Recording of event-related potentials (P300) from human cortex.

Auditory event-related potentials were recorded simultaneously from chronically implanted subdural electrodes and from scalp electrodes in three patients who were being evaluated for surgical treatment of epilepsy. These three cases showed clearly defined scalp-P300 and scalp-N300. A cortex-P300 was recorded from the midtemporal area, and a cortex-N300 was recorded from the inferior frontal area with some reflection at the basal temporal region. There were no potentials from an interhemispheric region. We could not observe any component from the cortex studied corresponding to scalp-recorded N200. Therefore, while the activity generated from the mesial temporal lobe may only make minor contributions to scalp-P300, that generated from the midtemporal area might make a major contribution to the scalp-P300. Additionally, generators of N200, P300, and N300 are different from each other. These findings, together with previous reports regarding the generator source of P300, also suggest that P300 is a complex arising from multifactorial generator sources, including the midtemporal and inferior frontal area.     

Cognitive- and movement-related potentials recorded in the human basal ganglia.

Sources of potentials evoked by cognitive processing of sensory and motor activities were studied in 9 epilepsy surgery candidates with electrodes implanted in the basal ganglia (BG), mostly in the putamen. Several contacts were also located in the pallidum and the caudate. The recorded potentials were related to a variety of cognitive and motor activities (attentional, decisional, time estimation, sensory processing, motor preparation, and so on). In five different tests, we recorded P3-like potentials evoked by auditory and visual stimuli and sustained potential shifts in the Bereitschaftspotential and Contingent Negative Variation protocols. All of the studied potentials were generated in the BG. They were recorded from all over the putamen. Various potentials on the same lead or nearby contacts were recorded. A functional topography in the BG was not displayed. We presume that the cognitive processes we studied were produced in clusters of neurons that are organized in the basal ganglia differently than the known functional organization, e.g., of motor functions. The basal ganglia, specifically the striatum, may play an integrative role in cognitive information processing, in motor as well as in nonmotor tasks. This role seems to be nonspecific in terms of stimulus modality and in terms of the cognitive context of the task.     

Signal-, set-, and movement-related activity in the human premotor cortex

Single unit recording studies in non-human premotor cortex have revealed neurons with motor-related activity. Other neurons, however, seem to be involved in prior movement selection and preparation processes, and have activity related to visual instruction signals or movement preparation ('set'). We have used single pulse transcranial magnetic stimulation (TMS) to identify similar processes in human subjects. In Experiment 1 subjects performed a cued movement task while being stimulated with TMS over three sites: sensorimotor cortex, posterior premotor cortex and anterior premotor cortex. TMS slowed movements when applied at 140 ms after the visual cue over the anterior premotor site, at 180 ms after the visual cue over the posterior premotor site, and at 220 ms and later after the visual cue over the sensorimotor cortex. The results are consistent with a change from signal to movement-related processing when moving from premotor to motor cortex. In Experiment 2 there was a preparatory set period between the instruction signal that informed subjects which movement to make and the 'go' signal that informed them when to actually make the movement. TMS was applied over the anterior premotor site and the sensorimotor site during the set period. At both sites TMS had similar effects on slowing subsequent movements. The results suggest set activity in both premotor and motor cortices in human subjects.     

Source analysis of scalp-recorded movement-related electrical potentials

We used brain electric source analysis to study the sources generating the movement-related cortical potentials during the interval from 200 msec before to 200 msec after the movement onset. Dipole solutions were obtained for the peak of the negative slope (pNS′) and the frontal peak of the motor potential (fpMP) on scalp-recorded movement-related electrical potentials elicited by self-paced, repetitive unilateral finger movements in 10 normal volunteers. Two sources in homologous areas on each side of a spherical head model provided a satisfactory solution for the activity occurring at the instant of the pNS′ in all subjects. The fpMP was modeled by a contralateral source and a midline source in 6 subjects and by a single contralateral source in the remaining 4 subjects. The percentage of the residual variance, or goodness-of-fit, over the interval from −200 to 200 msec, using the solutions derived at pNS′ and fpMP, was low. The results support the hypothesis that the NS′ originates from the activity of bilateral generators in the sensorimotor cortex, and the motor potential arises from the combined activity of sources in the contralateral postcentral regions and the supplementary motor area.     

