[Processing of optic and acoustic sensory perception in the brain. 2].
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Animals↗
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Localization of brainstem auditory evoked potentials in primates: a comparison of localization techniques applied to deep brain sources.
The objective of this study was to evaluate the performance of source localization techniques through localization of deep brain sources. To accomplish this, two replications of a brainstem auditory evoked potential (BAEP, left ear 60 dB nHL clicks) were recorded from five normal rhesus monkeys. We analyzed waves III and IV, as this portion of the BAEP corresponds to the deepest signal. Data were analyzed using five different source localization techniques: Moving Dipoles, Fixed Dipoles, MUSIC (Multiple Signal Classification) dipole scan, LORETA (Low Resolution Tomography), and LCMV (Linearly Constrained Minimum Variance) spatial filtering. The moving dipole, fixed dipole and MUSIC solutions were found to be, on average, 25.1 mm from the brainstem generators. LORETA detected sources within the brainstem 65% of the time. However, 90% of these localization results also included false detections defined as regions of the brain that were more than 2 cm away from the auditory pathway. LCMV included the brainstem in 90% of the trials and false detections in 40% of the cases. These findings indicate that evoked electrical activity from deep brain sources can be localized with cm accuracy. The dipole methods performed better than LORETA and LCMV. Given the depth and amplitude of the sources analyzed in this study, these results can be interpreted as an upper bound on the accuracy of each technique.
Acoustic Stimulation↗
Development of brainstem auditory evoked potentials in heterozygous and homozygous jaundiced Gunn rats.
Bilirubin toxicity is a significant clinical problem causing neurologic and audiologic sequelae. To better understand the pathogenesis of bilirubin toxicity in the immature nervous system we studied the development of brainstem auditory evoked potentials (BAEPs) in jaundiced (jj) Gunn rats and their non-jaundiced (Jj) littermates. Littermate pairs of Jj and jj rats were studied serially from early infancy to adulthood. Replicated BAEPs to click stimuli at two different intensities (45 and 75 dB SPL) and rates (33 and 89/s) were obtained from animals anesthetized with ketamine and acepromazine and maintained at a constant rectal temperature. Jaundiced (jj) rats had increased latencies of waves II and III and the I-II and I-III intervals, and decreased amplitudes of waves II and III from 17 days of age through adulthood. For both groups, all latencies and interwave intervals decreased with age (P less than 0.0001 for each wave and interwave interval by repeated measures ANOVA), and the amplitude of II increased with age (P less than 0.0001). No group differences were found in wave I latency or amplitude, or in the latency change of waves I, II or III as a function of intensity (about 11 microseconds/dB at all ages), suggesting that peripheral auditory function is normal in jj rats. Finally, there were no different effects of stimulation rate on BAEP wave latencies between groups. The findings suggest dysfunction of the central (brainstem) auditory pathways at and rostral to the cochlear nuclei, and are consistent with studies showing destruction of the cochlear nuclei in this animal model and in humans with bilirubin toxicity. The central abnormalities previously found in adult, jaundiced rats are now demonstrated in animals as early as 17 days of age, when serum bilirubin concentration is maximum. The BAEP findings are similar to changes found in hyperbilirubinemic human neonates, and support the use of the Gunn rat animal model for the study of bilirubin encephalopathy.
Acoustic Stimulation↗
Effect of residual hearing prior to cochlear implantation on speech perception in children.
We examined the impact of residual hearing prior to cochlear implantation on pre- and postimplantation speech perception outcomes in children. Stimulation of the auditory system prior to implantation because of the presence of residual hearing is important for development of the central auditory pathways, whereas, in the absence of such stimulation, the pathways show less development. We hypothesized that children who had some degree of residual hearing preimplantation achieve better speech perception skills than their peers with poorer hearing. From the 133 children followed in our program, we identified 37 children who had an audiometric pure-tone average of better than 95 dB HL in the better ear at any time preimplantation. Psychophysical speech perception measures, the Word Identification Picture Inventory and the Phonetically Balanced Kindergarten list, in these children were compared with those of 96 implanted children who had poorer hearing prior to implantation. Children with more residual hearing showed higher speech perception scores both before implantation and over their first year of implant use than children with poorer hearing, suggesting that there is an advantage in having a greater degree of residual hearing preimplantation. We suggest that this advantage is promoted, in part, by the greater potential for auditory stimulation provided by high-gain hearing aids in children with greater degrees of residual hearing. This advantage appears to be maintained at least over 1 year postimplantation, yet the rates of development of postimplantation speech perception are not different between the groups. We suggest that this may be due to the unique aspects of electrical stimulation from a cochlear implant. Our findings suggest that it is important to minimize the delay of speech perception skills in the preimplantation phase, particularly in children with poor residual hearing. This can be accomplished by implanting children with congenital severe to profound hearing loss at young ages and children with acquired hearing loss soon after the onset. Also, auditory stimulation prior to implantation should be maximized through the consistent use of hearing aids and therapy that emphasizes development of auditory skills.
