Michele Butti

Politecnico di Milano, Milano, Lombardy, Italy

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Publications (12)9.26 Total impact

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    ABSTRACT: Sustained attention is one of the most important cognitive abilities for the management of everyday life, but it is often studied only at the behavioral level, while functional correlates are scarcely investigated. In this article, the authors address the topic of characterizing the dynamics of cerebral metabolism in the prefrontal cortex during a task of prolonged attention. By means of multichannel time-resolved functional near-infrared spectroscopy and generalized linear model based data processing, the authors measured the hemodynamic response of the prefrontal cortex from 19 healthy subjects to a shortened version of a sustained attention task (Conners' Continuous Performance Test), lasting for 10 min. The task elicited significant brain activation, which did not remain constant for the entire task, but showed a drop not correlated with performance decay 4 min after the beginning of the task. Furthermore, oxygenated hemoglobin showed an increasing trend also during the first phase of the recovery, just after the end of the task. The results indicate a nontrivial dynamics of neural activation, habituation processes, and hemodynamic/metabolic coupling. These results encourage further studies about continuous stimulation of cognitive functions on both healthy and pathological subjects.
    Medical Physics 09/2009; 36(9):4103-14. · 2.91 Impact Factor
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    ABSTRACT: To determine whether automated classifiers can be used for correctly identifying target categorization responses from averaged event-related potentials (ERPs) along with identifying appropriate features and classification models for computer-assisted investigation of attentional processes. ERPs were recorded during a target categorization task. Automated classification of average target ERPs versus average non-target ERPs was performed by extracting different combinations of features from the P300 and N200 components, which were used to train six classifiers: Euclidean classifier (EC), Mahalanobis discriminant (MD), quadratic classifier (QC), Fisher linear discriminant (FLD), multi-layer perceptron neural network (MLP) and support vector machine (SVM). The best classification performance (accuracy: 91-92%; sensitivity: 85-86%; specificity: 95-99%) was provided by QC, MLP, SVM on feature vectors extracted from P300 recorded at multiple sites. In general, non-linear and non-parametric classifiers (QC, MLP, SVM) performed better than linear classifiers (EC, MD, FLD). The N200 did not explain variance beyond that of P300 recorded at multiple sites. The results suggest that automatic characterization and classification of average target and non-target ERPs is feasible. Features of P300 recorded at multiple sites used to train non-linear classifiers are recommended for optimal classification performance. Automatic characterization of target ERPs can provide an objective approach for detecting and diagnosing abnormalities and evaluating interventions for clinical populations, paving the way for future real-time monitoring of attentional processes.
    Clinical neurophysiology: official journal of the International Federation of Clinical Neurophysiology 01/2009; 120(2):264-74. · 3.12 Impact Factor
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    ABSTRACT: 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.
    Annals of Biomedical Engineering 08/2008; 36(7):1216-27. · 3.23 Impact Factor
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    ABSTRACT: A Generalised Linear Model (GLM) was used to interpret time domain NIRS data during a Go-NoGo task to identify cerebral areas activated during a sustained attention protocol in a control group.
    Biomedical Optics; 03/2008
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    ABSTRACT: We evaluated frontal brain activation during a Working Memory task with graded levels of difficulty in a group of 15 healthy subjects, by means of fNIRS technique. Brain activation (% signal change with respect to the baseline) was computed and load-related increases of blood oxygenation were found for the four different levels of task difficulty. Generalized Linear Models were applied to the data in order to evaluate the metabolic processes occurring during the mental effort and, possibly, their involvement in short term memorization. The Cognitive Failure Questionnaire was also administered in order to assess its diagnostic relevance in clinics. Results attest a monotous increase of brain oxygenation with WM load during the first half of task, persisting through the central resting period and prevailing in the left hemisphere. Decreasing WM load is also coupled with oxygenated hemoglobin decrease.
    Conference proceedings: ... Annual International Conference of the IEEE Engineering in Medicine and Biology Society. IEEE Engineering in Medicine and Biology Society. Conference 02/2008; 2008:4024-7.
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    ABSTRACT: A time-domain fNIRS multichannel system was used in a sustained attention protocol (continuous performance test) to study activation of the prefrontal cortex. Preliminary results on volounteers show significant activation (decrease in deoxy-hemoglobin and increase in oxy-hemoglobin) in both left and right prefrontal cortex.
