Magneto-encephalographic correlates of the lateralized readiness potential.

To determine the onset of movement-related EEG activity accompanying stimulus-induced movements, it is commonly isolated from overlapping stimulus-related activity by a subtraction procedure, yielding the lateralized readiness potential (LRP). In order to elucidate the generation of the LRP and to explore whether magnetoencephalographic (MEG) measures have advantages over the LRP as a measure of response selection, MEG activity was recorded in four healthy adults during self-paced and stimulus-induced hand movements. Self-paced movements were preceded by readiness fields in all subjects, explained by sources in contralateral and (for 2/8 response sides) also ipsilateral hemispheres. Movement-related activity preceding stimulus-induced movements could only be modeled adequately when stimulus-related activity was removed by subtracting MEG signals for left and right hand movements. Thus identified source locations showed no systematic deviation from the sources for readiness fields, supporting a generation of the movement-related activity in primary motor cortex. The corresponding source waveforms allowed latency determinations of motor cortex activity as markers for response-choice timing. MEG thus provides information on the time course of hand-specific motor cortex activation for each hemisphere separately, where the electro-encephalographic LRP provides a composite measure for both hemispheres.     

Implication of sensorimotor integration in the generation of periodic dystonic myoclonus in subacute sclerosing panencephalitis (SSPE).

To clarify the mechanism of periodic dystonic myoclonus in subacute sclerosing panencephalitis (SSPE), a 22-year-old patient with a clinical diagnosis of SSPE was electrophysiologically investigated. Involuntary movements consisted of generalized dystonic posturing which occurred quasiperiodically once every 4 to 8 seconds. Effects of sensory stimuli and voluntary movements were studied by means of polygraphic recording of surface electromyogram (EMG), scalp electroencephalogram (EEG), and magnetoencephalogram (MEG). EEG showed quasi-periodic, generalized, transient complexes synchronous to each dystonic myoclonus, which were preceded by a slow negative EEG shift at the parietal region by approximately 5 seconds. Neither external stimuli nor self-paced movements alone influenced the periodicity of dystonic myoclonus or EEG complexes. In the reaction time task, however, the external stimuli given as an imperative cue to execute a motor task elicited dystonic myoclonus and generalized EEG complexes only if they were presented in the latter segment of the interval between the two successive EEG complexes while the slow negative EEG shift appeared. These findings suggest that EEG complexes and periodic movements spontaneously occur when cortical excitability reaches a certain critical level, but both phenomena are elicited even before if the sensory stimuli as an imperative signal requiring motor execution are presented. This finding most likely implies involvement of the sensorimotor integration mechanism in these periodic phenomena.     

Movement-related slow potentials. I. A contrast between finger and foot movements in right-handed subjects

Movement-related potentials ( MRPs ) preceding a finger flexion and a plantar flexion of the foot on either side were compared over the frontal, central and parietal areas of both hemispheres. MRP amplitudes were larger preceding foot than preceding finger movements. In the first case their onset was earlier and their presence in the frontal area was more marked. Prior to a finger flexion amplitudes over the hemisphere contralateral to the movement side were larger than those recorded over the ipsilateral hemisphere. On the contrary, prior to a plantar flexion of the foot, amplitudes were larger over the hemisphere ipsilateral to the movement. These findings point to differently localized sources of the MRPs in the two cases. In other experiments larger amplitudes preceding foot movements were found near the midline. It is suggested that the ipsilateral preponderance prior to foot movements is caused by a contralateral source in the depth near the longitudinal fissure. The dipoles are presumably directed obliquely to the median plane. The ipsilateral preponderance is present both prior to and following the plantar flexion. This suggests comparable directions of the dipoles in the motor and somatosensory areas.     

