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PubMed2003

Simultaneous ERP and fMRI of the auditory cortex in a passive oddball paradigm.

Infrequent occurrences of a deviant sound within a sequence of repetitive standard sounds elicit the automatic mismatch negativity (MMN) event-related potential (ERP). The main MMN generators are located in the superior temporal cortex, but their number, precise location, and temporal sequence of activation remain unclear. In this study, ERP and functional magnetic resonance imaging (fMRI) data were obtained simultaneously during a passive frequency oddball paradigm. There were three conditions, a STANDARD, a SMALL deviant, and a LARGE deviant. A clustered image acquisition technique was applied to prevent contamination of the fMRI data by the acoustic noise of the scanner and to limit contamination of the electroencephalogram (EEG) by the gradient-switching artifact. The ERP data were used to identify areas in which the blood oxygenation (BOLD) signal varied with the magnitude of the negativity in each condition. A significant ERP MMN was obtained, with larger peaks to LARGE deviants and with frontocentral scalp distribution, consistent with the MMN reported outside the magnetic field. This result validates the experimental procedures for simultaneous ERP/fMRI of the auditory cortex. Main foci of increased BOLD signal were observed in the right superior temporal gyrus [STG; Brodmann area (BA) 22] and right superior temporal plane (STP; BA 41 and 42). The imaging results provide new information supporting the idea that generators in the right lateral aspect of the STG are implicated in processes of frequency deviant detection, in addition to generators in the right and left STP.

Adult↗
PubMed2003

Additional neuromagnetic source activity outside the auditory cortex in duration discrimination correlates with behavioural ability.

In magneto- and electroencephalographic experiments on an oddball paradigm we compared the components of the auditory evoked fields and potentials of "attend" with "nonattend" conditions in 17 subjects. The former consisted of the performance of a duration discrimination task, where we observed augmented activity for the auditory sustained response. A multiple source analysis showed this effect mainly stemming from a third source outside the auditory cortices. The dipole moment of this specific activation was increased by 150% under the attend condition. Having anatomical 3D MRI data sets of 12 subjects the likely location of the third source was shown to be within the area of the precuneus or the posterior cingulate gyrus, which, along with its waveform, suggests it to be a CNV equivalent. Further, the dipole moment is correlated significantly to the subjects' psychometrically derived discriminative abilities.

Acoustic Stimulation↗
PubMed2003

Exploring the nature of switch cost: inferences from P300 and the lateralized readiness potentials.

We describe a protocol to examine various hypothetical models of task switching. This protocol analyzes two event-related potentials--lateralized readiness potential (LRP) and P300--to infer the roles of advance reconfiguration and carry-over effect on task switching. Participants performed two tasks in a random order. On each trial a task from the previous trial would be repeated, or the other task would be carried out. In one scenario, each stimulus was preceded either by an informative cue specifying which of the two tasks to perform (task-cueing conditions) or by a non-informative cue (no task-cueing conditions). The results showed that the mean reaction time and the stimulus-locked LRP intervals were longer for switch than for repeated trials. This suggested that task switching affected stage processes such as stimulus identification and response selection that occur before the onset of LRP. A further analysis of P300 confined the phenomenon of task switching to the processes that occur after the stimulus identification stage. Moreover, the results of additivity between task cueing and task switching suggested that the two factors affected a distinct stage of processing. A further implication would be that there was no switch-specific control process supporting the view of carry-over effect of switch cost.

Adult↗
PubMed1997

The bereitschaftspotential paradigm in investigating voluntary movement organization in humans using magnetoencephalography (MEG).

In 1965, Kornhuber and Deecke first described the bereitschaftspotential (BP), a paradigm for investigating the organization of voluntary movement in humans, using electroencephalography (EEG). This paradigm has since been used in many studies for investigating motor control in healthy humans and patients. Over the last years, the advantages of magnetoencephalography (MEG) have been applied to the BP paradigm by a number of researchers. The main advantage of magnetoencephalography over electroencephalography is that MEG has a higher localization accuracy. This is due to the fact that the different structures of the head (brain, liquor cerebrospinalis, skull and scalp) influence the magnetic fields less than the volume current flow that causes the EEG. Additionally, the MEG is reference free, so that the localization of sources with a given precision is easier for MEG than it is for EEG. The present protocol shows in detail how the bereitschaftspotential paradigm can be applied using MEG. Some additional paradigms for investigating motor plasticity, somatosensory gating, Parkinson disease, and the efference copy theory are suggested as well.

