Giovanni Bianco

State-Dependent Effects of Transcranial Oscillatory Currents on the Motor System: What You Think Matters

Imperceptible transcranial alternating current stimulation (tACS) changes the endogenous cortical oscillatory activity in a frequency-specific manner. In the human motor system, tACS coincident with the idling beta rhythm of the quiescent motor cortex increased the corticospinal output. We reasoned that changing the initial state of the brain (i.e., from quiescence to a motor imagery task that desynchronizes the local beta rhythm) might also change the susceptibility of the corticospinal system to resonance effects induced by beta-tACS. We tested this hypothesis by delivering tACS at different frequencies (theta, alpha, beta, and gamma) on the primary motor cortex at rest and during motor imagery. Motor-evoked potentials (MEPs) were obtained by transcranial magnetic stimulation (TMS) on the primary motor cortex with an online-navigated TMS–tACS setting. During motor imagery, the increase of corticospinal excitability was maximal with theta-tACS, likely reflecting a reinforcement of working memory processes required to mentally process and “execute” the cognitive task. As expected, the maximal MEPs increase with subjects at rest was instead obtained with beta-tACS, substantiating previous evidence. This dissociation provides new evidence of state and frequency dependency of tACS effects on the motor system and helps discern the functional role of different oscillatory frequencies of this brain region. These findings may be relevant for rehabilitative neuromodulatory interventions.

Time Course of Corticospinal Excitability and Autonomic Function Interplay during and Following Monopolar tDCS.

While polarity-specific after-effects of monopolar transcranial direct current stimulation (tDCS) on corticospinal excitability are well-documented, modulation of vital parameters due to current spread through the brainstem is still a matter of debate, raising potential concerns about its use through the general public, as well as for neurorehabilitation purposes. We monitored online and after-effects of monopolar tDCS (primary motor cortex) in 10 healthy subjects by adopting a neuronavigated transcranial magnetic stimulation (TMS)/tDCS combined protocol. Motor evoked potentials (MEPs) together with vital parameters [e.g., blood pressure, heart-rate variability (HRV), and sympathovagal balance] were recorded and monitored before, during, and after anodal, cathodal, or sham tDCS. Ten MEPs, every 2.5-min time windows, were recorded from the right first dorsal interosseous (FDI), while 5-min epochs were used to record vital parameters. The protocol included 15 min of pre-tDCS and of online tDCS (anodal, cathodal, or sham). After-effects were recorded for 30 min. We showed a polarity-independent stabilization of cortical excitability level, a polarity-specific after-effect for cathodal and anodal stimulation, and an absence of persistent excitability changes during online stimulation. No significant effects on vital parameters emerged both during and after tDCS, while a linear increase in systolic/diastolic blood pressure and HRV was observed during each tDCS condition, as a possible unspecific response to experimental demands. Taken together, current findings provide new insights on the safety of monopolar tDCS, promoting its application both in research and clinical settings.

Cortico-Cortical Connectivity between Right Parietal and Bilateral Primary Motor Cortices during Imagined and Observed Actions: A Combined TMS/tDCS Study

Previous transcranial magnetic stimulation (TMS) studies showed functional connections between the parietal cortex (PC) and the primary motor cortex (M1) during tasks of different reaching-to-grasp movements. Here, we tested whether the same network is involved in cognitive processes such as imagined or observed actions. Single pulse TMS of the right and left M1 during rest and during a motor imagery and an action observation task (i.e., an index–thumb pinch grip in both cases) was used to measure corticospinal excitability changes before and after conditioning of the right PC by 10 min of cathodal, anodal, or sham transcranial direct current stimulation (tDCS). Corticospinal excitability was indexed by the size of motor-evoked potentials (MEPs) from the contralateral first dorsal interosseous (FDI; target) and abductor digiti minimi muscle (control) muscles. Results showed selective ipsilateral effects on the M1 excitability, exclusively for motor imagery processes: anodal tDCS enhanced the MEPs’ size from the FDI muscle, whereas cathodal tDCS decreased it. Only cathodal tDCS impacted corticospinal facilitation induced by action observation. Sham stimulation was always uneffective. These results suggest that motor imagery, differently from action observation, is sustained by a strictly ipsilateral parieto-motor cortex circuits. Results might have implication for neuromodulatory rehabilitative purposes.

Tms interference with primacy and recency mechanisms reveals bimodal episodic encoding in the human brain

A classic finding of the psychology of memory is the “serial position effect.” Immediate free recall of a word list is more efficient for items presented early (primacy effect) or late (recency effect), with respect to those in the middle. In an event-related, randomized block design, we interfered with the encoding of unrelated words lists with brief trains of repetitive TMS (rTMS), applied coincidently with the acoustic presentation of each word to the left dorsolateral pFC, the left intraparietal lobe, and a control site (vertex). Interference of rTMS with encoding produced a clear-cut double dissociation on accuracy during immediate free recall. The primacy effect was selectively worsened by rTMS of the dorsolateral pFC, whereas recency was selectively worsened by rTMS of the intraparietal lobe. These results are in agreement with the double dissociation between short-term and long-term memory observed in neuropsychological patients and provide direct evidence of distinct cortical mechanisms of encoding in the human brain.

Bi-hemispheric effects on corticospinal excitability induced by repeated sessions of imagery versus observation of actions.

