Different activation of presupplementary motor area, supplementary motor area proper, and primary sensorimotor area, depending on the movement repetition rate in humans

Altered frontal-mediated inhibition and white matter connectivity in pediatric chronic tic disorders

Tics are unique from most movement disorders, in that they are partially suppressible. As part of the inhibitory motor network, the pre-supplementary motor area is engaged in motor control and may be involved in tic physiology. We used dual-site transcranial magnetic stimulation to assess inhibitory connectivity between right pre-supplementary motor area and left primary motor cortex, which has previously been demonstrated in healthy adults. We also used diffusion tensor imaging to investigate white matter connectivity in children with chronic tics. Twelve children with chronic tic disorder and fourteen typically developing controls underwent MRI with diffusion tensor imaging indices analysis followed by single and paired-pulse transcranial magnetic stimulation with conditioning pulse over the right pre-supplementary motor area followed by left motor cortex test pulse. Neurophysiologic and imaging data relationships to measures of tic severity and suppressibility were also evaluated in tic patients. Pre-supplementary motor area-mediated inhibition of left motor cortex was present in healthy control children but not in chronic tic disorder participants. Less inhibition correlated with worse tic suppressibility (ρ = - 0.73, p = 0.047). Imaging analysis showed increased fractional anisotropy in the right superior longitudinal fasciculus, corpus callosum, corona radiata and posterior limb of the internal capsule (p < 0.05) in tic participants, which correlated with lower self-reported tic suppressibility (ρ = - 0.70, p = 0.05). Physiologic data revealed impaired frontal-mediated motor cortex inhibition in chronic tic participants, and imaging analysis showed abnormalities in motor pathways. Collectively, the neurophysiologic and neuroanatomic data correlate with tic suppressibility, supporting the relevancy to tic pathophysiology.

Closed-loop intracranial stimulation alters movement timing in humans

BACKGROUND

A prime objective driving the recent development of human neural prosthetics is to stimulate neural circuits in a manner time-locked to ongoing brain activity. The human supplementary motor area (SMA) is a particularly useful target for this objective because it displays characteristic neural activity just prior to voluntary movement.

OBJECTIVE

Here, we tested a method that detected activity in the human SMA related to impending movement and then delivered cortical stimulation with intracranial electrodes to influence the timing of movement.

METHODS

We conducted experiments in nine patients with electrodes implanted for epilepsy localization: five patients with SMA electrodes and four control patients with electrodes outside the SMA. In the first experiment, electrocorticographic (ECoG) recordings were used to localize the electrode of interest during a task involving bimanual finger movements. In the second experiment, a real-time sense-and-stimulate (SAS) system was implemented that delivered an electrical stimulus when pre-movement gamma power exceeded a threshold.

RESULTS

Stimulation based on real-time detection of this supra-threshold activity resulted in significant slowing of motor behavior in all of the cases where stimulation was carried out in the SMA patients but in none of the patients where stimulation was performed at the control site.

CONCLUSIONS

The neurophysiological correlates of impending movement can be used to trigger a closed loop stimulation device and influence ongoing motor behavior in a manner imperceptible to the subject. This is the first report of a human closed loop system designed to alter movement using direct cortical recordings and direct stimulation.

Time to Move Again: Does the Bereitschaftspotential Covary with Demands on Internal Timing?

When Bereitschaftspotentials (BPs) are measured, participants are required to voluntarily perform a predefined number of identical movements, with varying intervals between movements, exceeding some obligatory minimum interval. Participants might cope with these demands on timing by installing a slow, broadly tuned rhythm of activation, serving as an internal trigger for executing movements in time. The BP might reflect the rising phase of this activation, culminating at the movement. If so (i) not only should BP amplitudes become larger, but BPs should also have their onsets earlier before movements when longer minimum intervals are required between movements (Experiment 1). Further, (ii) BP amplitudes should covary with demands on internal timing: decrease when internal timing is less necessary and increase in the other case. Variation of timing demands was realized by requiring participants to count vs. not to count the seconds between movements (Experiment 1) and by regular vs. irregular vs. no ticking of a clock (Experiment 2). Prediction (i) was confirmed while prediction (ii) was not. Thus, BP onsets did vary in accordance with the temporal constraints about when the movements should be performed, suggesting some relation to timing mechanisms, but we could not provide evidence for the notion that the process reflected by BPs is this timing mechanism.