Adult↗
PubMed2000

Brain mapping of bilateral interactions in attention deficit hyperactivity disorder and control boys.

OBJECTIVES: Children with attention deficit hyperactivity disorder (ADHD) are thought to have deficits in attentional control, whereas the status of deficits at visual and pre-motor processing stages is unclear. METHODS: The timing of such deficits was examined with event-related potential (ERP) microstates (stimulus- and response-related) and continuous force recordings in 15 ADHD and 16 control boys in a choice reaction time task. Unilateral and bilateral stimulus and response conditions were used to assess bilateral interactions at visual, central, and pre-motor stages. RESULTS: ADHD boys showed poorer performance, particularly in the bilateral conditions. In the visual P1 microstates, they exhibited less suppression of visual evoked potential (VEP) amplitudes but similar speeding of VEP latencies in the bilateral compared to the summed unilateral condition. The central P3 and pre-/post-response microstates were attenuated and topographically altered in ADHD boys. The attenuation was most pronounced in the bilateral condition and was similar for stimulus- and response-related averages. The lateralized readiness potential was also reduced in ADHD boys; this was most pronounced for the left hand responses. CONCLUSIONS: Brain mapping during uni- and bilateral stimulus and response conditions thus indicates multilevel deficits in ADHD boys affecting visuo-attentional, central, and pre-motor processes.

Adolescent↗
PubMed2001

Steep early negative slopes can be demonstrated in pre-movement bereitschaftspotential.

OBJECTIVES: The study presents data suggesting that the classic bereitschaftspotential hides in its early component (BP1) steep increases of negativity which precede the movement at varying intervals in repeated trials. METHODS: In 12 volunteers, surface EEG from Fz, Cz, C3, C4, and Pz electrodes and EMG from the flexor digitorum communis were recorded during self-paced wrist flexions. Two hundred trials were collected from each subject. The single trials were grouped for averaging in two different ways. In the first one, single trials for each subject were used to create individual averages. In the second, all single trials were divided into groups according to the point in time of small steep negative shift from the baseline detected on sweeps before the movement and time group averages were created. The identification of small shifts was based on the comparison of calculated mean amplitudes in the first and the second half of the 1 s time window moved along the time axis. RESULTS: The small negative shifts were identified in 97.2% of analyzed records. In each subject, their position on the time axis varied considerably. Individual averages exhibited the characteristics of classical readiness potential, i.e. slow early component, steep late component, laterality over motor cortices. On the other hand, all time group averages (26) displayed an early steep negative shift followed by plateau which, about 0.5 s before the movement, gave rise to the second, late steep negative shift. The slope values calculated in the definite segments of averaged curves were used as a measure of the amplitude of these shifts over various brain areas. MANOVA showed a significant effect of the electrode position both in the case of early slopes (F(4,115)=9.7; P<0.000) and in the case of late slopes (F(4,115)=22.5; P<0.000). In both cases, the largest value was demonstrated under Cz electrode. In contrast to the late slopes, the values of early slopes did not exhibit laterality and suggested greater importance of pre-frontal regions in their formation. CONCLUSION: We have suggested that the formation of steep early negative shifts from the baseline in time group averages was due to synchronization of a mental process which, under classical averaging procedure, was dispersed uniformly throughout the pre-movement period.

Adult↗
PubMed2001

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.

Adult↗
PubMed2002

Motor-related cortical potentials accompanying enslaving effect in single versus combination of fingers force production tasks.

