Abnormal premovement brain potentials in schizophrenia.

We assessed scalp-recorded movement related potentials (MRPs) generated prior to voluntary movements in chronic, medicated schizophrenics (n = 9) and age matched normal controls (n = 9). MRPs were recorded in a self-paced button press task in which subjects pressed a button with either their right, left or both thumbs (experimental condition I, II and III respectively). Controls generated a slowly rising readiness potential (RP) at about 1000 ms, a negative shift (NS') at about 450 ms and a motor potential (MP) at about 100 ms prior to movement. The initial MRP components (RP and NS') were reduced in schizophrenics indicating an impairment of the voluntary preparatory process in schizophrenia. Results of the present study indicate a similarity of MRP findings in schizophrenics and reported MRPs (Singh and Knight, 1990) in patients with unilateral lesions of the dorsolateral prefrontal cortex. These findings provide further support for frontal lobe dysfunction in schizophrenia.     

Movement-related cortical potentials in aged subjects]

Cortical potentials related to freely-executed voluntary wrist flexion (MRPs) were studied in 35 subjects aged 23-80 years. The characteristics of the MPRs in aged subjects were determined in comparison data from 14 young subjects aged 23-40 years. The analysis concerned 3 components of the MRPs: the slow negative shifts (NS1 and NS2) before the movement onset and the motor potential (MP). In the aged subject, the latencies measured at Cz show a significant lengthening of the NS1 and of the duration of NS2 (NS' of Shibasaki et al, 1980). The mean amplitude of the NS1 peak at Cz is decreased, and those of N1 (the negative peak before the movement) and MP are not significantly different from those of the young subjects. The NS2 component in the aged subject (between NS1 and N1) is thus increased. In contrast to the young subjects, who present a predominance of N1 and MP amplitudes of the contralateral motor cortex over the ipsilateral cortex, the aged subjects lose lateralization of these components. Recording of MRPs with subdural electrodes (Neshige et al, 1988) shows taht NS1 results from the activity of the supplementary motor area and from the ipsi-contralateral primary motor cortex. The increase in NS2 might be interpreted as an expression of activity coming from other structures to compensate for the reduction in NS1 in the aged subject and to maintain the level of the motor potential MP.     

Deafferentation of neighbouring motor cortex areas does not further enhance saturated practice-dependent plasticity in healthy adults

OBJECTIVE: To assess effects of deafferentation of the arm representation of primary motor cortex (M1) on practice-dependent plasticity in healthy adults. METHODS: Twelve healthy, right-handed adults (18-48 years, median 20.2 years) performed two consecutive experiments (exp. 1 and exp. 2). Exp. 1 consisted of a motor practice (MP) of repeated ballistic flexion movements of the left thumb. This was followed by exp. 2 consisting of selective anaesthesia of the upper brachial plexus (SPA) to disinhibit the training M1 and a second period of the same MP. Peak acceleration of the trained thumb movement and the motor evoked potential (MEP) amplitude in the flexor pollicis brevis muscle elicited by single-pulse transcranial magnetic stimulation of the training M1 were studied before and after exp. 1 and after exp. 2. RESULTS: After exp. 1 all subjects demonstrated an increase of peak acceleration (baseline: 19.23+/-3.81ms(-2); after exp. 1: 43.28+/-17.63ms(-2), p=0.008) and MEP amplitude (from 0.46+/-0.23mV to 1.26+/-0.77mV, p=0.03). There was no additional increase of these measures after exp. 2 (44.37+/-19.56ms(-2), p=0.78, 1.69+/-1.21mV (p=0.07)). CONCLUSIONS: Training of ballistic thumb movements leads to behavioural improvement as well as to an increased excitability of the corresponding M1 representation. These effects do not increase further during deafferentation of the training M1. In contrast to stroke patients [Muellbacher W, Richards C, Ziemann U, Wittenberg G, Weltz D, Boroojerdi B, et al. Improving hand function in chronic stroke. Arch Neurol 2002;59:1278-82], practice-dependent plasticity in healthy subjects cannot be enhanced by deafferentation of neighbouring motor cortex areas. SIGNIFICANCE: Healthy subjects, in contrast to patients with central motor lesions, are capable of saturating practice-dependent plasticity to a level that cannot be further enhanced by experimental manipulation.     

Cortical topography of premotor and motor potentials preceding self-paced, voluntary movement of dominant and non-dominant hands.

