Late Cortical Responses Research Articles

State-Dependent Motor Cortex Stimulation Reveals Distinct Mechanisms for Corticospinal Excitability and Cortical Responses.

Transcranial magnetic stimulation (TMS) is a noninvasive brain stimulation method that modulates brain activity by inducing electric fields in the brain. Real-time, state-dependent stimulation with TMS has shown that neural oscillation phase modulates corticospinal excitability. However, such motor evoked potentials (MEPs) only indirectly reflect motor cortex activation and are unavailable at other brain regions of interest. The direct and secondary cortical effects of phase-dependent brain stimulation remain an open question. In this study, we recorded the cortical responses during single-pulse TMS using electroencephalography (EEG) concurrently with the MEP measurements in 20 healthy human volunteers (11 female). TMS was delivered at peak, rising, trough, and falling phases of mu (8-13 Hz) and beta (14-30 Hz) oscillations in the motor cortex. The cortical responses were quantified through TMS evoked potential components N15, P50, and N100 as peak-to-peak amplitudes (P50-N15 and P50-N100). We further analyzed whether the prestimulus frequency band power was predictive of the cortical responses. We demonstrated that phase-specific targeting modulates cortical responses. The phase relationship between cortical responses was different for early and late responses. In addition, pre-TMS mu oscillatory power and phase significantly predicted both early and late cortical EEG responses in mu-specific targeting, indicating the independent causal effects of phase and power. However, only pre-TMS beta power significantly predicted the early and late TEP components during beta-specific targeting. Further analyses indicated distinct roles of mu and beta power on cortical responses. These findings provide insight to mechanistic understanding of neural oscillation states in cortical and corticospinal activation in humans.

Effect of auditory memory load on speech-evoked P300 in healthy adolescents

Abstract Background: The P300 is a late cortical neurophysiological response that can be elicited with auditory and visual stimulation, by presenting the stimuli in an odd-ball paradigm. When deviant stimuli are elicited using auditory stimuli, the P300 is recorded as a large positive peak approximately 300 ms after the stimulus onset in the waveform. Adolescent brain development is heavily influenced by hormonal and physical transitions. Most of the investigations have been done in children and adults, with a limited focus on adolescents. Hence, there is a need to understand the characteristics of P300 in this group. Objective: The current research was planned to measure the effect of auditory memory load on speech-evoked P300 in healthy adolescents. Methods: A total of 14 late adolescents aged between 18.1 and 24 years participated in the study. The P300 was used to record speech stimuli in N-back (zero-back, one-back, and two-back) tasks using 64 channels. Results: There was a significant difference in the latency and amplitude of P300 across the N-back tasks. The mean amplitude of P300 was the highest in a zero-back task and the lowest in a one-back task, and the mean latency of P300 was the lowest in a zero-back task and the highest in a one-back task. Conclusion: Prolonged latency and smaller amplitude of the P300 as the N-back difficulty level increased from zero-back to one-back and then two-back tasks in healthy adolescents.

Early nociceptive evoked potentials (NEPs) recorded from the scalp

ObjectiveNeurophysiological investigation of nociceptive pathway has so far been limited to late cortical responses. We sought to detect early components of the cortical evoked potentials possibly reflecting primary sensory activity. MethodsThe 150 IDE micropatterned electrode was used to selectively activate Aδ intraepidermic fibres of the right hand dorsum in 25 healthy subjects and 3 patients suffering from trigeminal neuralgia. Neurographic recordings were performed to assess type of stimulated fibres and check selectivity. Cortical evoked potentials were recorded from C3′-Fz and Cz-Au1. ResultsNeurographic recordings confirmed selective activation of Aδ fibres. Early components were detected after repetitive stimulation (0.83/s rate and 250–500 averages); the first negative component occured at 40 ms (N40) on the contralateral scalp. ConclusionsThe provided data support the hypothesis that N40 could be the cortical primary response conducted by fast Aδ fibres. SignificanceThis is the first report of early, possibly primary, cortical responses in humans by nociceptive peripheral stimulation. Although not perfected yet to allow widespread diagnostic use, this is probably the only method to allow fully objective evaluation of the nociceptive system, with important future implications in experimental and clinical neurophysiology.

