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Evoked potentials (EPs) in a daily practice consist of somatosensory evoked potentials (SEP), visual evoked potentials (VEP), auditory brainstem response (ABR) and motor evoked potentials (MEP). EPs can confirm the presence of lesions in patients with suspected involvement, and document the presence of clinically unsuspected lesions in multiple sclerosis (MS) patients. MEP has the highest sensitivity while VEP is the second sensitive. Furthermore, we are able to obtain an increase in sensitivity by using multimodality evoked potentials (MuEP). By doing so, there is a significant correlation between EP abnormalities and Expanded Disability Status Scale. Thus, EPs are useful for the diagnosis or evaluation of MS and predicting neurological disabilities.

Despite being the most important of organs, the brain is disproportionately unmonitored compared to other systems such as cardiorespiratory in anesthesia settings. In order to optimize level of anesthesia, it is important to quantify the brain activity suppressed by anesthetic agents. Adverse cerebral outcomes remain a continued problem in patients undergoing various surgical procedures. By providing information on a range of physiologic parameters, brain monitoring may contribute to improve perioperative outcomes. This article addresses the various brain monitoring equipments including bispectral index (BIS), auditory evoked potentials (AEP), near-infrared spectroscopy (NIRS), transcranial Doppler ultrasonography (TCD) and oxygen saturation of the jugular vein (Sjv(O2)).

The processes of fear conditioning and extinction are thought to be related to the pathophysiology of anxiety disorders, including obsessive-compulsive disorder (OCD), panic disorder, and posttraumatic stress disorder. We have reported alterations of auditory P50 suppression in human fear conditioning and extinction in healthy control subjects (Kurayama, et al., 2009). In addition, we have reported that P50 suppression in fear extinction was impaired in patients with OCD (Nanbu, et al., 2010). The present report reviewed the studies about relationship between sensory gating and fear conditioning. In the acquisition phase of classical fear conditioning, 10 pairings of the conditioned stimulus (CS; a visual stimulus from a light-emitting diode) and the unconditioned stimulus (US; an electrical stimulus to the wrist) were administered; in the extinction phase, 10 CS without US were administered. P50 auditory evoked potentials were measured as the first stimulus sound (S1) and the second stimulus sound (S2) in a double-click paradigm with a 500 ms interval (shorter than usual), and P50 S2/S1 ratios were used to evaluate P50 suppression. In healthy controls, the mean P50 S2/S1 ratio in the fear acquisition phase was significantly elevated compared with the ratio found in the control phase, while it recovered to basal level in the extinction phase. The mean P50 S2/S1 ratio in patients with OCD was significantly higher than the ratio in controls (P = 0.022) in the extinction phase, in contrast to the lack of significant difference found in the baseline and acquisition phases. Sensory gating mechanisms may be physiologically associated with fear conditioning, and OCD may involve abnormal sensory gating in fear extinction.

We recorded the auditory-evoked fields in five patients with psychogenic hearing impairment and ten healthy controls. The maximum N100m peak amplitude and latency were measured under 1000 and 2000-Hz tone burst stimuli in each ear. The mean N100m amplitude in the patients was smaller than that in the controls. Especially, regardless of the side of stimulation, the mean amplitude in the left-hemisphere was significantly smaller in the patients than in the controls, except for the 2000-Hz stimulus condition in the left ear. There was no significant difference in the latency of the N100m peak between patients and controls. We attribute the findings of attenuation of the N100m amplitude to the peculiar auditory perception in patients with psychogenic hearing impairment. Concerning the cause of this finding, we suggest two possible mechanisms: inhibitory auditory processing and attention deficit.

Gaucher's disease is caused by a lack of glucocerebrosidase, and in type 2 various neurological symptoms can occur;however, the detailed pathogenesis of the condition remains undetermined. Here we performed neurophysiological examinations in an 18-month-old girl with Gaucher's disease type 2 to specify the brainstem lesions. Developmental delay occurred from the age of 8 months, and the patient subsequently showed strabismus, loss of head control, failure to thrive and irregular respiration. She was admitted to our hospital at the age of 18 months. A definite diagnosis of Gaucher's disease type 2 was made from the presence of Gaucher cells and reduced glucocerebrosidase activity. Clinically, limited ocular movements, poor facial expression and bulbar palsy indicated disturbances in the nuclei of oculomotor, trochlear, abducent, facial and ambiguous nerves, although magnetic resonance imaging (MRI) failed to visualize any structural changes in the brain including the brainstem. Neurophysiologically, auditory brainstem response and somatosensory evoked potential demonstrated lesions in the cochlear nucleus and medial lemniscus, respectively. On polysomnography, disturbed sleep parameters during rapid eye movement sleep, in addition to the lack of modification of respiratory patterns by sleep stage, suggested dysfunctions in the locus ceruleus, raphe nuclei and pontine reticular formations. It is likely that these neurophysiological tests can be useful to identify functional lesions that are not detectable by MRI, and should help exploit new treatments for child-onset neurodegenerative disorders such as Gaucher's disease.

Auditory evoked potentials (AEPs) are an electrical manifestation of the brain response to an auditory stimulus. The waveform represents the passage of electrical activity provoked by auditory stimuli from the cochlea to cortex. The waves represented by I-VII are generated mainly in the brainstem. These waves are called the brain stem auditory evoked potentials (BAEPs) or the auditory brain stem response (ABR). The middle latency AEPs (MLAEP) are generated from the medial geniculate and primary auditory cortex. The long latency AEPs (LLAEP) are generated from the frontal cortex and association areas. The BAEPs appear to be an exquisitely sensitive monitor for pathological events during surgery. Anesthetics and mild hypothermia have minimum effect, if any, on the BAEPs. The BAEPs are useful during the microvascular decompression of the fifth or seventh cranial nerve, resection of acoustic neuroma and posterior fossa operations. Because the auditory pathway occupies a small area in the brainstem, combined use of other evoked potentials such as short latency sensory evoked potentials is recommended. The MLAEPs are most promising evoked responses for monitoring awareness or depth of anesthesia. When the concentration of anesthetics is increased, the amplitudes of the MLAEP's peaks are decreased and their latencies are elongated. Commercially developed A-line AEP monitor or aepEX can extract the AEPs waveform in a short period and automatically analyze the changes in the MLAEPs. These AEP based monitors may be superior to bispectral index (BIS) in detecting the transition from unconsciousness to consciousness.