The cortical potentials preceding movement, negative slope (NS'), premovement positivity (PMP), and the initial slope of motor potential (MP), were studied in detail with a 29-channel averaged EEG mapping technique in normal subjects. Self-paced, voluntary movements of the right and left index fingers were performed up to 150 times, and topographic color maps were created from the averaged wave forms. The maps revealed NS' of the dominant hand on the vertex and NS' of the non-dominant hand on the contralateral centroparietal area. PMP appeared on the ipsilateral precentral area, and the initial slope of MP appeared on a small, distinct contralateral precentral area, presumably the hand motor area. The amplitudes of the potentials did not show significant differences between dominant and non-dominant hands. PMP and the initial slope of MP appeared significantly earlier preceding non-dominant hand movement as compared with dominant movement. The findings indicate some difference in cortical activity relating to dominant and non-dominant hand movement.     

Impaired movement-related potentials in acute frontal traumatic brain injury.

OBJECTIVE: Focal brain lesions due to traumatic brain injury (TBI) do not only lead to functional deficits in the lesion area, but also disturb the structurally intact neuronal network connected to the lesion site. Therefore we hypothesized dysfunctions of the cortical motor network after frontal TBI. The movement related potential (MRP) is an EEG component related to voluntary movement consisting of the Bereitschaftspotential (BP), the negative slope (NS), and the motor potential (MP). The aim of our study was to demonstrate alterations in the movement related cortical network in the acute stage after TBI by comparing our patients' MRPs to those of a healthy control group. METHODS: EEGs of 22 patients with magnetic resonance imaging defined contusions of the prefrontal cortex were recorded within 8 weeks after TBI. We further recruited a healthy control group. The paradigm consisted of self-paced abductions of the right index finger. RESULTS: Compared to healthy controls, the BP in the patient group was significantly reduced and its onset delayed. Moreover, an enhanced contribution of the postrolandic hemisphere ipsilateral to the movement and a reduced contribution of the left frontal cortex, ipsilateral to the lesion in the majority of the patients, were observed during motor execution (MP). CONCLUSIONS: Anatomical connections between the prefrontal cortex and the supplementary motor area (SMA) are known to exist. We suggest that prefrontal lesions lead to reduced neuronal input into the SMA. This deficit in the preparatory motor network may cause the reduced BPs in our patients. Moreover, an increased need for attentional resources might explain the enhanced motor potentials during movement execution. In conclusion, we demonstrated altered MRPs in the acute stage after frontal TBI, which are a consequence of disturbed neuronal networks involved in the preparation and execution of voluntary movements.     

Gating of somatosensory input by human prefrontal cortex

Somatosensory evoked potentials (SEPs) to median nerve stimulation were recorded in controls and in patients with focal lesions in dorsolateral prefrontal cortex (PFCx). Unilateral PFCx lesions increased the amplitude of the P26 component generated in postcentral areas 1 and 2. The amplitudes of the N28, P45 and N67 SEP components recorded over post-rolandic and frontal electrodes were also enhanced by PFCx damage. In contrast, the N19 component generated in postcentral area 3b was unaffected by PFCx lesions. The results indicate that PFCx exerts inhibitory modulation on sensory processing that may be mediated by corticocortical PFCx-parietal connections.     

Abnormal movement related potentials in patients with lesions of basal ganglia and anterior thalamus.

Movement-related cortical potentials (MRCPs) were recorded from scalp electrodes during wrist flexion in 15 dystonic patients with bilateral (nine) or unilateral (six) circumscribed lesions in the striatum (eight), pallidum (six), or anterior thalamus (one). The results were compared with those of 10 age-matched healthy volunteers. The early (BP) and late (NS') MRCP components were assessed in terms of their gradients and distribution on the scalp in Cz, C3', and C4'. The gradients of both BP and NS' components were significantly flatter in the patients with bilateral lesions than in the control subjects. Also, the BP gradient was maximum at Cz, and the NS' component was contralaterally predominant in the control subjects but not in the patients. In patients with unilateral lesions, the gradients were flatter (p < 0.05) during movement of the dystonic wrist than during movement of the normal wrist. This difference was significant for BP and NS', regardless of the location of the electrodes. Also, the normal topographic predominance of BP at Cz and of contralateral NS' disappeared. The BP and NS' components of the MRCPs are thought to reflect preparatory activity in the supplementary motor area and the primary motor cortex before movement. Reduced BP and NS' gradients in patients with both bilateral and unilateral lesions of the basal ganglia, which project towards the supplementary motor area, are consistent with this hypothesis. The bilateral nature of these reductions suggests that both the ipsilateral and the contralateral motor cortex are involved in the genesis of the MRCPs and that the dystonia in these patients is associated with impaired motor preparation.     

