Memory processes and evoked potentials.
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Electrophysiologic response audiometry: state of the art.
Electrophysiologic response audiometry (ERA) is based upon recording neuroelectric potentials from sites extending from the cochlea to the cortex. These recordings rely on the use of averaging computers to extricate desired neuroelectric responses from the ongoing background electrical activity of the human auditory system and brain. The different neuroelectric responses are distinguished by response latency, response waveform, and probable site of origin. Responses which occur within the latency range of 1 to 5 msec originate from the cochlea and auditory nerve. Responses in the 4- to 8-msec latency range have the brain stem as their origin. Responses with latencies from about 8 to 50 msec presumably arise from the upper brain stem and primary projection areas. Responses with a fast waveform include those with latencies between 1 and 50 msec. Slow wave responses from about 50 to 300 msec originate as a secondary discharge from the primary cortical projection areas and surrounding secondary and association areas. The longest latency potentials (300 msec) are slow shifts that appear to arise from the prefrontal and secondary or association areas of the cortex. These response classes are discussed in terms of their clinical utility for threshold estimation and diagnostic value.
Action Potentials↗
Event-related brain potentials preceding speech and nonspeech oral movements of varying complexity.
Cortical preparation for movement is reflected in the readiness potential (RP) waveform preceding voluntary limb movements. In the case of oral movements, the RP may be affected by the complexity or linguistic nature of the tasks. In this experiment, EEG potentials before a nonspeech task (lip pursing), a speech-like task (lip rounding), and single word production were recorded from scalp electrodes placed at the cranial vertex (Cz) and over the left and right motor strips (C3' and C4'). Seven right-handed female subjects produced at least 70 repetitions of the three tasks, in each of five repeated sessions. EEG records were averaged with respect to EMG onset at the lip. The word task, as opposed to the other tasks, was associated with greater negative amplitude in the RP waveform at the vertex site. Differences between the waveforms recorded at the right- and left-hemisphere sites were insignificant. Although intersubject variability was high, individuals had relatively stable patterns of response across sessions. Results suggest that the RP recorded at the vertex site is sensitive to changes in task complexity. The RP did not reflect lateralized activity indicative of hemispheric dominance.
Adult↗
Cognitive evoked potentials to anticipated oesophageal stimulus in humans: quantitative assessment of the cognitive aspects of visceral perception.
Evoked potential studies provide an objective measure of the neural pathways involved with perception. The effects of cognitive factors, such as anticipation or awareness, on evoked potentials are not known. The aim was to compare the evoked potential response to oesophageal stimulation with the cortical activity associated with anticipation of the same stimulus. In 12 healthy men (23.5 +/- 4 years), oesophageal electrical stimulation (15 mA, 0.2 Hz, 0.2 msec) was applied, and the evoked potentials recorded using scalp electrodes. A computerized model of randomly skipped stimuli (4:1 ratio) was used to separately record the evoked potentials associated with stimulation and those associated with an anticipated stimulus. The electrical stimulus represented the nontarget stimulus and the skipped impulse the target (anticipatory) stimulus. This anticipatory evoked potential was also compared to auditory P300 evoked potentials. Reproducible evoked potentials and auditory P300 responses were elicited in all subjects. Anticipatory evoked potentials (peak latency 282.1 +/- 7.9 msec, amplitude 8.2 +/- 0.7 microV, P < 0.05 vs auditory P300 evoked potential) were obtained with the skipped stimulus. This anticipatory evoked potential was located frontocentrally, while the auditory P300 potential was located in the centro-parietal cortex. The anticipatory evoked potential associated with expectation of an oesophageal stimulus, although of similar latency to that of the auditory P300 evoked response, originates from a different cortical location. The recording of cognitive evoked potentials to an expected oesophageal stimulus depends on attention to, and awareness of, the actual stimulus. Anticipatory evoked potentials to GI stimuli may provide an objective electrophysiological tool for the assessment of the cognitive factors associated with visceral perception.
Adult↗
A negative component superimposed on event-related potentials during light drowsiness.