We report a 7-year-old boy with Landau-Kleffner syndrome (LKS), with emphasis on the effect of therapy and serial MEG. The equivalent current dipoles (ECDs) of spike discharges accumulated in the bilateral Heschl gyri, predominantly on the right. Although spike discharges on the scalp EEGs disappeared by treatment with clonazepam and sodium valproate, the auditory agnosia did not improve. Therapeutic trials with conventional antiepileptic drugs were unsuccessful. A high-dose corticosteroid was effective, with disappearance of ECDs, appearance of auditory evoked fields (AEF) in the bilateral Heschl gyri on MEG, and improvement of behavioral problems and amelioration of acquired aphasia. The clinical course of this patient suggests that MEG findings are useful not only in making precise diagnosis of LKS but also in assessing and predicting the effects of treatment.

The degree of hearing loss and audiogram shape vary in patients with perilymphatic fistula. The cause of variability is not well known. To determine the effect of perilymphatic fistula on cochlear function, we studied the effect of round window membrane rupture on cochlear blood flow (CBF) by placing a laser-Doppler probe to the basal turn in 20 guinea pigs. In 10, endocochlear potential (EP) was measured by inserting a glass microelectrode through the stria vascularis of the basal turn. During 60 minutes following round window membrane rupture, CBF decrease of more than 15% was observed in 9 of 20 animals, and EP decrease of more than 15% was observed in 5 of 10. A significant correlation was observed between the degree of CBF reduction and EP reduction. In 3 animals in which CBF decreased after round window membrane rupture, temporal bones were studied histologically. One cochlea showed endolymphatic hydrops and another cochlea showed significant hemorrhage in the scala tympani after rupture. These results suggested that CBF impairment is associated with cochlear dysfunction in perilymphatic fistula.

The literature has reports on the influence of spontaneous otoacoustic emission (SOAE) on transiently evoked otoacoustic emission (TEOAE), but most do not take factors such as age, gender, and hearing level into consideration. We focused on these conditions. Subjects were 78 women with normal hearing aged 19 to 24 years (mean = 21.4). All had pure tone thresholds of 15 dB HL or better at 1 kHz, 2 kHz, and 4 kHz. ILO88 was used to record TEOAE and SOAE. Echo power (EP) and reproducibility (Repro) were compared between groups with and without SOAE. No significant audiometric difference was seen between groups. Total echo power (TEP) and whole reproducibility (WR) were significantly greater in the group having SOAE, consistent with previous reports (p < 0.01). EP and Repro classified by frequency bands were also significantly greater in the group having SOAE at 1 kHz to 4 kHz. Subjects were divided based on the number of SOAE and the above parameters compared. We found that as the SOAE number increased, EP and Repro increased. In conclusion, the existence of SOAE influences TEOAE parameters and must be taken into account during clinical testing.

Two experiments were conducted to investigate the degree of semantic processing for unattended words. In a dichotic listening task, each participant was required to attend selectively to either a word sequence in one ear or a speech passage in the opposite ear. The selective listening was confirmed by attenuated P1-N1 and N400 waves of the event-related brain potential to unattended words. The N400 attenuation with semantic priming was observed only for attended words. In a following recognition test with a booklet and auditory presentation, the percentage of false alarms for "new" words (or lures) semantically related to "old" words was higher when the "old" words were attended in selective listening than when unattended. These findings suggest that selective attention can act before and/or at a level of semantic processing.

We report a 57-year-old woman with superficial siderosis of the central nervous system. On physical examination, sensorineural hearing impairment, cerebellar ataxia, pyramidal tract signs, dysarthria, and neurogenic bladder were seen. Brain and spinal cord MRI (T2 and proton weighted images) revealed cerebellar atrophy and marginal hypointensity of the Sylvian fissure and brain stem, cerebellum and spinal cord. We diagnosed this patient as superficial siderosis because of the clinical course and specific findings on MRI. We consider this case idiopathic superficial siderosis because the source of the bleeding was unknown. Neuro-otological tests and BAEP disclosed retrocochlear deafness. Her central motor conduction time on MEP was delayed. We discussed the pathogenic mechanism of these conditions, and we concluded that we must take notice of myelinopathy in superficial siderosis and that MEP was useful for detecting them.

Recently, spinal cord stimulation (SCS) has been used for the treatment of patients in prolonged coma. However, the results of SCS in unresponsive patients with hypoxic encephalopathy at the chronic stage have not been satisfactory. Considering these circumstances, we began SCS from one month after the onset of hypoxic encephalopathy and evaluated its effect. Twelve patients (5 males and 7 females) with hypoxic encephalopathy, ranging in age from 7 to 72 years, were treated with SCS. The causes of hypoxia were acute cardiac failure in 4, automobile exhaust gas poisoning in 2, and asthma, pneumothorax, anaphylaxis, asphyxia, drowning and hypotension during aortic surgery in one patient each. One month after the onset, an electrode for electrical stimulation was implanted in the epidural space at the C2-C4 level under general anesthesia. The spinal cord was stimulated for 8 hours each day, starting on the day after implantation, and was continued for 3 months. Magnetic resonance imaging (MRI), cerebral blood flow (CBF) measurement using xenon-computed tomography (Xe-CT), and measurement of auditory evoked potential (AEP) and somatosensory evoked potential (SEP) were carried out 3 weeks after the onset for presurgical evaluation. Among the 12 patients, 7 (58%) showed clinical improvement, beginning within two weeks after starting stimulation. They were able to communicate with others and to express their emotion. However, disturbance of writing, picture drawing and calculation were not improved by stimulation. From presurgical evaluation, cases in which SCS therapy was effective had the following features: 1) No hemorrhagic infarction in the basal ganglia was demonstrable by MRI. 2) Mean hemispheric CBF measured by the Xe-CT method exceeded 25 ml/100 g per min. 3) The mean increase in hemispheric CBF 20 min after acetazolamide administration exceeded 5 ml/100 g per min. 4) An N20 peak was evident on the median nerve SEP, SCS appears to be an effective supplementary for unresponsive patients with hypoxic encephalopathy at the subacute stage, in addition to rehabilitation and drug therapy.

