Pierpaolo Busan

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

Background Cerebral activation during planning of reaching movements occurs both in the superior parietal lobule (SPL) and premotor cortex (PM), and their activation seems to take place in parallel. Methodology The activation of the SPL and PM has been investigated using transcranial magnetic stimulation (TMS) during planning of reaching movements under visual guidance. Principal Findings 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. Conclusions 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.

Motor excitability evaluation in developmental stuttering: a transcranial magnetic stimulation study.

INTRODUCTION Developmental stuttering (DS) is viewed as a motor speech-specific disorder, although several lines of research suggest that DS is a symptom of a broader motor disorder. We investigated corticospinal excitability in adult DS and normal speakers. METHODS Transcranial magnetic stimulation (TMS) was administered over left/right hand representation of the motor cortex while recording motor evoked potentials (MEPs) from the contralateral first dorsal interosseous (FDI) muscle. Resting, active motor thresholds, silent period threshold and duration were measured. A stimulus-response curve at resting was also obtained to evaluate MEP amplitudes. RESULTS Lower corticospinal responses in the left hemisphere of DS were found, as indicated by a reduction of peak-to-peak MEP amplitudes compared to normal speakers. CONCLUSIONS This provides further evidence that DS may be a general motor deficit that also involves motor non-speech-related structures. Moreover, our results confirm that DS may be related to left hemisphere hypoactivation and/or lower left hemisphere dominance. The present data and protocol may be useful for diagnosis of subtypes of DS that may benefit from pharmacological treatment by targeting the general level of cortical excitability.

Parieto-occipital cortex and planning of reaching movements: a transcranial magnetic stimulation study.

A large amount of evidence supports a role for the parietal and frontal cortex in the planning of reaching movements. Nevertheless, neither the timing of involvement of these areas nor if and how their activity can be influenced by external stimuli has been clarified. The parieto-occipital cortex has been investigated by applying transcranial magnetic stimulation (TMS) at 25% (Time 1), 50% (Time 2) and 75% (Time 3) of the reaction time from a go signal to hand movement. No local effect was found with Time 1, since pulses were administered before subjects opened their eyes. Reduction of reaction time was observed at Time 2 when stimuli were applied over the anterior occipital lobe, parieto-occipital cortex and posterior parietal cortex. The effect on the posterior parietal cortex reverted when Time 3 was used. The present data confirm the existence, in humans, of a dorso-medial set of areas involved in on-line planning of reaching movements. Moreover, they provide novel evidence on the time course of this involvement. Finally, present data show that it is possible to interact with the flow of activity along this stream by appropriately delivering TMS pulses.

Investigating the efficacy of paroxetine in developmental stuttering.

Objectives:Paroxetine has been reported to be useful for management of stuttering symptoms, but only a few reports have examined its effects. We have investigated the efficacy of paroxetine in a randomized, placebo-controlled study. Methods:Five stuttering subjects received paroxetine at 20 mg once daily at night for 12 weeks, and 5 received placebo. The percentages of stuttered words and stuttering-associated movements during speech were measured at baseline and after 6 and 12 weeks of treatment. Moreover, left primary motor cortex excitability was measured using transcranial magnetic stimulation. Specifically, resting and active motor thresholds and the cortical silent period (CSP) were obtained at the same periods in both groups. Results:Paroxetine did not affect the percentage of stuttered words between groups. Stuttering-associated movements, however, during speech in facial muscular districts were significantly reduced in subjects treated with paroxetine. Finally, paroxetine administration shortened the CSP with no effect on motor thresholds. Conclusion:Paroxetine may be useful in qualitative management of stuttering symptoms and may act on the stuttering brain by diminution of intracortical inhibition, as revealed by the shortening of the CSP after paroxetine administration.

Transcranial magnetic stimulation and preparation of visually-guided reaching movements

To better define the neural networks related to preparation of reaching, we applied transcranial magnetic stimulation (TMS) to the lateral parietal and frontal cortex. TMS did not evoke effects closely related to preparation of reaching, suggesting that neural networks already identified by our group are not larger than previously thought. We also replicated previous TMS/EEG data by applying TMS to the parietal cortex: new analyses were performed to better support reliability of already reported findings (Zanon et al., 2010; Brain Topography 22, 307–317). We showed the existence of neural circuits ranging from posterior to frontal regions of the brain after the stimulation of parietal cortex, supporting the idea of strong connections among these areas and suggesting their possible temporal dynamic. Connection with ventral stream was confirmed. The present work helps to define those areas which are involved in preparation of natural reaching in humans. They correspond to parieto-occipital, parietal and premotor medial regions of the left hemisphere, i.e., the contralateral one with respect to the moving hand, as suggested by previous studies. Behavioral data support the existence of a discrete stream involved in reaching. Besides the serial flow of activation from posterior to anterior direction, a parallel elaboration of information among parietal and premotor areas seems also to exist. Present cortico-cortical interactions (TMS/EEG experiment) show propagation of activity to frontal, temporal, parietal and more posterior regions, exhibiting distributed communication among various areas in the brain. The neural system highlighted by TMS/EEG experiments is wider with respect to the one disclosed by the TMS behavioral approach. Further studies are needed to unravel this paucity of overlap. Moreover, the understanding of these mechanisms is crucial for the comprehension of response inhibition and changes in prepared actions, which are common behaviors in everyday life.

