Contralateral Motor Cortex Research Articles

The activity in the contralateral primary motor cortex, dorsal premotor and supplementary motor area is modulated by performance gains.

There is growing experimental evidence that the engagement of different brain areas in a given motor task may change with practice, although the specific brain activity patterns underlying different stages of learning, as defined by kinematic or dynamic performance indices, are not well understood. Here we studied the change in activation in motor areas during practice on sequences of handwriting-like trajectories, connecting four target points on a digitizing table “as rapidly and as accurately as possible” while lying inside an fMRI scanner. Analysis of the subjects' pooled kinematic and imaging data, acquired at the beginning, middle, and end of the training period, revealed no correlation between the amount of activation in the contralateral M1, PM (dorsal and ventral), supplementary motor area (SMA), preSMA, and Posterior Parietal Cortex (PPC) and the amount of practice per-se. Single trial analysis has revealed that the correlation between the amount of activation in the contralateral M1 and trial mean velocity was partially modulated by performance gains related effects, such as increased hand motion smoothness. Furthermore, it was found that the amount of activation in the contralateral preSMA increased when subjects shifted from generating straight point-to-point trajectories to their spatiotemporal concatenation into a smooth, curved trajectory. Altogether, our results indicate that the amount of activation in the contralateral M1, PMd, and preSMA during the learning of movement sequences is correlated with performance gains and that high level motion features (e.g., motion smoothness) may modulate, or even mask correlations between activity changes and low-level motion attributes (e.g., trial mean velocity).

34. Modulation of cortical activity by botulinum toxin type a in patients with post-stroke arm spasticity

There is growing evidence of remote effects of botulinum toxin. We aimed to use functional MRI (fMRI) to localize brain activation changes in stroke patients treated by botulinum toxin A (BoNT) for arm spasticity. 14 ischemic stroke patients with hand weakness and spasticity were studied. Spasticity was scored by modified Ashworth scale (MAS). FMRI was performed 3 times: before (W0) and 4 (W4) and 11 weeks (W11) after BoNT. Group A: 7 patients with hand plegia, who imagined moving fingers. Group B: 7 age-matched patients able to perform sequential finger movement. Difficulty was scored with visual analog scale. Statistical analysis (FSL) yielded group session-wise statistic maps and paired between-session contrasts. BoNT-A transiently lowered MAS in W4 in both groups. Performance difficulty did not change. In group A, activation of frontal premotor cortex dominated (as in healthy). At W4, ipsilateral cerebellum engaged as well, and persisted at W11. Paired contrasts showed activation decrease in bilateral occipital cortex W0 > W4 and left-sided occipitoparietal increase W4 < W11. These can be attributed to occipital deactivation (also precuneus and medial orbitofrontal cortex) at W4.Group B additionally activated contralateral motor and parietal cortex and bilateral cerebellum. From W0 to W4, activation was markedly reduced, which persisted at W11. Paired contrasts confirmed differences W0 > W4 (extensive ipsilateral parietal, occipital and premotor) and W0 > W11 (occipitoparietal). The effect of deactivation at was limited. Study of 2 age-matched groups with mild and severe weakness demonstrated different effect of BoNT-lowered spasticity on motor system engagement. Group A during movement imagery at maximum BoNT effect manifested deactivation of visual and default mode system, perhaps a change from visual to kinesthetic imagery, with cerebellum participating. Group B during movement also manifested motor pattern normalization, especially reduced activation extent. Supported by IGA MZ CR NT13575.

