Stimulus-locked Averages Research Articles

Tone-Inhibiting Insoles Enhance the Reciprocal Inhibition of Ankle Plantarflexors of Subjects With Hemiparesis After Stroke: An Electromyographic Study

BackgroundSpasticity is a common sequela of upper motor neuron pathology, such as cerebrovascular diseases and cerebral palsy. Intervention for spasticity of the ankle plantarflexors in physical therapy may include tone-inhibiting casting and/or orthoses for the ankle and foot. However, the physiological mechanism of tone reduction by such orthoses remains unclarified. ObjectiveTo investigate the electrophysiologic effects of tone-inhibiting insoles in stroke subjects with hemiparesis by measuring changes in reciprocal Ia inhibition (RI) in the ankle plantarflexor. DesignAn interventional before–after study. SettingAcute stroke unit or ambulatory rehabilitation clinic of a university hospital in Japan. ParticipantsTen subjects (47-84 years) with hemiparesis and 10 healthy male control subjects (31-59 years) were recruited. MethodsRI of the spastic soleus in response to the electrical stimulation of the deep peroneal nerve was evaluated by stimulus-locked averaging of rectified electromyography (EMG) of the soleus while subjects were standing. Main Outcome MeasurementsThe magnitude of RI, defined as the ratio of the lowest to the baseline amplitude of the rectified EMG at approximately 40 milliseconds after stimulation, was measured while subjects were standing with and without the tone-inhibiting insole on the hemiparesis side. ResultsEnhancement of EMG reduction with the tone-inhibiting insole was significant (P < .05) in the subjects with hemiparesis, whereas no significant changes were found in controls. ConclusionTone-inhibiting insoles enhanced RI of the soleus in subjects after stroke, which might enhance standing stability by reducing unfavorable ankle plantarflexion tone. Level of EvidenceIII

New insights into old waves. Matching stimulus- and response-locked ERPs on the same time-window

We compared the effect of locking the event-related potentials (ERPs) on the stimulus vs. the response in a simple (SRT) and in a discriminative (DRT, equally probable Go/No-go) visuo-motor task. The accurate alignment of stimulus- and response-locked ERPs on the same time scale was obtained selecting a group of 27 participants with low inter-individual response time (RT) variation in the two tasks to reduce the jitter of RTs. Two-second epochs were defined for the analyses based on averaged RTs in the two tasks. Results show that the preparatory pre-stimulus activities (i.e., the pN and the BP components) were not affected by the different locking in both SRT and DRT. As expected, the exogenous post-stimulus P1 and N1 components (and the P2, present only in SRT) were larger in stimulus- than response-locked averaging; the same trend was observed for the less-known prefrontal N1 and P1 components (pN1 and pP1) that were larger in stimulus-locked averaging (the effect was not significant in SRT). The prefrontal pP2 component was only present in DRT peaking around 370 ms, and did not show an effect of locking. The frontal-central N2 component was enhanced by response-locked averaging in SRT, while it did not show effects of locking in DRT. The P3 component peaked at about 350ms over central sites in SRT, and at about 500ms over parietal sites in DRT; in both cases its amplitude was larger in response- than in stimulus-locked averaging. Overall, the amplitude of the preparatory components was independent from locking, the exogenous components were enhanced by stimulus locking, and the late components were more related to the response than to the stimulus. Concluding, to investigate action preparation, perception, and perceptual-decisional activity ERP studies should adopt stimulus-locked averaging with an appropriate baseline and longer pre-stimulus interval, or use both types of locking.

Bridging events and actions: P3b in healthy people and in Parkinson’s disease

Ever since the first reports about the P3 component, its meaning has been debated. The majority view has taken for granted that P3b depends on processing («evaluation») of stimuli only rather than on selecting responses. To further explore this matter, we used the oddball-effect on P3b in choice-response tasks where rare or frequent stimuli (S1) were followed by ancillary stimuli (S2). Rare S1s evoked a large P3b. But this P3b became abolished when S1, though still relevant, did not define the response. In this line, by comparing response- to stimulus-locked averages, we tested whether P3b reflects the fragility of stimulus–response links in Parkinson’s disease. Indeed, conspicuously, patients’ P3b was overlapped by response-related negativity above the mesial motor cortex. Thus, conceiving of P3b as an indicator of integrated stimulus–response links will continue to provide good new possibilities for basic and applied research.