Movement related slow potentials. II. A contrast between finger and foot movements in left-handed subjects

Finger and foot movement related potentials (MRPs) were recorded over the frontal, central and parietal areas of both hemispheres in 20 left-handed subjects. A unilateral flexion of the index finger and a plantar flexion of the foot were studied on either side. MRPs were larger preceding foot movements than preceding finger movements, their onset being earlier also. Prior to a finger flexion amplitudes were larger over the hemisphere contralateral to the movement than over the ipsilateral hemisphere. Preceding a foot movement, however, amplitudes were larger over the ipsilateral hemisphere. These results indicate differently localized sources of the MRPs in the two kinds of movement, in accordance with data obtained in right-handed subjects. No indication of a hemisphere effect, possibly related to motor dominance, was found in left-handers. This is in contrast to a slight hemisphere effect found with foot movements in right-handed subjects in the former study.     

Ictal magnetic source imaging as a localizing tool in partial epilepsy

OBJECTIVE: To determine the feasibility and usefulness of ictal magnetoencephalography (MEG) recordings in the presurgical evaluation of patients with epilepsy. METHODS: Twenty patients with frequent or predictable seizures were studied with the intent to capture seizures using a large array single-probe 37-channel or dual-probe 74-channel biomagnetometer. RESULTS: Successful ictal MEG recordings were made in 6 of 20 patients with neocortical epilepsy. In one other patient, a seizure was captured but movement artifact made MEG recordings impossible. As determined by invasive EEG recording and postsurgical outcome, ictal MEG provided localizing information that was superior to interictal MEG in three of the six patients. Localization of ictal onset by MEG was at least equivalent to invasive EEG in five of the six patients, and was superior in two patients as determined by postsurgical outcome. CONCLUSION: Larger studies are necessary to confirm that ictal MEG recordings in patients with frequent or easily provoked neocortical seizures can contribute localizing information equivalent or superior to invasive EEG recording.     

Vestibular-oculomotor interaction in cat eye-head movements

When cats make slow scanning head movements, intersaccadic counterrotary eye movements are driven by the vestibulo-ocular reflex, but reset or forward saccades are not directly affected by vestibular afference. When the movements are rapid (approximately 200 deg./sec), large (greater than 40 degrees), and executed in single step shifts gaze (whether in the dark or during visual fixation shifts between known targets), there is no longer any clear vestibular effect on any eye movements during the gaze shift. The vestibulo-ocular reflex is active only at the beginning of head rotation and again at its termination as the gaze reaches its goal, even in the absence of vision. It is postulated that head-in-space and eye-in-orbit movements are perfectly monitored to adjust the amplitude of gaze shifts, despite the lack of overt vestibular effects on eye movements.     

Advance movement preparation of eye, foot, and hand: a comparative study using movement-related brain potentials

The present study was designed to test the inter-relationship between generalized motor programs (GMPs) and movement preparation by asking participants to perform movements with eye, foot, or hand. In two independent experiments a response precuing task was employed that combined the recording of movement-related brain potentials (MRPs) with dipole source analysis. Behavioral results indicated the utilization of advance information about movement direction and effector. When eye and hand movements were involved (experiment1) partial advance information about response side but not effector induced parallel motor programming of eye and hand at an abstract but not effector-specific level. In contrast, when partial precues specified side of a forthcoming hand or foot movement (experiment 2) foot and hand were prepared in parallel both at abstract and at effector-specific levels of motor programming. Consistent with the GMP view, these results indicate that effector-specific preparation is possible even when the effector is not yet known as long as a common motor program controls the demanded movements. However, because parallel specification of divergent movement pattern (eye, hand) at an abstract level was not predicted by the GMP, we propose a model of advance movement preparation that takes into account neurofunctional considerations.     

Ambulatory foot temperature measurement: a new technique in polyneuropathy evaluation

Complaints of abnormal foot temperature are common among patients with polyneuropathy. However, there is no published method of ambulatory foot temperature measurement to identify possible thermoregulatory disturbances in these patients. We configured a digital electronic thermometer and thermocouple to measure and record distal foot and ambient temperatures simultaneously every minute for 24 to 48 h. Sixteen patients with polyneuropathy and 5 normal subjects were studied; 12 patients with polyneuropathy and 4 normal subjects had at least 24 h of successful recording. The data obtained from these patients were consistent and easily summarized by standard statistical methods. In the others, technical difficulties produced nonphysiological readings. In the patients with polyneuropathy, changes in foot temperature mirrored ambient temperature fluctuations more closely than in normal subjects. This technique shows promise in studying temperature regulation in the feet and may provide new insights into neuropathy-associated pain and the pathogenesis of polyneuropathy.     