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.     

Time course of motor excitability before and after a task-related movement.

AIMS OF THE STUDY: The time course of motor excitability during a task-related unilateral right thumb movement was studied using sub-threshold transcranial magnetic stimulation (TMS) to the contralateral left motor cortex. The level of stimulation evoked a motor evoked potential (MEP) in the thumb when the subject was at rest in approximately 10% of the trials. METHODS: Subjects made a brief right thumb movement to the predictable omission of regularly presented tone bursts allowing experimental definition of TMS relative to the cue to move. Motor cortical excitability was characterized by amplitude and/or probability of eliciting MEPs. RESULTS: There were four periods of altered motor excitability during task performance compared to a control resting state: a first period of weak facilitation before movement between -500 to -200 ms, a second period without increased excitability approximately 150 ms before movement onset when MEPs amplitude was below that seen in rest, a third period of strong facilitation between -100 ms before movement and +200 ms after facilitation and a fourth period of weak facilitation between +200 to +500 ms. CONCLUSION: These results show that during performance of a task requiring a motor response, motor cortical excitability is increased above resting for hundreds of millisecond before and after the response, except for a transient period between 75 and 150 ms prior to movement onset. The temporal pattern of these excitability changes is compatible with multiple excitatory and inhibitory inputs interacting on motor cortex.     

Influence of task-related ipsilateral hand movement on motor cortex excitability.

OBJECTIVE: The time course of the right motor cortex excitability in relation to a task-related voluntary right thumb twitch was studied using sub-threshold transcranial magnetic stimulation (TMS) to the right motor cortex. METHODS: Motor excitability was studied in 8 adult subjects who made a brief right thumb twitch to the predictable omission of every fifth tone in a series of tones 2.5 s apart. This paradigm avoided an overt sensory cue, while allowing experimental control of TMS timing relative to both movement and the cue to move. Motor excitability was characterized by several measures of motor evoked potentials (MEPs) recorded from the left thenar eminence in response to TMS over the right scalp with a 9 cm coil: probability of eliciting MEPs, incidence of MEPs and amplitude of MEPs. RESULTS: All subjects showed suppression of motor excitability immediately following a voluntary right thumb twitch (ipsilateral response), and up to 1 s after it. However, two distinctly different effects on motor excitability were observed before the response: two subjects showed excitation, beginning about 500 ms before response until 300 ms after it, followed by the post-movement suppression; 6 subjects displayed pre-movement suppression, beginning about 600 ms before the response and persisting for the duration. CONCLUSIONS: The net effect of an ipsilateral response on motor cortex can be either inhibitory or excitatory, changing with time relative to the response. These findings are compatible with two separate processes, inhibitory and excitatory, which interact to determine motor excitability ipsilateral to the responding hand.     

Topography of scalp-recorded motor potentials in human finger movements

Four distinct negative events were identified in the averaged, scalp-recorded EEGs of normal subjects before and after the onset of self-paced, voluntary finger movements; reaction-time movements and passive movements were also studied. These events are the peak of the negative slope (NS'), the initial slope of motor potential (isMP), the parietal peak of motor potential (ppMP), and the frontal peak of motor potential (fpMP). For self-paced movements, NS' and isMP occurred before the onset of electromyographic (EMG) activity, and ppMP and fpMP occurred after the onset of EMG activity. NS' had a wide distribution, covering the parietal region with slight contralateral predominance. The isMP mapped focally over the contralateral hand motor area on the scalp. The location of ppMP was similar to that of isMP. The fpMP was localized anterior and medial to motor cortex with a contralateral preponderance and possible location over the supplementary motor area. The isMP and fpMP also were identified in the recordings of reaction-time movements, but only the fpMP persisted in the recordings of passive movements. The isMP appears to reflect activation of the cortical cells in the hand area of motor cortex for the execution of voluntary movement, and the fpMP appears to reflect proprioceptive feedback from the periphery.     