Sometimes we have to intentionally focus on the details: Incidental encoding and perceptual change decrease recognition memory performance and the ERP correlate of recollection

Prior studies suggest that memory retrieval is based on two independent processes: Recollection and familiarity. Here, we investigated the role of incidental and intentional encoding, and specifically whether perceptual changes between study and test affects behavioral and electrophysiological correlates of both retrieval processes. During retrieval, participants distinguished between identical and changed exemplars as well as novel distractors. Following incidental encoding, participants had difficulty identifying changed exemplars; item and feature recognition increased after intentional encoding, in particular for changed exemplars. Reflecting this increase in memory performance, the ERP correlate of recollection was larger after intentional encoding and for identical item repetitions, whereas the ERP correlate for familiarity was largely unaffected. Pre-response old/new effects corresponding to later aspects of recollection (700–1000ms relative to stimulus onset) were larger in response-compared to stimulus-locked averages, but also of similar magnitude for identical and changed exemplars. These results corroborate previous findings suggesting that the electrophysiological signature of recollection is modulated as a function of memory performance. The role of task characteristics and material retrieved from memory for modulations in familiarity-based retrieval processes is discussed.

Re-examination of Chinese semantic processing and syntactic processing: evidence from conventional ERPs and reconstructed ERPs by residue iteration decomposition (RIDE).

A number of studies have explored the time course of Chinese semantic and syntactic processing. However, whether syntactic processing occurs earlier than semantics during Chinese sentence reading is still under debate. To further explore this issue, an event-related potentials (ERPs) experiment was conducted on 21 native Chinese speakers who read individually-presented Chinese simple sentences (NP1+VP+NP2) word-by-word for comprehension and made semantic plausibility judgments. The transitivity of the verbs was manipulated to form three types of stimuli: congruent sentences (CON), sentences with a semantically violated NP2 following a transitive verb (semantic violation, SEM), and sentences with a semantically violated NP2 following an intransitive verb (combined semantic and syntactic violation, SEM+SYN). The ERPs evoked from the target NP2 were analyzed by using the Residue Iteration Decomposition (RIDE) method to reconstruct the ERP waveform blurred by trial-to-trial variability, as well as by using the conventional ERP method based on stimulus-locked averaging. The conventional ERP analysis showed that, compared with the critical words in CON, those in SEM and SEM+SYN elicited an N400–P600 biphasic pattern. The N400 effects in both violation conditions were of similar size and distribution, but the P600 in SEM+SYN was bigger than that in SEM. Compared with the conventional ERP analysis, RIDE analysis revealed a larger N400 effect and an earlier P600 effect (in the time window of 500–800 ms instead of 570–810ms). Overall, the combination of conventional ERP analysis and the RIDE method for compensating for trial-to-trial variability confirmed the non-significant difference between SEM and SEM+SYN in the earlier N400 time window. Converging with previous findings on other Chinese structures, the current study provides further precise evidence that syntactic processing in Chinese does not occur earlier than semantic processing.

The response-locked P3 component as indicator of pathophysiology in parkinson's disease

Event Abstract Back to Event The response-locked P3 component as indicator of pathophysiology in parkinson's disease Rolf Verleger1* 1 University of Lübeck, Germany For long, the P3b component of the event-related EEG potential has been considered an indicator of response-independent processes. Correspondingly, studies on the P3 component in Parkinson's disease have looked at stimulus-locked averages only. Differences between patients and healthy persons remained diffuse. However, P3b actually forms a bridge between stimulus and response in healthy persons (Gerson et al., 2005; Verleger et al., 2005) with latencies and amplitudes of P3 peaks varying across trials in such a way that P3 waves are equally large in stimulus-locked and response-locked averages. Research on basal ganglia has suggested that making stimulus-response sequences precede automatically is a most relevant function of these structures. Therefore, when studying disorders of basal ganglia, as Parkinson's disease, it might make sense to focus on P3's function as a bridge between stimuli and responses. Thus, we compared stimulus- and response-locked P3b between patients with Parkinson's disease and healthy control groups in a choice-response task. In patients, P3 was distinctly smaller in response-locked than in stimulus-locked averages whereas, again, both amplitudes were equal in healthy participants. The difference in patients was due to a fronto-central negative shift, overlapping P3 during the final 100 ms before the response. Presumably, in order to compensate for the deficient automatic process, patients have to use additional activation of their supplementary motor areas. This difference is diluted when averaging is stimulus-locked. The specific reduction of response-locked P3 might qualify as a marker of basal-ganglia dysfunction. Keywords: Attention, Parkinson Conference: XI International Conference on Cognitive Neuroscience (ICON XI), Palma, Mallorca, Spain, 25 Sep - 29 Sep, 2011. Presentation Type: Poster Presentation Topic: Poster Sessions: Neurophysiology of Cognition and Attention Citation: Verleger R (2011). The response-locked P3 component as indicator of pathophysiology in parkinson's disease. Conference Abstract: XI International Conference on Cognitive Neuroscience (ICON XI). doi: 10.3389/conf.fnhum.2011.207.00321 Copyright: The abstracts in this collection have not been subject to any Frontiers peer review or checks, and are not endorsed by Frontiers. They are made available through the Frontiers publishing platform as a service to conference organizers and presenters. The copyright in the individual abstracts is owned by the author of each abstract or his/her employer unless otherwise stated. Each abstract, as well as the collection of abstracts, are published under a Creative Commons CC-BY 4.0 (attribution) licence (https://creativecommons.org/licenses/by/4.0/) and may thus be reproduced, translated, adapted and be the subject of derivative works provided the authors and Frontiers are attributed. For Frontiers’ terms and conditions please see https://www.frontiersin.org/legal/terms-and-conditions. Received: 22 Nov 2011; Published Online: 28 Nov 2011. * Correspondence: Dr. Rolf Verleger, University of Lübeck, Lübeck, Germany, 665948@frontiersin.org Login Required This action requires you to be registered with Frontiers and logged in. To register or login click here. Abstract Info Abstract The Authors in Frontiers Rolf Verleger Google Rolf Verleger Google Scholar Rolf Verleger PubMed Rolf Verleger Related Article in Frontiers Google Scholar PubMed Abstract Close Back to top Javascript is disabled. Please enable Javascript in your browser settings in order to see all the content on this page.