OBJECTIVES: This study examined behavioral indices and motor-related cortical potentials (MRCP) of the enslaving phenomenon (i.e. interdependency of finger movement) during isometric force production tasks using each of the four fingers separately and in combination. We examined MRCP preceding force production and those during the achievement of the desired force (ramp phase) and its maintenance (static phase). METHODS: Our experimental design systematically controlled the isometric force output, including both ramp and static phases of force production. We applied time-domain averaging of electroencephalographic single trials in order to extract 3 components of MRCP (Bereitshaftspotential, motor potentials, and motor monitoring potentials) preceding and accompanying force responses. RESULTS: We report two major findings. First, we found the index finger to be more independent, accurate, and to display the larger MRCP amplitude whereas the ring finger was more dependent, less accurate, and displayed smaller MRCP amplitude. Second, adding the neighboring finger when the ring finger produced the task significantly reduced its dependency on uninvolved fingers and increased the accuracy of both ramp and static phases which was not the case with the index finger. The amplitude of MRCP was increased when the ring finger produced the task in combination as compared to when the ring finger performed the task in isolation. In contrast, the amplitude of MRCP was significantly reduced when the index finger produced the task in combination with other fingers when compared to when the index finger performed the task in isolation. CONCLUSIONS: Overall, the amount of the fingers' dependency on the uninvolved fingers (e.g. amount of enslaving) during isometric force production tasks was inversely related with the amplitude of MRCP indicating the contribution of central mechanisms to the enslaving phenomenon.

Adult↗
PubMed2002

Scalp-recorded Bereitschaftspotential is the result of the activity of cortical and subcortical generators--a hypothesis.

OBJECTIVE: The source of scalp-recorded Bereitschaftspotential (BP) remains a subject of ongoing discussion. This paper presents arguments in favour of the hypothesis that explains scalp-recorded BP as the result of the activity of both cortical and subcortical BP generators. METHODS: Intracranial recordings of BP were performed, mostly with depth electrodes in epilepsy surgery candidates. In some patients undergoing intracranial exploration, an electrode may have had contacts in the subcortical structures. RESULTS: BP is generated in several cortical and subcortical structures that are known to be directly or indirectly linked with motor control. Cortical sources of BP were displayed contralaterally to the movement in the primary motor cortex and somatosensory cortex, and bilaterally in the supplementary motor area (SMA), in the preSMA, and in the cingulate. A few other generators may be revealed in structures that have not yet been sufficiently explored. Subcortical generators of BP were found in the putamen, pallidum, caudate, and in the thalamus. In earlier recordings, BP was described rostrally to the thalamic region and in the brainstem, i.e. in the pes peripedunculi, nucleus peripeduncularis, pulvinar, and medial geniculate. CONCLUSIONS: Our observations do not explain the generation of scalp-recorded BP by the contribution of either cortical or subcortical sources alone. Intracranial cortical recordings contradict a wide distribution of scalp-recorded BP. Widely synchronised cerebral electromagnetic activity can be recorded on the scalp. We presume that in the case of BP, the weak deep dipoles might reach the scalp, as they are produced by a relatively huge mass of subcortical neuronal tissue. We strongly suspect that scalp-recorded BP represents a summation of potentials that are generated simultaneously in several cortical as well as in several subcortical structures.

Cerebral Cortex↗
PubMed2003

Distinct cortical areas for motor preparation and execution in human identified by Bereitschaftspotential recording and ECoG-EMG coherence analysis.

OBJECTIVE: To clarify the cortical areas involved in motor preparation and execution by investigating Bereitschaftspotentials (BPs) and electrocorticogram-electromyogram (ECoG-EMG) coherence from subdural electrodes placed around the rolandic area. METHODS: BPs and ECoG-EMG coherence were investigated for presurgical evaluation in a patient with cavernoma in the left frontal lobe. BPs were recorded in association with the tongue, right hand and right foot movements. ECoG-EMG coherence was calculated in association with weak muscle contraction of the right hand. RESULTS: Two cortical areas related to voluntary motor control were identified; one in the primary hand motor area, which generated surface-negative BPs with hand movements and showed significant coherence of ECoG with EMG of the contralateral hand muscle, and the other in the ventral rolandic area posterior to the central sulcus, which generated surface-positive BPs with voluntary movements of multiple sites (hand, tongue and foot) but did not show any ECoG-EMG coherence. CONCLUSIONS: It is postulated that the former area represents the primary motor area involved in both motor preparation and execution, and the latter area represents the non-primary motor area involved in motor preparation. SIGNIFICANCE: BP recording combined with ECoG-EMG coherence analysis could reveal the functional roles of motor cortices and the reorganization induced by structural brain lesion.

Brain Mapping↗
PubMed2003

The spatial distribution of attentional selectivity in touch: evidence from somatosensory ERP components.