PURPOSE To investigate whether repeated sessions of motor imagery and action observation modulate corticospinal excitability (CE) over time, whether these processes are susceptible of any training effect and if such effect might be different for the dominant and non dominant hemisphere. METHODS 11 subjects underwent three sessions, spaced 5-7 days, of single-pulse Transcranial Magnetic Stimulation (TMS) of right and left primary motor cortex. Subjects were asked to imagine or observe pinch-grip actions with either hand. Motor evoked potentials (MEPs) were recorded bilaterally from the First Dorsal Interosseus muscle (FDI), acting as main agonist during precision grip. RESULTS Motor imagery consistently enhanced CE with respect to action observation, regardless of hemispheric lateralization and of separate testing sessions. However, motor imagery increased CE only when measured over the non-dominant hemisphere, during the third session with respect to the first one. The increase of CE induced by action observation in the first session was not further modified throughout the remaining two sessions, in either hemisphere. CONCLUSIONS Results suggest that motor imagery is sustained by a cortical network susceptible to training effects only for the non-dominant hemisphere. Such an effect was lacking for action observation, likely because of the innateness of these mechanisms. Results might have implications for rehabilitative purposes.

A clinically silent, but severe, duodenal complication of duodopa infusion.

Duodenal levodopa/carbidopa gel infusion (Duodopa) is an efficacious therapeutic strategy for motor and non-motor symptoms in advanced Parkinsons disease (PD).1–3 Technical issues like kinking, knotting or obstruction of the tube are frequent, as well as complications due to the procedure, such as buried bumper syndrome, local infection and dislocation of the tube in the stomach (57%–69% of the patients), but they are seldom associated with severe adverse effects.1 3 4 In most cases, they are generally easy to suspect due to the immediate lack of therapeutic efficacy or malfunction of the infusion pump. We describe a rare and very serious gut complication associated with the device, which is difficult to recognise because of the persistence of clinical benefit on motor signs. A 72-year-old man with a medical history of hypertension and chronic obstructive pulmonary disease, and with a …

P14.21 Frequency-dependent tuning of human motor system induced by transcranial oscillatory potentials

F. Cogiamanian1, M. Vergari2, G. Ardolino2, E. Scelzo2, M. Ciocca2, S. Barbieri2, A. Priori3 1Centro Clinico per la Neurostimolazione, le Neurotecnologie ed i Disordini del Movimento, UO Neurofisiopatologia, Fondazione IRCCS Ospedale Maggiore Policlinico, Milan, Italy, 2UO Neurofisiopatologia, IRCCS Fondazione Cà Granda Ospedale Maggiore Policlinico, Milan, Italy, 3Centro Clinico per la Neurostimolazione, le Neurotecnologie ed i Disordini del Movimento, IRCCS Fondazione Cà Granda Ospedale Maggiore Policlinico, Università di Milano, Dipartimento di Scienze Neurologiche, Milan, Italy

P699: Lack of behavioural effects of high-frequency rTMS in vegetative state: a randomised, double blind, sham-controlled, cross-over study

A quantitative assessment of visual tracking could help to distinguish Vegetative State (VS) from Minimally Conscious State (MCS) (Trojano, 2011). In the present study we assess whether affective saliency modifies visual tracking in VS and MCS. 13 VS and 13 MCS patients, with traumatic or non-traumatic etiology. Exclusion criteria: lack of visual evoked potentials, premorbid or current ocular pathologies, oculomotor dysfunctions. Eleven age-matched normal subjects were assessed as controls. We recorded visual pursuit by means of a computerized infrared eye-tracker system. Stimuli: a circle, a parrot, and the face of one patient’s relative (5 4 cm). All stimuli slowly moved on a pc-monitor (total recording time: 162 s). Measures: number of fixations on or off the target. Distribution of onand off-target fixations differed significantly between MCS and VS. Moreover in MCS the proportion of onand off-target fixations for relatives’ face was significantly higher than for other stimuli, whereas in VS and controls did not. The proportion of on-target fixations seems able to discriminate MCS and VS. Affective saliency of the stimulus enhances visual tracking in MCS. Although the clinical evaluation represents the gold standard, the present findings can help in differential diagnosis in DoC.

P25.3 Are motor imagery and action observations innate or learned mechanisms? A single-pulse TMS study

mechanism is unknown although intermittent hypoxia and reperfusion injury during apneas may have a role. The treatment of OSA may reverse the floppy eyelid syndrome. Objectives: Our aim is to show the high prevalence of sleep apneas in a serie of seven patients previously diagnosed with FES. Methods: We report seven subjects (all men, aged from 46 to 73 years old, mean 60) diagnosed with FES who were studied by polisomnography. Results: Six of them (85%) had pathological apnea/hipopnea index (AHI) (ranged from 16.6 to 63), and in some cases with severe drops in oxygen saturation. Two of our subjects had predominantly central apneas. Only one patient was negative for OSA. Conclusions: It is known the morbidity of OSA. Patients with FES should be considered for polisomnography studies since FES may be a presenting symptom in patients with undiagnosed OSA. In our serie we have found two patients with central apneas predominantly, (previously not described in the literature).

P29-17 Cortico-cortical connectivity between parietal and primary motor cortices during imagined and observed actions: A TMS/tDCS study

effects emerged for the left M1 stimulation during imagery. Action observation tasks did not change corticospinal output in both hemispheres. Conclusions: These findings suggest that motor imagery is sustained by a cortical network susceptible to learning only for the non-dominant hemisphere. On the other hand, the absence of any effects of observation tasks may depend of the more innate nature of these processes.