Cortical involvement in the StartReact effect

The rapid release of prepared movements by a loud acoustic stimulus capable of eliciting a startle response has been termed the StartReact effect (Valls-Solé et al., 1999), and premotor reaction times (PMTs) of <70ms are often observed. Two explanations have been given for these short latency responses. The subcortical storage and triggering hypothesis suggests movements that can be prepared in advance of a “go” signal are stored and triggered from subcortical areas by a startling acoustic stimulus (SAS) without cortical involvement. Alternatively, it has been hypothesized that the SAS can trigger movements from cortical areas through a faster pathway ascending from subcortical structures. Two experiments were designed to examine the possible role of the primary motor cortex in the StartReact effect. In Experiment 1, we used suprathreshold transcranial magnetic stimulation (TMS) during the reaction time (RT) interval to induce a cortical silent period in the contralateral primary motor cortex (M1). Thirteen participants performed 20° wrist extension movements as fast as possible in response to either a control stimulus (82dB) or SAS (124dB). PMTs for startle trials were faster than for control trials, while TMS significantly delayed movement onset compared to No TMS or Sham TMS conditions. In Experiment 2, we examined the StartReact effect in a highly cortically represented action involving speech of a consonant–vowel (CV) syllable. Similar to previous work examining limb movements, a robust StartReact effect was found. Collectively, these experiments provide evidence for cortical (M1) involvement in the StartReact effect.

Decoding the individual finger movements from single‐trial functional magnetic resonance imaging recordings of human brain activity

Multivariate pattern classification analysis (MVPA) has been applied to functional magnetic resonance imaging (fMRI) data to decode brain states from spatially distributed activation patterns. Decoding upper limb movements from non-invasively recorded human brain activation is crucial for implementing a brain-machine interface that directly harnesses an individual's thoughts to control external devices or computers. The aim of this study was to decode the individual finger movements from fMRI single-trial data. Thirteen healthy human subjects participated in a visually cued delayed finger movement task, and only one slight button press was performed in each trial. Using MVPA, the decoding accuracy (DA) was computed separately for the different motor-related regions of interest. For the construction of feature vectors, the feature vectors from two successive volumes in the image series for a trial were concatenated. With these spatial-temporal feature vectors, we obtained a 63.1% average DA (84.7% for the best subject) for the contralateral primary somatosensory cortex and a 46.0% average DA (71.0% for the best subject) for the contralateral primary motor cortex; both of these values were significantly above the chance level (20%). In addition, we implemented searchlight MVPA to search for informative regions in an unbiased manner across the whole brain. Furthermore, by applying searchlight MVPA to each volume of a trial, we visually demonstrated the information for decoding, both spatially and temporally. The results suggest that the non-invasive fMRI technique may provide informative features for decoding individual finger movements and the potential of developing an fMRI-based brain-machine interface for finger movement.

Dynamic metabolic changes after permanent cerebral ischemia in rats with/without post-stroke exercise: a positron emission tomography (PET) study

Objectives:Recent studies have suggested that rehabilitation therapy can accelerate functional recovery after a stroke. Although often overlooked, the cortical hemisphere contralateral to an infarction plays an important role. This study investigates alterations in metabolism of both the damaged (‘ipsilateral’) as well as the undamaged (‘contralateral’) hemisphere using 18F-fluorodeoxyglucose (FDG)-micro-positron emission tomography (PET) in a rat permanent stroke model (with or without post-injury exercise) in order to elucidate the relative importance of either hemisphere to the recovery process following stroke.Methods:Thirty-six adult, male Sprague-Dawley rats were divided into four groups before subsequent surgery: sham controls with or without exercise, and ischemic (‘stroke’) groups with or without exercise. Fluorodeoxyglucose micro-PET imaging was performed at 7, 14, and 21 days after the designated procedure according to group assignment. The imaging data was analyzed by ANOVA using SPMratIHEP software.Results:Both exercise and ischemia have measurable effects on the motor cortex as well as on the striatum, the effects of which notably include the contralateral hemisphere. To that end, regions of the contralateral motor cortex and striatum have been found to be in a hypermetabolic state following exercise. We further observed that exercise reversed the hypometabolism caused by ischemia back to control levels from day 7 through day 21 on the ipsilateral side. Its effect on the contralateral hemisphere, notably, bolsters an already vigorous response observed after ischemic insult. Thus, the beneficial effect of exercise, as inferred by an increase in metabolic activity, is evident in both hemispheres.Discussion:These findings suggest that the contralateral hemisphere can compensate for the damaged cortex by remodeling neuronal activity. Thus, clinical treatments specifically targeted to the ‘intact’ hemisphere following stroke may provide a complimentary strategy for promoting recovery of functional deficits and for improving quality of life in stroke patients.