Lateralization of movement-related potentials and the size of corpus callosum

Using structural MRI and whole-head EEG recordings, we analyzed the correlations between the anatomical parameters of the corpus callosum and the hemispheric distribution of the cortical movement-related potentials during right finger and shoulder movements in nine right-handed men. Statistically significant correlation was found only in finger movements. A relatively large genu and the anterior part of the truncus of the corpus callosum correlated with enhanced pre-movement EEG potential over the ipsilateral M1/S1 area. The lateralization of the movement-related potentials correlates with the size of those callosal regions which connect the homologous areas of the primary sensorimotor and frontal cortices.     

Intracranial recordings of movement-related potentials to voluntary saccades

Movement-related potentials evoked by voluntary and self-initiated horizontal saccades were recorded from subdural electrodes placed over the lateral (premotor and motor cortex) and the mesial (supplementary motor area) surfaces of the frontal lobe, in four patients with intractable focal seizures. An extremely localized bereitschaftspotential showing approximately the same latencies and amplitudes was simultaneously recorded from the frontal eye field and supplementary motor area (SMA). Our data suggest that both regions are equally active prior to saccades and do not support the view that the SMA acts as a supramotor cortex, being activated during the planning of the movement and the primary motor cortex only later on, close to the execution of the movement. In addition, we never observed the spike potential in our intracranial recordings, thus supporting the hypothesis of its extracerebral origin.     

Mirror movement: application of movement-related cortical potentials

In a patient with Kallmann's syndrome (hypogonadotropic hypogonadism and anosmia) manifesting mirror movement, cortical potentials associated with unilateral and bilateral simultaneous voluntary middle finger extensions were studied. Premovement negative slope, which has been shown to reflect preparatory excitation of motor cortex corresponding to the voluntary movement, was recorded bilaterally in this patient in spite of intended unilateral hand movement. It is suggested that mirror movement in this particular patient is generated by unintended excitation of the opposite motor cortex.     

Diagonistic dyspraxia: case report and movement-related potentials

We report unusual motor behavior of the left hand dissociated from conscious volition in a 51-year-old right-handed man. This patient had sustained damage to the anterior two-thirds of the corpus callosum, the rostral and lower parts of the right medial frontal lobe, and a small portion of the left medial frontal lobe. He subsequently showed 4 types of abnormal motor behavior in the left hand that were triggered by voluntary activities of the right hand: symmetric or antagonistic left hand movements; irrelevant movements of the left hand to the right hand; and a tendency to close the fingers of the left hand into a fist. Recordings of movement-related potentials revealed a marked attenuation of the Bereitschaftspotential (BP) over the right hemisphere observed only when the patient initiated voluntary activity with the right hand. Since the BP is believed to represent a cerebral cortical activity preparatory for voluntary movement, we infer that the level of dysfunction in this patient is at the motor preparatory level caused by a disconnection of the right hemisphere from the left.     

Recording cortico-cortical evoked potentials of the human arcuate fasciculus under general anaesthesia

ObjectiveWe examined the feasibility of using cortico-cortical evoked potentials (CCEPs) to monitor the major cortical white matter tract involved in language, the arcuate fasciculus (AF), during surgery under general anaesthesia.MethodsWe prospectively recruited nine patients undergoing surgery for lesions in the left peri-sylvian cortex, for whom awake surgery was not indicated. High angular resolution diffusion imaging (HARDI) tractography was used to localise frontal and temporal AF terminations, which guided intraoperative cortical strip placement.ResultsCCEPs were successfully evoked in 5/9 patients, showing a positive potential (P1) at 12 ms and a negative component (N1) at 21 ms when stimulating from the frontal lobe and recording in the temporal lobe. CCEP responses peaked in the posterior middle temporal gyrus. No CCEPs were evoked when stimulating temporal sites and recording from frontal contacts.ConclusionFor the first time, we show that CCEPs can be evoked from the peri-sylvian cortices also in adult patients who are not candidates for awake procedures. Our results are akin to those described in the awake setting and suggest the recorded activity is conveyed by the arcuate fasciculus.SignificanceThis intraoperative approach may have promising implications in reducing deficits in patients that require surgery in language areas under general anesthesia.     

