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PubMed1995

K-complex evoked in NREM sleep is accompanied by a slow negative potential related to cognitive process.

Evoked cortical responses to two kinds of auditory stimuli (rare and frequent) were analyzed to determine whether or not a K-complex evoked in stage 2 of NREM sleep is accompanied by some endogenous cognitive components of the event-related potential. All the 7 subjects examined in this sleep state failed to provide the correct behavioral response to auditory stimuli, but a K-complex was evoked more frequently by rare stimuli than by frequent stimuli. EEG segments in stage 2 were averaged separately according to the presence or absence of K-complexes emerging just after the stimulation. In cases where K-complexes did not emerge, a long-lasting negative potential of relatively low voltage appeared in the difference wave, which was obtained by subtracting the averaged EEG for frequent stimuli from that for rare stimuli. In cases where K-complexes emerged, a similar long-lasting negative potential of large amplitude appeared in the difference wave. These data may indicate that a K-complex evoked by an external stimulus is accompanied by a potential related to a cognitive process, which appears with greater amplitude in cases where a K-complex is evoked.

Acoustic Stimulation↗
PubMed1996

Localization of functional regions of human mesial cortex by somatosensory evoked potential recording and by cortical stimulation.

We describe methods of localizing functional regions of the mesial wall, based on 47 patients studied intraoperatively or following chronic implantation of subdural electrodes. Somatosensory evoked potentials were recorded to stimulation of posterior tibial, dorsal pudendal, median, and trigeminal nerves. Bipolar cortical stimulation was performed, and in 4 cases movement-related potentials were recorded. The cingulate and marginal sulci formed the inferior and posterior borders of the sensorimotor areas and the supplementary motor area (SMA). The foot sensory area occupied the posterior paracentral lobule, while the genitalia were represented anterior to the foot sensory area, near the cingulate sulcus. The foot motor area was interior and superior to the sensory areas, but there was overlap in these representations. There was a rough somatotopic organization within the SMA, with the face represented anterior to the hand. However, there was little evidence of the "pre-SMA" region described in monkeys. Complex movements involving more than one extremity were elicited by stimulation of much of the SMA. The region comprising the supplementary sensory area was not clearly identified, but may involve much of the precuneus. Movement-related potentials did not provide additional localizing information, although in some recordings readiness potentials were recorded from the SMA that appeared to be locally generated.

Adolescent↗
PubMed1996

Subdural potentials at orbitofrontal and mesial prefrontal areas accompanying anticipation and decision making in humans: a comparison with Bereitschaftspotential.

Field potentials associated with the execution of a warned choice Go/No-Go reaction task were recorded from prefrontal supplementary (SMA) and primary motor cortex (MI) by using subdural electrodes in 5 epileptic patients during presurgical evaluation. The choice was between a Go and a No-Go imperative stimulus (S2) in the S1-S2 paradigm. Orbitofrontal and mesial prefrontal areas generated a slow preceding potential before S2 (most likely late CNV), and bilateral mesial prefrontal areas generated a transient potential, most likely related to decision making, upon S2 in both Go and No-Go conditions. In self-paced, repetitive movement, the Bereitschaftspotential was seen only at SMA and MI, but not in the prefrontal area. The present result, therefore, suggests that in humans orbitofrontal and mesial frontal areas play an important role in preparation for cognition and in decision making, whereas SMA and MI do so in motor preparation.

Adult↗
PubMed1996

Slow negative cortical potential preceding the onset of postural adjustment.

We investigated whether a cortical potential exists, that is similar to the Bereitschaftspotential, preceding postural adjustment followed by voluntary ballistic rising on tiptoe in 10 healthy subjects. On the basis of the electromyogram (EMG) activities of the soleus muscle, the onsets of the premotion silent period (PMSP) and EMG discharge were determined. The negative potentials associated with a voluntary rise-on-tiptoe movement with respect to EMG onset were similar to the readiness potential associated with voluntary foot movement. The slopes of the slow negative potential associated with the PMSP onset were significantly more negative than those of the potential associated with rise-on-tiptoe movement, particularly over the frontal electrode positions. The results suggest that a cortical potential precedes postural adjustment that is followed by voluntary rising on tiptoe.

Adult↗
PubMed1996

Movement-related slow cortical magnetic fields and changes of spontaneous MEG- and EEG-brain rhythms.

