Ambiti applicativi dell'EEG e della fMRI nello studio dei processi cognitivi

L’obiettivo della mia tesi è quello di presentare e confrontare due tipologie di tecniche di indagine cerebrale, l’EEG (Elettroencefalogramma) e la fMRI (Risonanza Magnetica funzionale), evidenziandone i vantaggi e gli svantaggi, e le loro applicazioni in campo medico. Successivamente è presentato lo sviluppo di un modello sperimentale volto allo studio del fenomeno della sinestesia, a partire da dati estratti mediante le tecniche precedenti.

Sviluppo di un sistema bci eeg-based per il controllo del movimento di un modello di arto superiore

Nel presente lavoro di tesi è stato sviluppato e testato un sistema BCI EEG-based che sfrutta la modulazione dei ritmi sensorimotori tramite immaginazione motoria della mano destra e della mano sinistra. Per migliorare la separabilità dei due stati mentali, in questo lavoro di tesi si è sfruttato l'algoritmo CSP (Common Spatial Pattern), in combinazione ad un classificatore lineare SVM. I due stati mentali richiesti sono stati impiegati per controllare il movimento (rotazione) di un modello di arto superiore a 1 grado di libertà, simulato sullo schermo. Il cuore del lavoro di tesi è consistito nello sviluppo del software del sistema BCI (basato su piattaforma LabVIEW 2011), descritto nella tesi. L'intero sistema è stato poi anche testato su 4 soggetti, per 6 sessioni di addestramento.

Ricostruzione delle sorgenti corticali da segnali EEG in task di discriminazione visiva: Effetto di training multisensoriale

I neuroni in alcune regioni del nostro cervello mostrano una risposta a stimoli multisensoriali (ad es. audio-visivi) temporalmente e spazialmente coincidenti maggiore della risposta agli stessi stimoli presi singolarmente (integrazione multisensoriale). Questa abilità può essere sfruttata per compensare deficit unisensoriali, attraverso training multisensoriali che promuovano il rafforzamento sinaptico all’interno di circuiti comprendenti le regioni multisensoriali stimolate. Obiettivo della presente tesi è stato quello di studiare quali strutture e circuiti possono essere stimolate e rinforzate da un training multisensoriale audio-visivo. A tale scopo, sono stati analizzati segnali elettroencefalografici (EEG) registrati durante due diversi task di discriminazione visiva (discriminazione della direzione di movimento e discriminazione di orientazione di una griglia) eseguiti prima e dopo un training audio-visivo con stimoli temporalmente e spazialmente coincidenti, per i soggetti sperimentali, o spazialmente disparati, per i soggetti di controllo. Dai segnali EEG di ogni soggetto è stato ricavato il potenziale evento correlato (ERP) sullo scalpo, di cui si è analizzata la componente N100 (picco in 140÷180 ms post stimolo) verificandone variazioni pre/post training mediante test statistici. Inoltre, è stata ricostruita l’attivazione delle sorgenti corticali in 6239 voxel (suddivisi tra le 84 ROI coincidenti con le Aree di Brodmann) con l’ausilio del software sLORETA. Differenti attivazioni delle ROI pre/post training in 140÷180 ms sono state evidenziate mediante test statistici. I risultati suggeriscono che il training multisensoriale abbia rinforzato i collegamenti sinaptici tra il Collicolo Superiore e il Lobulo Parietale Inferiore (nell’area Area di Brodmann 7), una regione con funzioni visuo-motorie e di attenzione spaziale.

Association of individual resting state EEG alpha frequency and cerebral blood flow

Cognitive task performance differs considerably between individuals. Besides cognitive capacities, attention might be a source of such differences. The individual's EEG alpha frequency (IAF) is a putative marker of the subject's state of arousal and attention, and was found to be associated with task performance and cognitive capacities. However, little is known about the metabolic substrate (i.e. the network) underlying IAF. Here we aimed to identify this network. Correlation of IAF with regional Cerebral Blood Flow (rCBF) in fifteen young healthy subjects revealed a network of brain areas that are associated with the modulation of attention and preparedness for external input, which are relevant for task execution. We hypothesize that subjects with higher IAF have pre-activated task-relevant networks and thus are both more efficient in the task-execution, and show a reduced fMRI-BOLD response to the stimulus, not because the absolute amount of activation is smaller, but because the additional activation by processing of external input is limited due to the higher baseline.