Invasive recording of movement-related cortical potentials in humans.

Movement-related cortical potentials (MRCPs), especially the premovement components seen only in association with voluntary movements, may represent the higher brain functions related to preparation for voluntary movements. Recent advances in many aspects (single unit and field potential recordings in animals, intracranial recording of MRCPs in epileptic patients, magnetoencephalography, and positron emission tomography) have provided new information about the physiological significance of MRCPs. In contrast to the findings on scalp recordings, in which the early potentials prior to movement onset are seen more widely, the main cortical generators appear to be discretely localized in bilateral primary and supplementary motor areas with a contralateral predominance. This review outlines the findings in scalp-recorded MRCPs and compares them with the results of invasive recordings, paying special attention to their physiological significance.     

Preparation to respond as manifested by movement-related brain potentials

Ten subjects were instructed to squeeze a dynamometer in a prescribed manner in order to assess the effects of motor preparation on event-preceding brain potentials. Right and left hand responses were required in 5 different experimental conditions allowing different degrees of advance preparation. Six channels of EEG (F3, F4, C3′, C4′, P3, P4) and two channels of EMG were digitized over a 3000 msec epoch, and response-locked averages were computed. Event-preceding negative potentials were evident well in advance of movement if the subject was informed of the timing of the response. These premovement potentials were asymmetrical on the scalp (contralaterally dominant at the central sites) if the subject knew which hand would be required to respond. Thus, we conclude that the appearance and asymmetry of these potentials reflect preparation to execute specific motor acts.     

Effect of an attentional strategy on movement-related potentials recorded from subjects with Huntington's disease.

Huntington's disease patients perform automatic movements in a bradykinetic manner, somewhat similar to patients with Parkinson's disease. Cortical activity relating to the preparation of movement in Parkinson's disease is significantly improved when a cognitive strategy is used. It is unknown whether patients with Huntington's disease can utilise an attentional strategy, and what effect this strategy would have on the premovement cortical activity. Movement-related potentials were recorded from 12 Huntington's disease patients and controls performing externally cued finger tapping movement, allowing an examination of cortical activity related to movement performance and bradykinesia in this disease. All subjects were tested in two conditions, which differed only by the presence or absence of the cognitive strategy. The Huntington's disease group, unlike controls, did not produce a rising premovement potential in the absence of the strategy. The Huntington's disease group did produce a rising premovement potential for the strategy condition, but the early slope of the potential was significantly reduced compared with the control group's early slope. These results are similar to those found previously with Parkinson's disease patients. The strategy may have put the task, which previously might have been under deficient automatic control, under attentional control.     

Characteristics of the ipsilateral movement-related neuron in the motor cortex of the monkey

The characteristics of the precentral neuron activity related to ipsilateral movements were studied while the monkey was performing finger, wrist and arm movements on either side.Out of 197 task-related neurons, 134 discharged in association with contralateral movements, but not with any one of 3 ipsilateral movements. Fifty neurons discharged with bilateral movements.Thirteen neurons discharged in association with ipsilateral movements (ipsi-neurons). Ten were recorded from the trunk or shoulder area of the motor cortex and were accompanied by contraction of those muscles by intracortical stimulation (ICS). The remaining 3 were related to elbow or wrist, but no ipsi-neurons were related to finger muscle contractions.In ipsilateral task performance, 7 ipsi-neurons discharged in association with finger and/or wrist movements in addition to arm movement. Five others were associated with arm movement. The last one discharged with wrist movement. Most of the units showed similar response to contralateral movement.Ipsi-neurons were classified into two groups. One group was recorded around the sulcus precentralis superior, had the lower threshold current and was mostly associated with finger, wrist and arm movements. The other was recorded in the rostral motor cortex, and had the higher threshold current and was related to arm movement.Among 185 neurons to which pyramidal tract stimulation was delivered, 2 out of the 80 PTNs and 11 out of the 105 non-PTNs were ipsi-neurons.EMGs were recorded from various muscles involved in the forelimb movements. Arm and finger muscles showed no activity when the monkey used the ipsilateral hand, while most of the shoulder and trunk muscles showed tonic or moderate transient changes in the activity during the ipsilateral tasks. The ipsi-neuron activity was discussed in consideration with EMGs.     