Phase-Interpolated Averaging for Analyzing Electroencephalography and Magnetoencephalography Epochs

Stimulus-locked averages of electroencephalography (EEG) and magnetoencephalography (MEG) epochs reveal characteristic waveforms. EEG/MEG generation models to have reconstruct such waveforms have been recently proposed. These models assume that evoked, phase-modulated, and amplitude-modulated activities occur solely or simultaneously. We propose a two-stage stimulus-locked averaging method, called phase-interpolated averaging, to investigate the EEG/MEG generation process. First, virtual EEG/MEG epochs, which would be obtained as if instantaneous phases for each time sampling point were on a phase-grid, are interpolated from actually measured EEG/MEG epochs. Then, the virtual EEG/MEG epochs are discrete Fourier transformed. A simulation revealed that the zeroth Fourier term revealed the evoked activity, the first Fourier term revealed the amplitude-modulated activity, and the condition number of the interpolation reflected the phase-modulated activity. On the basis of these facts, a preliminary EEG analysis implied that the evoked activity is much smaller than what would be expected by using conventional averaging, the evoked and phase-modulated activities simultaneously occur, and the amplitude-modulated activity occasionally associates with the evoked and phase-modulated activities. To the best of our knowledge, this is the first time that these three activities have been shown to coexist by actually separating them.

Neural correlates of late positivities associated with infrequent visual events and response errors

The P3 response has been one of the most extensively studied event-related potential (ERP) components. Still, the exact functional role and cortical basis of P3 has remained unsettled. To explore the cortical processes underlying the generation of late positivities, we recorded the activation evoked by frequent Go and infrequent NoGo stimuli and correct versus erroneous responses using combined magnetoencephalography (MEG) and ERP measurements during a visual Go/NoGo task. The stimulus-locked signals in the ERP channels revealed an enhanced negative N2 and a prominent late positive component (LPC) after the complex NoGo stimuli associated with successfully withheld responses. The response-locked ERP signals revealed error-related negativity (ERN) and positivity (Pe) after erroneous responses. The positive LPC and Pe components were coupled with functionally and temporally comparable MEG signals. This MEG activation detected during the positive components was localized bilaterally in the posterior temporal cortex. In the response-locked averages, the temporal activity was enhanced around 200 ms after a commission of an error. In the stimulus-locked averages, the activation was also enhanced after infrequent NoGo stimuli around 500 ms after stimulus onset and delayed about 80 ms for the initially miscategorized NoGo stimuli accompanied by erroneous response. The results suggest that the cortical correlates of Pe are not specifically related to commission of an error, but both the LPC and Pe components, and bilateral temporal cortices, are more generally involved in stimulus-driven attentional processing evoked by unexpected stimuli. The negative ERP components evoked by NoGo stimuli (N2) and erroneous responses (ERN) were found to be associated with partly non-overlapping neural sources.

Simultaneous Measurement of Perceptual and Motor Cortical Potentials

Psychomotor slowing is a common manifestation of traumatic brain injury. Previous electrophysiological studies of traumatic brain injury have focused on abnormal attentional and perceptual responses to incoming stimuli. We hypothesize that traumatic brain injury is also associated with abnormal cortical components of motor execution. To test this hypothesis, we analyzed event-related potentials of 22 subjects (11 with a history of severe traumatic brain injury and 11 age-matched healthy subjects) during oddball discrimination tasks. In addition to the usual stimulus-locked averaging of electrophysiological data to reveal cognitive components, such as the P300, we also analyzed subjects' response-locked data to reveal motor potential waveforms. To focus on generalized effects across modality, analyses were performed on composite measures from both auditory and visual event-related potentials. (1) Traumatic brain injury subjects had abnormal P300 responses (with reduced amplitude and prolonged latency) in both sensory modalities. (2) Traumatic brain injury subjects' motor potential waveforms showed significantly reduced amplitude in both sensory modalities. (3) Abnormalities in P300 latency, amplitude, and motor potential amplitude (effect sizes = 1.2-1.5 SD) were greater than behavioral slowing, as measured by reaction times (0.7 SD). (4) P300 latency and motor potential amplitude together accounted for much of the reaction time prolongation (r = 0.73). This study demonstrates the value of concurrently analyzing stimulus-locked and response-locked event-related potential data to evaluate cortical components of perceptual and motor processing. The present findings indicate that patients with traumatic brain injury have impairments in both the perceptual interpretation of incoming stimuli and the execution of motor responses and that both abnormalities contribute to psychomotor slowing in patients with traumatic brain injury.