Early and late cortical responses to directly gazing faces are task dependent.

Gender categorisation of human faces is facilitated when gaze is directed toward the observer (i.e., a direct gaze), compared with situations where gaze is averted or the eyes are closed (Macrae, Hood, Milne, Rowe, & Mason, Psychological Science, 13(5), 460-464, 2002). However, the temporal dynamics underlying this phenomenon remain to some extent unknown. Here, we used electroencephalography (EEG) to assess the neural correlates of this effect, focusing on the event-related potential (ERP) components known to be sensitive to gaze perception (i.e., P1, N170, and P3b). We first replicated the seminal findings of Macrae et al. (2002, Experiment 1) regarding facilitated gender discrimination, and subsequently measured the underlying neural responses. Our data revealed an early preferential processing of direct gaze as compared with averted gaze and closed eyes at the P1, which reverberated at the P3b (Experiment 2). Critically, using the same material, we failed to reproduce these effects when gender categorisation was not required (Experiment 3). Taken together, our data confirm that direct gaze enhances the early P1, as well as later cortical responses to face processing, although the effect appears to be task dependent.

Event-related neuronal responses to acoustic novelty in single-sided deaf cochlear implant users: Initial findings

Objective: A cochlear implant (CI) is an auditory prosthesis restoring profound hearing loss. However, CI-transmitted sounds are degraded compared to normal acoustic hearing. We investigated cortical responses related to CI-degraded against acoustic listening.Methods: Event-related potentials (ERPs) were recorded from eight single-sided deaf CI users who performed a three-stimulus oddball task, separately with their normal hearing ear and CI ear. The oddball tones were occasionally intermitted by novel sounds. ERP responses were compared between electric and acoustic listening for the auditory (N1) and auditory-cognitive (Novelty P3, Target-P3) ERP components.Results: CI-degraded listening was associated with attenuated sensory processing (N1) and with attenuated early cortical responses to acoustic novelty whereas the late cortical responses to acoustic novelty and the target-P3 did not differ between NH and CI ears.Conclusion: The present study replicates the CI-attenuation of Novelty-P3 amplitudes in a within-subject comparison. Further, we show that the CI-attenuation of Novelty-P3 amplitudes extends to early cortical responses to acoustic novelty, but not to late novelty responses.Significance: The dissociation into CI-attenuated P3 early Novelty-P3 amplitudes and CI-unaffected late Novelty-P3 amplitudes represents a cortical fingerprint of CI-degraded listening. It further contributes to general claims of distinct auditory Novelty-P3 sub-components.

Dynamic Causal Modeling of the Cortical Responses to Wrist Perturbations.

Mechanical perturbations applied to the wrist joint typically evoke a stereotypical sequence of cortical and muscle responses. The early cortical responses (<100 ms) are thought be involved in the “rapid” transcortical reaction to the perturbation while the late cortical responses (>100 ms) are related to the “slow” transcortical reaction. Although previous studies indicated that both responses involve the primary motor cortex, it remains unclear if both responses are engaged by the same effective connectivity in the cortical network. To answer this question, we investigated the effective connectivity cortical network after a “ramp-and-hold” mechanical perturbation, in both the early (<100 ms) and late (>100 ms) periods, using dynamic causal modeling. Ramp-and-hold perturbations were applied to the wrist joint while the subject maintained an isometric wrist flexion. Cortical activity was recorded using a 128-channel electroencephalogram (EEG). We investigated how the perturbation modulated the effective connectivity for the early and late periods. Bayesian model comparisons suggested that different effective connectivity networks are engaged in these two periods. For the early period, we found that only a few cortico-cortical connections were modulated, while more complicated connectivity was identified in the cortical network during the late period with multiple modulated cortico-cortical connections. The limited early cortical network likely allows for a rapid muscle response without involving high-level cognitive processes, while the complexity of the late network may facilitate coordinated responses.