The present study examined the nature of the negative shift of event-related potential (ERP) recorded during the fully awake state, wakefulness with minor awareness deficit (light drowsiness) and stage 1 of NREM sleep. The cortical responses evoked by two types of auditory stimuli were recorded in nine subjects at the different levels of consciousness described above. A negative component with peak latency of 250-350 msec, N300, was identified in ERP during light drowsiness but not in the fully awake state. In stage 1a (stage 1 without vertex sharp waves), the amplitude of N300 was higher than that in light drowsiness, and it was higher in stage 1b than in stage 1a. The scalp distribution of N300 was predominantly on the vertex. It also confirmed that the vertex sharp wave evoked during stage 1 is maximal on the vertex and its peak latency is approximately 300 msec. Considering the similarity in scalp distribution and peak latency between N300 and vertex sharp wave, it is possible that these electroencephalogram phenomena are generated by an identical synchronizing mechanism in the brain. We assumed that N300 observed during light drowsiness may be an incomplete product of vertex sharp wave.
Adult↗
Sound presentation rate is represented logarithmically in human cortex.
The encoding of temporal information is critical to auditory processing. Since the mismatch negativity component of the auditory event-related brain potential is thought to reflect properties of auditory sensory memory, we used it to examine the representation of acoustic time intervals in the human cortex. The mismatch negativity occurs in response to deviations in acoustic regularities, which are stored in sensory memory. We used 16 stimulus conditions, randomly presenting short trains of tones with fixed onset-to-onset intervals of 100, 200, 300 or 400 ms (all tones in the study were identical). The first four intervals between the tones established the acoustic regularity on each train (i.e. the 'standard'). The fifth tone in each train was preceded by an interval that varied randomly among the same four intervals. If this interval was different from the standard for that trial, it violated the acoustic regularity (i.e. it was a 'deviant'). The mismatch response to the fifth tone differed significantly among stimulus conditions and was proportional to the absolute value of the logarithm of the deviant/standard interval ratio. This indicates that short acoustic time intervals are represented with a ratio scale in the human cortex. When the fifth tone occurred 100 ms after the fourth, it elicited a somewhat different, although proportional response, supporting the hypothesis that a special integration mechanism may exist for very short time intervals.
Acoustic Stimulation↗
Attention capture by auditory significant stimuli: semantic analysis follows attention switching.
Event-related potentials (ERPs) were recorded from the scalp to investigate a long-standing controversy in auditory attention research, namely when the 'breakthrough of the unattended' takes place in the human brain. Nine subjects classified visual stimuli appearing 300 ms after task-irrelevant standard tones (80%, i.e. P = 0.8) or novel sounds (20%, i.e. P = 0.2) into odd/even categories. After the recording session, subjects scored the novel sounds as to whether they had any particular meaning (identifiable) or were perceived as a burst of noise (non-identifiable), and performance and ERPs were analysed according to this classification. A control condition, in which the visual stimuli were presented with no sounds, showed that subjects covertly monitored the task-irrelevant sounds during visual task-performance, and a further condition, in which the auditory and visual stimuli appeared regardless of each other, made it possible to trace the processing of the distracters during allocation of attention outside the auditory environment. Results yielded identical N1-enhancement for the two types of novel sounds, indicating similar attention switching triggered to these two types of unexpected sounds. However, there was a stronger orientating of attention towards identifiable novel sounds, as indicated both by behavioural distraction and by larger novelty-P3. Furthermore, this stronger orientating of attention was due to the sounds being contingent on the visual stimuli, as no increase in novelty-P3 to identifiable novel sounds was observed in the control condition, in which the sounds occurred outside the attentional set. Therefore, provided that the N1-enhancement reflects a call for focal attention, and novelty-P3 the effective orientating of attention towards the eliciting sounds, the present results suggest that semantic analysis of significant sounds occurs after a transitory switch of attention towards the eliciting stimuli. Moreover, as the novelty-P3 increase in amplitude was observed only when subjects covertly monitored the sounds, the present data suggest that semantic analysis of irrelevant sounds depends on the top-down cognitive influences of the attentional set.
Acoustic Stimulation↗
Effect of peppermint and eucalyptus oil preparations on neurophysiological and experimental algesimetric headache parameters.
The effects of peppermint oil and eucalyptus oil preparations on neurophysiological, psychological and experimental algesimetric parameters were investigated in 32 healthy subjects in a double-blind, placebo-controlled, randomized cross-over design. Four different test preparations were applied to large areas of the forehead and temples using a small sponge and their effect was evaluated by comparing baseline and treatment measure. The combination of peppermint oil, eucalyptus oil and ethanol increased cognitive performance and had a muscle-relaxing and mentally relaxing effect, but had little influence on pain sensitivity. A significant analgesic effect with a reduction in sensitivity to headache was produced by a combination of peppermint oil and ethanol. The essential plant oil preparations often used in empiric medicine can thus be shown by laboratory tests to exert significant effects on mechanisms associated with the pathophysiology of headache.
