P50 sensory gating disorders of auditory evoked potentials (AEP) in persons with schizophrenia

The paper presents a review of recent data on research and clinical significance of gating of the P50 component of the auditory evoked potentials (AEP). Information filters are a necessary element for the proper functioning of the brain. It appears as though they have an important role in the information-transfer mechanisms. Neurophysiologically, they appear hypothetically in the sensory gating of the P50 component of the AEP. Schizophrenic patients and their first degree relatives do not have proper sensory gating of the P50 AEP. This suggests that there is a common biological base for these disorders. Some clinical aspects of the schizophrenic psychoses can be linked to this disordered gating. There are also notes which show the contrary. Currently we do not know whether the improper sensory gating of the P50 AEP is a trait endophenotypically linked to schizophrenia, or only something that partially explains the pathophysiology of the illness--especially since the described phenomena may be evoked in healthy persons.     

A preliminary report of evoked potential marker study of pattern shift visual evoked potentials (PS-VEP) and auditory evoked potentials (AEP) on schizophrenic twins

This paper reports the result of electroneurophysiological study of the pattern shift visual evoked potentials (PS-VEP) and auditory evoked potentials (AEP) on six pairs of schizophrenic twins. The result indicated that there were significant differences in the inter-pair variance between MZ and DZ in latency P2, amplitude P2-N2 and P2 of using PS-VEP. AEP was also used for this group cases, and the result showed the presence of statistical differences in the inter-pair variance of latency N2, amplitude N1-P2 and P2. The authors speculated upon that the above six electrophysiological markers may be related to genetic factors, which had been proved by the blood group, character, clinical symptoms and treatment response of those patients.     

Brain-stem involvement in multiple sclerosis: a comparison between brain-stem auditory evoked potentials and the acoustic stapedius reflex

Summary Brain-stem auditory evoked potentials (BAEPs) and the acoustic stapedius reflex (ASR) were recorded in 68 patients with definite, probable and possible multiple sclerosis (using the definitions of McAlpine). The high incidence of abnormal results, 68% and 60%, respectively, pointed to the diagnostic value of these two measures in detecting brain-stem dysfunction. Combination of the methods increased the diagnostic yield to 85%. Since in part the same brain-stem generator sites underlie BAEPs and the ASR, it was considered that a study of their correlation might serve to increase the reliability and validity of these techniques. There was 71% agreement overall between results from the two measures. Furthermore, 72% of the joint BAEP and ASR abnormalities corresponded in detection of the brain-stem lesion site. It was concluded that the combined approach may supply powerful, complementary information on brain-stem dysfunction, which may aid in establishing the diagnosis of multiple sclerosis.This study was supported by the M. Sackler Foundation for Multiple Sclerosis Research     

Single-epoch analysis of interleaved evoked potentials and fMRI responses during steady-state visual stimulation

ObjectiveAim of the study was to record BOLD-fMRI interleaved with evoked potentials for single-epochs of visual stimulation and to investigate the possible relationship between these two measures.MethodsSparse recording of fMRI and EEG allowed us to measure BOLD responses and evoked potentials on an epoch-by-epoch basis. To obtain robust estimates of evoked potentials, we used blocks of contrast-reversing visual stimuli eliciting steady-state visual evoked potentials (SSVEPs). For each block we acquired one volume of fMRI data and we then tested for co-variations between SSVEPs and fMRI signals. Our analyses tested for frequency-specific co-variation between the two measurements that could not be explained by the mere presence/absence of the visual stimulation.ResultsCondition-specific single-epoch SSVEPs and fMRI responses were observed at occipital sites. Combined SSVEPs–fMRI analysis at the single-epoch level did not reveal any significant correlation between the two recordings. However, both signals contained stimulation-specific linear decreases that may relate to neuronal habituation.ConclusionsOur findings demonstrate robust estimation of single-epoch evoked potentials and fMRI responses during interleaved recording, using visual steady-state stimulation.SignificanceSingle-epochs analysis of evoked potentials and fMRI signals is feasible for interleaved SSVEPs–fMRI recordings.     