A spatial oculomotor memory-task performance produces a task-related slow shift in human electroencephalography

Electroencephalographic (EEG) deflections in humans related to the performance of memory-guided saccades were studied in this work. The EEG deflections were recorded during 2 spatial oculomotor delayed response tasks in which the subject was instructed to make a saccade either to the right or to the left depending on the spatial location of the cue which had been shown in the beginning of the delay period. The EEG deflections were compared to those recorded during a control task in which the subject also made a saccade to the right or to the left after a delay but the requirement to keep spatial information actively in mind was minimized. A slow delay-related shift was recorded during all task conditions. The slow shift was positive in the most frontal and negative in the more posterior recording sites. The negative slow shift in the more posterior recording sites was larger in the memory tasks than in the control task. Since the memory and the control tasks differed mainly in their requirement to hold spatial information in mind it is suggested that the difference in the magnitude of slow shifts between the memory and the control tasks reflects neural activity related to spatial working memory. But although the oculomotor responses in all tasks were similar, the preparatory activities for the impending eye movements may not have been similar and in addition to working memory may have contributed to the observed differences in the slow shifts.     

Spatio-temporal brain dynamics underlying saccade execution, suppression, and error-related feedback

Human and nonhuman animal research has outlined the neural regions that support saccadic eye movements. The aim of the current work was to outline the sequence by which distinct neural regions come on-line to support goal-directed saccade execution and error-related feedback. To achieve this, we obtained behavioral responses via eye movement recordings and neural responses via magnetoencephalography (MEG), concurrently, while participants performed an antisaccade task. Neural responses were examined with respect to the onset of the saccadic eye movements. Frontal eye field and visual cortex activity distinguished subsequently successful goal-directed saccades from (correct and erroneous) reflexive saccades prior to the deployment of the eye movement. Activity in the same neural regions following the saccadic movement distinguished correct from incorrect saccadic responses. Error-related activity in the frontal eye fields preceded that from visual regions, suggesting a potential feedback network that may drive corrective eye movements. This work provides the first empirical demonstration of simultaneous remote eyetracking and MEG recording. The coupling of behavioral and neuroimaging technologies, used here to characterize dynamic brain networks underlying saccade execution and error-related feedback, demonstrates a novel within-paradigm converging evidence approach by which to outline the neural underpinnings of cognition.     

Cortical potentials preceding voluntary movement: evidence for three periods of preparation in man

We have recorded movement-related cortical potentials (MRCPs) to voluntary middle finger extension from 10 young and 10 old subjects free of neurological disease using the method of detecting EMG onset associated with each movement described by Barrett et al. (1985). The slow potential shifts preceding movement were measured by fitting a linear regression line to the wave forms to obtain a measure of their slope. Three separate potential shifts were identified. The first had a scalp distribution and onset latency similar to the Bereitschaftspotential (BP) first reported by Kornhuber and Deecke (1964, 1965). The potential shift immediately preceding movement corresponded with the NS' of Shibasaki et al. (1980). We identified, for the first time, a third shift intervening between BP and NS' and named it the intermediate shift (IS). The onset of BP occurred about 1.6 sec before EMG onset and was followed by IS which began about 875 msec before movement. The onset of NS' occurred 300 msec before EMG onset and terminated about 90 msec before this event. The slope of BP preceding right finger movement was steeper than that preceding left hand movement in all our right-handed subjects. The distribution of BP was symmetric about the midline. The IS potential shift had a slope which was steeper on the average preceding left finger movement than right. The distribution of IS was symmetric about the midline preceding left finger movement but had a contralateral tendency preceding right hand movement. NS' had a maximum slope at contralateral electrodes over the hand motor area and parietal areas. It was suggested that the BP potential shift originates in the supplementary motor area on the medial surface of the cerebral cortex. The differing distribution of the IS shift for the two hands suggests that this potential may be generated bilaterally preceding left finger movement but from the contralateral hemisphere only preceding movement of the right finger. The most likely origin of this potential was thought to be superior premotor cortex. NS' was considered to originate in primary motor cortex with possible contributions from other cortical areas associated with movement.     