Noise-robust cortical tracking of attended speech in real-world acoustic scenes

Selectively attending to one speaker in a multi-speaker scenario is thought to synchronize low-frequency cortical activity to the attended speech signal. In recent studies, reconstruction of speech from single-trial electroencephalogram (EEG) data has been used to decode which talker a listener is attending to in a two-talker situation. It is currently unclear how this generalizes to more complex sound environments. Behaviorally, speech perception is robust to the acoustic distortions that listeners typically encounter in everyday life, but it is unknown whether this is mirrored by a noise-robust neural tracking of attended speech. Here we used advanced acoustic simulations to recreate real-world acoustic scenes in the laboratory. In virtual acoustic realities with varying amounts of reverberation and number of interfering talkers, listeners selectively attended to the speech stream of a particular talker. Across the different listening environments, we found that the attended talker could be accurately decoded from single-trial EEG data irrespective of the different distortions in the acoustic input. For highly reverberant environments, speech envelopes reconstructed from neural responses to the distorted stimuli resembled the original clean signal more than the distorted input. With reverberant speech, we observed a late cortical response to the attended speech stream that encoded temporal modulations in the speech signal without its reverberant distortion. Single-trial attention decoding accuracies based on 40–50s long blocks of data from 64 scalp electrodes were equally high (80–90% correct) in all considered listening environments and remained statistically significant using down to 10 scalp electrodes and short (<30-s) unaveraged EEG segments. In contrast to the robust decoding of the attended talker we found that decoding of the unattended talker deteriorated with the acoustic distortions. These results suggest that cortical activity tracks an attended speech signal in a way that is invariant to acoustic distortions encountered in real-life sound environments. Noise-robust attention decoding additionally suggests a potential utility of stimulus reconstruction techniques in attention-controlled brain-computer interfaces.

Physiological consequences of abnormal connectivity in a developmental epilepsy.

Many forms of epilepsy are associated with aberrant neuronal connections, but the relationship between such pathological connectivity and the underlying physiological predisposition to seizures is unclear. We sought to characterize the cortical excitability profile of a developmental form of epilepsy known to have structural and functional connectivity abnormalities. We employed transcranial magnetic stimulation (TMS) with simultaneous electroencephalographic (EEG) recording in 8 patients with epilepsy from periventricular nodular heterotopia and matched healthy controls. We used connectivity imaging findings to guide TMS targeting and compared the evoked responses to single-pulse stimulation from different cortical regions. Heterotopia patients with active epilepsy demonstrated a relatively augmented late cortical response that was greater than that of matched controls. This abnormality was specific to cortical regions with connectivity to subcortical heterotopic gray matter. Topographic mapping of the late response differences showed distributed cortical networks that were not limited to the stimulation site, and source analysis in 1 subject revealed that the generator of abnormal TMS-evoked activity overlapped with the spike and seizure onset zone. Our findings indicate that patients with epilepsy from gray matter heterotopia have altered cortical physiology consistent with hyperexcitability, and that this abnormality is specifically linked to the presence of aberrant connectivity. These results support the idea that TMS-EEG could be a useful biomarker in epilepsy in gray matter heterotopia, expand our understanding of circuit mechanisms of epileptogenesis, and have potential implications for therapeutic neuromodulation in similar epileptic conditions associated with deep lesions.

Neurophysiological and psychometric evaluation of cognition in the normal aging population

Background Assessment of cognitive function in normal aging has been considered as an important issue nowadays. There is a generalized proportional decline in mental processing speed among elderly adults that affects all elements of mentation equally. Objective The aim of this study was to assess cognitive functions in normal elderly individuals using psychometric cognitive assessment scales and electrophysiological studies including late cortical responses, P300 and contingent negative variation (CNV). Methods Thirty-five healthy elderly individuals of both sexes were included. Their ages ranged from 60 to 75 years. The participants were subjected to thorough clinical assessment, cognitive evaluation using psychometric scales and neurophysiological tests in the form of P300 and CNV. Results The results of P300 showed a significant positive correlation between reaction time and age. A significant negative correlation was found between reaction time and performance on the Wechsler Intelligence Scale (WIS) ( P = 0.03). The mean amplitude of P300 wave recorded from the parietal region was significantly greater in male participants than in female participants. As regards the results of CNV, a significant negative correlation was noted between N2 latency and the verbal scale of WIS. Comparison of the mean CNV parameters between male and female participants showed that the mean latency of P2 wave was significantly higher in the male population compared with the female population. No significant correlation was revealed between P300 and CNV parameters and scores of Wechsler Memory Scale subtests and parameters of Wisconsin Card Sorting Test. Conclusion Results suggest that the psychiatric scales do not provide a substitute for electrophysiological tests in evaluating the cognitive changes that occur with normal aging. However, there was a limitation for the study in detecting changes because of the narrow age range of the cases.