Child↗
Auditory orienting and detection in rats following lesions of the superior colliculus.
Rats were trained to run towards a lighted target following either bilateral lesions of the superior colliculus (SC) or control lesions of the overlying cortex. At 4 months post-surgery, the animals were tested for the disruptive effects of an auditory tone. An increase in running times was found in both groups, attributable to frequent freezing reactions in all animals. However, only the control rats made orienting reactions to the tones. It is argued that the freezing responses show that the SC lesions did not impair sensory detection; consequently, the orienting failure cannot be attributed to a sensory deficit.
Animals↗
The neural circuitry underlying the executive control of auditory spatial attention.
Although a fronto-parietal network has consistently been implicated in the control of visual spatial attention, the network that guides spatial attention in the auditory domain is not yet clearly understood. To investigate this issue, we measured brain activity using functional magnetic resonance imaging while participants performed a cued auditory spatial attention task. We found that cued orienting of auditory spatial attention activated a medial-superior distributed fronto-parietal network. In addition, we found cue-triggered increases of activity in the auditory sensory cortex prior to the occurrence of an auditory target, suggesting that auditory attentional control operates in part by biasing processing in sensory cortex in favor of expected target stimuli. Finally, an exploratory cross-study comparison further indicated several common frontal and parietal regions as being involved in the control of both visual and auditory spatial attention. Thus, the present findings not only reveal the network of brain areas underlying endogenous spatial orienting in the auditory modality, but also suggest that the control of spatial attention in different sensory modalities is enabled in part by some common, supramodal neural mechanisms.
Acoustic Stimulation↗
Auditory enhancement of visual temporal order judgment.
Although numerous studies have shown that response times can be speeded by the presentation of multisensory stimuli, here we show that such speeding can be seen even when the second sensory channel fails to provide any task-relevant (i.e. redundant) information, and where cueing appears an unlikely explanation. Study participants performed a visual temporal order judgment task in the presence of task uninformative auditory cues, with the latter sound delayed relative to the latter visual cue. Responses were maximally speeded when the auditory stimulus was delayed by a short time (i.e. 100 ms) relative to the second visual target. These results illustrate a unique form of temporal benefit underlying a multisensory interaction, and form the basis for a novel explanation of these perceptual enhancements.
Acoustic Stimulation↗
Gated visual input to the central auditory system.
The central auditory system translates sound localization cues into a map of space guided, in part, by visual experience. In barn owls, this process takes place in the external nucleus of the inferior colliculus (ICX). However, to date, no trace of visual activity has been observed in this auditory nucleus. Here we show that strong visual responses, which are appropriate to guide auditory plasticity, appear in the ICX when inhibition is blocked in the optic tectum. Thus, visual spatial information is gated into the auditory system by an inhibitory mechanism that operates at a higher level in the brain.
Acoustic Stimulation↗
Auditory cortex disconnection associated with thalamic tumor. A case report.
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Audiometry↗
[Follow-up studies of patients with neonatal icterus using acoustic evoked potential audiometry].
Neonatal hyperbilirubinaemia is a common cause of sensorineural hearing loss. There is no exact method to detect the neurotoxicity of bilirubin. On the other hand the auditory pathway is known to be one of the most sensitive part of the CNS to this toxic agent. 39 one-year-old children were examined by BERA, who had had hyperbilirubinaemia in the newborn period. According to the risk factors the patients were divided into two groups but there was no significant difference in BERA changes. Two infants were found suffering serious hearing loss, who required hearing aids. Five more had some subclinical BERA changes. The authors emphasize the value of acoustic evoked potentials in evaluation infants after neonatal jaundice.
Audiometry↗
Detection of brainstem lesions in multiple sclerosis: comparison of brainstem auditory evoked potentials with nuclear magnetic resonance imaging.