Cortical current source estimation from electroencephalography in combination with near-infrared spectroscopy as a hierarchical prior

Previous simulation and experimental studies have demonstrated that the application of Variational Bayesian Multimodal EncephaloGraphy (VBMEG) to magnetoencephalography (MEG) data can be used to estimate cortical currents with high spatio-temporal resolution, by incorporating functional magnetic resonance imaging (fMRI) activity as a hierarchical prior. However, the use of combined MEG and fMRI is restricted by the high costs involved, a lack of portability and high sensitivity to body-motion artifacts. One possible solution for overcoming these limitations is to use a combination of electroencephalography (EEG) and near-infrared spectroscopy (NIRS). This study therefore aimed to extend the possible applications of VBMEG to include EEG data with NIRS activity as a hierarchical prior. Using computer simulations and real experimental data, we evaluated the performance of VBMEG applied to EEG data under different conditions, including different numbers of EEG sensors and different prior information. The results suggest that VBMEG with NIRS prior performs well, even with as few as 19 EEG sensors. These findings indicate the potential value of clinically applying VBMEG using a combination of EEG and NIRS.

Reconstruction of two-dimensional movement trajectories from selected magnetoencephalography cortical currents by combined sparse Bayesian methods

Reconstruction of movements from non-invasively recorded brain activity is a key technology for brain-machine interfaces (BMIs). However, electroencephalography (EEG) or magnetoencephalography (MEG) inevitably records a mixture of signals originating from many cortical regions, and thus it is not only less effective than invasive methods but also poses more difficulty for incorporating neuroscience knowledge. We combined two sparse Bayesian methods to overcome this difficulty. First, thousands of cortical currents were estimated on the order of millimeters and milliseconds by a hierarchical Bayesian MEG inverse method, and then a sparse regression method automatically selected only relevant cortical currents in accurate reconstruction of movements by a linear weighted sum of their time series. Using the combined methods, we reconstructed two-dimensional trajectories of the index fingertip during pointing movements to various directions by moving the wrist joint. A good generalization (reconstruction) performance was observed for test datasets: mean error between the predicted and actual positions was 15 mm, which was 7% of the path length of the required movement. The reconstruction accuracy of the proposed method was significantly higher than directly using MEG sensor signals. Moreover, spatial distribution and temporal characteristics of weight values revealed that the primary sensorimotor, higher motor, and parietal regions mainly contributed to the reconstruction with expected time courses. These results suggest that the combined sparse Bayesian methods provide effective means to predict movement trajectory from non-invasive brain activity directly related to sensorimotor control.

Encoding of speed and direction of movement in the human supplementary motor area

OBJECT

The supplementary motor area (SMA) plays an important role in planning, initiation, and execution of motor acts. Patients with SMA lesions are impaired in various kinematic parameters, such as velocity and duration of movement. However, the relationships between neuronal activity and these parameters in the human brain have not been fully characterized. This is a study of single-neuron activity during a continuous volitional motor task, with the goal of clarifying these relationships for SMA neurons and other frontal lobe regions in humans.

METHODS

The participants were 7 patients undergoing evaluation for epilepsy surgery requiring implantation of intracranial depth electrodes. Single-unit recordings were conducted while the patients played a computer game involving movement of a cursor in a simple maze.

RESULTS

In the SMA proper, most of the recorded units exhibited a monotonic relationship between the unit firing rate and hand motion speed. The vast majority of SMA proper units with this property showed an inverse relation, that is, firing rate decrease with speed increase. In addition, most of the SMA proper units were selective to the direction of hand motion. These relationships were far less frequent in the pre-SMA, anterior cingulate gyrus, and orbitofrontal cortex.

CONCLUSIONS

The findings suggest that the SMA proper takes part in the control of kinematic parameters of endeffector motion, and thus lend support to the idea of connecting neuroprosthetic devices to the human SMA.