Auditory-evoked potentials as a tool for follow-up of fibromyalgia

In this study, we assessed the value of auditory-evoked potentials (AEPs) as objective measurable reproducible tests for the follow-up of patients with fibromyalgia (FM) in response to pharmacologic and rehabilitative therapy. This study included 30 female FM patients and 10 age-matched female controls. All participants underwent a clinical examination, a psychiatric and functional assessment (sleep score, Fibromyalgia Impact Questionnaire, and Hospital Anxiety and Depression Scale) and measurement of AEPs elicited by tones of increasing intensity (60, 70, 80, and 90 dB) known as late cortical responses and cognitive auditory potentials (P300). Patients were subdivided into three equal groups. Group 1 received pregabalin, group 2 received fluoxetine, and group 3 included patients who performed a graded aerobic exercise program. Assessment was repeated at the end of the 8-week treatment period. Patients had significantly shorter N1 latencies at 60 and 70 dB, significantly shorter P2 latencies at all the studied intensities, and significantly higher N1P2 amplitudes at 90 dB.There was a statistically significant decrease in amplitude and a significant increase in P300 latency when compared with controls. Changes in AEP values before and after treatment were closely associated with the changes in psychiatric and functional assessment parameters. Improvement in the clinical assessment of the different symptoms of FM goes hand in hand with the improvement in the late cortical and cognitive components of AEPs, which provides evidence of the value of AEP as a simple, noninvasive, objective, and reproducible follow-up tool for assessment of hypervigilance and cognitive function in FM patients.

AB0653 Auditory evoked potentials in diagnosis of fibromyalgia

BackgroundAt present, the lack of an objective laboratory test or an imaging technique hampers fibromyalgia (FM) recognition and hence treatment (Lerma et al., 2012). The most agonizing symptom in FM...

Processing of emotional words after stroke: An electrophysiological study

ObjectiveAuditory evoked potentials (EP) were used to examine the neural processing of personal–emotional and neutral words, in a group of 14 people with post-stroke aphasia and an equal sized control group to determine whether the EP differed between groups and word types. MethodsEffects of the emotional value of the words and participant group were assessed on EP. Latencies and amplitudes of EP were analyzed for the two groups (aphasia and control) in response to word type (emotional and neutral). ResultsN1 amplitudes were smaller and P2 and P3 were delayed in the aphasia group, for both word types, indicating effects of stroke on processing of both neutral and emotional words. P3 amplitudes were larger for emotional words in both groups. These differences in late cortical responses between word types for both groups suggest distinct neural networks involved in the response to emotional and neutral words, even with post-stroke language impairment. ConclusionsThe neurophysiological processing of affective speech in aphasia has been revealed. This opens up the interpretation of these results to the critical assessment and therapeutic identification of emotional language in people with aphasia. SignificanceThis study has implications not just for aphasia but allows for further exploration of other neurological conditions.

Subliminal presentation of other faces (but not own face) primes behavioral and evoked cortical processing of empathy for pain

Current research on empathy for pain emphasizes the overlap in the neural response between the first-hand experience of pain and its perception in others. However, recent studies suggest that the perception of the pain of others may reflect the processing of a threat or negative arousal rather than an automatic pro-social response. It can thus be suggested that pain processing of other-related, but not self-related, information could imply danger rather than empathy, due to the possible threat represented in the expressions of others (especially if associated with pain stimuli). To test this hypothesis, two experiments considering subliminal stimuli were designed. In Experiment 1, neutral and semantic pain expressions previously primed with own or other faces were presented to participants. When other-face priming was used, only the detection of semantic pain expressions was facilitated. In Experiment 2, pictures with pain and neutral scenarios previously used in ERP and fMRI research were used in a categorization task. Those pictures were primed with own or other faces following the same procedure as in Experiment 1 while ERPs were recorded. Early (N1) and late (P3) cortical responses between pain and no-pain were modulated only in the other-face priming condition. These results support the threat value of pain hypothesis and suggest the necessity for the inclusion of own- versus other-related information in future empathy for pain research.