Cortical activity was recorded from 5 healthy adults with a 122-channel whole-head magnetometer while the subjects performed during unilateral finger movements at self-paced intervals exceeding 6 s. The readiness field (RF) started over the contralateral somatomotor area 0.3-1 s prior to the movement onset in subjects (Ss) 1, 2, and 4, and culminated in the motor field (MF) 30 ms after it (Ss 1-4). These signals were followed by movement evoked fields MEFI (Ss 1-5) and MEFII (Ss 1-4) at 100-150 ms and 200-250 ms after the movement onset, respectively. One subject showed clear RF over the ipsilateral hemisphere as well. The contralateral dominance of the RF contrasted the more symmetric distribution of the simultaneously recorded electric Bereitschaftspotential (BP). The RF onset never preceded the BP onset. We suggest that BP receives contribution from the early bilateral activation of the crown of the precentral gyrus, whereas RF reflects later activity of the fissural motor cortex. Spontaneous oscillations in the background activity (spontaneous activity) of approximately 10 Hz started to dampen 2-3 s prior to the movement onset in the somatomotor areas of both hemispheres with contralateral predominance (S1 and S3), and returned to a steady level 0.8-2 s after the movement onset in all subjects. Higher frequency bands in the same area displayed a prominent rebound about 1 s after the movement onset in 4 subjects. Execution of self-paced movements is evidently expressed differently in the slow movement-related fields and in the cortical spontaneous activity.

Adult↗
PubMed1996

Dipole source analysis suggests selective modulation of the supplementary motor area contribution to the readiness potential.

The readiness potential preceding voluntary movement is modulated by the mode of movement selection, i.e. it has a higher amplitude preceding freely selected than before prescribed movements (Praamstra, P., Stegeman, D.F., Horstink, M.W.I.M., Brunia, C.H.M. and Cools, A.R. Movement-related potentials preceding voluntary movement are modulated by the mode of movement selection. Exp. Brain Res., 1995, 103: 429-439). One cortical area that is likely to be involved in this modulation is the supplementary motor area (SMA). Recent attempts to elucidate the neural generators of the readiness potential using spatiotemporal dipole source analysis, however, failed to establish a significant SMA contribution to the readiness potential. This might be explained by a failure of the proposed analyses to discriminate between SMA and motor cortex contributions to the readiness potential. We applied a dipole source analysis approach that better separates these overlapping source activities. The resulting source model includes an SMA source generating pre-movement activity consistent with evidence from intracranial recordings in humans. The SMA source accounts almost completely for the modulation of the readiness potential by different modes of movement selection. On the basis of these results, the relation between scalp-recorded movement-related activity, intracranially recorded potentials, and findings from functional imaging studies of voluntary movement, appears more transparent than suggested by previous dipole source analyses of premovement potentials.

Adult↗
PubMed1996

Linear estimation discriminates midline sources and a motor cortex contribution to the readiness potential.

Spatiotemporal dipole modelling of the generators of the readiness potential (RP) prior to voluntary movements has yielded diverging results concerning the contributions of supplementary motor area (SMA) and primary motor cortex. We applied an alternative approach (i.e. linear estimation theory) to measurements of the RP preceding fixed and freely selected finger movements, measured at 28 electrodes of the extended 10-20 system. The volume conductor properties of the head were modelled by 3 concentric spheres. Current densities were reconstructed on a spherical surface, placed at a depth of 5 mm from the inside of the skull. Lead field normalization was applied. The analysis shows activity on the midline as well as near the primary motor area. Although some features of the reconstructions are not readily interpretable, separate contributions of midline sources (including presumably SMA) and motor cortex to the RP are clearly distinguished.

Adult↗
PubMed1992

Eighteen-month course of two patients with grafts of fetal dopamine neurons for severe Parkinson's disease.

Two patients with advanced Parkinson's disease were followed for 6 months before, and 18 months after, receiving stereotaxic grafts of fetal mesencephalic tissue from aborted human fetuses. Parameters studied included a series of standardized tests of movement, response to levodopa, electrophysiological recording of the motor readiness potential, and positron emission tomography (PET) with ligands based upon levodopa and upon the dopamine reuptake inhibitor nomifensine. The patients each received stereotaxic implantation of ventral mesencephalic tissue containing midbrain dopamine neurons from aborted human fetuses of 8 to 10 weeks gestational age into the caudate and putamen of one hemisphere. Throughout their 18-month course, the patients were treated with cyclosporine, azathioprine, and glucocorticoids to minimize the risk of graft rejection. There were no significant complications from the procedure, but there was also no major change in their assessment of impairment on the Hoehn and Yahr scale. However, significant changes were observed in clinical, electrophysiological, and PET measures. Changes in these parameters, apparent at 6 months postoperatively, were described in detail in a previous report. The purpose of this present report is to provide follow-up data from the subsequent year with an emphasis on longitudinal evaluation methodology. Standardized clinical testing showed a small but long-term improvement in the first of the two patients. Following the operation, she was able to walk in "off" periods, which she had not been able to do preoperatively. This improvement was accompanied by increased walking speed and reduction in the time necessary to perform a series of pronation and supination movements using both hands. Although these improvements have continued throughout the postoperative period, they have not alleviated her basic neurological impairment. The second patient showed similar improvement during the first 6 months; she then reverted to her preoperative status at the end of the 18-month follow-up period. The electrophysiological recordings were consistent with the clinical findings. Both patients had significant changes in the motor readiness (bereitschafts) potential amplitude, which was greatest 5 to 7 months postoperation. The amplitude of the potential declined subsequently for both patients, but remained significantly elevated over the preoperative baseline for patient 1. The analysis of the PET scans was somewhat compromised by technical problems in the preoperative scans. However, they are also consistent with the clinical data. In comparisons of the operated and the unoperated sides, fluoro-dopa showed increased uptake in the caudate nucleus of patient 1 at 6 months and at 13 months.(ABSTRACT TRUNCATED AT 400 WORDS)

Brain Tissue Transplantation↗
PubMed1988

Event-related potentials and the matching of familiar and unfamiliar faces.