Task-related modulation of crossed spinal inhibition between human lower limbs

Crossed reflex action mediated by muscle spindle afferent inputs has recently been revealed in humans. This raised the question of whether a complex spinal network involving commissural interneurons receiving inputs from proprioceptors and suprasegmental structures, as described in cats, persists in humans and contributes to the interlimb coordination during movement. First, we investigated the neurophysiological mechanisms underlying crossed reflex action between ankle plantar flexors and its corticospinal control from primary motor cortex. Second, we studied its modulation during motor tasks. We observed crossed inhibition in contralateral soleus motoneurons occurring with about 3 ms central latency, which is consistent with spinal transmission through oligosynaptic pathway. The early phase of inhibition was evoked with lower stimulus intensity than the late phase, suggesting mediation by group I and group II afferents, respectively. The postsynaptic origin of crossed inhibition is confirmed by the finding that both H-reflex and motor-evoked potential were reduced upon conditioning stimulation. Transcranial magnetic stimulation over ipsilateral and contralateral primary motor cortex reduced crossed inhibition, especially its late group II part. Last, late group II crossed inhibition was particularly depressed during motor tasks, especially when soleus was activated during the walking stance phase. Our results suggest that both group I and group II commissural interneurons participate in crossed reflex actions between ankle plantar flexors. Neural transmission at this level is depressed by descending inputs activated by transcranial magnetic stimulation over the primary motor cortex or during movement. The specific modulation of group II crossed inhibition suggests control from monoaminergic midbrain structures and its role for interlimb coordination during locomotion.

Functional Recovery After Ischemic Stroke Is Associated With Reduced GABAergic Inhibition in the Cerebral Cortex

Background: γ-Aminobutyric acid (GABA) plasticity plays an important role in stroke motor recovery in a mouse model. However, little is known about changes over time in neuronal excitability mediated by GABA receptors in human stroke patients. Objectives: To establish the mechanism of neuroplasticity during the recovery phase following ischemic stroke by assessing the changes in cerebral GABA activity using [18F]flumazenil ([18F]FMZ) positron emission tomography (PET). Methods: A total of 10 patients with unilateral ischemic stroke were studied at 1 month (T0) and 3 months (T1) postonset using [18F]FMZ PET. Changes in regional GABAergic activity were assessed longitudinally, and values were also compared with those in 15 age-matched controls. Upper-extremity motor function was evaluated using the Fugl-Meyer score (FMS). Results: During the follow-up period, statistical parametric mapping analysis demonstrated a decrease in GABAA receptor availability throughout the cerebral cortex and cerebellum, especially the contralateral hemisphere. GABAA availability in the bilateral primary motor cortex, contralateral supplemental motor cortex, and globus pallidus at T0 was positively correlated with the FMS score at T1. Conclusions: This is the first prospective, controlled longitudinal study showing that the change in GABA receptor availability over time is significantly related to motor recovery after stroke in humans. This work supports the rationale for a novel strategy to promote motor recovery after stroke.

Reduced activity-dependent protein levels in a mouse model of the fragile X premutation

Environmental enrichment results in increased levels of Fmrp in brain and increased dendritic complexity. The present experiment evaluated activity-dependent increases in Fmrp levels in the motor cortex in response to training on a skilled forelimb reaching task in the CGG KI mouse model of the fragile X premutation. Fmrp, Arc, and c-Fos protein levels were quantified by Western blot in the contralateral motor cortex of mice following training to reach for sucrose pellets with a non-preferred paw and compared to levels in the ipsilateral motor cortex. After training, all mice showed increases in Fmrp, Arc, and c-Fos protein levels in the contralateral compared to the ipsilateral hemisphere; however, the increase in CGG KI mice was less than wildtype mice. Increases in Fmrp and Arc proteins scaled with learning, whereas this relationship was not observed with the c-Fos levels. These data suggest the possibility that reduced levels of activity-dependent proteins associated with synaptic plasticity such as Fmrp and Arc may contribute to the neurocognitive phenotype reported in the CGG KI mice and the fragile X premutation.

