The form and distribution of auditory evoked potentials and CNVs when stimuli and responses are lateralized.
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Auditory Perception↗
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Neurophysiological correlates of human concept formation.
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Acoustic Stimulation↗
An imaging system for monitoring receptive field dynamics.
The paper describes a computerized method, termed receptive field imaging (RFI), for the rapid mapping of multiple receptive fields and their respective sensitivity distributions. RFI uses random stimulation of multiple sites, in combination with an averaging procedure, to extract the relative contribution from each of the stimulated sites. Automated multi-electrode stimulation and recording, with spike detection and counting, are performed on-line by the RFI programme. Direct user interpretation of receptive field changes is made possible by a user-friendly graphic interface. A series of imaging experiments was carried out to evaluate the functional capacity of the system. RFI was tested on the receptive fields in the nociceptive withdrawal reflex (NWR) system in the rat. RFI replicates the results obtained with conventional methods and allows the display of receptive field dynamics induced by topical spinal cord application of morphine and naloxone on a minute-to-minute time scale. Data variance was estimated, and proved to be small enough to yield a stable representation of the receptive field, thereby achieving a high sensitivity in dynamic imaging experiments. The large number of stimulation and registration sites that can be monitored in parallel permits detailed network analysis of synaptic sets, corresponding to 'connection weights' between individual neurones.
Analysis of Variance↗
Auditory sensory memory in schizophrenia: inadequate trace formation?
This study explored duration mismatch negativity reductions observed in individuals with schizophrenia, in particular, the relationship to behavioural measures of temporal discrimination and two event-related potential (ERP) components occurring during the first phase of auditory sensory memory. Twenty-two patients with a DSM-IV and ICD-10 diagnosis of schizophrenia and 25 healthy comparison volunteers participated in a behavioural and an ERP testing session. Both groups performed equivalently on behavioural estimates of filled interval duration discrimination and gap detection. In contrast, electrophysiological measures revealed a significant reduction in patients' duration mismatch negativity and a significant difference in patients for the pattern of N100 facilitation over short stimulus onset asynchronies. Whilst behavioural results indicate intact temporal processing of filled intervals and equal temporal resolution limits in schizophrenia, both ERP measures indicated differences in auditory processing that may be traced to activity occurring during the first 250 ms. Results highlight the possibility of abnormalities in the process of auditory trace formation and temporal summation in schizophrenia.
Acoustic Stimulation↗
Error-related brain activity in obsessive-compulsive undergraduates.
Error-related negativity (ERN/Ne) is a component of the event-related brain potential (ERP) associated with monitoring action and detecting errors. It is a sharp negative deflection that generally occurs from 50 to 150 ms following response execution and has been associated with activity involving the anterior cingulate cortex (ACC). An enhanced ERN has recently been observed in patients with obsessive-compulsive disorder (OCD). We extended these findings by measuring the ERN in college undergraduates with OC characteristics as measured by the Obsessive-Compulsive Inventory (OCI). Eighteen high-OC subjects and 17 low-OC subjects performed a modified Stroop task with equal emphasis placed on speed and accuracy. Response-locked ERPs revealed a frontally maximal negativity associated with erroneous responses that was significantly larger in the high-OCI group. There were no performance differences between the two groups. Our results support the view that the characteristics associated with OCD are related to hyper-functioning error and action-monitoring processes.
Adolescent↗
Test-retest reliability of the rat N40 auditory evoked response: preliminary data.
The N40 auditory evoked potential (EP) in rats has been used to develop an animal model for the study of sensory gating mechanisms. In an examination of the test-retest reliability of sensory gating indices, derived from the rat N40 EP, six rats were tested four times daily for 5 consecutive days. A paired-click paradigm (S1-S2) was used, and both the S2/S1 amplitude ratio and the S1-S2 amplitude difference measures of sensory gating capacity were calculated. Based on the means of four daily trials, reliability coefficients were as follows; r = 0.69 for S1, and r = 0.66 for S2 amplitudes. A reliability coefficient of 0.59 was found for the S1-S2 difference measure, and one of 0.47 for the S2/S1 ratio measure. These results suggest that the N40 can be used to study sensory gating, but caution has to be exercised in interpreting the data particularly in a repeated measures design.