The N100m source of the auditory evoked magnetic fields (AEFs) is located more posterior in the left than the right hemisphere in male subjects. However, whether this asymmetry exists in female subjects is controversial. The present study, analyzed the N100m source positions of the AEFs due to monaural tone stimuli using a helmet-shaped 66-channel magnetoencephalography system (CTF Systems) in 62 right-handed normal adults (24 females and 38 males). The best fit sphere was calculated for each subject from the head shape reconstructed from three-dimensional magnetic resonance images. N100m source positions were estimated using a double-dipole model. The contralateral N100m response to the stimulated ear was measured relative to the midpoint of the bilateral auricular points. Statistical analysis used a standardized head size for each subject based on the mean value of all subjects (r = 8.27 cm). In females, the N100m dipole positions were 0.00 +/- 1.02 cm anterior in the left hemisphere and 0.35 +/- 0.74 cm in the right (p < 0.02). In males, the N100m dipole positions were -0.31 +/- 0.81 cm (mean +/- standard deviation) anterior in the left hemisphere and 0.61 +/- 0.78 cm in the right (p < 0.0001). The interhemispheric difference in the N100m positions was 0.35 +/- 0.65 in females and 0.92 +/- 0.77 in males (p < 0.005). In conclusion, the left hemispheric N100m is located more posterior to the right in both genders. However, this functional asymmetry is more evident in males, like previous findings of more evident anatomical asymmetry in males.

It is now well documented that in cases of Menière's disease/endolymphatic hydrops, the electrocochleography (ECochG) evoked by a broad-band click is often characterized by an enlarged summating potential (enlarged-SP) and a large negative summating potential to action potential ratio (large -SP/AP) but these mechanism have not been clarified. The aim of this study was to find clues to the mechanism of enhanced -SP and large -SP/AP in Menière's disease, by using long-tone burst stimuli. We also sought to determine the significance of SP measurement for evaluating the cochlear function in Menière's disease/endolymphatic hydrops. ECochG was performed on 29 ears of patients with Menière's disease and 12 ears of adults with normal hearing as a control group. Extratympanic ECochG was carried out using an HN-7 electrode. The sound intensity used for measuring the SP and SP/AP was 90dBnHL. Both SP and AP were elicited by clicks and long-tone bursts of 50 ms duration with a 1-ms rise-fall time. The clicks and long-tone bursts with frequencies of 0.5, 1, 2, and 4 kHz were delivered by the tubal transducer (NC-3). In most of the patients with Menière's disease, SP evoked by the long tone burst stimuli showed negative polarity (-SP) at each frequency. Analysis of variance (X2test) indicated a significant difference in -SP at 0.5 and 1 kHz between Menière's disease and the control group (0.5 kHz: p < 0.001, 1 kHz: p < 0.02). When setting the normal upper limit of the -SP/AP to 0.4, we found that the number of cases over 0.4 which showed -SP at 0.5 and 1 kHz was much larger than those below 0.4 in the 29 ears of patients with Menière's disease. There was no difference between the types of Menière's disease or glycerol test and SP polarity elicited by long-tone burst stimuli. The enhanced -SP and large -SP/AP obtained by the broad band clicks seem to reflect a component of negative SP polarity in the low and middle frequency ranges. It was assumed that the reverse phenomena of SP polarity in the low and middle frequency ranges were related to changes in hydrodynamic characteristics in the upper cochlear turns due to abnormal endolymphatic pressure. Our findings suggest that SP recording by long-tone burst stimuli is useful in detecting changes in cochlear partition due to abnormal intracochlear pressure, most likely in the early phase of Menière's disease based on the wide frequency information of SP.

We examined auditory evoked potentials and passive event-related potentials in two patients with hydranencephaly. In the middle latency response, a Na component was observed in both cases. Mismatch negativity was elicited in response to tone bursts and three patterns of vowel sounds in Patient 1, and three patterns of vowel stimuli in Patient 2. These results implicate the subcortical components of the auditory system in the generation of mismatch negativity.

Auditory evoked magnetic field (AEF) is known to be suitable to separate left and right hemispheric activities while auditory evoked potential is not. To evaluate cortical auditory function in ten patients with temporal lobe gliomas, we measured AEF for monaural tone stimuli using a helmet-shaped 66-channel MEG system. Latency of the N 100 m, the most prominent peak with a latency around 90 ms, was measured in the hemisphere contralateral to the stimulus onset. In five patients, the N 100 m latency was within our normal range (mean +/- 2 s.d.). In these five cases, tumor was located in the anterior or the inferior part of the temporal lobe. We observed significant delay of the N 100 m latency in four patients and disappearance of the N 100 m in another patient. In the later five patients, tumor extended to the superior and posterior part of the temporal lobe. AEF can be used to evaluate cortical auditory function noninvasively in cases with temporal lobe gliomas.

We investigated the blink reflex in 27 severely handicapped patients. 15 males and 12 females, from 5 to 60 years old. They were divided into three groups; the tube-feeding group (9 patients), the oral-feeding group (9 patients), and the mixed-feeding group (9 patients). Seven normal subjects also were included in this study. There was a significant difference in the late ipsilateral component (R2) between the tube-feeding and oral-feeding groups. The average R 2 time were 43.0 msec. in the tube-feeding group and 36.7 msec. in the oral feeding group. The auditory brainstem response (ABR) showed no significant difference between the two groups. These results suggested that the swallowing function in the patients needed for tube feeding was affected by not only the cortical lesions but also the brainstem ones. Furthermore, it is speculated that the degree of brainstem dysfunction in the tube-feeding group was more severe than in the non-tube-feeding group. The blink reflex is one of the useful electrophysiological parameters for evaluating the brainstem function in severely handicapped patients with dysphagia.