The latency of motor-evoked potentials (MEPs) can predict whether cTBS will exert an inhibitory or excitatory effect on the ipsilateral and contralateral primary motor cortex

Event Abstract Back to Event The latency of motor-evoked potentials (MEPs) can predict whether cTBS will exert an inhibitory or excitatory effect on the ipsilateral and contralateral primary motor cortex Gan Huang1* and André Mouraux1* 1 Université catholique de Louvain, Institute of Neuroscience (IONS), Belgium Repetitive transcranial magnetic stimulation (rTMS) is increasingly used as a research tool to probe the function of a given brain structure, or as a non-invasive therapeutic approach in neurology and psychiatry. However, its effect is highly variable between individuals. For example, Hamada et al. (2012) showed that continuous theta burst stimulation (cTBS) delivered over the primary motor cortex (M1) increases M1 excitability in 58% of subjects, and decreases it in 42% of subjects. The authors found that the excitatory or inhibitory effect of cTBS on M1 can be predicted by the latency of motor-evoked potentials (MEPs), suggesting that this inter-individual variability could be related to differences in the neuronal circuits preferentially activated by TMS. Here, we further explore this hypothesis by characterizing the relationship between MEP latency and the effects of cTBS on M1 excitability, measured using both MEPs and TMS-evoked brain potentials (TEPs). The recording of TEPs can provide useful information about the responsiveness and connectivity between the brain region targeted by TMS and brain regions sampled using EEG (Bonato et al. 2006). cTBS was delivered over the left or right M1 using biphasic pulses delivered over the central sulcus in an anterior-posterior (A-P) or posterior-anterior (P-A) direction. MEPs and TEPs elicited by stimulation of both the ipsilateral and contralateral M1 were recorded before (T0), immediately after (T1) and 20 minutes after (T2) cTBS. Confirming the results of Hamada et al. (2012), we found a positive correlation between MEP latency at T0 and the effect of cTBS on excitability of the ipsilateral M1. MEPs of shorter latency were associated with an increase of MEP amplitude after cTBS (i.e. M1 facilitation), whereas MEPs of longer latency were associated with a decrease of MEP amplitude after cTBS (i.e. M1 inhibition). At T1, this correlation was significant for A-P pulses (r=-0.672, p=.017) but not for P-A pulses (r=-0.137, p=.671). At T2, this correlation was no longer significant (A-P pulses: r=-0.201, p=.552; P-A pulses: r=0.082, p=.800). Most interestingly, there was also a significant but reverse relationship between MEP latency and the effect of cTBS on excitability of the contralateral M1 which was significant for A-P pulses (T1: r=+0.693, p=.012; T2: r=0.623, p=.030) but not P-A pulses (T1: r=+0.31, p=.354; T2: r=-0.03, p=0.925). Furthermore, there was a highly significant relationship between MEP latency and the effect of cTBS on the N100 peak of TEPs elicited by stimulation of the contralateral M1 (T1: r=0.730, p=.007; T2: r=0.714, p=.009). In contrast there was no relationship between MEP latency and the effect of cTBS on the N100 peak elicited by stimulation of the ipsilateral M1 (T1: r=-0.143, p=.658; T2: r=-0.088, p=.785). Taken together, our results confirm that the inter-individual variability of the effect of cTBS on M1 excitability can be predicted by MEP latency, indicating that it is related to individual differences in the neuronal circuits activated by TMS. Furthermore, our results show that variability in MEP latency also predicts the remote effect of cTBS on the contralateral M1, as measured using MEPs and TEPs. Acknowledgements This work was supported by ERC Starting Grant PROBING-PAIN (336130)