Direction-dependent visual cortex activation during horizontal optokinetic stimulation (fMRI study)

Looking at a moving pattern induces optokinetic nystagmus (OKN) and activates an assembly of cortical areas in the visual cortex, including lateral occipitotemporal (motion-sensitive area MT/V5) and adjacent occipitoparietal areas as well as ocular motor areas such as the prefrontal cortex, frontal, supplementary, and parietal eye fields. The aim of this functional MRI (fMRI) study was to investigate (1) whether stimulus direction-dependent effects can be found, especially in the cortical eye fields, and (2) whether there is a hemispheric dominance of ocular motor areas. In a group of 15 healthy subjects, OKN in rightward and leftward directions was visually elicited and statistically compared with the control condition (stationary target) and with each other. Direction-dependent differences were not found in the cortical eye fields, but an asymmetry of activation occurred in paramedian visual cortex areas, and there were stronger activations in the hemisphere contralateral to the slow OKN phase (pursuit). This can be explained by a shift of the mean eye position of gaze (beating field) in the direction of the fast nystagmus phases of approximately 2.6 degrees, causing asymmetrical visual cortex stimulation. The absence of a significant difference in the activation pattern of the cortical eye fields supports the view that the processing of eye movements in both horizontal directions is mediated in the same cortical ocular motor areas. Furthermore, no hemispheric dominance for OKN processing was found in right-handed volunteers.     

Magnetic stimulation motor evoked potential in multiple sclerosis. Comparison with visual evoked potentials, brain stem auditory evoked potentials and somatosensory evoked potentials]

This study consists of 45 patients with clinically definite MS, laboratory supported definite MS and clinically probable MS. We compared MEP results with other multimodal evoked potentials (VEP, BAEP and SEP). The abnormal rate of MEP was 87.6%, which was the highest. Abnormal MEP showed prolonged central motor conduction time (CMCT), consistent with pathological change of the demyelination. There was a evident correlation between the abnormal MEP and VEP, which is consistent with the most common MS (Devic Syndrome) in our country.     

Auditory evoked potentials and magnetic fields in patients with lesions of the auditory cortex

Auditory evoked potentials and magnetic fields of 40-200 ms latencies were measured from 4 patients with temporal lobe infarcts and compared with results from healthy subjects. Magnetic fields over the diseased hemisphere were abnormal in all 4; the responses were missing in 2. In one patient the responses were of abnormally high amplitude, and in one parts of the response sequence were missing. Evoked potentials were also abnormal in all 4 patients and the results were in accordance with the findings in the magnetic field measurements.     

Recording click-evoked myogenic potentials (CEMPs) with a setup for brainstem auditory evoked potentials (BAEPs).

AIM OF THE STUDY: Click-evoked myogenic potentials (CEMPs) originate in the sternocleidomastoid (SCM) muscle through a reflex loop involving the sacculus and the vestibular nerve. In this study we suggest that they can be picked up from the mastoid reference used for auditory evoked potential (AEP) recording by using standard filters for brainstem AEPs (BAEPs). They consist of a P13-N20 complex. METHODS: Fifty normal subjects were investigated. Recordings were performed with the same setting as that used for conventional BAEPs but without artifact rejection and using a wide time window (100 ms). Unilateral auditory stimulations were used. All acquisitions were performed in both sitting and supine positions. In nine subjects CEMPs and BAEPs were simultaneously recorded at both earlobe and both SCM muscles. RESULTS: In all subjects, a CEMP P13-N20 component could be evidenced in sitting, but not in supine position at both the ipsilateral earlobe and the ipsilateral SCM muscle. Its latency was 0.7 ms lower at the earlobe. It obeyed the same relationship to stimulus intensity at both earlobe and SCM muscle. CONCLUSION: These results demonstrate the possibility to get simultaneous information on the brainstem auditory pathways and on a reflex probably mediated through the sacculus and the vestibular nerve. Further studies on patients with selective vestibular nerve impairment should be conducted to confirm the clinical utility of this approach.     

Impaired auditory evoked potentials and oscillations in frontal and auditory cortex of a schizophrenia mouse model

Objectives: In patients with schizophrenia, γ-band (30–70?Hz) auditory steady-state electroencephalogram responses (ASSR) are reduced in power and phase locking. Here, we examined whether γ-ASSR deficits are also present in a mouse model of schizophrenia, whose behavioural changes have shown schizophrenia-like endophenotypes. Methods: Electroencephalogram in frontal cortex and local field potential in primary auditory cortex were recorded in phospholipase C β1 (PLC-β1) null mice during auditory binaural click trains at different rates (20–50?Hz), and compared with wild-type littermates. Results: In mutant mice, the ASSR power was reduced at all tested rates. The phase locking in frontal cortex was reduced in the β band (20?Hz) but not in the γ band, whereas the phase locking in auditory cortex was reduced in the γ band. The cortico-cortical connectivity between frontal and auditory cortex was significantly reduced in mutant mice. Conclusions: The tested mouse model of schizophrenia showed impaired electrophysiological responses to auditory steady state stimulation, suggesting that it could be useful for preclinical studies of schizophrenia”.     