A Japanese girl developed tonic spasms in series at two months after birth. When she was admitted at 4 months, she had generalized muscle hypotonia and could not control her head. She had atotal agenesis of the corpus callosum on MRI, reticulo-lacunitis revealed by ophthalmologic examination, and hypsarrhythmia in EEG. Brain stem auditory evoked potentials and flash-visual evoked potentials exhibited abnormally asymmetrical findings. The cortical components of somatosensory evoked potentials were not elicited on admission, but some components became to be recognized on median nerve stimulation in accordance with improvement of EEG findings after various therapeutic trials. We concluded that these neurophysiological examinations were useful to investigate the abnormal lesions of the central nervous system in patients with Aicardi syndrome.

It is well known that the auditory evoked N100m response is dominant in the contralateral hemisphere to the stimulated ear: N100m latency is shorter and N100m amplitude is larger in the contralateral hemisphere than the ipsilateral hemisphere. Interhemispheric asymmetry of the N100m responses were reported in terms of the equivalent dipole localization: the right hemispheric N100m dipole is more anterior to the left hemispheric dipole. In the present study, we investigated interhemispheric asymmetry of the auditory evoked P50m and N100m response in terms of signal amplitude. A helmet-shaped whole head magnetoencephalography system was employed to see small but significant differences between two hemispheres. Thirty-seven right-handed healthy subjects, 31 males and 6 females, participated in the study. The helmet-shaped whole head MEG system (CTF Systems-Osaka Gas) consists of an array of 66 MEG sensor sites uniformly distributed over the entire head. The monaural auditory stimuli, 2000 Hz tone burst of 50 msec duration were delivered to the left and then the right ear sequentially, with an intensity of 80 dB SPL at the ear. White noise of 50 dB SPL was delivered to the opposite ear. The inter-stimulus intervals were randomized in the range from 2.5 to 4.7 sec. In a total of 37 subjects, N100m dipole pattern appeared on both hemispheres either left or right ear stimuli. When P50m peak amplitude was compared between contralateral responses, the right-hemispheric response (141.5 +/- 16.3 fT, mean +/- s.e.m.) was slightly larger than the left-hemispheric response (134.3 +/- 10.2 fT). Differences, however, were not significant. When P50m peak amplitude was compared between ipsilateral responses, the right-hemispheric response (135.1 +/- 11.0 fT) was slightly larger than the left-hemispheric response (115.3 +/- 10.9 fT). Differences were not significant, either. When N100m peak amplitude was compared between contralateral responses, the right-hemispheric response (484.4 +/- 28.4 fT) was statistically (p < 0.01) larger than the left-hemispheric response (375.6 +/- 28.0 fT). When N100m peak amplitude was compared between ipsilateral responses, the right-hemispheric response (405.8 +/- 27.9 fT) was statistically (p < 0.02) larger than the left-hemispheric response (315.1 +/- 24.8 fT). Previously, we reported that the right hemispheric latency is shorter than the left hemispheric latency in the auditory evoked field N100m responses. Present study indicated another evidence of the right hemispheric dominancy in the auditory evoked responses, namely the lager amplitude in the right hemispheric response at least for pure-tone stimuli. The whole-head MEG system is suitable to analyze differences of auditory function between two hemispheres.

It is known that the auditory evoked N100m response appears faster in the contralateral hemisphere than in the ipsilateral hemisphere to the stimulated ear. For the middle latency response named P50m, however, there have been only few studies with controversial findings. In the present study, auditory evoked responses to the unilateral tone stimuli were measured in 36 right-handed normal subjects, using a helmet-shaped whole head magnetoencephalography system. In a total of 72 hemispheres of 36 subjects, P50m dipolar patterns were observed statistically (p > 0.02) frequently in the contralateral hemispheres (63.9%) compared to the ipsilateral hemispheres (43.0%). N100m dipolar patterns were observed over both left and right hemispheres either by left or right ear stimuli. Peak latency of the P50m was statistically (p < 0.02) shorter in the contralateral hemisphere (45.0 +/- 8.5ms, mean +/- s.d.) compared to the ipsilateral hemisphere (54.4 +/- 11.5ms). Peak latency of the N100m was also statistically (p < 0.001) shorter in the contralateral hemisphere. Moreover, when compared between contralateral responses, the left-ear stimulated right-hemispheric response (84.6 +/- 8.4) was statistically (p < 0.05) faster than the right-ear stimulated left-hemispheric response (89.3 +/- 10.2ms). These results indicate that contralateral auditory cortex dominates the ipsilateral cortex at the middle as well as the long latency components. Moreover, at least for pure-tone stimuli, right hemispheric dominance was indicated for the N100m responses. The whole-head MEG system is suitable to analyze small but significant interhemispheric difference of auditory function.

In 10 consented patients (ASA I-II) we quantitated the hypnotic potencies of 0.7 MAC nitrous oxide and 0.7 MAC sevoflurane by measuring auditory evoked response (AER), and compared the hypnotic potency of nitrous oxide with that of sevoflurane at the same MAC. In each patient, measurements of AER waves were performed in the following three stages, 0.7 MAC nitrous oxide, 0.7 MAC sevoflurane and 0.7 MAC nitrous oxide after induction of anesthesia. Analysis of variance was used to compare the hypnotic potencies between two inhaled anesthetics. Pa and Nb latencies with sevoflurane were longer than those with nitrous oxide, and Pa and Nb amplitudes with sevoflurane were greater than those with nitrous oxide. However, we found that there were no statistical significances in our results. In conclusion, nitrous oxide exerts as much hypnotic effect as sevoflurane.