Signal quality of simultaneously recorded invasive and non-invasive EEG

Both invasive and non-invasive electroencephalographic (EEG) recordings from the human brain have an increasingly important role in neuroscience research and are candidate modalities for medical brain-machine interfacing. It is often assumed that the major artifacts that compromise non-invasive EEG, such as caused by blinks and eye movement, are absent in invasive EEG recordings. Quantitative investigations on the signal quality of simultaneously recorded invasive and non-invasive EEG in terms of artifact contamination are, however, lacking. Here we compared blink related artifacts in non-invasive and invasive EEG, simultaneously recorded from prefrontal and motor cortical regions using an approach suitable for detection of small artifact contamination. As expected, we find blinks to cause pronounced artifacts in non-invasive EEG both above prefrontal and motor cortical regions. Unexpectedly, significant blink related artifacts were also found in the invasive recordings, in particular in the prefrontal region. Computing a ratio of artifact amplitude to the amplitude of ongoing brain activity, we find that the signal quality of invasive EEG is 20 to above 100 times better than that of simultaneously obtained non-invasive EEG. Thus, while our findings indicate that ocular artifacts do exist in invasive recordings, they also highlight the much better signal quality of invasive compared to non-invasive EEG data. Our findings suggest that blinks should be taken into account in the experimental design of ECoG studies, particularly when event related potentials in fronto-anterior brain regions are analyzed. Moreover, our results encourage the application of techniques for reducing ocular artifacts to further optimize the signal quality of invasive EEG.

What is the Bereitschaftspotential?

Since discovery of the slow negative electroencephalographic (EEG) activity preceding self-initiated movement by Kornhuber and Deecke [Kornhuber HH, Deecke L. Hirnpotentialänderungen bei Willkurbewegungen und passiven Bewegungen des Menschen: Bereitschaftspotential und reafferente Potentiale. Pflugers Archiv 1965;284:1-17], various source localization techniques in normal subjects and epicortical recording in epilepsy patients have disclosed the generator mechanisms of each identifiable component of movement-related cortical potentials (MRCPs) to some extent. The initial slow segment of BP, called 'early BP' in this article, begins about 2 s before the movement onset in the pre-supplementary motor area (pre-SMA) with no site-specificity and in the SMA proper according to the somatotopic organization, and shortly thereafter in the lateral premotor cortex bilaterally with relatively clear somatotopy. About 400 ms before the movement onset, the steeper negative slope, called 'late BP' in this article (also referred to as NS'), occurs in the contralateral primary motor cortex (M1) and lateral premotor cortex with precise somatotopy. These two phases of BP are differentially influenced by various factors, especially by complexity of the movement which enhances only the late BP. Event-related desynchronization (ERD) of beta frequency EEG band before self-initiated movements shows a different temporospatial pattern from that of the BP, suggesting different neuronal mechanisms for the two. BP has been applied for investigating pathophysiology of various movement disorders. Volitional motor inhibition or muscle relaxation is preceded by BP quite similar to that preceding voluntary muscle contraction. Since BP of typical waveforms and temporospatial pattern does not occur before organic involuntary movements, BP is used for detecting the participation of the 'voluntary motor system' in the generation of apparently involuntary movements in patients with psychogenic movement disorders. In view of Libet et al.'s report [Libet B, Gleason CA, Wright EW, Pearl DK. Time of conscious intention to act in relation to onset of cerebral activity (readiness-potential). The unconscious initiation of a freely voluntary act. Brain 1983;106:623-642] that the awareness of intention to move occurred much later than the onset of BP, the early BP might reflect, physiologically, slowly increasing cortical excitability and, behaviorally, subconscious readiness for the forthcoming movement. Whether the late BP reflects conscious preparation for intended movement or not remains to be clarified.

Prefrontal cortex activity in self-initiated movements is condition-specific, but not movement-related

Activity of the prefrontal cortex (PFC) has been observed in previous block-design brain imaging studies of self-initiated movements. However, the meaning of these activations remained unclear. A functional MRI experiment was carried out, which utilized an epoch and an event-related analysis approach to the data. We hypothesized that event-related activity of the PFC would argue for a contribution to movement preparation. In contrast, epoch-, but not event-related activity pointed to tonic activations, probably reflecting enhanced attentional states or working memory processing. Twenty-one subjects were examined with 845 T2*-weighted images. During active phases, subjects were instructed to perform self-initiated movements of the right index finger with intertrial intervals of about 8 s. On single subject level, epoch- and event-related regressors were entered into a combined model, estimating the exclusive contribution of either regressor. For statistical inference on multisubject level, random effects analyses were performed. For the epoch regressor, activity within the right dorso- and ventrolateral prefrontal cortex, the bilateral insula, and the right inferior parietal lobe was observed. The event-related regressor detected activity within the right inferior parietal lobe, ventral from the activity found with the epoch regressor. The present results indicate a condition-, but not a movement-related function of the PFC in self-initiated movements. Furthermore, anatomically distinct regions within the inferior parietal cortex seem to be involved in condition-specific and movement-related processes. The observed condition-specific activations are suggested to reflect attentional or working memory processes, supervising task performance, rather than movement preparation or initiation.