Structural analysis of Heschl's gyrus in schizophrenia patients with auditory hallucinations

Heschl's gyrus (HG) is functionally involved in the genesis of auditory verbal hallucinations (AVH). This dysfunction seems to be structurally facilitated. The aim of the study was to analyze macrostructural features of HG in a group of patients reporting AVH who demonstrated white matter diffusion tensor imaging abnormalities reported previously.

Peri-ictal correlation dynamics of high-frequency (80-200 Hz) intracranial EEG

To assess (1) how large-scale correlation of intracranial EEG signals in the high-frequency range (80-200Hz) evolves from the pre-ictal, through the ictal into the postictal state and (2) whether the contribution of local neuronal activity to large-scale EEG correlation differentiates epileptogenic from non-epileptogenic brain tissue.

Development of an auditory implant manipulator for minimally invasive surgical insertion of implantable hearing devices

To present the auditory implant manipulator, a navigation-controlled mechanical and electronic system which enables minimally invasive ('keyhole') transmastoid access to the tympanic cavity.

EEG correlation and power during maintenance of wakefulness test after sleep-deprivation

To investigate whether there are any objective EEG characteristics that change significantly between specific time periods during maintenance of wakefulness test (MWT) and whether such changes are associated with the ability to appropriately communicate sleepiness.

Forbidden ordinal patterns of periictal intracranial EEG indicate deterministic dynamics in human epileptic seizures

Epileptic seizures typically reveal a high degree of stereotypy, that is, for an individual patient they are characterized by an ordered and predictable sequence of symptoms and signs with typically little variability. Stereotypy implies that ictal neuronal dynamics might have deterministic characteristics, presumably most pronounced in the ictogenic parts of the brain, which may provide diagnostically and therapeutically important information. Therefore the goal of our study was to search for indications of determinism in periictal intracranial electroencephalography (EEG) studies recorded from patients with pharmacoresistent epilepsy.

When that tune runs through your head: A PET investigation of auditory imagery for familiar melodies

The present study used positron emission tomography (PET) to examine the cerebral activity pattern associated with auditory imagery forfamiliar tunes. Subjects either imagined the continuation of nonverbaltunes cued by their first few notes, listened to a short sequence of notesas a control task, or listened and then reimagined that short sequence. Subtraction of the activation in the control task from that in the real-tune imagery task revealed primarily right-sided activation in frontal and superior temporal regions, plus supplementary motor area(SMA). Isolating retrieval of the real tunes by subtracting activation in the reimagine task from that in the real-tune imagery task revealedactivation primarily in right frontal areas and right superior temporal gyrus. Subtraction of activation in the control condition from that in the reimagine condition, intended to capture imagery of unfamiliarsequences, revealed activation in SMA, plus some left frontal regions. We conclude that areas of right auditory association cortex, together with right and left frontal cortices, are implicated in imagery for familiartunes, in accord with previous behavioral, lesion and PET data. Retrieval from musical semantic memory is mediated by structures in the right frontal lobe, in contrast to results from previous studies implicating left frontal areas for all semantic retrieval. The SMA seems to be involved specifically in image generation, implicating a motor code in this process.

When that tune runs through your head: a PET investigation of auditory imagery for familiar melodies

The present study used positron emission tomography (PET) to examine the cerebral activity pattern associated with auditory imagery for familiar tunes. Subjects either imagined the continuation of nonverbal tunes cued by their first few notes, listened to a short sequence of notes as a control task, or listened and then reimagined that short sequence. Subtraction of the activation in the control task from that in the real-tune imagery task revealed primarily right-sided activation in frontal and superior temporal regions, plus supplementary motor area (SMA). Isolating retrieval of the real tunes by subtracting activation in the reimagine task from that in the real-tune imagery task revealed activation primarily in right frontal areas and right superior temporal gyrus. Subtraction of activation in the control condition from that in the reimagine condition, intended to capture imagery of unfamiliar sequences, revealed activation in SMA, plus some left frontal regions. We conclude that areas of right auditory association cortex, together with right and left frontal cortices, are implicated in imagery for familiar tunes, in accord with previous behavioral, lesion and PET data. Retrieval from musical semantic memory is mediated by structures in the right frontal lobe, in contrast to results from previous studies implicating left frontal areas for all semantic retrieval. The SMA seems to be involved specifically in image generation, implicating a motor code in this process.