Inter-hemispheric lateralization of event related potentials; motoric versus non-motoric cortical activity

To study hemispheric lateralization of cortical potentials associated with motoric and non-motoric function, cortical activity was recorded accompanying either finger extension or saccadic eye movements in a contingent negative variation (CNV) paradigm. Subjects viewed computer-generated pacing stimuli, presented in the left visual hemi-field, and were instructed to either initiate or inhibit a motor response following an imperative signal. Motoric lateralization was assessed by means of the lateralized readiness potential (LRP). In addition, a measure complementary to the LRP was introduced to investigate non-motoric lateralization (NML). Contralateral inter-hemispheric lateralization was evident in the LRP preceding finger movement, but was absent prior to eye movements. However, pre-saccadic cortical response profiles did exhibit a right hemispheric, non-motoric lateralization (NML) during stimulus presentation. Comparable non-motoric lateralization was found for finger extension. Results of the present study suggest that non-motoric lateralization may be a contributing factor to the frequently reported inter-hemispheric asymmetry preceding self-initiated saccadic eye movements. Results of the present study also suggest that the latter may be related to a covert shift of visuospatial attention toward the saccadic target. Associated shifts of attention are suppressed in a CNV paradigm, where attentional focus is primarily on the CNV stimulus during the pre-saccade period.     

Neural responses to rigidly moving faces displaying shifts in social attention investigated with fMRI and MEG

A widely adopted neural model of face perception (Haxby, Hoffman, & Gobbini, 2000) proposes that the posterior superior temporal sulcus (STS) represents the changeable features of a face, while the face-responsive fusiform gyrus (FFA) encodes invariant aspects of facial structure. ‘Changeable features’ of a face can include rigid and non-rigid movements. The current study investigated neural responses to rigid, moving faces displaying shifts in social attention. Both functional magnetic resonance imaging (fMRI) and magnetoencephalography (MEG) were used to investigate neural responses elicited when participants viewed video clips in which actors made a rigid shift of attention, signalled congruently from both the eyes and head. These responses were compared to those elicited by viewing static faces displaying stationary social attention information or a scrambled video displaying directional motion. Both the fMRI and MEG analyses demonstrated heightened responses along the STS to turning heads compared to static faces or scrambled movement conditions. The FFA responded to both turning heads and static faces, showing only a slight increase in response to the dynamic stimuli. These results establish the applicability of the Haxby model to the perception of rigid face motions expressing changes in social attention direction. Furthermore, the MEG beamforming analyses found an STS response in an upper frequency band (30-80 Hz) which peaked in the right anterior region. These findings, derived from two complementary neuroimaging techniques, clarify the contribution of the STS during the encoding of rigid facial action patterns of social attention, emphasising the role of anterior sulcal regions alongside previously observed posterior areas.     

Motor excitability during imagination and observation of foot dorsiflexions

To explore the effects of motor imagery (MI) and action observation (AO) of foot movements on motor excitability. Fifteen healthy subjects were studied at rest, during MI of foot dorsiflexions and during watching a video of foot dorsiflexions. Transcranial magnetic stimulation was used to explore corticospinal and intracortical excitability by comparing amplitudes of motor-evoked potentials during the different conditions. F waves were recorded to test the spinal motoneuronal excitability. MI and AO increased corticospinal excitability, but MI was more effective than AO. During MI, intracortical inhibition was reduced. Intracortical facilitation and spinal motoneuronal excitability remained unchanged. Excitability increases were similar for the right and the left leg when recording from the side the subjects had focused their MI on. However, MI of left foot dorsiflexions did not increase excitability in the right tibial anterior muscle. MI and AO of foot dorsiflexions enhance motor excitability. MI induced a disinhibition in the motor cortex. The lack of excitability increase during MI of contralateral foot movements might be related to the alternating movement pattern during walking. MI and AO effects could support the restitution of motor deficits in neurological diseases with impaired motor excitability.     