Emotions in word and face processing: Early and late cortical responses

Recent research suggests that emotion effects in word processing resemble those in other stimulus domains such as pictures or faces. The present study aims to provide more direct evidence for this notion by comparing emotion effects in word and face processing in a within-subject design. Event-related brain potentials (ERPs) were recorded as participants made decisions on the lexicality of emotionally positive, negative, and neutral German verbs or pseudowords, and on the integrity of intact happy, angry, and neutral faces or slightly distorted faces. Relative to neutral and negative stimuli both positive verbs and happy faces elicited posterior ERP negativities that were indistinguishable in scalp distribution and resembled the early posterior negativities reported by others. Importantly, these ERP modulations appeared at very different latencies. Therefore, it appears that similar brain systems reflect the decoding of both biological and symbolic emotional signals of positive valence, differing mainly in the speed of meaning access, which is more direct and faster for facial expressions than for words.

Lassen sich auditive Verarbeitungs- und Wahrnehmungsstörungen (AVWS) bei Kindern mit Lese-Rechtschreib-Störungen nachweisen?

In this paper the dichotic tests and the CERA (Cortical Evoked Response Audiometry) of children with dyslexia had been examined, in order to find out if there are auditory processing and perception disorders. 33 children with dyslexia had been compared with 28 children without problems of writing and reading. The mean age of the children was 9 years. All of the children had been examined by the following audiometric measurements: tympanometry, pure-tone-audiometry, speech-audiometry, dichotic Tests by Uttenweiler and Feldmann and the Cortical Evoked Response Audiometry (CERA) rated according to Esser. The intelligence quotients were in the group of dyslexic children significantly lower. The Uttenweiler and Feldmann tests were in dyslexic children significantly lower in the control group as well. The late cortical responses ware normal or near normal in both groups. Dichotic speech tests indicate central auditory processing and perception deficits in dyslexia. These tests are confounded, however, by attention and memory deficits. The CERA rated according to Esser does not point out to these auditory disorders in dyslexia.

Anesthetics and Memory: On Memory at the Cognitive and Cellular Levels

University of Iowa Hospitals and Clinics, Iowa City, Iowa. mohamed-ghoneim@uiowa.eduI read with interest the article by Naruo et al. entitled “Sevoflurane Blocks Cholinergic Synaptic Transmission Postsynaptically but Does Not Affect Short-term Potentiation.” I agree with the authors about the importance of studies at the cellular and molecular levels, which in conjunction with studies at the cognitive science level should provide a comprehensive account of effects of anesthetics on memory. However, my enthusiasm for the authors' excellent work was marred by the following points. It is not clear how the neurons used in the cell culture are relevant to memory processes. For example, in a similar aquatic invertebrate, Aplysia , the sensory and motor neurons of the gill withdrawal reflex are commonly used. The reflex in the intact animal can be classically conditioned and undergoes habituation and sensitization. Does this occur with the neurons used in this report?It is inaccurate to state that numerous studies found no effect of anesthesia on various types of memories. Anesthetics (in anesthetizing dosages) abolish both short- and long-term memories. The authors cite as a reference, an article that was presented at a symposium in 1995 where the authors sent a questionnaire to a number of consultants regarding their opinions about the existence of implicit learning and memory during anesthesia. However, such existence remains controversial, as best exemplified by the lack of replication of any positive findings (except for one recent work by Deeprose et al. ).5,6Although it is true that the anesthetized brain is able to process auditory information, this does not allow cognitive processing during adequate anesthesia. Looking at the auditory evoked responses, the brainstem response is resistant to anesthetic effects. The early or midlatency responses that reflect neural transmission through the medical geniculate body in the thalamus to the primary auditory cortex disappear with deep anesthesia. The late cortical responses that reflect transmission through cortical association areas, the frontal cortex and the hippocampus, and are engaged in cognitive processes are abolished with loss of consciousness. The authors give as a reference for persistence of cognitive processing during anesthesia a meta-analysis of studies of implicit memory before 1996. More studies have been published since then, and as with any meta-analysis, the results are dependent on the quality of the reviewed articles. Finally, the authors state that cellular studies are important in resolving the issue of whether anesthetics affect learning and memory. Perhaps it would be more productive for investigators to start with the forgone conclusion that anesthetics do affect learning and memory and to elucidate the sites and mechanisms of this important interaction.University of Iowa Hospitals and Clinics, Iowa City, Iowa. mohamed-ghoneim@uiowa.edu