Long-range neural activity evoked by premotor cortex stimulation: a TMS/EEG co-registration study.

The premotor cortex is one of the fundamental structures composing the neural networks of the human brain. It is implicated in many behaviors and cognitive tasks, ranging from movement to attention and eye-related activity. Therefore, neural circuits that are related to premotor cortex have been studied to clarify their connectivity and/or role in different tasks. In the present work, we aimed to investigate the propagation of the neural activity evoked in the dorsal premotor cortex using transcranial magnetic stimulation/electroencephalography (TMS/EEG). Toward this end, interest was focused on the neural dynamics elicited in long-ranging temporal and spatial networks. Twelve healthy volunteers underwent a single-pulse TMS protocol in a resting condition with eyes closed, and the evoked activity, measured by EEG, was compared to a sham condition in a time window ranging from 45 ms to about 200 ms after TMS. Spatial and temporal investigations were carried out with sLORETA. TMS was found to induce propagation of neural activity mainly in the contralateral sensorimotor and frontal cortices, at about 130 ms after delivery of the stimulus. Different types of analyses showed propagated activity also in posterior, mainly visual, regions, in a time window between 70 and 130 ms. Finally, a likely “rebounding” activation of the sensorimotor and frontal regions, was observed in various time ranges. Taken together, the present findings further characterize the neural circuits that are driven by dorsal premotor cortex activation in healthy humans.

Involvement of ipsilateral parieto-occipital cortex in the planning of reaching movements: evidence by TMS.

Involvement of the ipsilateral hemisphere during planning of reaching movements is still matter of debate. While it has been demonstrated that the contralateral hemisphere is dominant in visuo-motor integration, involvement of the ipsilateral hemisphere has also been proposed. Furthermore, a dominant role for left posterior parietal cortex has been shown in this process, independently of the hand and visual field involved. In this study, the possible involvement of ipsilateral parieto-occipital cortex in planning of reaching movements was investigated by transcranial magnetic stimulation (TMS). TMS was applied on four points of the parietal and occipital cortex at 50% (Time 1), 75% (Time 2) and 90% (Time 3) of reaction time from a go-signal to hand movement. The only effect observed was an increase in reaction time when a region around the parieto-occipital junction was stimulated at Time 2. These results provide further support to the hypothesis that, in the posterior parietal cortex, planning of reaching movements also relies on the ipsilateral hemisphere, in addition to the contralateral or dominant one.

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).

Transcranial magnetic stimulation in developmental stuttering: Relations with previous neurophysiological research and future perspectives

Developmental stuttering (DS) is a disruption of the rhythm of speech, and affected people may be unable to execute fluent voluntary speech. There are still questions about the exact causes of DS. Evidence suggests there are differences in the structure and functioning of motor systems used for preparing, executing, and controlling motor acts, especially when they are speech related. Much research has been obtained using neuroimaging methods, ranging from functional magnetic resonance to diffusion tensor imaging and electroencephalography/magnetoencephalography. Studies using transcranial magnetic stimulation (TMS) in DS have been uncommon until recently. This is surprising considering the relationship between the functionality of the motor system and DS, and the wide use of TMS in motor-related disturbances such as Parkinsons Disease, Tourettes Syndrome, and dystonia. Consequently, TMS could shed further light on motor aspects of DS. The present work aims to investigate the use of TMS for understanding DS neural mechanisms by reviewing TMS papers in the DS field. Until now, TMS has contributed to the understanding of the excitatory/inhibitory ratio of DS motor functioning, also helping to better understand and critically review evidence about stuttering mechanisms obtained from different techniques, which allowed the investigation of cortico-basal-thalamo-cortical and white matter/connection dysfunctions.

A multimenu system based on the P300 component as a time saving procedure for communication with a brain-computer interface

The present study investigates a Brain-Computer Interface (BCI) spelling procedure based on the P300 evoked potential. It uses a small matrix of words arranged in a tree-shaped organization (“multimenu”), and allows the user to build phrases one word at a time, instead of letter by letter. Experiments were performed in two sessions on a group of seven healthy volunteers. In the former, the “multimenu” was tested with a total of 60 choices: 30 “externally-imposed” selections and 30 “free-choice” selections. In the latter, 3 × 3 matrices were compared with 6 × 6 matrices. Each matrix was composed of letters or words, for a total of four matrices. Differences in classifier accuracy, bit rate and amplitude of the evoked P300 were evaluated. Average accuracy in all subjects was 87% with no differences between the selection methods. The 3 × 3 “multimenu” obtained the same level of classifier accuracy as the 6 × 6 matrices, even with a significantly lower amplitude of the P300. Bit rate was increased when using the 3 × 3 matrices compared to the 6 × 6 ones. The “multimenu” system was equally effective, but faster than conventional, letter-based matrices. By improving the speed of communication, this method can be of help to patients with severe difficulties in communication.