Cerebellar theta burst stimulation in stroke patients with ataxia

Evidence for effective improvement of the symptoms of cerebellar stroke is still limited. Here, we investigated the effects of repetitive transcranial magnetic stimulation (rTMS) applied over the injured cerebellar hemisphere in six patients with posterior circulation stroke. We applied a two-week course of cerebellar intermittent theta burst stimulation (iTBS). Before and after the iTBS treatment, paired-pulse TMS methods were used to explore: i) the functional connectivity between the cerebellar hemisphere and the contralateral primary motor cortex (M1), by means of the cerebellar brain inhibition (CBI) protocol; and ii) the intracortical circuits in the contralateral M1, by means of the short intra-cortical inhibition (SICI) and intra-cortical facilitation (ICF) protocols. Patients were also evaluated using the Modified International Cooperative Ataxia Rating Scale (MICARS). Cerebellar iTBS induced a decrease in CBI and an increase in ICF at an interstimulus interval of 15 msec. These neurophysiological changes were paralleled by a clinical improvement, shown by the MICARS posture and gait subscale scores. Cerebellar iTBS could be a promising tool to promote recovery of cerebellar stroke patients.

Increased Bilateral Interactions in Middle-Aged Subjects

A hallmark of the age-related neural reorganization is that old versus young adults execute typical motor tasks by a more diffuse neural activation pattern including stronger ipsilateral activation during unilateral tasks. Whether such changes in neural activation are present already at middle age and affect bimanual interactions is unknown. We compared the amount of associated activity, i.e., muscle activity and force produced by the non-task hand and motor evoked potentials (MEPs) produced by magnetic brain stimulation between young (mean 24 years, n = 10) and middle-aged (mean 50 years, n = 10) subjects during brief unilateral (seven levels of % maximal voluntary contractions, MVCs) and bilateral contractions (4 × 7 levels of % MVC combinations), and during a 120-s-long MVC of sustained unilateral index finger abduction. During the force production, the excitability of the ipsilateral (iM1) or contralateral primary motor cortex (cM1) was assessed. The associated activity in the “resting” hand was ~2-fold higher in middle-aged (28% of MVC) versus young adults (11% of MVC) during brief unilateral MVCs. After controlling for the background muscle activity, MEPs in iM1 were similar in the two groups during brief unilateral contractions. Only at low (bilateral) forces, MEPs evoked in cM1 were 30% higher in the middle-aged versus young adults. At the start of the sustained contraction, the associated activity was higher in the middle-aged versus young subjects and increased progressively in both groups (30 versus 15% MVC at 120 s, respectively). MEPs were greater at the start of the sustained contraction in middle-aged subjects but increased further during the contraction only in young adults. Under these experimental conditions, the data provide evidence for the reorganization of neural control of unilateral force production as early as age 50. Future studies will determine if the altered neural control of such inter-manual interactions are of functional significance.

Cortical activation associated with asterixis in manifest hepatic encephalopathy

Severe hepatic encephalopathy gives rise to asterixis, a striking motor symptom also called flapping tremor, which is characterized by a sudden ceasing of muscle tone in all muscles of a limb. In this study, we aimed at scrutinizing the cortical activation associated with asterixis and unraveling the underlying pathophysiological mechanisms. We recorded simultaneously neural activity with magnetoencephalography (MEG) and muscle activity with surface EMG in nine patients with manifest hepatic encephalopathy showing asterixis. Asterixis events were detected semiautomatically and served as triggers for averaging MEG signals. Evoked responses averaged time-locked to asterixis events were subjected to equivalent current dipole (ECD) modeling. Additionally, we localized the strongest cortico-muscular coherence in the frequency of the co-occurring tremulousness. Evoked fields averaged time-locked to asterixis events were best explained by a single dipolar source in the contralateral primary motor cortex (M1, Talairach coordinates of mean localization: -40, -20, and 64; Brodmann area 4). This dipole showed a twofold field reversal, that is biphasic wave, with frontal dipole orientation at 49 ms before flap onset and 99 ms after flap onset. Conversely, two maxima with occipital dipole orientation were observed 2 ms and 160 ms after flap onset. Cortico-muscular coherence for the tremulousness was likewise localized in the contralateral M1 confirming earlier findings in the present patient cohort. Our results reveal an involvement of M1 in the generation of asterixis. As also tremulousness, also called mini-asterixis, was shown to originate in M1, asterixis and mini-asterixis may share common pathophysiological mechanisms.