Event-related brain potentials associated with both somatosensory and auditory detection tasks were recorded from the scalp in a 63-year-old man with finger agnosia and right-left disorientation resulted from cerebral infarction located around the region of the left angular gyrus. In a somatosensory oddball paradigm for discrimination between the right index finger (target, P = 0.2) and the left index finger (non-target, P = 0.8), early cognitive components P100, N140 and processing negativity were observed both in the target responses and non-target responses, however, no P300 component was recorded in both paradigms. In another paradigm to discriminate the index finger (target, P = 0.2) from small finger (non-target, P = 0.8) in the right hand, no P300 was evoked and only processing negativity was recorded both in the target responses and nontarget responses. These phenomena were obtained through characteristic behavior that the patient paid attention to the target stimuli as well as non-target stimuli and mentally counted them without discrimination. In contrast, in an auditory oddball paradigm P300 was clearly demonstrated to target stimuli that the patient correctly could count. The normal appearance of P300 in auditory detection tasks strongly suggests that the neural generator for the P300 was reserved intact. These results indicate that somatosensory information processing might be disturbed at the level of sensory discrimination needed for generation of P300 in our patient. It is also proposed that the neural events for somatosensory discrimination and auditory discrimination would take separate channels each other to reach the common generator of p300 in information processing.

Mismatch negativity (MMN) of the event related potential (ERP) is generated when patients can discriminate two different kinds of stimuli even if he or she is not conscious of their differences. The authors examined auditory ERPs of passive paradigm in 16 patients with severe multiple handicaps. All patients showed no or scarce clinical response to human voices or environmental sounds. This study investigated whether they showed MMN, since it is hard to evaluate their auditory perception clinically. Auditory stimuli were the tone bursts of 700 and 1,000 Hz in frequency offered at a 4:1 occurrence. Nine of 16 patients showed a definite N2 wave followed by an N 1 wave. The latency of the N 2 wave ranged from 150 to 596 milliseconds after the onset of the target stimuli. This N 2 was considered compatible with mismatch negativity (MMN) in healthy patients. These results suggest that the patients could discriminate subtle difference in two kinds of tones, although their responses to auditory stimuli were very poor.

Authors compared MR anatomy and magneto-encephalographic (MEG) functional methods in locating auditory cortex in 20 normal volunteers and 56 patients with intracranial structural lesions. Auditory evoked response was measured over the entire head, using a helmet shaped 64 channel MEG system. In each subject, three dimensional MR image was obtained with identical coordinate system of MEG. Best fit sphere to each subject's head was calculated from MRI data. Signal source of auditory evoked MEG was estimated using a two dipole model in the best fit sphere. Position and orientation of dipoles were superimposed on each subject's MRI. Both left and right dipolar patterns appeared about 100 ms after unilateral auditory stimuli (N100m) in 19 normal subjects and 47 patients. These dipolar patterns overlap each other across the midline. A two dipole model successfully localized bilateral N100m dipoles in the upper surface of superior temporal planes. N100m response was missing unilaterally in 1 normal subjects and 9 patients inspite of normal audiometry findings, suggesting sub-clinical auditory dysfunction. The MR-linked whole head MEG is a non-invasive tool to localize source of auditory evoked N100m response even in the case with intracranial structural lesions.

In order to investigate features of cognitive impairment in idiopathic Parkinson's disease (PD) and suitable methods for the cognitive evaluation of patients with PD, 23 PD patients and 15 normal control subjects were studied using neuropsychological tests and auditory event-related potential (ERP). The two groups did not differ from each other in age or education. Clinical severity of the patients based on Hoehn & Yahr's staging ranged from stage I to IV: 7 patients at stage I, 8 at stage II, 7 at stage III and 1 at stage IV. All patients achieved the Mini-Mental State test (MMS) scores of 24 or greater, and none of the patients showed middle or serious grade of dementia based on the Diagnostic and Statistical Manual of Mental Disorders-Third edition-Revised (DSM-III-R). All patients and controls underwent MMS, the Hasegawa's Dementia Screening Scale (HDS), the Wechsler Adult Intelligence Scale-Revised (WAIS-R), the Raven's coloured progressive matrices (RCPM), The Wisconsin Card Sorting Test (WCST) and the Benton Visual Retention Test (BVRT). Auditory ERPs by standard oddball paradigm (two-choice reaction time task) were elicited (band-pass 0.1-50 Hz) from Cz electrode sites on all subjects with a random series of binaural 1,000 (standard; 80%) or 2,000 (target; 20%) Hz tones presented every 2 sec at 70 dB SPL. In RCPM, N100 peak latencies of ERP (target and standard), performance-IQ of WAIS-R (especially block design and digit symbol subtests) and in error scores of BVRT there were striking differences between the two groups (p < 0.001).(ABSTRACT TRUNCATED AT 250 WORDS)

Auditory and somatosensory ERPs were studied in patients with dementia of the Alzheimer type (DAT), those with vascular dementia and demented patients with idiopathic Parkinson disease. In both auditory and somatosensory modalities, the P3 latency in the demented patient group was significantly prolonged compared with the control data. However, comparisons of the P3 latency among the patients with DAT, vascular dementia and demented Parkinson did not reveal any significant differences. Patients with vascular dementia had significantly prolonged N140 and P200 latencies in somatosensory ERPs, whereas N1 and P2 latencies in auditory ERPs did not show any significant differences. Patients with acute onset hippocampal amnesia showed normal auditory P3 and somatosensory P3, whereas patients with diencephalic amnesia had prolonged auditory P3 and somatosensory P3 in addition to the abnormal short latency somatosensory evoked potentials. Analysis of passively evoked P3 component and comparison between target P3 and passively evoked P3 may be useful for evaluation of demented patients with a variety of etiologies. Single-trial analysis showed a greater variance of P3 latency in demented patients than in control subjects. A greater variance of P3 resulted in 'absent P3' in conventional averaging in some of the demented patients. As vigilance levels changed from trial to trial, evaluation of P3 latency variance has been proven to be useful.