Sources of movement-related cortical potentials derived from foot, finger, and mouth movements.

Movement-related cortical potentials (MRCPs) register brain electrical activity before and during movement execution. In an attempt to delineate the components of MRCPs that reflect common sources to various movements and that are movement-specific, simple self-paced voluntary foot, finger, and mouth movements were studied. MRCPs were recorded in eight healthy volunteers with 30 electrodes placed on the scalp. Data were analyzed using Brain Electric Source Analysis software, and multiple equivalent dipole models were developed to separate spatial and temporal aspects of brain activity related to the execution of voluntary movements. Independent models were separately developed for the grand average data and for the individual subjects' data for each movement type. MRCPs derived from foot movements were accounted for using a 5-dipole model, finger movements using an 8-dipole model, and mouth movements with a 7-dipole model, yielding the grand average residual variances of 3%, 2%, and 6%, respectively. Based on individual models, intersubject variability of dipole locations was less than 10 mm (+/- SD). Overlaying the mean dipole coordinates onto the stereotaxic atlas provided proof that the sensorimotor cortical areas, supplementary motor area, and also cerebellum and thalamus were active in all three movements. Locations of the dipoles in the contralateral sensorimotor area clearly implied well-known medial to lateral somatotopic organization of foot, finger, and mouth movements. Temporal separation of the activity spread over different brain areas was demonstrated by evolution in the moments of dipole source potentials. The authors' models support the view of simultaneous activation of the primary motor cortex and supplementary motor area at the time of movement execution. Multiple equivalent dipole models developed in this study implied the activity originating in corresponding brain areas as previously detected by positron emission tomography or functional magnetic resonance imaging. However, MRCPs provided additional information regarding the temporal evolution of the brain activity related to the execution of voluntary movements. Thus, the concurrent use of MRCPs and other imaging techniques may provide complementary information not easily obtained by the other imaging techniques themselves.     

Input-output organization of jaw movement-related areas in monkey frontal cortex

The brain mechanisms underlying mastication are not fully understood. To address this issue, we analyzed the distribution patterns of cortico-striatal and cortico-brainstem axon terminals and the origin of thalamocortical and intracortical fibers by injecting anterograde/retrograde tracers into physiologically and morphologically defined jaw movement-related cortical areas. Four areas were identified in the macaque monkey: the primary and supplementary orofacial motor areas (MIoro and SMAoro) and the principal and deep parts of the cortical masticatory area (CMaAp and CMaAd), where intracortical microstimulation produced single twitch-like or rhythmic jaw movements, respectively. Tracer injections into these areas labeled terminals in the ipsilateral putamen in a topographic fashion (MIoro vs. SMAoro and CMaAp vs. CMaAd), in the lateral reticular formation and trigeminal sensory nuclei contralaterally (MIoro and CMaAp) or bilaterally (SMAoro) in a complex manner of segregation vs. overlap, and in the medial parabranchial and K?lliker-Fuse nuclei contralaterally (CMaAd). The MIoro and CMaAp received thalamic projections from the ventrolateral and ventroposterolateral nuclei, the SMAoro from the ventroanterior and ventrolateral nuclei, and the CMaAd from the ventroposteromedial nucleus. The MIoro, SMAoro, CMaAp, and CMaAd received intracortical projections from the ventral premotor cortex and primary somatosensory cortex, the ventral premotor cortex and rostral cingulate motor area, the ventral premotor cortex and area 7b, and various sensory areas. In addition, the MIoro and CMaAp received projections from the three other jaw movement-related areas. Our results suggest that the four jaw movement-related cortical areas may play important roles in the formation of distinctive masticatory patterns.