Event-related potentials (ERPs) were recorded from one midline and three pairs of lateral sites while subjects made same/different judgements on sequentially presented pairs of familiar or unfamiliar faces. During the interval between the first and second face, a slow wave was more negative-going over the right than the left hemisphere, particularly when the faces were familiar. Following the second face, two regions of the waveforms were more negative-going when this face did not match the identity of its predecessor. In the early region (less than 160 msec), this effect was confined to posterior electrode sites and familiar faces. In the later region (greater than 250 msec), the match/non-match effect was widespread across the scalp and was evident for both familiar and non-familiar faces, although in the latency range 350-450 msec (encompassing the "N400" component), it was greater in magnitude in the case of familiar stimuli. It is suggested that the slow wave asymmetries reflect the engagement of short-term memory mechanisms lateralized to the right hemisphere. The match/non-match differences are thought to reflect multiple processes, including the modulation of the "N400" component. The sensitivity of this component to the familiarity manipulation is consistent with the hypothesis that the amplitude of N400 reflects an item's compatibility with currently activated memory representations.

Adult↗
PubMed1989

Asymmetries in event-related potentials during rhyme-matching: confirmation of the null effects of handedness.

Event-related potentials (ERPs) were recorded from 16 right- and 16 left-handed subjects during two variants of a sequential rhyme-judgement task. These variants manipulated the demands placed on short-term memory, by requiring subjects to match a word either with one or with three previously presented words. In both tasks, ERPs exhibited two lateral asymmetries: (i) during the interval prior to the final word, the CNV was more negative over the left hemisphere, and (ii) rhyme/non-rhyme differences in the amplitude of the N450 component of the ERPs to the final word were larger over the right than the left hemisphere. Neither of these asymmetries was smaller or more variable in left- than in right-handed subjects. It is suggested that these data may indicate that some aspects of language processing are, irrespective of handedness, relatively invariant in the direction and degree of their cerebral lateralization.

Adult↗
PubMed1989

Event-related potentials and the semantic matching of faces.

Event-related brain potentials (ERPs) were recorded while subjects determined whether two sequentially presented famous faces depicted individuals belonging to the same or to different occupational categories. During the 1.56 sec interval between the onset of the faces, ERPs recorded from right hemisphere electrodes were more negative-going than those from electrodes over the left hemisphere. The ERPs evoked by the second face on each trial differed as a consequence of whether or not the person depicted belonged to the occupational category specified by the first face. This difference took the form of a bilaterally-distributed negative-going shift in the ERPs evoked by non-matching as opposed to matching faces. This negativity was maximal around 450 msec post-stimulus. The ERP asymmetries during the inter-stimulus interval are interpreted as evidence for the engagement of cognitive processes lateralized to the right hemisphere. The match/non-match differences are considered to reflect the modulation of an "N400" component similar to that evoked by words, and thus suggest that such components can be modulated by associative priming between non-linguistic stimuli.

Adult↗
PubMed1991

While an undergraduate waits.

The search for the intracranial sources of components of the ERP using non-human species can benefit from an analysis of the functional significance of these components. Such analysis provides criteria, based on the response of the components to experimental manipulations, for identifying those aspects of the ERP recorded in other species that are analogous to specific ERP components recorded from human subjects. This thesis is illustrated by examining the problems presented by the data recorded in monkeys by Donchin et al. (Electroenceph. clin. Neurophysiol. 31, 115-127, 1971). The different ERP components they observed in the monkeys could not be fully interpreted because a detailed analysis of the ERPs recorded during similar paradigms in humans was lacking. We review studies of the Lateralized Readiness Potential using human subjects which indicate how the activity recorded during such waiting intervals which specifically relates to motor preparation can be identified.

Animals↗
PubMed1993

Event-related potentials associated with covert orientation of visual attention in Parkinson's disease.

Event-related potentials (ERPs) were measured in a group of patients with idiopathic Parkinson's disease and compared with a matched control group during a task involving covert orientation of visual attention. Central warning cues directed attention to the probable location of a lateralized signal that required a button-press response. Parkinson patients had enhanced post-cue P1 (at Oz) and P2 (at Cz) amplitudes, delayed N1 (at Oz) latencies, and diminished CNV amplitudes. Post-target amplitudes were similar to controls, except for an enhanced P1 to invalidly cued targets, and delayed N1 and P3 target latencies. These results indicate that Parkinson patients, in addition to their motor deficits, process spatial cues more effortfully and slowly, have impaired response preparation, and process imperative stimuli more slowly.

Aged↗