Intracranial EEG and human brain mapping

This review is an attempt to highlight the value of human intracranial recordings (intracranial electro-encephalography, iEEG) for human brain mapping, based on their technical characteristics and based on the corpus of results they have already yielded. The advantages and limitations of iEEG recordings are introduced in detail, with an estimation of their spatial and temporal resolution for both monopolar and bipolar recordings. The contribution of iEEG studies to the general field of human brain mapping is discussed through a review of the effects observed in the iEEG while patients perform cognitive tasks. Those effects range from the generation of well-localized evoked potentials to the formation of large-scale interactions between distributed brain structures, via long-range synchrony in particular. A framework is introduced to organize those iEEG studies according to the level of complexity of the spatio-temporal patterns of neural activity found to correlate with cognition. This review emphasizes the value of iEEG for the study of large-scale interactions, and describes in detail the few studies that have already addressed this point.

Neuroelectric source imaging of steady-state movement-related cortical potentials in human upper extremity amputees with and without phantom limb pain

Whereas several studies reported a close relationship between changes in the somatotopic organization of primary somatosensory cortex and phantom limb pain, the relationship between alterations in the motor cortex and amputation-related phenomena has not yet been explored in detail. This study used steady-state movement-related cortical potentials (MRCPs) combined with neuroelectric source imaging to assess the relationship of changes in motor cortex and amputation-related phenomena such as painful and non-painful phantom and residual limb sensations, telescoping, and prosthesis use. Eight upper limb amputees were investigated. A significant positive relationship between reorganization of the motor cortex (distance of the MRCP source location from the mirrored source for hand movement) and phantom limb pain was found. Non-painful phantom sensations as well as painful and non-painful residual limb sensations were unrelated to motor cortical reorganization. A higher amount of motor reorganization was associated with less daily prosthesis use, which also tended to be related to more severe phantom limb pain. These results extend previous findings of a positive relationship between somatosensory reorganization and phantom limb pain to the motor domain and suggest a potential positive effect of prosthesis use on phantom limb pain and cortical reorganization.

Human eye fields in the frontal lobe as studied by epicortical recording of movement‐related cortical potentials

We studied the generator location of premovement subcomponents of movement-related cortical potentials (MRCPs) [Bereitschaftspotential (BP), negative slope (NS') and motor potential (MP)] associated with voluntary, self-paced horizontal saccade in the human frontal lobe. Self-paced horizontal saccade, wrist (or middle finger) extension and foot dorsiflexion were employed in 10 patients (lateral surface of the frontal lobe in seven and mesial in three) as part of the presurgical evaluation, and data of five patients (lateral in four and mesial in three) were used in the final analysis. On the lateral frontal lobe, the maximum BP, NS' or MP with horizontal saccade was seen at or 1-2 cm rostral to the hand, arm or face area of the primary motor cortex (MI) in all four subjects investigated. This area exactly corresponded to the frontal eye field (FEF) identified by electrical stimulation. The amplitude of MRCPs with saccade was smaller than that with hand movements. On the mesial surface, within the supplementary motor area (SMA) proper, BP and/or NS' for horizontal saccade was located 1-2 cm rostral to that for hand and foot movements. BP and/or NS' delineated the supplementary eye field (SEF) at the rostral part of the SMA proper, and SEF partly overlapped with the hand and foot areas of the SMA proper. At the area just rostral to the vertical anterior commissure line and/or the pre-SMA defined by electrical stimulation, BP and/or NS' was seen invariably, regardless of the sites of movements, and in contrast with the SMA proper, there was no somatotopic representation. No clear MPs were elicited by eye movements on the mesial surface. In one of the two subjects whose MRCPs with horizontal saccade were recorded simultaneously from the lateral and mesial surfaces of the frontal lobe, BP from the SEF and pre-SMA preceded that from the FEF. It is concluded that MRCPs with horizontal saccade are useful for defining the FEF, SEF and pre-SMA, and that the SEF and pre-SMA become active in preparation for horizontal saccade earlier than the FEF.

