Effect of Transcranial Magnetic Stimulation (TMS) on Parietal and Premotor Cortex during Planning of Reaching Movements

The activation of the superior parietal lobule (SPL) and premotor cortex (PM) has been investigated using transcranial magnetic stimulation (TMS) during planning of reaching movements under visual guidance. A facilitory effect was found when TMS was delivered on the parietal cortex at about half of the time from sight of the target to hand movement, independently of target location in space. Furthermore, at the same stimulation time, a similar facilitory effect was found in PM, which is probably related to movement preparation. This data contributes to the understanding of cortical dynamics in the parieto-frontal network, and suggests that it is possible to interfere with the planning of reaching movements at different cortical points within a particular time window. Since similar effects may be produced at similar times on both the SPL and PM, parallel processing of visuomotor information is likely to take place in these regions

Altered Modulation of Silent Period in Tongue Motor Cortex of Persistent Developmental Stuttering in Relation to Stuttering Severity

Motor balance in developmental stuttering (DS) was investigated with Transcranial Magnetic Stimulation (TMS), with the aim to define novel neural markers of persistent DS in adulthood. Eleven DS adult males were evaluated with TMS on tongue primary motor cortex, compared to 15 matched fluent speakers, in a "state" condition (i.e. stutterers vs. fluent speakers, no overt stuttering). Motor and silent period thresholds (SPT), recruitment curves, and silent period durations were acquired by recording tongue motor evoked potentials. Tongue silent period duration was increased in DS, especially in the left hemisphere (P<0.05; Hedge's g or Cohen's dunbiased = 1.054, i.e. large effect size), suggesting a "state" condition of higher intracortical inhibition in left motor cortex networks. Differences in motor thresholds (different excitatory/inhibitory ratios in DS) were evident, as well as significant differences in SPT. In fluent speakers, the left hemisphere may be marginally more excitable than the right one in motor thresholds at lower muscular activation, while active motor thresholds and SPT were higher in the left hemisphere of DS with respect to the right one, resulting also in a positive correlation with stuttering severity. Pre-TMS electromyography data gave overlapping evidence. Findings suggest the existence of a complex intracortical balance in DS tongue primary motor cortex, with a particular interplay between excitatory and inhibitory mechanisms, also in neural substrates related to silent periods. Findings are discussed with respect to functional and structural impairments in stuttering, and are also proposed as novel neural markers of a stuttering "state" in persistent DS, helping to define more focused treatments (e.g. neuro-modulation)

BCI-Based Neuro-Rehabilitation Treatment for Parkinson’s Disease: cases Report

Parkinson's Disease (PD) is characterized by motor and cognitive decay, coupled to an alteration of brain oscillatory patterns. In this study a novel neuro-rehabilitation tool, based on the application of motor imagery into a Brain Computer Interface system, is presented with some preliminary data. Three patients were evaluated (with motor, neuropsychological and EEG testing) before and after a neuro-rehabilitation protocol made by 15 experimental sessions. Patients showed a decrease of freezing of gait severity, an improvement in alpha and beta EEG bands power, and a better performance on some attention and executive tasks

Stuttering as a matter of delay in neural activation: A combined TMS/EEG study

Objective: Brain dynamics in developmental stuttering (DS) are not well understood. The supplementary motor area (SMA) plays a crucial role, since it communicates with regions related to planning/execution of movements, and with sub-cortical regions involved in paced/voluntary acts (such as speech). We used TMS combined with EEG to shed light on connections in DS, stimulating the SMA. Methods: TMS/EEG was recorded in adult DS and fluent speakers (FS), stimulating the SMA during rest. TMS-evoked potentials and source distribution were evaluated. Results: Compared to FS, stutterers showed lower activity of neural sources in early time windows: 66\u2013 82 ms in SMA, and 91\u2013102 ms in the left inferior frontal cortex and left inferior parietal lobule. Stutterers, however, showed higher activations in later time windows (i.e. from 260\u2013460 ms), in temporal/premotor regions of the right hemisphere. Conclusions: These findings represent the functional counterpart to known white matter and cortico- basal-thalamo-cortical abnormalities in DS. They also explain how white matter abnormalities and cortico-basal-thalamo-cortical dysfunctions may be associated in DS. Finally, a mechanism is proposed in which compensatory activity of the non-dominant (right) hemisphere is recruited. Significance: DS may be a disorder of neural timing that appears to be delayed compared to FS; new mechanisms that support stuttering symptoms are inferred; the SMA may be a promising target for neuro-rehabilitation