Transcranial direct current stimulation reverses neurophysiological and behavioural effects of focal inhibition of human pharyngeal motor cortex on swallowing

The human cortical swallowing system exhibits bilateral but functionally asymmetric representation in health and disease as evidenced by both focal cortical inhibition (pre-conditioning with 1 Hz repetitive transcranial magnetic stimulation; rTMS) and unilateral stroke, where disruption of the stronger (dominant) pharyngeal projection alters swallowing neurophysiology and behaviour. Moreover, excitatory neurostimulation protocols capable of reversing the disruptive effects of focal cortical inhibition have demonstrated therapeutic promise in post-stroke dysphagia when applied contralaterally. In healthy participants (n = 15, 8 males, mean age (±SEM) 35 ± 9 years), optimal parameters of transcranial direct current stimulation (tDCS) (anodal, 1.5 mA, 10 min) were applied contralaterally after 1 Hz rTMS pre-conditioning to the strongest pharyngeal projection. Swallowing neurophysiology was assessed in both hemispheres by intraluminal recordings of pharyngeal motor-evoked responses (PMEPs) to single-pulse TMS as a measure of cortical excitability. Swallowing behaviour was examined using a pressure-based reaction time protocol. Measurements were made before and for up to 60 min post intervention. Subjects were randomised to active or sham tDCS after 1 Hz rTMS on separate days and data were compared using repeated measures ANOVA. Active tDCS increased PMEPs bilaterally (F1,14 = 7.4, P = 0.017) reversing the inhibitory effects of 1 Hz rTMS in the pre-conditioned hemisphere (F1,14 = 10.1, P = 0.007). Active tDCS also enhanced swallowing behaviour, increasing the number of correctly timed challenge swallows compared to sham (F1,14 = 6.3, P = 0.025). Thus, tDCS to the contralateral pharyngeal motor cortex reverses the neurophysiological and behavioural effects of focal cortical inhibition on swallowing in healthy individuals and has therapeutic potential for dysphagia rehabilitation.

The ipsilateral motor cortex does not contribute to long‐latency stretch reflex amplitude at the wrist

BackgroundA capacity for modulating the amplitude of the long-latency stretch reflex (LLSR) allows us to successfully interact with a physical world with a wide range of different mechanical properties. It has recently been demonstrated that stretch reflex modulation is impaired in both arms following monohemispheric stroke, suggesting that reflex regulation may involve structures on both sides of the motor system.MethodsWe examined the involvement of both primary motor cortices in healthy reflex regulation by eliciting stretch reflexes during periods of suppression of the motor cortices contra-and ipsilateral to the extensor carpi radialis in the nondominant arm.ResultsLLSRs were significantly attenuated during suppression of the contralateral, but not ipsilateral, motor cortex. Modulation of the LLSR was not affected by suppression of either primary motor cortex.ConclusionOur results confirm the involvement of the contralateral motor cortex in the transmission of the LLSR, but suggest that the ipsilateral motor cortex plays no role in reflex transmission and that neither motor cortex is involved in stability-dependent modulation of the LLSR. The implications of these results for reflex impairments following stroke are discussed.

Preserved Foot Motor Cortex in Patients With Complete Spinal Cord Injury

Background. Since the brain is intact, persons with a spinal cord injury (SCI) might benefit from a brain–computer interface (BCI) to improve mobility by making use of functional near-infrared spectroscopy (fNIRS). Objective. We aimed to use fNIRS to detect contralateral primary motor cortex activity during attempted foot movements in participants with complete SCI. Methods. A 6-channel fNIRS, including 2 reference channels, measured relative concentration changes of oxy- (HbO) and deoxy-hemoglobin (HbR) in the contralateral motor cortex for the right foot. Seven subjects, studied within 18 months after injury, performed 12 trials of attempted right foot and real hand movements. Results. T tests revealed significant HbO and HbR responses of the left motor cortex for attempted foot movements, but not for right hand movements. A 2-way repeated-measures analysis of variance revealed a larger decrease in HbR for attempted foot movements compared to hand movements. Individual results show major interindividual differences in (number of) channels activated and the sensitive chromophore (HbR or HbO). Conclusions. On group level, activity in the motor cortex of the foot can be measured with fNIRS in patients with complete SCI during attempted foot movements and might in principle be used in future BCI studies and applications.