Administration, Topical↗
Early neural activity in Necker-cube reversal: evidence for low-level processing of a gestalt phenomenon.
Normally we experience the visual world as stable. Ambiguous figures provide a fascinating exception: On prolonged inspection, the "Necker cube" undergoes a sudden, unavoidable reversal of its perceived front-back orientation. What happens in the brain when spontaneously switching between these equally likely interpretations? Does neural processing differ between an endogenously perceived reversal of a physically unchanged ambiguous stimulus and an exogenously caused reversal of an unambiguous stimulus? A refined EEG paradigm to measure such endogenous events uncovered an early electrophysiological correlate of this spontaneous reversal, a negativity beginning at 160 ms. Comparing across nine electrode locations suggests that this component originates in early visual areas. An EEG component of similar shape and scalp distribution, but 50 ms earlier, was evoked by an external reversal of unambiguous figures. Perceptual disambiguation seems to be accomplished by the same structures that represent objects per se, and to occur early in the visual stream. This suggests that low-level mechanisms play a crucial role in resolving perceptual ambiguity.
Adult↗
Disturbance of semantic processing in temporal lobe epilepsy demonstrated with scalp ERPs.
We investigated event-related potentials (N400, LPC and CNV) elicited in temporal lobe epilepsy (TLE) patients and control subjects from scalp electrodes, using a word-pair category matching paradigm. Each prime consisted of a Japanese noun (constructed from 2-4 characters of the Hiragana) followed by a Chinese character (Kanji) as the target, the 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 under the mismatch condition in both subject groups. The N400 amplitude was reduced in TLE subjects under both conditions, although LPC and CNV amplitudes showed no significant differences. These results suggest that scalp N400 is capable of demonstrating disturbance of semantic processing in TLE non-invasively.
Adult↗
Scalp distribution of slow cortical potentials in schizophrenic patients.
Surface-negative slow cortical potentials (SPs) indicate increased excitability of the underlying cortical networks. Deviant patterns of SPs in schizophrenic patients may reveal in atypical regulation of cortical excitability. This hypothesis was examined by comparing SP-scalp distribution between patients with a chronic schizophrenic disorder and matched control Ss using reaction time paradigms. In study I (12 Ss/group) a CNV was evoked during a 3-s visual S1, while the parallel presentation of clicks at various time intervals should "probe" the brain state during the CNV. The CNV showed a frontal predominance in patients compared to a centroparietal maximum in controls, suggesting an atypical spatio-temporal regulation of SPs in patients. Similar modulation of probe-evoked responses parallel to the CNV in both groups indicated the functional significance of SPs to be similar in schizophrenics and controls. In study II (17 Ss/group) association between a visual S1 and a lateralised tactile S2 allowed fast responses with the respective hand. This association could be formed in one trial series, while the side of tactile stimulation was unpredictable in another. Feedback of response adequacy was provided 1.5 s after S2. Groupds did not differ in mean CNV-amplitudes or -lateralisation. On the other hand, patients developed a pronounced, broadly distributed feedback-preceding negativity (FNP) on all trials, while controls exhibited a right-hemisperic FPN only, when the side of S2 was unpredictable and feedback became salient.
Adult↗
PINV--topography and primary negative symptoms in chronic schizophrenia.
PINV was recorded during a warned reaction time paradigm in 16 chronic schizophrenics in remission. Clinical symptoms were assessed by BPRS, SANS, and the anhedonia scale of the Chapman Questionnaire. Ten healthy controls were studied in the same manner. Over the frontocentral area we found a significantly elevated PINV amplitude with an altered topographical distribution in the patient group. The difference values "PINVCz-PINVFz" were correlated negatively with primary negative symptoms of schizophrenia.
Adult↗
Negative difference (Nd), an ERP marker of stimulus relevance: different lateral asymmetries for paranoid and nonparanoid schizophrenics.