Visuomotor adaptation changes tactile discrimination: an ERP study

We recorded brain activity in SI, elicited by the electrical stimulation of the right forearm during a 2PTD task (the two point distance selected according to the individual threshold) after visuomotor adaptation sessions, including normal and extended reaches. A reliable increase in brain activity was observed after the visuomotor adaptation with extended but not normal reaches. Visuomotor adaptation changes body representation and preset the tactile circuits involved in the 2TPD task via top-down links from multisensory areas in the posterior parietal cortex into the somatosensory corte

stimolazione magnetica transcranica nella pianificazione e nell'esecuzione dei movimenti di raggiungimento

2007/2008The neurophysiology of the monkey and human brain shows that transformation of visuomotor coordinates is related to the activation of a distributed and complex population of parietal, premotor and motor neurons. We can think about these circuits like different cortical areas activated in different times during reaching and grasping planning and execution, with different relations and communications among them. In this theoretic field, my PhD project was aimed at investigating the organization of planning and execution of visually guided reaching movements in the human brain, by means of Transcranial Magnetic Stimulation (TMS) in healthy subjects. I obtained a temporal and spatial map of both hemispheres, in order to refine available information about this complex system. In the contra-lateral hemisphere, an acceleration of reaction time was found when delivering TMS, on superior occipital lobe, at 50% of medium reaction time, without preferences for reaching direction in the peripersonal space. With the same time of stimulation, an acceleration of reaction times was also evident when stimulating the region of the parieto-occipital sulcus, but only for straight-forward reaching. Finally, in posterior superior parietal lobule slower reaction times were evident when TMS was delivered at 75% of the medium reaction time, but only for straight-forward reaching. Another facilitation of reaction time was evident in one of the five points stimulated in left parietal cortex, when TMS was delivered at 75% of medium reaction time, with no peripersonal space preferences. In dorsal premotor cortex another facilitation in reaction time was found, when TMS was delivered at 75% of medium reaction time, again with no peripersonal space preferences. Finally, I investigated the right hemisphere in cortical points homologue to those of the left hemisphere. Results indicated that only the region of the dorsal parieto-occipital sulcus is bilaterally involved. In fact, slower reaction times were evident when TMS was delivered at 75% of the medium reaction time. This indicates temporal differences in activation between left and right parieto-occipital sulcus. In all the effective points, the execution of control experiments showed that findings were specifically related to the planning of reaching movements, excluding the possibility of attentional, motor or perceptual effects, and that they were not due to diffusion of current to primary motor cortex. When delivering TMS during execution of reaching movements, effects were evident only when pulses were applied at 50% of medium movement time. In particular, a delay in movement time was evident in the parietal and premotor regions. Also in this case, control experiments excluded that effects were due to current diffusion to primary motor cortex and assured the specificity of the effect for visually-guided reaching. Present findings suggest that planning of reaching with right hand in healthy subjects starts early in left superior occipital cortex and in parieto-occipital region. Successively, a parallel and diffuse pattern of activation is evident. This pattern involves a specific point of superior parietal lobule in a ventral and rostral left parietal position, and a more anterior point of the premotor dorsal cortex, where a parallelism in activation could be speculated. Moreover, an interference in late motor planning in right and ipsilateral parieto-occipital cortex was evoked, that could be in strict functional and temporal relation with the homologue result obtained in left parieto-occipital region. Consequently, it could be suggested that even if planning of reaching movements relies principally on contra-lateral hemisphere, a bilateral involvement might also occur at least in parieto-occipital cortex. On the other hand, cortical structures in contra-lateral hemisphere seem to be involved in the control of on-line reaching movements only when the hand is approaching the target. In the present study, effects were reported only for parietal and premotor cortices. This suggests that the affected areas might be more involved in the control of on-line movements, confirming the pivotal role of the parietal cortex in managing visuomotor information. In conclusion, this research project contributes to the understanding of the cortical dynamics involved in the planning and control of reaching movements. Specifically, new insights are provided about the temporal involvement of the different cortical regions being part of the process.Il raggiungimento e la prensione di un oggetto sotto la guida visiva sono movimenti che i soggetti sani riescono a realizzare molto semplicemente. La neurofisiologia del sistema nervoso centrale ha dimostrato che le trasformazioni visuo-motorie, necessarie per l’implementazione di questi movimenti, si basano sull’attivazione di una distribuita e complessa popolazione di neuroni parietali, motori e promotori della corteccia cerebrale. Possiamo immaginare tali circuiti come differenti regioni corticali che si attivano durante diverse finestre temporali, con diversi gradi di relazione ed elementi di comunicazione tra loro. Per capire meglio l’esatto ruolo giocato dalle diverse regioni parietali e frontali durante la pianificazione e l’esecuzione dei movimenti di raggiungimento e di prensione, sono stati eseguiti esperimenti su un totale di 269 volontari sani e consenzienti (età 19-56 anni, età media e deviazione standard 26.1 ± 6.4 anni), cui veniva applicata una Stimolazione Magnetica Transcranica (TMS) durante l’esecuzione di un compito visuo-motorio. I soggetti venivano fatti