Normal brain-stem auditory evoked potentials with abnormal latency-intensity studies in patients with acoustic neuromas

Brain-stem auditory evoked potentials (BAEPs) are highly sensitive for detecting acoustic neuromas but false-negative results occur. We studied BAEPs preoperatively in 39 cases of acoustic neuroma. Absolute and interpeak latencies ipsilateral to the tumor, and interaural latency differences, were normal in four patients with small tumors. In three of these, however, results of latency-intensity studies were abnormal. In one patient, the latency-intensity result became normal postoperatively. If acoustic neuroma is suspected, and BAEPs are normal by usual criteria, latency-intensity functions should be examined to maximize chances of detecting a small tumor.     

Paraspinal motor evoked potentials by magnetic stimulation of the motor cortex

The authors studied five patients with MS and four patients with HTLV-1 associated myelopathy (HAM) to investigate the usefulness of paraspinal motor evoked potentials (MEP) after magnetic stimulation of the motor cortex. In patients with MS, MEP disappeared or onset latencies were delayed below the lesion. In patients with HAM, the onset latencies were prolonged bilaterally. Thus, paraspinal MEP are very useful in detecting spinal cord lesions.     

Middle latency auditory evoked potentials (MLAEPs) in (MS)

Middle latency auditory evoked potentials (MLAEPs) were studied in 30 definite multiple sclerosis (MS) patients in addition to brain-stem auditory evoked potentials (BAEPs). BAEP abnormalities were detected in 18 (60%) patients. MLAEPs were abnormal in 22 (73%) of them. In 15 patients BAEPs and MLAEPs were both abnormal. MLAEPs were found abnormal in 7 of the 12 patients with normal BAEPs. In 18 patients with abnormal BAEPs only 3 had normal MLAEPs. MLAEPs abnormalities are consistent with a rostral auditory pathway involvement. Therefore, they can be used in combination with BAEPs to examine the whole auditory system to improve the sensitivity.     

Polysensory evoked potentials in rat parietotemporal cortex: combined auditory and somatosensory responses

A 64 channel microelectrode array was used to map auditory evoked potentials (AEP), somatosensory evoked potentials (SEP) as well as combined auditory and somatosensory evoked potentials (ASEP) from a 7 × mm² area in rat parietotemporal neocortex. Cytochrome oxidase (CO) stained sections of layer IV were obtained in the same animals to provide anatomical information underlying epicortical field potentials. Epicortical responses evoked by click or vibrissa stimuli replicated earlier findings from our laboratory, and appeared as a family of waveforms centered on primary auditory (AI) or somatosensory (SI) cortical areas as determined from CO histology. Selective microinjections of HRP to AI and SI further confirmed their specific sensory relay nuclei in the thalamus. A small polysensory area between AI and SI, responded uniquely with an enhanced negative sharp wave to combined auditory and somatosensory stimuli. HRP retrograde labeling revealed that the thalamocortical projections to this area were from the posterior nuclear group (Po) and medial division of the medial geniculate (MGm). These data establish close relationships between epicortical AEP, SEP, and especially ASEP and corresponding cortical structures and thalamocortical projections. The neurogenesis of unimodal and polysensory evoked potentials is discussed in terms of specific and non-specific systems.     

The effects of subcortical lesions on evoked potentials and spontaneous high frequency (gamma-band) oscillating potentials in rat auditory cortex

Functional subdivisions of auditory cortex in the rat were identified based on the distribution of temporal components of the mid-latency auditory evoked potential (MAEP) recorded with a multichannel epipial electrode array. Spontaneous data collected from the same location exhibited spindle-shaped bursts of oscillations in the gamma-band (20–40 Hz) whose location and spatial distribution were similar to that of the MAEP complex in that the bursts were localized to primary and secondary auditory cortex, the principle targets of thalamocortical projections. This suggested that the neural generators of these electrophysiological events may be similar. However, ablation of the medial geniculate nucleus (MG) of the thalamus revealed that while this nucleus is required for the generation of MAEPs, it is not required for the generation of spontaneous gamma-band oscillations. Ablation of subcortical cholinergic nuclei revealed that cholinergic input via the thalamus or the basal forebrain is not necessary for the generation of either MAEPs or spontaneous gamma-band oscillations recorded in this study. These results indicated that there may be networks of cells in sensory cortical areas endowed with an intrinsic capacity to oscillate independently of sensory or cholinergic input, but that may be modulated by this input.     

Decrement of somatosensory evoked potentials during repetitive stimulation

In normal subjects, cerebral potentials were evoked by brief, passive extension of the wrist joint at various interstimulus intervals (ISIs). The resulting somatosensory evoked potentials (SEPs) were found to decrease during repetitive stimulation. The greatest decrement occurred between the first and second responses of each series. After cessation of stimuli, the SEP amplitude returned to control values over a prolonged, exponential time course. The authors postulate that the observed response decrement may be a form of habituation, which provides a model for studying the neuronal substrates of behavior.