Animals↗
Event-related potentials in patients with total locked-in state due to fulminant Guillain-Barré syndrome.
A series of electrophysiological investigations were performed over a 6-month period in two patients affected by fulminant Guillain-Barré polyradiculoneuropathy, who developed an ascending paralysis leading, within 72 h, to flaccid quadriplegia, internal and external ophthalmoplegia, absence of all brainstem reflexes and no respiratory effort: the clinical state resembled brain death. Brain CTs were normal and spinal fluid examination revealed albuminocytological dissociation. All motor nerves tested were unexcitable, whereas sensory responses were markedly abnormal but present. Sequential EEG recordings revealed normal, partially reactive alpha rhythm in both patients. In one patient, normal auditory event-related potentials (ERPs: peak N1, P2, N2, P3, evoked in an 'oddball' paradigm) and CNV-like potentials could be recorded not earlier than the 20th day into the illness. In earlier recordings, N1 and P2 peaks as well as mismatch negativity (MMN) were present over the frontal and central scalp electrodes. This patient has now partially recovered motor functions and no cognitive defects are present, but he has little recollection of the events occurring in the first 2 weeks spent in the ICU, when he was completely paralyzed. The other patient generated normal N1 and P2 ERP peaks, but no N2, P3 and MMN were detected in a series of recordings. He died without having ever regained appropriate behavioral responses. The ERP abnormalities observed raise the matter of the origin of cognitive dysfunction in patients with severe and prolonged de-efferentation/de-afferentation. ERPs allow monitoring the level of alertness and attention and appear more specific than EEG in identifying a state of awareness in patients in which communication is severely impaired as a consequence of neurological disorders.
Adult↗
Frontal and parieto-temporal cortical ablations and diaschisis-like effects on auditory neurocognitive potentials evocable from apparently intact ipsilateral association areas in humans: five case reports.
The aim of this study was to investigate the effects of disruption on the warning auditory S1-elicited ERP and CNV complexes recordable on the site and on remote ipsilateral apparently normal anatomo-functionally interconnected brain regions. These effects in some cases showed aspects of a probable diaschisis-like phenomenon, due to resections of extensive frontal association cortex or of primary and secondary sensory parieto-temporal areas damaged by differing pathological processes. Using a standard CNV paradigm, 21/19 EEG electrodes connected with three different references, and scalp-topographic bidimensional mapping analysis, the S1 auditory binaural/monaural clicks N1a,b,c, P2, N2, P3 and CNV waves were recorded in 10 normal subjects and 11 patients. Nine of the latter had been submitted to unilateral frontal dorsolateral cortex ablation, one to bihemispheric dorsomedial cortex ablation, and one to unilateral ablation of sensory parieto-temporal cortex and underlying white matter, verified through CT/MRI examinations. No true S1ERP/CNV components were recordable over the ablated cortical areas, whereas normal ERP/CNV complexes were observable on the intact hemispheres. In five patients, four of whom with frontocortical ablations, the S1 ERP/CNV complexes appeared severely diminished or disrupted, in two cases in a slow, partially-reversible manner, also in the neuroradiologically normal ipsilateral functionally-connected post-rolandic sensory and association areas. Similar deactivation of some ERP components was observed in reverse on the unilateral dorsolateral frontocortical region in the fifth patient with parieto-temporal cortex ablation. Even when they are partially reversible, these ipsilateral remote ERP changes in apparently intact brain regions, due to ablations of functionally-interconnected cortical formations, probably reflect cortical deactivation or simply dysfacilitation deriving from functional unilateral diaschisis. If these changes are instead irreversible they may probably be interpreted as transneuronal degeneration phenomena, though they are not at present easy to document either neuroradiologically or electroclinically.
Adult↗
The generators of slow potentials obtained during verbal, pictorial and spatial tasks.