Control of hand movements after striatocapsular stroke: high-resolution temporal analysis of the function of ipsilateral activation

OBJECTIVE

Hemiparesis due to infarction of the middle cerebral artery has become an increasingly important focus of research on cortical plasticity. Positron emission tomography and functional magnetic resonance imaging studies in such patients found involvement of the hemisphere ipsilateral to the affected hand related to movements of this hand. To understand the function of this ipsilateral activation, the present study investigated movement-related electroencephalogram (EEG) potentials in patients and healthy control subjects to measure timing of ipsi- and contralateral activation relative to movement onset.

METHODS

Thirteen patients were investigated in their chronic stage. Their pyramidal tracts were affected by infarctions of the middle cerebral artery at striatocapsular level. EEG potentials were recorded from 26 scalp electrodes while patients were pressing a key with their right or left index finger within a warned choice-response task.

RESULTS

Beginning 200 ms before responses of the affected hand, there was normal contralateral preponderance of EEG negativity. Briefly after response onset, however, the other unaffected hemisphere, ipsilateral to the responding hand, became additionally active. This pattern did not occur with responses made by the unaffected hand nor in healthy participants.

CONCLUSIONS

The timing of the onset of ipsilateral activity precludes its role in response initiation. Rather, this activity may indicate reflex-like activation of the unaffected motor system to compensate for possible failure of the affected hand.

Cortical motor mapping in epilepsy patients: information from subdural electrodes in presurgical evaluation

It is essential to delineate an epileptogenic zone and to define the eloquent cortices at or close to the epileptogenic zone in patients with neocortical epilepsy for epilepsy surgery. Prolonged implantation of the subdural electrode in presurgical evaluation is currently one of the best clinical methods to provide the essential information before epilepsy surgery. Electric cortical stimulation and recording of sensory evoked potentials by means of subdural electrodes are widely used for functional cortical mapping. Bereitschaftspotential (BP) is clinically useful to delineate the primary and nonprimary motor cortices such as supplementary motor area proper (SMA proper) and pre-SMA, because BP occurs for any type of voluntary movements of the body, and because it is not associated with the risk of seizure induction in contrast with high-frequency cortical electric stimulation. Single-pulse electric cortical stimulation to record motor evoked potentials (MEPs) also could complement currently used high-frequency cortical electric stimulation, especially for mapping of the primary motor and premotor cortices with lower risk of seizure induction.

Increased synchronization of cortical oscillatory activities between human supplementary motor and primary sensorimotor areas during voluntary movements

In human, both primary and nonprimary motor areas are involved in the control of voluntary movements. However, the dynamics of functional coupling among different motor areas has not been fully clarified yet. Because it has been proposed that the functional coupling among cortical areas might be achieved by the synchronization of oscillatory activity, we investigated the electrocorticographic coherence between the supplementary motor and primary sensorimotor areas (SMA and S1-M1) by means of event-related partial coherence analysis in 11 intractable epilepsy patients. We found premovement increase of coherence between the SMA proper and S1-M1 at the frequency of 0-33 Hz and between the pre-SMA and S1-M1 at 0-18 Hz. Coherence between the SMA proper and M1 started to increase 0.9 sec before the movement onset and peaked 0.3 sec after the movement. There was no systematic difference within the SMA (SMA proper vs pre-SMA) or within the S1-M1, in terms of the time course as well as the peak value of coherence. The phase spectra revealed near-zero phase difference in 57% (20 of 35) of region pairs analyzed, and the remaining pairs showed inconsistent results. This increase of synchronization between multiple motor areas in the preparation and execution of voluntary movements may reflect the multiregional functional interactions in human motor behavior.

Cerebral activation during a simple force production task: changes in the time course of the haemodynamic response

An event-related paradigm was used to investigate the fMRI signal from the primary motor cortex (M1) and the supplementary motor area (SMA) during isolated isometric wrist extension at five different force levels. There was only a weak trend towards increased area of activation with increased force output, but there was a force-related increase in percentage change of signal within voxels in M1 (Kendall Tc = 0.48, p < 0.01), which may indicate control of force output by variation of neural firing rate. In SMA there was a correlation between peak force output and time-to-peak of the haemodynamic response in SMA (Kendall Tc = 0.74, p < 0.0001). This unexpected finding of a task-related change in the shape of the haemodynamic response within a single brain area requires further investigation. It may indicate a slower rise time at lower perfusion rates, or may be the result of inhibitory processes in motor control.