Changes in movement-related cortical potentials in Parkinson's patients before and after treatment with levodopa

Cortical potentials associated with voluntary, self-paced wrist flexion (MRPs) were recorded from 3 scalp locations (Cz and psi contralateral hand motor area) in patients with Parkinson's disease (9 de novo patients and 30 L-Dopa treated patients). The analysis concerned 3 components of the MRPs: the 2 slow negative shifts (NS1 and N1) before the movement onset and the motor potential (MP). The NSI amplitude was measured at Cz, the peak negativity N1 and MP from contralateral hand motor area location. The potential distribution was also studied. The amplitude of the MRPs components was the same as in the normals. But in de novo patients, the potential distribution of the NS1 component was different; a Cz preponderance of the NS1 amplitude was not found. In patients treated with L-Dopa, there is a negative correlation between the changes in amplitude and the changes in clinical rating for NS1, N1 and MP components. The decrease in the MRPs components was significant from stage III and IV of the Hoehn and Yahr scales. After L-Dopa therapy, the NS1 component from de novo patients was increased in amplitude. The amplitude of the MRPs components from patients with L-Dopa induced clinical fluctuations was reduced during "off" period in comparison to "on" period. The findings suggest that the NS1 potential and the N1 and MP components share 2 distinct systems for the control of voluntary movement. Their mechanism in Parkinson's disease is discussed.     

Lateralised cortical activity due to preparation of saccades and finger movements: a comparative study

The topography and time course of event-related asymmetries of the EEG associated with horizontal saccadic eye movements and finger movements was compared in a 4-choice response task, where the subjects had to respond to the imperative stimulus (S2) by moving the right or left index finger or by making a saccade to the right or the left. The cue stimulus (S1) contained full, partial, or no information about the direction and the effector. In case of finger movements 3 distinct lateralisations were found: (1) increased negativity over the motor cortex contralateral to the future movement direction, (2) increased contralateral negativity at temporoparietal sites beginning 200 ms after delivery of the directional information, and (3) increased ipsilateral negativity at temporo-parietal sites beginning 350–500 ms after delivered direction and effector information. The early temporo-parietal lateralisation was also visible in case of saccadic eye movements and in case of effector-unspecific directional information. Before saccadic eye movements no other distinct lateralisation could be observed at any recording site. In sum, lateralised cortical activities due to preparation processes for finger movements and due to effector-unspecific processing of directional information for motor preparation by the posterior parietal cortex could be demonstrated, whereas no distinct lateralisation due to preparation for saccadic eye movements was visible.     

Movement-related potentials accompanying unilateral and bilateral finger movements with different inertial loads.

The present study was aimed at investigating the effect of inertial loading on movement-related potentials (MRPs) recorded from the scalps of normal subjects while performing finger movements. Two experiments were performed. Experiment 1. MRPs preceding and accompanying the execution of voluntary, unilateral finger movements were investigated in 8 subjects under the 3 experimental conditions of: no inertial load, small inertial load (250 g), and large inertial load (400 g). A significant effect of the inertial load on Bereitschaftspotential (BP) amplitude was observed for the 100 msec period preceding movement onset (BP -100 to 0) at precentral electrode sites and following movement onset (N0 to 100) at both precentral and parietal electrode sites. Pairwise comparisons revealed that significant effects were due to differences between the loading and non-loading conditions and not for different amounts of loading. No significant differences were observed for BP onset or early BP amplitudes, indicating that scalp negativity immediately prior to, and during, movement onset is primarily influenced by conditions of inertial loading. Experiment 2. This experiment examined the effect of inertial loading on MRPs for bilateral, simultaneous voluntary finger movements in 10 subjects under conditions of: no inertial load, inertial load applied separately to the left and right fingers, and with identical inertial loads applied to both fingers. No significant effect of inertial load on MRP amplitude was observed. These results are contrasted with those of experiment 1 which show significant effects of inertial loading for unilateral movements and are interpreted in terms of the hypothesis that bilateral movement organization involves 'higher' aspects of motor control than those reflecting adjustment to conditions of inertial loading.     

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.     

Movement-related potentials in the basal ganglia: a SEEG readiness potential study.