Topographical information provided by brainstem auditory evoked potentials (BAEPs) was investigated in 43 patients by comparison with cerebral nuclear magnetic resonance imaging (NMR). Lesions in the region of the brainstem auditory pathways were demonstrated by BAEPs in 44.2%, and in 39.5% by NMR. As regards brainstem levels, in 15/21 (71.4%) with abnormal findings at least one lesion was verified by NMR-matched BAEP results. The study confirms the topographical information provided by the BAEPs on the different levels of the brainstem, but not the assumption that generation of the BAEPs is predominantly ipsilateral. BAEPs retain their importance for the detection of disseminated lesions in the diagnosis of multiple sclerosis (MS) in the era of expensive imaging methods.
Adolescent↗
Development of chondroitin sulfate proteoglycans in the central auditory system of rats correlates with acquisition of mature properties.
Chondroitin sulfate proteoglycans (CSPGs) are macromolecules which regulate the structural organization of the extracellular matrix and can mediate cell migration and axonal growth. Here the spatiotemporal distribution of CSPGs in the central auditory system of rats was investigated using a polyclonal antiserum. In adult brains, CSPGs surrounded many neuronal cell bodies and proximal dendrites at all stations of the auditory pathway except the medial geniculate body. During development, CSPG expression became visible at postnatal day (P) 4 in the superior olivary complex, at P8 in the midbrain, and at P18 in the cortex. Immunoreactivity increased strongly until P12 in the brainstem and until P24 in the cortex. The adult-like pattern in the pontine nuclei, the midbrain, and the cortex was seen at P12, P29, and P35, respectively. The relatively late expression of strong immunoreactivity indicates that the CSPGs are involved in the maturation of axonal connections, but not in early processes such as cell migration or neurite outgrowth.
Animals↗
Comparison of auditory brainstem responses and pneumograms in intensive care nursery infants.
Central slowing of auditory brainstem responses (ABRs) and excessive breathing irregularity on pneumogram recordings indicate dysfunction in central auditory pathways and brainstem respiratory control mechanisms, respectively. These centers are anatomically proximate within the brainstem so that ABR slowing and respiratory instability might be expected to occur concomitantly, reflecting overall dysfunction of this part of the central nervous system. To examine the relationship between these two assessments, testing results were compared for 15 infants in the intensive care nursery who had ABRs and 12-hour pneumograms performed at about the same age for separate clinical indications. Wave V latency at 70 dB was found to correlate significantly with three pneumogram measurements of breathing irregularity: the density of short apneas during sleep (p less than 0.01), the number of episodes of periodic breathing per 100 minutes of sleep (p less than 0.05), and the percentage of sleep time spent in periodic breathing (p less than 0.05). Interwave interval I-V correlated significantly with the density of short apneas during sleep (p less than 0.01). The auditory brainstem response and the pneumogram appeared to serve as related indicators of brainstem function in these infants.
Brain Stem↗
The fiber connections of the temporal lobe with emphasis on the rhesus monkey.
The temporal lobe has three functionally distinct areas which have minimal interconnections within the lobe, but extensive connections with other parts of the brain. The superior temporal gyrus contains primary and association auditory areas. Inferotemporal cortex is exclusively a visual association area. The temporal pole is involved in social behavior. In addition, the superior temporal sulcus functions as a sensory integration area. From a review of the literature, a schema is proposed for organizing the reciprocal connections of the three functional areas into a series of loops which follow both cortical and subcortical routes. The afferent and efferent connections of the temporal lobe, phylogenesis, and deficits from lesions are discussed.
Amygdala↗
Preoperative radiologic evaluation in cochlear implantation.
AIM OF STUDY: Assess the value of computed tomography (CT) in the evaluation of abnormalities in the cochlea and auditory pathways. MATERIAL AND METHODS: We used CT to evaluate 108 children before cochlear implantation surgery. Children's ages at implantation ranged from 21 months to 16 years (mean age, 5.4 years). The etiology of deafness was meningitis in 44 children (40.8%), congenital in 51 (47.2%), and other in 13 children (12%). RESULTS: Eighteen of the 108 (16.6%) children and 34% of the postmeningitic children were found to have at least partial obliteration of the cochlea. Two (2%) children had congenital malformations of the cochlea and 12 children (11.1%) had abnormalities in the brain CT-scan. CT diagnostic values in postmeningitic children regarding cochlear obliteration were accuracy, 75%; sensitivity, 62%; specificity, 82%; positive predictive value, 66.6%; and negative predictive value, 79.3%. In six (20.6%) of postmeningitic children with normal CT-scans, some scala tympani drillout was required. CONCLUSION: CT-scan is capable neither of predicting with certainty the presence of minor degrees of cochlear obliteration nor of specifically imaging either the auditory nerve or its central connections.