Auditory event-related potentials (ERPs) were recorded from 131 epileptic children of 4 to 20 years of age, and the related factors affecting P300 latencies were evaluated using multiple regression analysis. The examined factors were as follows: (1) age at P300 recording and duration of illness, (2) seizure types and epileptic syndromes, (3) anti-epileptic drugs (AEDs), (4) seizure prognosis, (5) organic brain dysfunctions, (6) x-ray CT and (7) EEG background activity and frequency of paroxysms. ERPs were elicited with the oddball paradigm. Five factors of them had significant correlations with P300 latencies. 1) P300 latencies were gradually shortened with age. 2) P300 latencies were prolonged in the patients before and during AED medication compared with those during the period of off-therapy. 3) Symptomatic partial epilepsy showed obviously prolonged P300 latencies. 4) P300 latencies were shortened with increasing alpha 2 power of EEG. 5) P300 latencies became prolonged with the length of illness.

Evoked otoacoustic emissions (e-OAE) at a 2 kHz tone burst were measured in 37 ears of 21 cats. The e-OAE responses were detectable in 30 ears of 19 cats. In most cats (26 out of 30 ears) nonlinear behavior could be identified and saturated above 15 to 20 dBnHL. The responses had very short latencies (to their peak pressures) of 5.53 ms to 7.28 ms. Scanning electron microscopy (SEM) was used to examine feline cochleas for structural damage after exposure to a 2 kHz pure tone (105 dBSPL and 125 dBSPL). Following a 105dB exposure for 30 min acoustic response recovered to normal levels at 120 min after exposure with no significant loss of hair cell stereocilia. Fatigue induced changes in outer hair cell activity may be relevant to the production of TTS. The loss of stereocilia on outer hair cell row 1 and on inner hair cells was seen between 6 and 9 mm from the apex after exposure to a 125dBSPL, 2 kHz pure tone for 30 min and e-OAE disappeared after overstimulation in all these cases. We found that e-OAE was affected by minimal cochlear damage.

We investigated the effect of non-biological artifacts on the measurement of distortion product oto-acoustic emission (DPOAE) using guinea pigs, and the generation mechanism of this phenomenon is discussed in the present paper. When a sound pressure of a stimulating tone was too large, an overtone was produced within the acoustic probe. When the difference in sound pressure between f1 and f2 was too large, artifacts appeared at frequencies of 2f1-f2 or 2f2-f1. Similar responses were generated when f1 and f2 were identical in sound pressure but exceeded a certain critical level. These non-biological responses could be easily differentiated from biological responses by subjecting the animal to anoxia. The input-output curve of DPOAE was biphasic and clearly showed this critical level in each animal. The results obtained in the present study suggest that the levels of f1 and f2 should be almost equal and should not exceed the observed critical level when measuring DPOAE.

Abnormal event-related potential (ERP) has been reported in several types of dementing illness including Parkinson's disease (PD) and progressive supranuclear palsy (PSP). In this paper we report the result of EPR recordings obtained in normal control subjects (14 cases) and in patients with PSP (6 cases) and PD (32 cases). ERPs were recorded from 13 scalp electrodes, using the acoustic odd-ball paradigm. All PD patients were in early stage (Yahr stage 1 to 2), and all PSP patients were in the mild-to-moderate state. In control subjects and PD patients P3 was normal. In PSP patients, only one subject (17%) showed a normal P3 component, three cases (50%) demonstrated low amplitude and normal latency P3, and two cases (33%) featured lack of normal P3 sequence. The P3 abnormalities in PSP patients were not related with dementia, but with low amplitude P3 being observed in 2 of 3 non-demented patients, and abolished P3 in a patient with only mild dementia. The result suggests that the P3 changes in PSP patients develop earlier than the cognitive dysfunction, and they are related to the underlying subcortical lesion rather than dementia.

In order to assess the vulnerability of the inner ear, auditory function and morphology of the inner ear were compared between adult budgerigars and adult guinea pigs. Budgerigars have been considered to have an excellent auditory-vocal system. Two experimental conditions were produced in each species; one by acoustic hyperstimulation (1500 Hz, 120 dBSPL) for 96 hours, the other by administration of kanamycin (200 mg/kg) for 7 weeks. Measurement of auditory evoked potentials (AEP) and observation of hair cells by electron microscopy were performed both immediately and 14 days after exposure. In the acoustic hyperstimulation experiment, AEPs of budgerigars showed less damage and better recovery than those of guinea pigs, probably because of morphological differences between the two species in hair and supporting cells. Electron microscopic observation on the budgerigars showed that a small part of the hair cell area was damaged and that regeneration of hair cells had occurred in this area 14 days after exposure. Such observations in guinea pigs revealed that outer hair cells had been damaged and replaced by supporting cells 14 days after exposure. In the kanamycin administration experiment, AEPs showed the same degree of damage and recovery in both species. This suggests that blood supply and drug transport to the inner ear are almost the same although the structure of the inner ear differs markedly between the two species. Electron microscopic observation did not show an apparent regeneration of hair cells 14 days after administration in the budgerigars. Guinea pigs had a tendency to show progressive damage of both auditory function and inner ear morphology even after the cessation of administration. Regeneration of hair cells in the budgerigar differed under both experimental conditions, suggesting that there is a difference in the mode of auditory disturbance between acoustic hyperstimulation and administration of kanamycin. In conclusion, resistance to acoustic hyperstimulation is higher in the avian inner ear than in the mammalian inner ear, while resistance to administration of kanamycin does not differ significantly between the two species.

We studied age related correlations of mismatch negativity (MMN) auditory event-related potentials (ERPs) using odd ball paradigm in 121 normal subjects (from 6 months to 43 years) and 33 mentally retarded subjects (from 2 to 18 years). The subject was instructed to read a book in order to ignore the stimulus during the experiment, or no specific task was imposed on young child. The MMN wave form was clearly obtained in normal 6 month old subjects. As the age advanced from 6-months, the latencies of MMN progressively shortened till about 7 years, when the latency reached adult level. One-third of mentally retarded patients had prolonged MMN than that normal age-matched subjects. Reliable recording of P300 requires subject's cooperation and attentiveness, which are difficult to achieve in young children or mentally retarded patients. MMN may be utilized in children to evaluate the development of the cognitive function.

