanisms associated with the intense NBRs elicited by IPS in extra‐striate visual cortex. The EEG analysis showed that IPS induced a desynchronization of the basal rhythm, followed by the instauration of a novel rhythm driven by the visual stimulation. The most interesting results emerged from the EEG‐informed fMRI analysis, which suggested a relationship between the neuronal rhythms at 10 and 12 Hz and the BOLD dynamics in extra‐striate visual cortex. These findings support the hypothesis that NBRs to visual stimuli may be neuronal in origin rather than reflecting pure vascular phenomena. Hum Brain Mapp 37:2247–2262, 2016.

EEG indices correlate with sustained attention performance in patients affected by diffuse axonal injury

AbstractThe aim of this study is to assess the ability of EEG-based indices in providing relevant information about cognitive engagement level during the execution of a clinical sustained attention (SA) test in healthy volunteers and DAI (diffused axonal injury)-affected patients. We computed three continuous power-based engagement indices (Pβ/Pα, 1/Pα, and Pβ / (Pα + Pθ)) from EEG recordings in a control group (nxa0=xa07) and seven DAI-affected patients executing a 10-min Conners’ “not-X” continuous performance test (CPT). A correlation analysis was performed in order to investigate the existence of relations between the EEG metrics and behavioral parameters in both the populations. Pβ/Pα and 1/Pα indices were found to be correlated with reaction times in both groups while Pβ / (Pα + Pθ) and Pβ/Pα also correlated with the errors rate for DAI patients. In line with previous studies, time course fluctuations revealed a first strong decrease of attention after 2xa0min from the beginning of the test and a final fading at the end. Our results provide evidence that EEG-derived indices extraction and evaluation during SA tasks are helpful in the assessment of attention level in healthy subjects and DAI patients, offering motivations for including EEG monitoring in cognitive rehabilitation practice.n Graphical abstractThree EEG-derived indices were computed from four electrodes montages in a population of seven healthy volunteers and a group of seven DAI-affected patients. Results show a significant correlation between the time course of the indices and behavioral parameters, thus demonstrating their usefulness in monitoring mental engagement level during a sustained attention task.