Rearrangement of motor centers and its relationship to the neurological status of low-grade glioma examined on pre- and postoperative fMRI

ObjectiveWell-developed compensatory mechanisms, based on the phenomenon of brain plasticity, exist in patients with neuroepithelial tumors, especially with highly differentiated gliomas (WHO grade II). We studied phenomenon of rearrangement of sensorimotor cortex using functional magnetic resonance imaging (fMRI), and verified relationship between observed changes and results of neurological and neuropsychological assessment. MethodsStudy group included 20 patients with WHO grade II gliomas located within motor or sensory cortex. fMRI examination, as well as clinical, neurological (Karnofsky performance score [KPS] and Lovett's scale [Lo]), and neuropsychological assessment (Digit Coding Symbol Test and Digit Span Test) were performed pre-operatively and 3 months post-surgery. ResultsThere were no significant differences in pre- and postoperative performance status of patients. Although statistically insignificant, an increase in frequency of activation of primary and secondary cortical motor centers was observed postoperatively (p>0.05). Prior to surgery, motor centers were characterized by lower values of t-statistics than in postoperative period (p>0.05). In contrast, values of parameters describing the size of examined centers, i.e. mean number of clusters, were lower, but not statistically significant on postoperative examination (p>0.05). Compared to individuals without motor deficit, patients with preoperative Lo3/Lo4 paralysis showed significantly higher mean values of t-statistics in the accessory motor area on postoperative examination (p<0.05). ConclusionsThe processes of motor cortex rearrangement seemed to be associated with the pre- and postoperative neurological and neuropsychological status of patients. After contralateral primary motor cortex, accessory motor area was the second most frequently activated center, both pre- and postoperatively.

Transcranial Direct Current Stimulation (tDCS) of the Cortical Motor Areas in Three Cases of Cerebellar Ataxia

The excitability of the motor areas of the cerebral cortex is reduced in ataxia. Since transcranial direct current stimulation (tDCS) is a noninvasive neuromodulation technique able to increase the cortical excitability, we assessed the effect of anodal tDCS over the motor cortex in three patients with ataxia. A clinical evaluation, a video-taped SARA rating scale and a gait analysis with cinematic parameters, were performed pre- and post-sham and anodal tDCS cycle. The full cycle was composed by five consecutive constant current sessions of stimulation. Anodal tDCS (2.0 mA, 20 min,max current density: 0.0278 mA/cm2, max total charge:0.033 C/cm2) was performed on the M1 area of the most affected side. The contralateral primary motor cortex underwent cathodal stimulation (2.0 mA, 20 min, max current density:0.0278 mA/cm2, max total charge: 0.033 C/cm2). After anodal tDCS, gait analysis revealed an improvement of the symmetry of step execution and reduction of base-width lasting 30 days associated to patients’ perception of amelioration. No relevant changes were found after sham stimulation. Our results suggest tDCS can improve gait symmetry in patients with ataxia for a short-term period. Future researches are needed in order to standardize time, amplitude, and area of stimulation in order to reach a long lasting effect on cerebellar ataxia.

