Uso di tecniche bayesiane per il miglioramento delle performance in un sistema BCI basato sulla P300

Il Brain-Computer Interface è un sistema in grado di esprimere la volontà del soggetto senza alcuna mediazione del sistema nervoso e muscolare, ma con l’impiego di un segnale di attività celebrale. Il segnale di controllo utilizzato è la P300 e quindi tale sistema si basa sul riconoscimento della componente ERP. Questa decisione è presa dal classificatore addestrato sulla base di features estratte dal segnale opportunamente elaborato. L’obiettivo di questa tesi è valutare l’effetto di un pre-processing bayesiano sulle performance del classificatore. In particolare, sono due le metodiche testate: un metodo bayesiano a due step (B2S) ed un metodo di Multi Task Learning (MTL). Per ognuno delle due tecniche si sono determinate le stime relative e sulla base di queste si sono addestrati numerosi classificatori e calcolati opportuni indici di errore. Infine si è eseguito un confronto di tali prestazioni, in particolare con quello ottenute mediante decomposizione IC

Long-latency components of somatosensory evoked potentials during passive tactile perception of gratings

Perception of tactile stimuli elicits Somatosensory Evoked Potentials (SEPs) that can be recorded via non-invasive electroencephalography (EEG). However, it is not yet clear how SEPs localization, shape and latency are modulated by different stimuli during mechanical tactile stimulation of fingertips. The aim of this work is thus to characterize SEPs generated by the tactile perception of gratings during dynamic passive stimulation of the dominant fingertip by means of a mechatronic platform. Results show that a random sequence of stimuli elicited SEPs with two long-latency components: (i) a negative deflection around 140 ms located in the frontal-central-parietal side in the contralateral hemisphere; (ii) a positive deflection around 250 ms located in the frontal-central midline. Time-frequency analysis revealed significant continuous bilateral desynchronization in the alpha band throughout the passive stimulation. These results are a fundamental step towards building a model of brain responses during perception of tactile stimuli for future benchmarking studies

Spatiotemporal Dynamics of the Cortical Responses Induced by a Prolonged Tactile Stimulation of the Human Fingertips

The sense of touch is fundamental for daily behavior. The aim of this work is to understand the neural network responsible for touch processing during a prolonged tactile stimulation, delivered by means of a mechatronic platform by passively sliding a ridged surface under the subject’s fingertip while recording the electroencephalogram (EEG). We then analyzed: (i) the temporal features of the Somatosensory Evoked Potentials and their topographical distribution bilaterally across the cortex; (ii) the associated temporal modulation of the EEG frequency bands. Long-latency SEP were identified with the following physiological sequence P100—N140—P240. P100 and N140 were bilateral potentials with higher amplitude in the contralateral hemisphere and with delayed latency in the ipsilateral side. Moreover, we found a late potential elicited around 200 ms after the stimulation was stopped, which likely encoded the end of tactile input. The analysis of cortical oscillations indicated an initial increase in the power of theta band (4–7 Hz) for 500 ms after the stimulus onset followed a decrease in the power of the alpha band (8–15 Hz) that lasted for the remainder of stimulation. This decrease was prominent in the somatosensory cortex and equally distributed in both contralateral and ipsilateral hemispheres. This study shows that prolonged stimulation of the human fingertip engages the cortex in widespread bilateral processing of tactile information, with different modulations of the theta and alpha bands across time

Behavioural and electrophysiological effects of tDCS to prefrontal cortex in patients with disorders of consciousness

9noOBJECTIVES: Left dorsolateral prefrontal cortex anodal transcranial direct current stimulation (tDCS) was applied in a group of patients with disorders of consciousness to determine the effects of modulation of spontaneous oscillatory brain activity. METHODS: 12 patients in an unresponsive wakefulness syndrome (UWS) and 12 in a minimally conscious state (MCS) underwent 2-weeks active and 2-weeks sham tDCS. Neurophysiological assessment was performed with EEG power spectra and coherence analysis directly before and after each session. RESULTS: An increase of power and coherence of the frontal and parietal alpha and beta frequency bands and significant clinical improvements were seen after the active tDCS in MCS patients. In contrast, UWS patients showed some local frontal changes in the slow frequencies. No treatment effect was observed after sham. CONCLUSIONS: tDCS could induce changes in cortical EEG oscillations, modulating the travel of alpha and beta waves between anterior and posterior brain areas when some cognitive functions were preserved. This plays an important role in consciousness by integrating cognitive-emotional processing with the state of arousal. In unresponsive people, brain integration seems to be lost. SIGNIFICANCE: Our results further support the critical role of long-range fronto-parietal connections in consciousness and show the potential therapeutic utility of tDCS.reservedmixedCavinato M.; Genna C.; Formaggio E.; Gregorio C.; Storti S.F.; Manganotti P.; Casanova E.; Piperno R.; Piccione F.Cavinato, M.; Genna, C.; Formaggio, E.; Gregorio, C.; Storti, S. F.; Manganotti, P.; Casanova, E.; Piperno, R.; Piccione, F