MEG imaging of recurrent gliomas reveals functional plasticity of hemispheric language specialization

In patients with gliomas, changes in hemispheric specialization for language determined by magnetoencephalography (MEG) were analyzed to elucidate the impact of treatment and tumor recurrence on language networks. Demonstration of reorganization of language networks in these patients has significant implications on the prevention of postoperative functional loss and recovery. Whole‐brain activity during an auditory verb generation task was estimated from MEG recordings in a group of 73 patients with recurrent gliomas. Hemisphere of language dominance was estimated using the language laterality index (LI), a measure derived from the task. The initial scan was performed prior to resection; patients subsequently underwent surgery and adjuvant treatment. A second scan was performed upon recurrence prior to repeat resection. The relationship between the shift in LI between scans and demographics, anatomic location, pathology, and adjuvant treatment was analyzed. Laterality shifts were observed between scans; the median percent change was 29.1% across all patients. Laterality shift magnitude and relative direction were associated with the initial position of language dominance; patients with increased lateralization experienced greater shifts than those presenting more bilateral representation. A change in LI from left or right to bilateral (or vice versa) occurred in 23.3% of patients; complete switch occurred in 5.5% of patients. Patients with tumors within the language‐dominant hemisphere experienced significantly greater shifts than those with contralateral tumors. The majority of patients with glioma experience shifts in language network organization over time which correlate with the relative position of language lateralization and tumor location.     

Painless legs and moving toes in a mother and her daughter.

Painful legs and moving toes (PLMT) is a rare syndrome which is characterised by involuntary movements of the toes and pain in the legs. We report on a mother and her daughter who both presented with involuntary movements of the toes similar to those seen in PLMT but without any associated pain. Neurological examination revealed intermittent 0.3 to 0.5-Hz flexion and extension of the toes and ankles of the right foot in the mother, and of both feet in the daughter. In both patients, the movements appeared during periods of rest that were uncorrelated with the time of day. Diagnostic work-up gave no evidence of radiculopathy or of focal neuropathy. Overnight polysomnography documented that movements of the toes and feet occurred only before sleep onset and during periods of nocturnal awakening or arousals. Because the movements observed in our patients were similar to those seen in patients with PLMT, we diagnosed an abortive form of this syndrome, which already has got the naming "painless legs and moving toes." The occurrence in a mother and her daughter may point to a hereditary component of this disorder.     

Detection of fetal auditory evoked responses by means of magnetoencephalography

MagnetoEncephaloGraphy (MEG) is proposed as a non-invasive technique to detect the physiological activity of fetal brain, due to its ability to record brain activity without direct contact with the head and the transparency of magnetic signals in passing through extracerebral fetal layers and the mother's abdomen. Healthy women with uncomplicated pregnancies and fetuses in breech presentation were examined; gestational ages at time of study ranged between 36 and 40 weeks. In order to evaluate fetal well-being, ultrasound and cardiotocographic data were assessed a few days before and after MEG recording sessions. The participating women were placed in a semi-reclining position in a magnetically shielded room; here the presentation of the fetus and precise region of the mother's abdomen corresponding to the fetal head were determined by ultrasound investigation in order to place the MEG detecting system as near as possible to the fetal brain. MEG recordings were performed by means of a 28-channel neuromagnetic system. Every MEG recording session was performed during the acoustic stimulation of fetuses, in order to detect the cerebral events evoked by peripheral stimuli. The auditory stimuli were delivered from a plastic tube placed on mother's abdomen, near the fetal head, and consisted of a 300 ms 103 dB pure tone at 500 and 1000 Hz, presented at a 0.4 c/s repetition rate. In six cases following accurate digital subtraction of maternal and fetal electrocardiographic (EKG) signals we remained with a stimulus-related response peaking at about 250 ms; this was considered to originate from the fetal brain. In favour of this in three cases a clear dipolar distribution was evident at the peak of brain response centered on the fetal head and consistent with a brain generator. Despite several technical problems requiring solution before a possible routine clinical application, MEG has been found to be suitable for the non-invasive exploration of the fetal brain.     