OBJECTIVES: The brain potentials preceding and accompanying self-paced acral limb movements (Bereitschaftspotential/readiness potential (RP) paradigm) were studied in 12 patients. METHODS: Intracranial electrodes were implanted in order to explore intractable epilepsy. The electrodes were introduced into sites corresponding to the electroclinical characteristics of each patient's epileptic seizures. In 7 patients, several depth electrodes were implanted orthogonally, in the temporal, fronto-orbital and prefrontal cortex. In 4 patients, subdural strip electrodes were used for the exploration of the fronto-temporal convexity. There were no RPs recorded in these areas. No contacts were placed in the central region known to generate cortical RP. In all the patients, one or two diagonal electrodes passed through or touched the basal ganglia to reach the amygdala and the hippocampus. The putamen was explored in 11 patients (in 3 of them bilaterally); the caudate head was explored in two patients, and the pallidum was explored in two patients. RESULTS: RP with a clear amplitude gradient was present in all explored structures, however a phase reversal was never observed. RP was observed in the caudate in all recordings, and in the pallidum in one patient. It was recorded in the putamen in 8 out of the 11 explored patients. RPs were displayed contralaterally to the movement 9 times in 13 explorations, and ipsilaterally 4 times in 9 explorations. The shape of RP resembled the RP shape in the cortex and on the scalp. Movement accompanying potentials (MAPs) were also present in all 3 explored structures. The electrophysiological characteristics of MAP differed from RP, indicating separate generators. In the basal ganglia, RPs preceded the onset of movement by 500-1500 ms, at an average of 1080 (+/-330) ms. It seems that the RP in the basal ganglia starts slightly later than the RP in the motor cortices. That should be definitely demonstrated in patients with simultaneous recordings from cortical and subcortical structures. RP and MAP were displayed synchronously in the cortex and in the basal ganglia during most of the premovement period, as well as during the execution of movement. RP generators were reported by several authors in other deeply located structures, i.e. in the thalamus and in the brain-stem. CONCLUSIONS: Based on all these recordings, we presume that the RPs recorded on the scalp are generated simultaneously in several cortical as well as subcortical structures.     

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. Hirnpotential?nderungen 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.     

The time course of changes in motor cortex excitability associated with voluntary movement.

The excitability of the motor cortex is modulated before and after voluntary movements. Transcranial magnetic stimulation studies showed increased corticospinal excitability from about 80 and 100 ms before EMG onset for simple reaction time and self-paced movements, respectively. Following voluntary movements, there are two phases of increased corticospinal excitability from 0 to approximately 100 ms and from approximately 100 to 160 ms after EMG offset. The first phase may correspond to the frontal peak of motor potential in movement-related cortical potentials studies and the movement-evoked magnetic field I (MEFI) in magnetoencephalographic (MEG) studies, and likely represents a time when decreasing output from the motor cortex falls below that required for activation of spinal motoneurons, but is still above resting levels. The second phase of increased corticospinal excitability may be due to peripheral proprioceptive inputs or may be centrally programmed representing a subthreshold, second agonist burst. This may correspond to the MEFII in MEG studies. Corticospinal excitability was reduced below baseline levels from about 500 to 1,000 ms after EMG offset, similar to the timing of increase in the power (event-related synchronization, ERS) of motor cortical rhythm. Similarly, motor cortex excitability is reduced at the time of ERS of motor cortical rhythm following median nerve stimulation. These findings support the hypothesis that ERS represents an inactive, idling state of the cortex. The time course of cortical activation is abnormal in movement disorders such as Parkinson's disease and dystonia, reflecting abnormalities in both movement preparation and in cortical excitability following movement.     

Effects of force–load on cortical activity preceding voluntary finger movement: Whole-scalp magnetoencephalography of the Bereitschaftsfeld

Neural activity preceding force-loaded voluntary finger movement (the Bereitschaftsfeld) was recorded using 143-channel whole-scalp magnetoencephalography (MEG) in order to determine how the level of force produced during voluntary finger movement is represented in activity over different premovement time intervals localized to different cortical areas. Eighteen healthy subjects performed voluntary right index-finger extension movements against an inertial load of either 0, 100, or 200 g. Results showed that the earliest component of premovement activity, beginning between 1.5 and 1.0 s prior to movement and localized to the central midline around the region of supplementary/cingulate motor areas, was not modulated by the level of force required for movement. However, later premovement activity, occurring between 500 and 200 ms prior to movement onset, was significantly greater for the highest force movements compared with both intermediate (p < 0.05) and no weight-load conditions (p < 0.01). This component was localized to primary sensorimotor cortical areas, with greater source strength on the left side contralateral to movement. Results indicate that, although early premovement activity of the supplementary/cingulate motor areas does not appear to encode movement force, later premovement activity of the primary motor cortex is significantly greater for movements made with more force, not only during movement execution but also up to 500 ms prior in readiness for intended movements of greater force.     

Inhibiting effect of the presentation of additional stimuli on neuronal responses in the cat sensorimotor cortex during a conditioned reflex

Conditional responses of the sensomotor cortex neurons were registered in awake cats which were trained to respond to presentation of conditional stimuli (a single sound click) by instrumental conditional movement. Those neuronal responses were registered 50-150 ms before realization of reflex movements. During external stimulation after the reflex beginning, conditional neuronal reactions appeared 50-250 ms later, but the latencies of conditional movements did not change. It is supposed that the studied phenomenon is a result of the growing exteroceptive attention of cats to external stimulation.