Event-related potentials (ERPs) during a two-tone discrimination task were recorded in 85 normal subjects and 110 schizophrenic subjects. We divided ERPs into 4 interpeak components. We named them A, A', B and B'. A is the component from the stimulus point to n100 peak. A' is the one from n100 peak to p200 peak. B is the one from p200 peak to n200 peak. B' is the one from n200 peak to p300 peak. Their latency was named Al, A'l, Bl, and B'l respectively. Their amplitude was also named Aa, A'a, Ba and B'a respectively. Bl and A'l of the schizophrenic group were both significantly longer than those of the normal group. B'a of the schizophrenic group was significantly smaller than that of the normal group. Interrelations between interpeak components of the normal group were examined statistically. Regarding latency, a significant negative correlation was seen between Al and A'l, and also between Bl and B'l. Regarding amplitude, a significant positive one was seen between Aa and A'a, and also between Ba and B'a. Interrelations between Al and A'l, Bl and B'l, Aa and A'a, and Ba and B'a of the schizophrenic group were the same as those of the normal group. These negative correlations in latency suggest that n100 peaks and n200 peaks have 'jitter'. A combination of interpeak components is supposed to reflect a higher function of the brain. There was a significant negative correlation between (A + A')l and (B + B')l in the normal group, but there was not a significant one between them in the schizophrenic group. The schizophrenic group is supposed to have a certain abnormality in a higher function of the brain. Our result suggests that we may possibly be able to associate an abnormal focus around p200 peak with some symptoms and signs of schizophrenia.

We studied latent (mild) pulmonary encephalopathy in 14 patients with mild chronic respiratory insufficiency due to the sequelae of pulmonary tuberculosis. All of the patients were between 49 and 62 (mean age: 57.9). None of them had any impairment of daily activities and apparently had a clear consciousness. First, the P300 component evoked by auditory stimuli was examined. Immediately after that, the PO2, PCO2, pH were measured. Then the Hasegawa's dementia scale, the mini-mental state, the "Kanahiroi" test, Zung's depression score, digit span test were also assessed in the 14 patients. P300 components in 7 age-matched normal volunteers were also examined and compared with those in the 14 patients. The mean P300 latency in the patients were significantly prolonged compared with that in the normal volunteers (p less than 0.01). The P300 latency was well correlated with the PCO2, PO2, pH. The results of the "Kanahiroi" test also correlated with these parameters. We suggest that patients with mild respiratory insufficiency due to the sequelae of pulmonary tuberculosis often have latent (mild) pulmonary encephalopathy, and that P300 latency and the "Kanahiroi" test are very useful to detect and evaluate such latent pulmonary encephalopathy.

Event-related potentials (ERPs) have been used to investigate cognitive dysfunction in alcoholics. Previous findings are not concordant. Thirty alcoholics, and sex and age matched healthy controls (N = 30) were tested. The average age of alcoholics and the controls were 43.8 +/- 10.3 years and 44.7 +/- 11.5 years, respectively. All subjects were right handed and free from medication. Alcoholics met the criteria of DSM-III-R for alcohol dependence. ERPs were recorded during presentation of auditory stimuli. The stimuli consisted of 1kHz tone bursts referred to as 'frequent (non-target) stimuli' and 2kHz tone-bursts referred to as 'rare (target) stimuli'. The probability of frequent stimuli and rare stimuli were 0.8 and 0.2, respectively. The amplitudes of N100 and P300 were smaller in alcoholics than the controls. However, the latencies of these components were not different between the groups. The amplitudes and latencies of both N200 and P200 were not different between two subject groups. Although in the controls the maxima of P300 were seen only at parietal region, in alcoholics P300 maxima were seen at parietal region (16 out of 30, 53.3%), at frontal region (11 out of 30, 36.7%) and at occipital region (3 out of 30, 10.0%). Correlations between the distributions of P300 maxima and brain CT findings were examined in alcoholics. While CT abnormalities were been in 2 out of 19 (10.5%) subjects having P300 maxima at pareital region, in subjects having P300 maxima at frontal region the abnormalities were seen in 10 out of 11 subjects (90.9%). Correlations between values of CT measurements and the amplitudes (Pz) of P300 were examined.(ABSTRACT TRUNCATED AT 250 WORDS)

Event-related potentials (ERPs) were recorded during a selective listening paradigm similar to a previous study (Okita, 1989). Stimuli were random sequences of five vowels and a tone pip in two "channels' (separated by location, left and right). The difficulty of between-channel selection was varied in discriminability of location, easy (EL) or hard (HL), whereas within-channel selection was manipulated by designating either tone (T), one vowel (1V), or two vowels (2V) as targets. Subjects were required to attend to one channel and detect targets therein. ERPs for the EL condition replicating the earlier study, confirmed the effects of within-channel selection on the early phase of attention-related negativity (Nd): the early Nd being larger, the higher the target/nontarget selection load. In the HL condition, however, the 1V/2V difference disappeared: the early Nd effect was reduced for 2V, but prolonged in duration for 1V. The interaction between selection processes of the between- and within-channel was discussed in relation to the allocation of limited attentional capacity for operations rechecking outcomes of a preattentive target-classification stage.

To study the effects of aging and gender differences of ERP components, auditory ERPs were recorded in 106 healthy subjects. Forty-three patients with dementia of the Alzheimer type and 24 patients with vascular dementia were also studied. In healthy subjects, there was a significant positive linear correlation between P300 latency and age, with P300 latency increasing at the rate of 1.5 msec/year. Neither N100 nor P200 component was correlated with age. The amplitudes of N100, P200 and P300 components in females were slightly larger than those in males, but the differences were not significant. Not only P300 latencies but also P200 latencies were significantly different in healthy subjects, patients with dementia of the Alzheimer type and those with vascular dementia. In 74.4% of patients with dementia of the Alzheimer type and 62.5% of those with vascular dementia, the P300 latency was over 2 SE above the age-estimated regression line. The difference of the P300 latency prolongation may have resulted from the severity of dementia but not from the etiology of dementia.

