The relationship between frontal somatosensory-evoked potentials and motor planning.
ABSTRACT Performance of efficient and precise movement requires the proper planning of motor parameters as well as the integration of sensory feedback. This study tests the hypothesis that the frontal components of the median nerve somatosensory-evoked potentials are differentially modulated, depending on (i) the stage of motor preparation and (ii) the moving limb. Participants were instructed to make intermittent voluntary contractions with either their right or left hands while receiving median nerve stimulation to the right wrist only. The results indicate that the frontal N30 demonstrated a significant increase in amplitude during the execution, but not the preparation, of a movement contralateral to median nerve stimulation. These data have implications for interhemispheric control of sensory information within the primary and premotor cortices.
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ABSTRACT: Kinesthetic responses of neurones in the motor cortex, including the primary motor (MI), the supplementary motor (SMA) and the postarcuate premotor (PMC) areas, were investigated in the awake, chronically prepared monkey. In all three subareas, neurones were recorded which responded to passive elbow flexions and extensions induced by a torque motor. In the SMA, such cells were restricted to its posterior portion where intracortical microstimulation produced limb and trunk movements. The majority of SMA cells responds to both displacement directions, a quarter to either flexion or extension. Although the total proportion of SMA neurones responding to arm displacements was low (15%), it was noted that in 'correct' somatotopic penetrations, the responsiveness could be prominent. The latency distribution of the kinesthetic responses was similar to that of MI neurones with slightly less response latencies shorter than 20 ms in the SMA. With manually applied stimuli, SMA neurones responded mostly to joint rotations, but not to light cutaneous stimuli. Only two SMA neurones with somatosensory responses were identified as descending projection neurones, and some neurones were found to be modulated also during active grasping. In the PMC, a higher proportion of neurones (27%) reacted to the standardized arm displacements, the majority again responding to both directions. The latency distribution of the kinesthetic responses was similar to that of SMA neurones. In contrast to SMA neurones, many PMC neurones responded to light cutaneous stimuli. It was found that some of the 'somatosensory' PMC neurones were sometimes driven also by moving visual and, rarely, by auditory stimuli. Although there are obvious differences in the nature and possibly also in the amount of sensory inputs to the three motor cortical areas, the present results indicate that all three subareas receive somatosensory feedback and that they might therefore all be implicated in the generation of sensory-driven motor output.Experimental Brain Research 02/1988; 69(2):289-98. · 2.22 Impact Factor
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ABSTRACT: 1. Using two magnetic stimulators, we investigated the effect of a conditioning magnetic stimulus over the motor cortex of one hemisphere on the size of EMG responses evoked in the first dorsal interosseous (FDI) muscle by a magnetic test stimulus given over the opposite hemisphere. 2. A single conditioning shock to one hemisphere produced inhibition of the test response evoked from the opposite hemisphere when the conditioning-test interval was 5-6 ms or longer. We shall refer to this as interhemispheric inhibition. However, the minimum latency of inhibition observed using surface EMG responses may have underestimated the true interhemispheric conduction time. Single motor unit studies suggested values 4-7 ms longer than the minimum interval observed with surface EMG. 3. Interhemispheric inhibition was seen when the test muscle was active or relaxed. Increasing the intensity of the conditioning stimulus increased the duration of inhibition: increasing the intensity of the test stimulus reduced the depth of inhibition. 4. The conditioning coil had to be placed on the appropriate area of scalp for inhibition to occur. The effect of the conditioning stimulus was maximal when it was applied over the hand area of motor cortex, and decreased when the stimulus was moved medial or lateral to that point. 5. The inhibitory effect on the test stimulus probably occurred at the level of the cerebral cortex. In contrast to the inhibition of test responses evoked by magnetic test stimuli, test responses evoked in active FDI by a small anodal electric shock were not significantly inhibited by a contralateral magnetic conditioning stimulus. Similarly, H reflexes in relaxed forearm flexor muscles were unaffected by conditioning stimuli to the ipsilateral hemisphere. However, inhibition was observed if the experiment was repeated with the muscles active.The Journal of Physiology 02/1992; 453:525-46. · 4.38 Impact Factor
Article: What is the Bereitschaftspotential?[show abstract] [hide abstract]
ABSTRACT: 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.Clinical Neurophysiology 12/2006; 117(11):2341-56. · 3.14 Impact Factor