Dynamic cortical involvement in implicit anticipation during statistical learning

The prediction of future events is fundamental in a large number of critical neurobehavioral contexts including implicit motor learning. This learning process relies on the probabilities with which events occur, and is a dynamic phenomenon. The aim of present study was to investigate the development of anticipatory processes during implicit learning. A decision making task was employed in which the frequency of trial types was manipulated such that one trial type was disproportionately prevalent as compared to the remaining three trial types. A 275 channel whole-head magnetoencephalography (MEG) system was used to investigate the spatiotemporal distribution of event-related desynchronization (ERD) and synchronization (ERS). The results revealed that oscillations within the alpha (10–12Hz) and beta (14–30Hz) frequencies were associated with anticipatory processes in distinct networks in the course of learning. During early phases of learning the contralateral motor cortex, the anterior cingulate, the caudate and the inferior frontal gyrus showed ERDs within beta and alpha frequencies, putatively reflecting preparation of next motor response. As the task progressed, alpha ERSs in occipitotemporal regions and putamen likely reflect perceptual anticipation of the forthcoming stimuli.

Determination of ECoG information flow activity based on Granger causality and Hilbert transformation

Analysis of directional information flow patterns among different regions of the brain is important for investigating the relation between ECoG (electrocorticographic) and mental activity. The objective is to study and evaluate the information flow activity at different frequencies in the primary motor cortex. We employed Granger causality for capturing the future state of the propagation path and direction between recording electrode sites on the cerebral cortex. A grid covered the right motor cortex completely due to its size (approx. 8cm×8cm) but grid area extends to the surrounding cortex areas. During the experiment, a subject was asked to imagine performing two activities: movement of the left small finger and/or movement of the tongue. The time series of the electrical brain activity was recorded during these trials using an 8×8 (0.016–300Hz band with) ECoG platinum electrode grid, which was placed on the contralateral (right) motor cortex. For detection of information flow activity and communication frequencies among the electrodes, we have proposed a method based on following steps: (i) calculation of analytical time series such as amplitude and phase difference acquired from Hilbert transformation, (ii) selection of frequency having highest interdependence for the electrode pairs for the concerned time series over a sliding window in which we assumed time series were stationary, (iii) calculation of Granger causality values for each pair with selected frequency. The information flow (causal influence) activity and communication frequencies between the electrodes in grid were determined and shown successfully. It is supposed that information flow activity and communication frequencies between the electrodes in the grid are approximately the same for the same pattern. The successful employment of Granger causality and Hilbert transformation for the detection of the propagation path and direction of each component of ECoG among different sub-cortex areas were capable of determining the information flow (causal influence) activity and communication frequencies between the populations of neurons successfully.

P 165. Transcranial electrical acceleration of motor skill learning: Direct comparison of different brain stimulation paradigms

Transcranial electrical stimulation (TES) has been shown to enhance motor learning. Several stimulation protocols are known to be effective, but have not yet been directly compared for practical motor learning. Electrode placement and stimulation parameters were varied on a realistic motor task to allow a direct comparison of their efficacy to enhance complex motor skill learning. A novel, complex, continuous motor task was developed for the study: the tracing task. Participants traced over a series of template words and shapes on a graphics tablet with their nondominant (left) hand in a manner similar to handwriting while performance was evaluated by calculating how close the trace was to the template. The experiment took place over three days in order to measure both online and offline learning effects. Electrode montages and stimulation parameters varied as follows: transcranial direct current stimulation (tDCS) with anodal stimulation over the contralateral motor cortex and cathodal stimulation over either the ipsilateral motor cortex or ipsilateral supraorbital area; high frequency (100–640 Hz) transcranial random noise stimulation (tRNS) over the supraorbital area and the contralateral motor cortex. These were compared with sham stimulation and tRNS of the supraorbital area and posterior temporal lobe (T6 of 10–20 system) as a reference active stimulation region. TES was applied for 20 min with a current density of 60 μ A/cm2 for tDCS and tRNS. TES of all types applied over the motor cortex improved motor skill acquisition over 2 days of training and a follow up compared to sham stimulation. In all groups, this effect was driven by large online effects within sessions, which developed faster in the tDCS groups compared to the tRNS group. In the active control experiment for region specificity (posterior temporal tRNS) tRNS was less effective and altered subcomponents of learning differently (offline stabilization). TES is effective at improving motor learning with motor cortex stimulation. tRNS is as effective as tDCS, and may be preferable as nonpolarised currents appear safer (demonstrated in deep brain stimulation) and do not have cathodal inhibition effects.