sedere comodamente, chiedendo loro di iniziare il compito con gli occhi chiusi e con la mano destra mantenuta in posizione di riposo sopra un sensore ottico (che permetteva di misurare il tempo di reazione), posizionato centralmente rispetto al loro corpo. Un segnale acustico indicava ai soggetti di aprire gli occhi e di raggiungere il più velocemente e accuratamente possibile un oggetto posizionato sul tavolo a 35 cm di distanza di fronte a loro, oppure spostato di 40° a destra o a sinistra. Ai soggetti veniva richiesto di mantenere sempre lo sguardo in posizione centrale per tutta la durata dell’esperimento. L’oggetto era collegato ad un sensore tattile, utile per registrare i tempi di movimento (cioè il tempo che intercorreva dal momento in cui la mano lasciava il sensore ottico fino al raggiungimento dell’oggetto). La TMS è stata somministrata al 25%, al 50%, al 75% e al 90% del tempo di reazione medio o al 25% e al 50% del tempo di movimento medio di ogni soggetto. Sono stati stimolati 33 punti corticali, comprendendo entrambi gli emisferi. In ogni esperimento, per ognuno dei punti corticali investigati, sono state raccolte 42 prove (21 con TMS e 21 senza), ugualmente distribuite nello spazio peripersonale. In linea generale, in ogni esperimento, cinque punti corticali sono stati stimolati nella corteccia parieto-occipitale dorsale, cinque nella corteccia parietale superiore e cinque nella corteccia premotoria dorsale, in entrambi gli emisferi. I risultati ottenuti dimostrano l’esistenza di un circuito ben definito nell’emisfero sinistro, che parte dalla corteccia occipitale per arrivare fino alla corteccia premotoria, dove è stato possibile interagire tramite somministrazione di TMS, ottenendo soprattutto un accorciamento dei tempi di reazione. Infatti, un’accelerazione dei tempi di reazione è stata individuata somministrando la TMS al 50% di essi nel lobo occipitale superiore, senza però individuare preferenze di direzione nello spazio peripersonale. Successivamente, nello stesso momento di stimolazione, è stato possibile individuare un’accelerazione dei tempi di reazione anche nel solco parieto-occipitale, ma solo quando il soggetto realizzava un movimento di raggiungimento verso il centro. Anche nella corteccia parietale superiore è stato possibile osservare un effetto facilitatorio nei tempi di reazione. In questo caso però, la TMS è stata somministrata al 75% del tempo di reazione medio: l’effetto si manifestava senza preferenze direzionali nello spazio peripersonale. Infine, nella corteccia premotoria dorsale è stato possibile individuare un ultimo effetto di facilitazione sui tempi di reazione, ancora una volta quando la TMS veniva somministrata al 75% del tempo di reazione medio, e senza preferenze direzionali nello spazio peripersonale. Tempi di reazione rallentati sono stati evocati solamente nella parte posteriore del lobulo parietale superiore, quando la TMS veniva somministrata al 75% del tempo di reazione medio dei soggetti, solamente nei movimenti di raggiungimento diretti verso il centro. Per quanto riguarda l’emisfero destro, quando la TMS è stata somministrata nei punti corticali omologhi a quello di sinistra, sono stati individuati solamente tempi di reazione più lenti dopo stimolazione parieto-occipitale al 75% del tempo di reazione medio, senza preferenze spaziali peripersonali. Quando la TMS è stata somministrata durante l’ esecuzione del movimento, quattro punti sono stati stimolati nella corteccia parieto-occipitale dorsale, cinque nella corteccia parietale e cinque nella corteccia dorsale premotoria, solamente nell’emisfero di sinistra. I risultati indicano che la TMS è stata efficace esclusivamente quando è stata applicata al 50% del tempo di movimento medio. In particolare, un ritardo nei tempi di movimento è stato individuato in un punto della corteccia parietale superiore e in un punto della corteccia premotoria dorsale. In entrambi i casi, non è stato possibile evidenziare alcuna preferenza nello spazio peripersonale. I risultati raccolti confermano che la pianificazione dei movimenti di raggiungimento eseguiti con la mano destra inizia precocemente nella corteccia occipitale superiore di sinistra e nella regione parieto-occipitale dello stesso lato, proseguendo poi fino a raggiungere la corteccia premotoria dorsale. Questo indica la presenza di un circuito specifico posizionato dorsalmente, con una tempistica di attivazione che fluisce in direzione postero-anteriore. E’ stato evidenziato anche come l’emisfero ipsilaterale partecipi a tale processo, dato che è stata verificata la possibilità di interferire con la pianificazione dei movimenti di raggiungimento nella corteccia parieto-occipitale ipsilaterale. Inoltre, considerando l’effetto facilitatorio della TMS quando veniva applicata nell’emisfero sinistro al 50% del tempo di reazione medio, e quello inibitorio al 75% dello stesso quando veniva applicata all’emisfero destro, può essere ipotizzata l’esistenza di una chiara differenza di attivazione temporale tra corteccia parieto-occipitale di destra e di sinistra. Infatti, anche se la pianificazione dei movimenti di raggiungimento si basa principalmente sulla corteccia controlaterale, abbiamo dimostrato l’esistenza di un’attivazione bilaterale, almeno nella corteccia parieto-occipitale. Il coinvolgimento delle strutture corticali nel controllo on-line dei movimenti di raggiungimento è stato dimostrato essere più efficace quando la mano sta per raggiungere il suo obiettivo. In questo studio, gli effetti della TMS sono stati evidenziati nella corteccia parietale anteriore e nella corteccia premotoria, e non in regioni parieto-occipitali. Ciò suggerisce che le aree coinvolte potrebbero partecipare al controllo on-line del movimento di raggiungimento in misura maggiore rispetto a regioni corticali posteriori, confermando il loro ruolo centrale nella gestione delle informazioni visuo-motorie. La novità dello studio consiste nella realizzazione di una mappatura completa del circuito di integrazione di coordinate visuo-motorie deputato alla pianificazione e all’esecuzione dei movimenti di raggiungimento, grazie all’applicazione della TMS e la conseguente possibilità di interagire con tale sistema. Nello specifico, vengono proposte delle nuove evidenze a proposito del coinvolgimento temporale delle differenti regioni corticali che fanno parte del processo.XXI Ciclo198