The purpose of this study was to test whether slow cortical electrical activity is specific to performance on verbal, pictorial and spatial tasks. Twenty-nine healthy subjects were required to compare pairs of visual stimuli separated by a delay of 2.5 s in a S1-S2 contingent negative variation-type paradigm. Slow potentials (SPs) were recorded by high-resolution EEG (123 channels) and their generators modeled by current density reconstruction using individual MRIs as source space models. Activity in each architectonic area of Brodmann was scored with respect to individual maximum current by a percentile method. Results showed a multifocal pattern of current density foci comprising the SP generators, including frontal and posterior cortices in all subjects, with the most active areas being common to the three tasks. In spite of the intersubject variability in the sets of active areas for each given task, a few cortical areas were observed to discriminate between tasks in a statistically significant way: the verbal task corresponded to stronger electrical activity in right area 45 than the other tasks; the spatial to weaker activity in right area 38 and left area 5 than the other tasks; the pictorial, compared to the spatial task, to stronger activity in left area 39; the verbal, compared to the spatial task, to stronger activity in left area 10, and compared to the pictorial, to weaker activity in right area 20. The present method of SP analysis may aid in the functional mapping of human association cortices in individual cases. We discuss our results emphasizing intersubject variability in cortical activity patterns and the possibility of finding more universal patterns.
Adult↗
Mismatch negativity: clinical research and possible applications.
This article provides a selective review on the perspectives of the clinical research and application of the mismatch negativity (MMN), a component of the auditory event-related potential generated by the brain's automatic response to any discriminable change in auditory stimulation. The MMN (and its magnetic equivalent MMNm) currently provide the only objective measure of auditory discrimination and sensory memory. It can be registered in the absence of attention and with no task requirements, which makes it particularly suitable for studying different clinical populations and infants.
Acoustic Stimulation↗
Permanent or transitory effects on neurocognitive components of the CNV complex induced by brain dysfunctions, lesions and ablations in humans.
Since the mid-1960s, essentially using electrophysiological methods, our research group has examined the effects of different brain diseases in humans, both on first- and second-order conditioned responses and on some types of neurocognitive potentials of the CNV complex. This didactic lecture will focus on our various attempts to identify and understand the neuroanatomical and neurophysiological substrates involved in cognitive information processing followed by the conception and execution of sensory-motor and behavioural responses evoked by significant acoustic stimuli, in both pathological situations and normal control subjects. Great interest was, e.g. aroused in the early 1970s by the rare, fortunately unrepeatable, opportunity of examining the CNV patterns in various psychiatric patients treated with psychosurgical Freeman-Watts bilateral prefrontal 'radical' lobotomy, also with repeated recordings (The Responsive Brain (1976) 158; Multidisciplinary Perspectives in Event-Related Brain-Potentials Research (1978) 376) or bimedial bifrontal cingulotomy (Multidisciplinary Perspectives in Event-Related Brain Potential Research (1978) 383). In the same period, investigations into CNV activity recorded in patients submitted to complete callosotomy ('split brain': Attention and Performance, vol. IV (1972) 221; Electroenceph. Clin. Neurophysiol. Suppl. 33 (1973) 161) were also begun and were continued into the 1980s, also with regard to other types of ERP (Brain 111 (1988) 553; J. Cog. Neurosci. 2 (1990) 258). All these data furnished unique information about the sub-second dynamics of unilateral or bihemispheric cortico-cortical and cortico-subcortical interconnections in humans. In recent years, with a classic method of analysis based on sequential scalp-topographic bidimensional neuroelectric mapping and 21/19 electrodes connected to three different references, and binaural/monaural clicks as warning signals (S1), we have repeatedly examined the CNV activity of 11 selected patients submitted to complete ablation of the damaged cortical areas, with uni- or bilateral lesions restricted to the prefrontal or associative parieto-temporal areas. We have always used the standard CNV paradigm (S1-S2 motor-response) which evokes a complex of neurocognitive potentials, including the P300 from S1, which are well-known, since they are certainly among the most studied ERPs in the various ages and races of normal subjects, psychiatric patients and subjects with different brain diseases. The most important results have been, (1) In normal subjects the MRI and the latency differences of CNV component measurements along the bidirectional pathways functionally interconnecting ipsilateral distant associative cortical areas (e.g. the arcuate-superior longitudinal complex bundle) were accounted for by the transcortical conduction time, which varies in our scalp recordings from 1 cm/0.74 to 1.28 ms ( approximately 9.8 m/s). (2) Constantly, no true auditory S1-elicited N1a, b, c, P2, N2, P300 components or CNV slow waves (O- and E-wave) were recordable over the whole of the ablated cortical areas, but only clearly identifiable volume-conducted EP/ERPs generated in other hemispheric structures. (3) The post-S1 ERP/CNV complexes on the intact hemisphere were found to be within the normal limits. (4) Effects of severe disruption on the S1 ERP/CNV complexes evocable on the site and on remote ipsilateral apparently normal anatomo-functionally interconnected brain regions were observed in 5 patients, 4 of whom had extensive frontocortical ablations. In two of the latter the distant disruptive action on the CNV components over the neuroradiologically normal ipsilateral two-way connected post-rolandic sensory and association areas was seen to be partially reversible, showing aspects of a probable slowly evolving diaschisis-like effect. Similar deactivation of some ERP components was observed in reverse on the ipsilateral dorsolateral frontocortical region in the fifth patient with a large parieto-temporal cortex ablation. These data require confirmahese data require confirmation, and when this phenomenon is observable, it must be appropriately monitored with different methods of functional neuroimaging. This will serve not only for medical and neuropsychophysiological diagnosis purposes, but also particularly for a correct and really useful planning of neuro-rehabilitation activities in selected cases.