What is the Role of Audition in Literacy?

What is the Role of Audition in Literacy?

Auditory late cortical response and speech recognition in Digisonic cochlear implant users.

The purpose of the study was to test for differences in late electrically evoked auditory potentials between subjects exhibiting "good" versus "poor" speech recognition performances with their cochlear implants. Late auditory evoked responses were measured in 30 subjects equipped with the Digisonic (MXM, Antibes, France) cochlear implant, 15 of whom had "good" speech recognition scores (i.e., more than 89% correct phoneme identification without lip reading). The 15 other subjects had poorer speech recognition scores (i.e., less than 85%). Differences in N1P2 amplitude, as well as P1, N1, and P2 latencies, and N1-P1 and N1-P2 latency intervals were tested. Wave P2 latency was found to be significantly different between the two groups (P =.016), being shorter in "good" than in "poor" performers. The strength of the statistical relationship between electrophysiological and speech recognition variables (r2 = 17%) was substantially smaller than that observed using electrically evoked auditory brainstem response (EABR) for the same implanted device (r2 = 49% for the EABR wave III-V latency interval). Some characteristics of late electrically evoked auditory potentials differ significantly among cochlear implant users depending on their speech recognition performance. However, the relationship between electrophysiological and speech recognition variables is more pronounced when early (brainstem) rather than late (cortical) evoked responses are considered.

Auditory Brainstem Response, Middle Latency Response, and Late Cortical Evoked Potentials in Children with Learning Disabilities

Auditory evoked potentials (AEPs) and behavioral tests were used to evaluate auditory processing in 10 children aged 7 to 11 years who were diagnosed as learning disabled (LD). AEPs included auditory brainstem responses (ABRs), middle latency responses (MLRs), and late cortical responses (P1, N1, P2, P3). Late cortical responses were recorded using an active listening oddball procedure. Auditory processing disorders were suspected in the LD children after a psychologist found phonologic processing and auditory memory problems. A control group of 10 age- and gender-matched children with no hearing or reported learning difficulties was also tested. Teacher ratings of classroom listening and SCAN Competing Words and Staggered Spondaic Word scores were poorer in the LD children. There were minor ABR latency differences between the two groups. Wave Na of the MLR was later and Nb was smaller in the LD group. The main differences in cortical responses were that P1 was earlier and P3 was later and smaller in the LD group.

Frontal cortex reactivity differentiates between schizophrenic subtypes: auditory ERP-evidence.

To extend the hypothesis that late auditory EP shifts represent pathophysiologcial markers in schizophrenia. Early negative (±100 μs) and late positive (>300 ms) auditory oddball and CNV responses are topographically compared in 3 medicated schizophrenic subtypes. Only late cortical responses differentiate between paranoid, residual and disorganised schizophrenia. Core features of the deficit residual state encompass low-voltage N2P3 responses and missing central initial CNV components. Both paranoid and disorganised schizophrenics show a distinctive reactivity of the frontal cortex. Paranoid schizophrenia is characterized by an extensive frontal spread of the task-related P3 response. Disorganised schizophrenia shows a specifically increased frontal CNV component indicating a nonspecific arousal reaction. Combinations of late auditory EP-patterns fairly fit with the cognitive/behavioral status observed in schizophrenia spectrum disorders.