OBJECTIVE: Somatosensory event-related brain potentials (ERPs) were measured to investigate the spatial distribution of selective attention in touch, and whether the focus of tactile attention can be split between non-contiguous areas of the body surface. METHODS: On each trial, vibratory tactile stimuli were delivered to one of 4 possible locations of the right hand. Participants had to attend to either one or two locations in order to detect infrequently presented target stimuli there. ERPs were recorded to tactile non-targets at attended and unattended locations. RESULTS: Attention directed to one finger versus another was reflected by amplitude modulations of the sensory-specific P100 component and a subsequent attentional negativity (Nd). These effects were smaller for within-finger as compared to between-finger selection. When attention was directed simultaneously to non-adjacent fingers, ERPs in response to stimuli delivered to spatially and anatomically intervening fingers showed no attentional modulations whatsoever. CONCLUSIONS: Allocating tactile-spatial attention to one finger versus another affects early modality-specific somatosensory processing stages, and these effects of within-hand attentional selectivity decrease gradually with increasing distance from the current attentional focus. Unlike vision, the focus of tactile attention can be split, and directed simultaneously to non-adjacent areas, thus excluding spatially and anatomically intermediate regions from attentional processing.

Adult↗
PubMed2003

The disruptive effect of chronic pain on mismatch negativity.

OBJECTIVE: To investigate the effect of chronic pain on processes that generate the mismatch negativity (MMN). METHODS: Twelve participants with a diagnosis of chronic intractable pain were tested before and after pain treatment. During testing, event-related potentials were recorded while participants performed tasks of varying difficulty. RESULTS: The amplitude of the MMN was found to be greater following a nerve block procedure compared to MMN amplitude when participants were experiencing chronic pain. This effect was found to occur in the MMN for difficult-to-detect tones elicited while participants were performing a simultaneous cognitively demanding visual task. MMN amplitude was found to be greater with attention to difficult-to-detect deviants during pain but not in no pain conditions. CONCLUSIONS: These results provide an electrophysiological correlate of previous findings that high levels of pain disrupt cognition during the performance of demanding tasks.

Acoustic Stimulation↗
PubMed2003

Event-related potentials associated with second language learning in children.

OBJECTIVE: In this study, we investigated learning-related changes in auditory event-related potentials (ERPs) of Finnish-speaking 3-6-year-old children caused by learning French language. METHODS: Using an oddball paradigm, ERPs to sounds of French language were recorded in the two groups of healthy children: those who were learning French (experimental group) and those who were not learning any foreign language (control peers). RESULTS: When the children from the experimental group were exposed to the foreign language, they automatically developed French-specific memory traces that helped them to discriminate, categorize, and pronounce utterances of the new language as indicated by the mismatch negativity (MMN) component of the ERPs in a previous study. We found that the learning process was also reflected by changes in P3a and late difference negativity (LDN) responses. Unlike MMN and P3a, the LDN has been discovered relatively recently and its functional role remains unclear. Similarly, as the MMN magnitude increased during the learning process, an increase of the P3a (known to reflect the involuntary attention switching toward deviant stimuli) and LDN amplitudes was observed. The ERPs of the control peers did not change significantly over the test period. CONCLUSIONS: When phonemes of a foreign language are learned, this process is accompanied with the increase in the MMN, P3a, and LDN amplitudes in children. Though the functional significance of LDN remains to be further investigated, our results support its possible link to reorienting processes following distraction.

Acoustic Stimulation↗
PubMed2003

The mismatch negativity and the P3a components of the auditory event-related potentials in autistic low-functioning subjects.