We studied Nd in psychotic patients with varying degrees of paranoid symptoms. Nd is an ERP measurement of the difference in the way a nonattended tone is registered and the way the same tone is registered when used later as a discrimination target. In a three-tone oddball paradigm with passive-tone presentation and active discrimination, we recorded from 19 sites in 22 young healthy subjects and 28 schizophrenics. Nd (200-260 ms) was bilaterally symmetrical in healthy subjects. Paranoid patients showed a left frontal/right temporoparietal amplitude reduction which was reversed in nonparanoid subjects (reduced at right frontal/left posterior sites). These asymmetries were clearer when the groups were separated according to active paranoid symptoms rather than by diagnosis. There would therefore seem to be functional asymmetries mediating stimulus relevance in schizophrenics which differ from controls and differ between patients with and without active paranoid symptoms.
Acoustic Stimulation↗
Evoked potentials, expectancy wave, and skin resistance in depressed patients and healthy controls.
Averaged evoked potentials, expectancy waves and number and amplitude of skin resistance responses to auditory stimuli are found to be significantly smaller in a group of 18 patients with primary depression than in 27 healthy controls. AEP amplitude attenuation is shown not to be an averaging artifact, due to varying response latencies. There are no simple relations between electrocortical and electrodermal parameters, but patients display more significant correlations between these two sets of variable than controls. Amplitude attenuations are interpreted as hyporesponsivity resulting from depressive inhibition. The narrower coupling of variables in the depressed group is viewed as a limitation in physiological plasticity.
Acoustic Stimulation↗
Event-related potential findings in healthy extremely pre-term (< week 29) children at age 10.
Ten healthy extremely pre-term (EPT) children, born before gestational week 29, were tested at age 10 using mismatch negativity (MMN) and a three-tone odd-ball task; the results were then compared to age-matched full-term controls. We found no difference in MMN. By contrast, EPT children had generally shorter N1 latencies and larger P2 amplitudes, possibly indicating a more stimulus-driven response mode. However, P300 parameters, indicative of controlled attention, were unaffected.
Brain Damage, Chronic↗
Simultaneous recording of eeg and direct current (DC) potential makes it possible to assess functional and metabolic state of nervous tissue.
It has been proposed to assess functional and metabolic state of the brain nervous tissue in terms of bioelectrical parameters. Simultaneous recording of the DC potential level and total slow electrical activity of the nervous tissue was performed in the object of study by nonpolarizable Ag/AgCl electrodes with a DC amplifier. The functional and metabolic state of the brain was determined in terms of enhancement or reduction in the total slow electrical activity and positive or negative shifts in the DC potential level.
Adenosine↗
Jaw deviation dystonia evaluated by movement-related cortical potentials and treated with muscle afferent block.
Jaw-deviation dystonia is characterized by the lateral shift of the mandible due to involuntary masticatory muscle contraction, causing difficulties in speech or mastication. We evaluated a patient with jaw-deviation dystonia by recording movement-related cortical potentials (MRCPs) and treated with muscle afferent block (MAB). MRCP associated with mandibular movements (mouth opening, closing, and left and right lateral movements) was recorded in the patient and ten age-matched healthy subjects. In the control subjects, the amplitude of Bereitschaftspotential (BP)/negative slope (NS') was significantly higher for left lateral movements than for the mouth closing. The cortical map of BP/NS' prior to mouth opening and closing showed symmetric distribution, whereas those of lateral movements showed a slight predominance in the ipsilateral hemisphere. The patient showed lower amplitude as compared with control subjects. The right lateral movement (homonymous task) showed task-specific markedly reduced potentials. After MAB by intramuscular injection of lidocaine and ethanol to the inferior head of the left lateral pterygoid muscle, the deviation abolished and severity in speech and mastication was significantly improved. This study suggests that jaw-deviation dystonia might have the same etiology as other focal dystonias.
Adult↗
Real-time monitoring of brain activity in patients with specific phobia during exposure therapy, employing a stereoscopic virtual environment.
Exposure therapy is a behavioral technique that is reported to be the most effective, long-lasting treatment for patients suffering from specific phobia. During the performance in enclosed spaces, the patients show a strong psychophysiological response to the phobic stimulus that is normally avoided. This psychophysiological response changes characteristically during the course of exposure. We implemented an electroencephalographic monitoring focusing on event-related potentials to resolve the modulation of preattentive information processing by the anxiety state of the subject. Therefore, mismatch-negativity (MMN) was chosen as parameter using a passive auditory oddball paradigm that does not interfere with performance in the virtual environment. The results of this neurophysiological monitoring are demonstrated in one patient suffering from claustrophobia.
Adult↗