    Proc SPIE 07/2007;
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    ABSTRACT: Cognitive activity is related to important changes in the local blood flow level and in the oxygenation of the blood. These two effects lead to a modification of the optical properties of the cerebral cortex. With the aid of the functional near infrared spectroscopy (fNIRS) technique it is possible, through optical measures, to achieve information about the hemodynamic features of the brain activation. The aim of this study was to find a method to identify and to map the cerebral areas activated during a sustained attention task (Conner's continuous performance test - CPT) in a group of healthy subjects. This information will be of fundamental interest for a following study on a group of patients that will be administered the same examination. We propose a new analysis method based on the theory of generalized linear model (GLM) in order to obtain intuitive cerebral activation maps during the performing of cognitive tasks
    Neural Engineering, 2007. CNE '07. 3rd International IEEE/EMBS Conference on; 06/2007
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    ABSTRACT: 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 subject's simultaneous electroencephalographic (EEG) activity, and particularly its frequency content. In this study, 9 healthy volunteers underwent a modified Conners' CPT test, while their EEG were 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.
    Conference proceedings: ... Annual International Conference of the IEEE Engineering in Medicine and Biology Society. IEEE Engineering in Medicine and Biology Society. Conference 02/2007; 2007:1298-301.
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    ABSTRACT: Attention domain is of crucial importance for goal-directed behaviors and it has been widely studied through response analysis to rare stimuli using electroencephalography (EEG). More recent researches have explored the brain circuitry of attention by applying neuroimaging techniques, such as functional magnetic resonance. This paper investigates for the first time the feasibility of automatic recognition of responses to rare stimuli by using functional near-infrared spectroscopy (fNIRS). fNIRS is a portable brain imaging modality that optically measures the cortical hemodynamic activation and may prove useful in monitoring localized activity changes in frontal cortex related to attention processes. In this preliminary study, Fisher Linear Discriminant (FLD) is used to discriminate between average responses to rare task-relevant stimuli and responses to task-irrelevant stimuli.
    12/2006: pages 473-476;
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    ABSTRACT: 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 activation's 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.
    Conference proceedings: ... Annual International Conference of the IEEE Engineering in Medicine and Biology Society. IEEE Engineering in Medicine and Biology Society. Conference 02/2006; 1:1040-3.
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    ABSTRACT: The study of cognitive functions is a major challenge of the modern functional imaging. Activation of specific cerebral area is obtained from the observation of physic characteristic affected by changes occurring in the blood flow resulting from an increased metabolic consumption. In this work two imaging techniques are used, the functional magnetic resonance (fMRI) and the near infrared spectroscopy (NIRS), in order to assess cerebral performance during the execution of a well known sustained attention task, the Conners' continuous performance test (CPT). With fMRI analysis were found activations in the frontal, parietal and supplementary motor areas, whereas NIRS system showed a region-wise difference in the variations of parameters and different activation trend localized in the middle-right frontal area. The combined analysis of the two techniques allows to obtain more detailed information and places itself as a first step toward a result of multimodal image integration.
    Conference proceedings: ... Annual International Conference of the IEEE Engineering in Medicine and Biology Society. IEEE Engineering in Medicine and Biology Society. Conference 02/2006; 1:1944-7.
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    ABSTRACT: The applicability of OSEM reconstruction algorithms with space dependent resolution recovery to clinical FDG-PET studies is verified. The performance of the 2D algorithm is improved by means of a low resolution initialization and by a infra-iteration Metz filtering. Effects of different rebinning algorithms on 3D data are assessed, concluding that they do not alter the transaxial plane blurring parameters, thus permitting a straightforward application of 2D OSEM reconstruction after rebinning, with the same system matrix. Finally axial degradation was also quantified, finding that FORE is the best rebinning method to be combined with the 2D OSEM reconstruction.
    Conference proceedings: ... Annual International Conference of the IEEE Engineering in Medicine and Biology Society. IEEE Engineering in Medicine and Biology Society. Conference 02/2004; 2:1365-7.