Brain Diseases↗
Responses to irrelevant probes during task-induced negative and positive shifts.
The functional significance of task-induced negative and positive cortical shifts were tested with the probe-stimulus method. Both shifts were induced within the same experimental situation in three variants of a CNV paradigm, where a slow positive wave (a variant of P300) appeared following S2. In Experiment I and II, S2 called for making or withholding a motor response (go/no-go); in Experiment III, S2 informed the subject about the correctness of a previous guess. Irrelevant probe-stimuli were applied in conjunction with the task during the CNV, the post-S2 positivity and the intertrial interval (ITI). The probe-evoked vertex EPs were smaller during the post-S2 positivity as compared to the CNV and the ITI. This was true not only for the motor task but also for the guessing task, where the effect is unlikely to have been contaminated by motor potentials. This indicates that positive shifts have an inhibitory effect on the processing of irrelevant probe-stimuli and possibly on information-processing in general.
Adolescent↗
ERPs, semantic processing and age.
ERPs (N400, LPC and CNV) were elicited in two sets of subjects grouped according to age (young vs. elderly) using a word-pair category matching paradigm. Each prime consisted of a Japanese noun (constructed from two to four characters of the Hiragana) followed by one Chinese character (Kanji) as the target, this latter representing one of five semantic categories. There were two equally probable target conditions: match or mismatch. Each target was preceded by a prime, either belonging to, or not belonging to, the same semantic category. The subjects were required to respond with a specified button press to the given target according to the condition. We found RTs to be longer in the elderly subjects and under the mismatch condition. N400 amplitude was reduced in the elderly subjects under the mismatch condition and there was no difference between match and mismatch response, which were similar in amplitude to that under match condition for the young subjects. In addition, the CNV amplitudes were larger in the elderly subjects. These results suggested that functional changes in semantic processing through aging (larger semantic networks and diffuse semantic activation) were the cause of this N400 reduction, attributing a subsidiary role to attentional disturbance. We also discuss the importance of taking age-related changes into consideration in clinical studies.
Adult↗
Effects of distracting stimuli on CNV amplitude and reaction time.
The present study investigated the reliability of CNV distraction and rebound effects, and their relation with reaction time. Twenty-four subjects were presented three blocks of trials: (1) a control block--a fixed foreperiod reaction time task consisting of a flash-tone-key press sequence; (2) a divided-attention block--randomly intermixed trials with and without a short-term memory task (three visually-presented letters) in the S1-S2 interval (50% of each); and (3) a second control block. In trials with the short-term memory task, subjects recalled the letters after the key press to the tone. Compared to the control block, CNV amplitudes during trials with letters were significantly smaller and reaction times to S2 were significantly slower (distraction effect). In contrast, CNV amplitudes during trials with no-letters were significantly larger (CNV rebound), but the reaction times were again significantly slower. This dissociation of CNV rebound and reaction time could provide an objective neurophysiological tool to probe attention functions in both normal and clinical populations.
Adolescent↗
Impaired mismatch negativity (MMN) generation in schizophrenia as a function of stimulus deviance, probability, and interstimulus/interdeviant interval.