Inefficient speech-motor control affects predictive speech comprehension: atypical electrophysiological correlates in stuttering

: Listeners predict upcoming information during language comprehension. However, how this ability is implemented is still largely unknown. Here, we tested the hypothesis proposing that language production mechanisms have a role in prediction. We studied 2 electroencephalographic correlates of predictability during speech comprehension-pre-target alpha-beta (8-30 Hz) power decrease and the post-target N400 event-related potential effect-in a population with impaired speech-motor control, i.e. adults who stutter (AWS), compared to typically fluent adults (TFA). Participants listened to sentences that could either constrain towards a target word or not, modulating its predictability. As a complementary task, participants also performed context-driven word production. Compared to TFA, AWS not only displayed atypical neural responses in production, but, critically, they showed a different pattern also in comprehension. Specifically, while TFA showed the expected pre-target power decrease, AWS showed a power increase in frontal regions, associated with speech-motor control. In addition, the post-target N400 effect was reduced for AWS with respect to TFA. Finally, we found that production and comprehension power changes were positively correlated in TFA, but not in AWS. Overall, the results support the idea that processes and neural structures prominently devoted to speech planning also support prediction during speech comprehension

When inefficient speech-motor control affects speech comprehension: atypical electrophysiological correlates of language prediction in stuttering

Abstract It is well attested that people predict forthcoming information during language comprehension. The literature presents different proposals on how this ability could be implemented. Here, we tested the hypothesis according to which language production mechanisms have a role in such predictive processing. To this aim, we studied two electroencephalographic correlates of predictability during speech comprehension \u2012 pretarget alpha\u2012beta (8-30 Hz) power decrease and the post-target N400 event-related potential (ERP) effect, \u2012 in a population with impaired speech-motor control, i.e., adults who stutter (AWS), compared to typically fluent adults (TFA). Participants listened to sentences that could either constrain towards a target word or not, allowing or not to make predictions. We analyzed time-frequency modulations in a silent interval preceding the target and ERPs at the presentation of the target. Results showed that, compared to TFA, AWS display: i) a widespread and bilateral reduced power decrease in posterior temporal and parietal regions, and a power increase in anterior regions, especially in the left hemisphere (high vs. low constraining) and ii) a reduced N400 effect (non-predictable vs. predictable). The results suggest a reduced efficiency in generating predictions in AWS with respect to TFA. Additionally, the magnitude of the N400 effect in AWS is correlated with alpha power change in the right pre-motor and supplementary motor cortex, a key node in the dysfunctional network in stuttering. Overall, the results support the idea that processes and neural structures prominently devoted to speech planning and execution support prediction during language comprehension. Significance Statement The study contributes to the developing enterprise of investigating language production and comprehension not as separate systems, but as sets of processes which may be partly shared. We showed that a population with impaired speech-motor control, i.e., adults who stutter, are characterized by atypical electrophysiological patterns associated with prediction in speech comprehension. The results highlight that an underlying atypical function of neural structures supporting speech production also affects processes deployed during auditory comprehension. The implications are twofold: on the theoretical side, the study supports the need for a more integrated view of language comprehension and production as human capabilities, while on the applied and clinical side, these results might open new venues for efficient treatments of developmental stuttering