Age-Related Changes in Executive Function: An Event-Related Potential (ERP) Investigation of Task-Switching

ABSTRACT Older adults have difficulty when executive control must be brought on line to coordinate ongoing behavior. To assess age-related alterations in executive processing, task-switching performance and event-related potential (ERP) activity were compared in young and older adults on switch, post-switch, pre-switch, and no-switch trials, ordered in demand for executive processes from greatest to least. In stimulus-locked averages for young adults, only switch trials elicited fronto-central P3 components, indicative of task-set attentional reallocation, whereas in older adults, three of the four trial types evinced frontal potentials. In response-locked averages, the amplitude of a medial frontal negativity (MFN), a component reflecting conflict monitoring and detection, increased as a function of executive demands in the ERPs of the young but not those of the older adults. These data suggest altered executive processing in older adults resulting in persistent recruitment of prefrontal processes for conditions that do not require them in the young.

Response-time corrected averaging of event-related potentials

Objective The present study presents a novel approach to averaging of event-related potentials (ERPs). Acknowledging latency variability of late ERP components as related to performance fluctuations across trials should improve the assessment of late portions of the ERP. Methods Prior to the averaging procedure stimulus-to-response epochs in the electroencephalogram (EEG) were expanded/compressed in time to match mean RT in a certain condition and participant. By means of several mathematical functions RT variability was differentially distributed over late vs. early portions of the ERP. Data from 20 participants from two conditions of an identity-based priming task were analyzed using traditional stimulus- and response-locked averaging, as well as four different RT-corrected averaging procedures. Results Area under the curve as an index of precision of LPC assessment was reliably enhanced for certain RT-corrected procedures relative to traditional ERP averaging. Moreover, a priming effect on amplitude of a distinct LPC subcomponent which could not be confirmed with traditional stimulus-locked averaging was reliably born out using a cubic RT-correction procedure. Conclusions RT-corrected ERP averaging can outperform traditional ERP averaging in the assessment of late portions of the ERP, and experimental effects upon. Significance Cognitive ERP researchers may take advantage of the improved capability of RT-corrected averaging to establish experimental effects on amplitudes in the late ERP range.

Evidence for an Integrative Role of P3b in Linking Reaction to Perception

Abstract. Hypotheses about the P3 component of the event-related EEG potential have usually assumed that P3b reflects some processing independent from organizing the response. In contrast, the notion that P3b is related to a decision process implies some mediating function between stimulus and response. If P3b does indeed reflect the link between perceptual processing and response preparation (1) amplitudes should be as large in response-locked averages as in stimulus-locked averages, (2) this should be true independent of response speed, for separate subaverages of slow and fast responses, and (3) latencies should vary across response speed both in stimulus-locked and in response-locked averages. These hypotheses were tested in data evoked by visual and auditory stimuli in choice-response tasks. All three predictions were confirmed. In contrast to this balanced relation to perception and responding, fronto-central P3 with auditory stimuli was stimulus-related and, for comparison, the peak amplitudes of both the response-force and of the lateralized readiness potential were response-related. We conclude that P3b reflects a process that mediates between perceptual analysis and response initiation, possibly monitoring whether the decision to classify some stimulus is appropriately transformed into action.

Time Course of Error Detection and Correction in Humans: Neurophysiological Evidence

Using event-related brain potentials, the time course of error detection and correction was studied in healthy human subjects. A feedforward model of error correction was used to predict the timing properties of the error and corrective movements. Analysis of the multichannel recordings focused on (1) the error-related negativity (ERN) seen immediately after errors in response- and stimulus-locked averages and (2) on the lateralized readiness potential (LRP) reflecting motor preparation. Comparison of the onset and time course of the ERN and LRP components showed that the signs of corrective activity preceded the ERN. Thus, error correction was implemented before or at least in parallel with the appearance of the ERN component. Also, the amplitude of the ERN component was increased for errors, followed by fast corrective movements. The results are compatible with recent views considering the ERN component as the output of an evaluative system engaged in monitoring motor conflict.