40Hz event related potential, or 40Hz-ERP, described by Galambos in 1981 has been considered as the useful potential in predicting hearing threshold across the audiometric frequencies. Although 40Hz-ERP was reported by Galambos as the summation of middle latency responses (MLR), its origin has not been clarified. Moreover reports of the clinical use of 40Hz-ERP in patients with the neurological disorders were rare. Therefore, we recorded ABR, MLR and 40Hz-ERP in 35 patients with central nerve system disorders, or CNS disorders, and analysed the relation between central lesions and modality of MLR- or 40Hz-ERP from the view point of phase spectral analysis comparing with the digital filtered waveform analysis. For the phase spectral analysis, synchrony measure method described by Fridman in 1984 was applied to MLR and 40Hz-ERP. Following results were obtained. 1) By the digital filtered waveform analysis, the latencies of Po, Na, Pa and the amplitudes of Po, Na, Pa, Nb were recorded clearly in normal cases. In cases with the central lesions, many of them were revealed reduction of the amplitude of Po, but other parameters were not useful for the detection of CNS disorders because of their wide normal ranges. 2) The parameters of the phase spectral analysis were obtained from 17 records of the normal subjects. The SM (30 + 40 + 50Hz), which is the average of CSM 30Hz, CSM 40Hz and CSM 50Hz, was applied to MLR, and the SM (40 + 80 + 120Hz) was applied to 40Hz-ERP.(ABSTRACT TRUNCATED AT 250 WORDS)

Seventeen patients with no auditory brainstem evoked response (ABR) who suffered from various neurological disorders were reported. We evaluated the possibilities of co-existent brainstem lesions in addition to the peripheral impairment in the auditory pathway, by assessing neurological findings and other laboratory examinations, including cranial CT and electrically elicited blink reflex. Patients who showed cranial nerve symptoms other than that of the acoustic nerve or abnormal postural reflexes were suspected to have brainstem dysfunction. It was difficult, however, to exclude the influence from the dysfunction in the more central level CNS. Definite brainstem atrophy was revealed radiologically only in one case who was at the end stage of the degenerative disease. Blink reflex was studied in eleven cases, four of whom revealed abnormal responses, also suggesting brainstem dysfunction. All the five cases, consistent with these abnormal laboratory findings, had shown severe delay in motor development. Other five patients who showed rather good auditory behavior were considered to have 'desynchronization' response to ABR in the auditory pathway at the peripheral level. Many pathophysiological conditions may be involved in the phenomenon of absent ABR, which should be carefully evaluated from the viewpoints of clinical neurology.

Middle latency auditory evoked potentials (ML-AEPs) have not yet been established as a device of assessing neurological events because their origins have not been definitely identified. In this study, we assessed the neurological usefulness of MLA-EPs through experimental approach using canine models of acute ischemia localized within the cerebral cortex or thalamus. Two types of localized cerebral ischemia were produced in mongrel dogs by clipping of major cerebral arteries and inducing of hypotension; they were, unilateral cortical ischemia involving the right primary auditory area (group A) and unilateral thalamic ischemia involving the right medial geniculate body (group B). Using these two ischemia models, auditory evoked potentials (AEPs) were intracranially and extracranially recorded in addition to the measurement of local cerebral blood flow (1-CBF). Prior to the induction of ischemia, it was confirmed that positive waves with a latency of 20 ms (P20) were evoked in the bilateral primary auditory areas by sound stimulation (90 dB 5 Hz click) given to the ear contralateral to the planned ischemic side in both groups. The right P20 disappeared when the 1-CBF in the right primary auditory area decreased below the ischemic flow threshold of synaptic transmission failure, approximately 18 ml/100 g/min, in group A, and when the 1-CBF in the right medial geniculate body decreased below the threshold, 10 ml/100 g/min, in group B.(ABSTRACT TRUNCATED AT 250 WORDS)

A case of occlusion of basilar artery in a boy aged 7 years was reported. Compared with CT, MR imaging was more valuable for the early diagnosis of this disease. SPECT with IMP was thought to be useful in evaluating cerebellar circulation. ABR revealed brain stem abnormalities that could not be detected by neuroradiological techniques.

Somatosensory (SSEPs) and brainstem auditory evoked potentials (BAEPs) were recorded for 44 patients with diabetes mellitus (age, 63.0 +/- 9.3 years, mean +/- SD) and 20 age-matched healthy controls (age, 67.3 +/- 9.1 years) to elucidate the involvement of the central nervous system (CNS) in diabetes mellitus. Furthermore, relationships between SSEP or BAEP and clinical variables such as autonomic nervous function, peripheral nerve conduction velocity, duration of diabetes, metabolic control (fasting blood sugar level, HbA1 and HbA1c levels) and therapeutic method, were studied. The central conduction time (CCT), which represents the peak latency between N13 and N20, in patients with diabetes mellitus was significantly longer than that of the healthy controls (p less than 0.005). Likewise, diabetic patients showed significant prolongation of interpeak latency between waves I and V (I-V IPL) compared to the healthy controls (p less than 0.005). Significant correlations between CCT and motor conduction velocity of median nerve (p less than 0.05) were observed although the correlation between CCT and sensory nerve conduction velocity was not found to be significant (p less than 0.1). Furthermore, I-V IPL was significantly correlated with the duration of illness (p less than 0.05). There were no significant correlations between CCT or I-V IPL and autonomic nervous dysfunction as determined by orthostatic hypotension and the coefficient variation of the R-R interval or metabolic control or therapeutic method. From the present results, it would appear that there is CNS involvement even in diabetic patients not manifesting overt CNS signs and symptoms and that it is correlated somewhat with impairment of the peripheral nervous system and duration of illness.