OBJECTIVE: In order to understand better the psychophysiological basis of auditory processing abnormalities in autism, we decided to study two automatic components of the auditory event-related potentials (ERPs): the mismatch negativity (MMN)--a component of the ERP which is recorded when, during repetitive auditory stimulation, rare changes are introduced--and the novelty-related P3a which is recorded as a response to unexpected novel events occurring in a sequence of repetitive stimuli. METHODS: Ten male subjects, mean age 12.3 years (SD 4.95), affected by autism and mental retardation were admitted to this study. All patients were also mentally retarded. Ten normal male subjects, mean age 12.2 years (SD 3.94), were used as controls. Auditory evoked potentials were recorded from 19 scalp electrodes (10-20 system), and stimuli were presented in sequences consisting of 2000 tones (70 dB, ISI=800 ms). Three types of stimuli were presented: (1) standard stimuli (1000 Hz tones, 80% of total stimuli), (2) deviant stimuli (1300 Hz tones, 10% of total stimuli), and (3) novel stimuli (complex and non-monotonal, 10% of total stimuli). To quantify the MMN, the evoked response to the standard tones was subtracted from the corresponding deviant stimulus response and its amplitude and latency at peak were measured over Fz, Cz and Pz; similarly, the P3a component of the ERP was obtained by subtracting the response to the standard tone from that to the novel stimuli and its amplitude and latency at peak were measured over Fz, Cz and Pz. Also, the amplitude and latency at peak for the N1 component of the auditory evoked potential obtained with the standard stimuli were measured over Fz, Cz and Pz. The correlation between age and MMN and P3a amplitude was also analyzed. RESULTS: N1 showed significantly shorter latencies in the autistic groups. MMN elicited by deviant stimuli, but not that elicited by novel stimuli, was found to be significantly larger in autistic children than in normal controls. P3a showed higher amplitude in autistic subjects than in normal controls during childhood; the opposite was observed during young adulthood. DISCUSSION: Our findings indicate that significant changes in ERPs can also be seen in non-cooperative individuals with autism and mental retardation, which might be different from the changes already reported for high-functioning autistic subjects and deserve further insight. These changes show developmental modifications that should be taken into consideration when analyzing data from autistic subjects.

Acoustic Stimulation↗
PubMed2004

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.

Adolescent↗
PubMed1999

Motoric response inhibition in finger movement and saccadic eye movement: a comparative study.

OBJECTIVE: To study cortical potentials associated with suppression of intended motoric actions. METHODS: Electro-encephalographic activity was recorded in a Go/NoGo reaction time paradigm. Subjects viewed computer-generated pacing stimuli, which provided information concerning the time at which an imperative Go/NoGo signal occurred. A motoric response was required following Go stimuli while motoric response inhibition was required following NoGo stimuli. To examine whether previously reported 'Go/NoGo effects' on event related potential (ERP) components may be generalized across movement modalities, the present experimental paradigm was performed with either finger movement or saccadic eye movement as required motoric response. RESULTS: For both movement modalities, comparable differences in the morphology, amplitude and scalp topography of ERP components were observed between Go trials, with proper movement execution, and NoGo trials, with complete suppression of motoric activity. In addition, for either movement modality a similar 'error related negativity' (ERN) was found for NoGo trials in which motoric activity was present. CONCLUSIONS: The results of the present study suggest that cortical activity underlying the Go/NoGo differences in ERP components represent general cortical processing associated with detection and/or suppression of inappropriate response behaviour, independent of movement modality.

Adult↗
PubMed2000

Dysfunction of the auditory cortex persists in infants with certain cleft types.

Language and learning disabilities occur in almost half of individuals with oral clefts. The characteristics of these cognitive dysfunctions vary according to the cleft type, and the mechanisms underlying the relation between cleft type, cognitive dysfunction, and cleft-caused middle-ear disease are unknown. This study investigates preattentive auditory discrimination, which plays a significant role in language acquisition and usage, in infants with different cleft types. A mismatch negativity (MMN) component of brain evoked potentials, which indexes preconscious sound discrimination, and brain responses to rare sine-wave tones were recorded in 12 healthy infants and 32 infants with oral clefts at the ages of 0 and 6 months. Infants with clefts were subdivided into two categories: those with cleft lip and palate (CLP) (n=11 at birth, n=6 at the age of 6 months) and those with cleft palate only (CPO) (n=17 at birth, n=8 at the age of 6 months). At both ages, brain responses to rare sounds tended to be smaller in both cleft subgroups than in healthy peers. However, in the latency range of 300 to 500 ms, the MMN was significantly smaller in infants with CPO. In infants with CLP, the MMN was comparable to that of healthy infants. Differences in auditory discrimination between infants with CLP and CPO, as reflected by MMN, were detectable at birth and persisted into later infancy. This pattern parallels known behavioural differences between children with these cleft types. Brain responses to rare sounds, in contrast, had no differentiative power with respect to the cleft type.

Auditory Cortex↗