Cortical potential shifts preceding voluntary movement are normal in parkinsonism

We have recorded movement-related cortical potentials (MRCPs) preceding voluntary finger extension from 10 subjects with Parkinson's disease and compared the results with those obtained from groups of young and old subjects described in the previous paper in this volume (Barrett et al. 1986). Three separate potential shifts preceding voluntary movement were identified in the wave forms of all subjects. There were no differences between the healthy aged subjects and those with Parkinson's disease in terms of the onset latencies or gradients of these potential shifts. The potential shift associated with the final phase of preparation (NS') was significantly less widespread over central scalp for the older subjects compared with the young. Equivalent results for a 35-year-old subject with Parkinson's disease were indistinguishable from those obtained from the young subjects suggesting that this restriction in the distribution of NS' is related to normal ageing rather than the disease process of parkinsonism. There were no differences within the group of parkinsonian subjects with respect to potential shifts associated with differing degrees of movement disability between the two hands. Our results contradict previous reports of abnormal MRCPs in Parkinson's disease (Deecke et al. 1977; Deecke and Kornhuber 1978; Shibasaki et al. 1978). We attribute this primarily to an improved method of recording MRCP which compensates for time jitter between EMG onset and the production of a trigger pulse for averaging (Barrett et al. 1985).     

Supraspinal Effects of Dorsal Root Ganglion Stimulation in Chronic Pain Patients

Objectives: Dorsal root ganglion stimulation (DRGS) has become a popular neuromodulatory treatment for neuropathic pain. We used magnetoencephalography (MEG) to investigate potential biomarkers of pain and pain relief, based on the differences in power spectral density (PSD) during varying degrees of pain and how these oscillations change during DRGS-mediated pain relief.Materials and Methods: Thirteen chronic pain patients with implanted dorsal root ganglion stimulators were included in the MEG analysis. MEG Recordings were performed at rest while the stimulator was turned ON or OFF. Numerical rating scale (NRS) scores were also recorded before and after DRGS was turned OFF and ON. Power spectral and source localization analyses were then performed on preprocessed MEG recordings.Results: With DRGS-OFF, patients in severe pain had significantly increased cortical theta (4–7 Hz) power and decreased cortical alpha (7–13 Hz) power compared to patients reporting less pain. This shift in power toward lower frequencies was contrasted by a shift toward the higher frequency power spectrum (low beta 13–20 Hz activity) during DRGS-mediated pain relief. A significant correlation was found between the increase in low beta activity and the degree of reported pain relief.Conclusion: Our results demonstrate increased low-frequency power spectral activity in chronic pain patients in the absence of stimulation which shifts toward higher frequency power spectrum activity in response to therapeutic DRGS. These cortical changes in response to DRGS provide support for the use of neuroimaging in the search for potential biomarkers of pain.     

Cortical regions involved in eye movements, shifts of attention, and gaze perception

Human vision is an active process that involves shifting attention across the visual scene, with or without moving the eyes. Such shifts of attention can be generated at will (endogenously) or be triggered automatically, i.e., generated in response to exogenous stimuli including socially relevant cues such as someone else's gaze. What are the common and distinct brain mechanisms involved in these processes? To address this question, we carried out a quantitative effect-location meta-analysis of 59 brain-imaging experiments whose results were published using standardized coordinates. For each condition of interest, namely voluntary and visually triggered eye movements, voluntary and visually triggered (covert) shifts of attention, and perception of someone else's gaze, we computed activation likelihood estimation (ALE) maps. Those maps represent at each voxel of the brain the probability of reporting a signal change related to the condition of interest. For eye movements, this analysis confirmed the spatial location of the frontal eye fields, supplementary eye fields, and parietal saccade-related regions. The map of covert shifts of attention demonstrated highest similarity with the map of saccadic eye movements. Gaze perception showed common activation likelihood with the other conditions in the right intraparietal sulcus and in the lateral precentral gyrus. It demonstrated more similarity with the reflexive than with the voluntary saccades and shifts of attention. We propose that a core network of frontoparietal and temporal brain regions is recruited when we shift the focus of our attention with or without eye movements in response to the appearance of a visual target, as well as when we see someone else shift his or her gaze.