Adolescent↗
Auditory symptoms: a critical clue for diagnosis of MELAS.
Mitochondrial encephalopathy, lactic acidosis with stroke-like episodes (MELAS) is a rare mitochondrial disorder that affects adults. MELAS syndrome can mimic cerebrovascular disease, encephalitis or toxic-metabolic encephalopathy. The authors reported two patients who presented with auditory symptoms before the onset of encephalopathy and stroke-like episodes. The first patient was a 28 year-old man, who presented with acute sensorineural hearing loss (SNHL) followed by headache, left hemiparesis and generalized tonic-clonic seizure. CT scan of the brain showed hypodensity lesion at the tip of right temporooccipital region. Audiogram and brainstem auditory evoked potential (BAEP) showed abnormal conduction of left brainstem auditory pathway. MRI of the brain showed a lesion involving gray and white matters of the right occipital, parietal and temporal lobes. The distribution of the lesions was not compatible with distribution of arterial supply. MRA was normal. The second patient was a 56 year-old woman with a one-year history of hearing loss. The audiogram revealed bilateral SNHL. A few days before admission, her hearing was acutely deteriorated She could not understand a conversation while she could communicate by writing. CT scan of the brain showed hypodensity in both temporal lobes and MRI revealed lesions in the same area. Pure tone audiogram showed moderate SNHL but BAEP was normal. One week later, she developed global dysphasia and generalized tonic-clonic seizure. Both patients had elevated cerebrospinal fluid and serum lactate: pyruvate ratio. Polymerase chain reaction-restriction fragment length polymorphism disclosed A3243G mtDNA mutation in the blood in the first patient and in muscle biopsy in the second patient. Ubiquinone supplement was prescribed The auditory symptoms in combination with stroke-like episode in supratentorium are important clues to diagnose MELAS syndrome.
Adult↗
Brain activity patterns in flying, echolocating bats (Pteronotus parnellii): assessment by high resolution autoradiographic imaging with [3H]2-deoxyglucose.
Brain activity patterns during echolocation and flight were assessed in mustached bats (Pteronotus parnellii parnellii). Bats were injected intraperitoneally with [3H]2-deoxyglucose and restrained in a foam holder or allowed to fly for 20 min. Under resting conditions, low levels of [3H]2-deoxyglucose uptake were observed throughout the forebrain but relatively high uptake was found in brainstem auditory and vestibular centers. In flying, echolocating bats, marked increases in regional [3H]2-deoxyglucose uptake were apparent. All structures of the classical ascending auditory pathway were intensely labeled in autoradiograms. Other brain regions that exhibited high [3H]2-deoxyglucose uptake in flying bats included the cingulate cortex, stratum lacunosum-moleculare of the hippocampus, thalamus, caudate-putamen, superior colliculus, pontine reticular formation, nucleus ambiguus, parts of the midbrain central gray, and cerebellum. In the cerebellum, the most prominent increase in [3H]2-deoxyglucose uptake was found in discrete patches of the granule cell layer. The results provide the first overview of brain activity patterns during echolocation and flight in bats. In addition, uptake of [14C]fluorodeoxyglucose was used to compare brain activity patterns in flying bats to bats that were imaging their environment via biosonar while hanging in a wire cage. The echolocating-not-flying bats emitted 6931 +/- 1226 pulses in 20 min compared to 8972 +/- 1273 pulses in 20 min for flying bats. The uptake of the metabolic marker was significantly more in the flying bats compared to the emitting-not-flying bats in the medial geniculate, superior colliculus, auditory cortex, cingulate cortex and thalamus. In the nucleus ambiguus, cochlear nucleus, and inferior colliculus, uptake was similar for the flying and emitting-not-flying bats. These results suggest that the high metabolic activity observed in forebrain auditory regions of flying bats is related in part to neural processes that involve sensory motor integration during flight and not simply the perception of acoustic information.
Animals↗
Healthy-side dominance of cortical neuromagnetic responses in sudden hearing loss.
Previous brain imaging and mapping studies have reported findings indicating functional reorganization in the central auditory pathways of patients with profound unilateral hearing loss. This study reports for the first time to our knowledge, using a whole-head neuromagnetometer with monaural stimulation of both intact and affected ears, a pattern of healthy-side dominance for cortical neuromagnetic responses in adult patients in the early stage of idiopathic sudden sensorineural hearing loss, and a pattern of contralateral dominance is verified in controls.
Adult↗