Schizophrenia is a severe mental disorder associated with disturbances in perception and cognition. Event-related potentials (ERP) provide a mechanism for evaluating potential mechanisms underlying neurophysiological dysfunction in schizophrenia. Mismatch negativity (MMN) is a short-duration auditory cognitive ERP component that indexes operation of the auditory sensory ('echoic') memory system. Prior studies have demonstrated impaired MMN generation in schizophrenia along with deficits in auditory sensory memory performance. MMN is elicited in an auditory oddball paradigm in which a sequence of repetitive standard tones is interrupted infrequently by a physically deviant ('oddball') stimulus. The present study evaluates MMN generation as a function of deviant stimulus probability, interstimulus interval, interdeviant interval and the degree of pitch separation between the standard and deviant stimuli. The major findings of the present study are first, that MMN amplitude is decreased in schizophrenia across a broad range of stimulus conditions, and second, that the degree of deficit in schizophrenia is largest under conditions when MMN is normally largest. The pattern of deficit observed in schizophrenia differs from the pattern observed in other conditions associated with MMN dysfunction, including Alzheimer's disease, stroke, and alcohol intoxication.
Acoustic Stimulation↗
The mismatch negativity for duration decrement of auditory stimuli in healthy subjects.
The amplitude and latency of the mismatch negativity (MMN) elicited by occasional shorter-duration tones (25 and 50 ms) in a sequence of 75 ms standard tones were studied in 40 healthy subjects (9-84 years). The replicability and age dependence of the MMN-responses were determined. The 25 ms deviant tone evoked a clear response in 39 of the subjects, while the 50 ms deviant tone evoked an observable MMN only in 32 of the subjects. The MMN peak amplitude for the 25 ms deviants was significantly larger than for the 50 ms deviants. There was no significant difference in the peak latencies (measured from stimulus offset). For the 25 ms deviant, the amplitude diminished with increasing age. The MMN curves for the 25 ms deviant, measured on separate days in 14 subjects, looked very replicable. As a result of noise and filtering effect, the product-moment correlations were poor. The results indicate that the signal-to-noise ratio for the MMN to 25 ms deviants, obtained even in a 25 min recording session, is large enough for clinical use and individual diagnostics when undetectable (or very low amplitude) MMN is used as a sign of pathology. However, judged from the low correlation coefficients, despite the good replicability in visual evaluation, better methods for MMN quantification have to be used for clinical follow-up.
Acoustic Stimulation↗
Enhanced negative slope of the readiness potential preceding a target force production task.
Readiness potentials (RPs) preceding a trigger pulling movement were recorded in 9 right-handed male subjects. We investigated two tasks, non-purposive and purposive movement tasks. In this study we defined simple trigger pull as non-purposive, and target force production by pulling the trigger as purposive. In the non-purposive task, the subjects were instructed to pull the trigger at their own pace and at an easily-exerted force level. After two sessions in the non-purposive movement task, the subjects were submitted to the purposive movement task, and were requested to pull the trigger in an attempt to produce target force, the range of which was decided individually on the basis of mean force level in the second session of the non-purposive movement task. The RP preceding the purposive movement was larger than that preceding the non-purposive movement. In addition, enhancement of the RP was specific to the negative slope (NS'). Since neither peak force nor time to peak force of the movement differed in the two tasks, it was concluded that the increased NS' was due to a psychological change associated with execution of the purposive movement.
Adult↗
An event-related potential study of age-related changes in sensitivity to stimulus deviance.
The mismatch negativity (MMN) of the event-related (brain) potential (ERP) has been shown to reflect the storage of information in sensory memory and is thought to reflect the operation of a mechanism that compares frequently occurring standard with infrequently occurring deviant acoustic events. The MMN was recorded from young (mean = 23 years) and elderly (mean = 72 years) adults to small (50 Hz) and large (300 Hz) frequency deviants and to a variety of novel, environmental sounds. At each level of deviance, MMN amplitude was smaller in the ERPs of older relative to younger adults. Young, but not older adults showed robust MMNs at the smallest level of deviance. Moreover, a P3 component was observed in the ERPs of the young to both large tonal and novel deviants, whereas a robust P3 component was evident only to the novel deviants in the ERPs of the old. The data suggest that older adults demonstrate less sensitivity to stimulus deviance and that only highly deviant events are likely to involuntarily capture their attention.
Adult↗