Kimitaka Kaga

Evidence for a primary cortical origin of a middle latency auditory evoked potential in cats

The origin of the scalp-recorded auditory evoked potential, Pa, was examined in cats anesthetized with chloralose-urethane and immobilized with gallamine triethiodide. This potential is a prominent positive wave which peaks approximately 12--15 msec following click stimuli. Mapping revealed that Pa is distributed on the scalp in the region overlying cortical area AI, contralateral to the stimulated ear. The cortical potential recorded from AI was a surface-positive wave, restricted to the anterior portion of AI. Laminar analysis of the cortical evoked potentials demonstrated the existence of a dipole generator at that area. The onset of this potential coincided with the onset of the scalp-recorded Pa. Comparison of the scalp and the cortex-recorded potentials showed that both the amplitude-intensity function and the amplitude-rate function for the scalp-recorded potential closely paralleled those recorded from AI. Acute and chronic lesion studies showed that extirpation of AI (particularly the anterior part) almost completely abolished the Pa response. This evidence indicates that the scalp-recorded Pa of cats is generated almost entirely from the anterior part of the contralateral AI.

‘Cat P300’ disappears after septal lesions ☆

Endogenous responses were recorded from 9 awake cats with loud and soft clicks randomly presented as rare (P = 0.15) or frequent (P = 0.80) stimuli; a reinforced tone CS (P = 0.05) resulted in a conditioned eye blink response and focused the cats attention on the auditory stimuli. Subsequent to 12 preoperative recording sessions the medial septal area was lesioned in 7 cats and similar but more rostral lesions were placed in 2 cats. Thereafter, 12 postoperative recording sessions were carried out, the animals were terminated, and the brains processed for AChE histochemistry and histology of the lesioned areas. Destruction of the medial septum and vertical limb of the diagonal band of Broca resulted in a transient postoperative cat P300 followed by reduction and disappearance of the response. The hippocampus of these animals was characterized by marked AChE depletion. In contrast, the animals with lesions rostral to the medial septal area showed no postoperative change in the P300 response and no depletion of hippocampal AChE. These data indicate an important role for the medial septal area as a modulator of cat P300 generation possibly through the cholinergic component of the septohippocampal projection system.

Pure word deafness due to left hemisphere damage

We report the case of a 55 year-old right-handed man who presented with a long lasting pure word deafness following left thalamic bleeding. There was no sign of aphasia. The auditory deficit was specific for language, while recognition of music and environmental sounds was normal. CT, MRI and PET examinations showed that the lesion was anatomically and functionally confined to the left cerebral hemisphere, mainly the white matter of the temporal and parietal lobes. Wernickes area was largely preserved. It is proposed that pure word deafness was consequent to the isolation of Wernickes area from incoming auditory information due to the interruption both of the association fibers from the right auditory area traveling across the corpus callosum and of the left auditory radiations.

INFLUENCE OF LABYRINTHINE HYPOACTIVITY ON GROSS MOTOR DEVELOPMENT OF INFANTS

In adults, bilateral dysfunction of the vestibular labyrinths may be manifested by unsteadiness, but loss of postural control is rare so long as visual cues are available. In infants and children with hypoactive labyrinths, however, loss of postural control is much more cummon and development of gross motor function is delayed.2 These children do catch up with normals because proprioceptive, visual, and motor systems compensate for the deficit, but the length of the delay in acquiring normal gross motor skills is a controversial issue. Many authors have pointed out that vestibular impairment most likely is to be found in children with severe or profound hearing loss since the vestibular end organ and cochlea are closely related in their anatomy and ontogeny and may he affected by the same developmental or noxious factor^..^.^ Those deaf infants and children who do have an accompanying vestibular dysfunction are reported to he delayed in acquisition of head control, sitting, and walking.. These reports, however, have lacked data about the vestibular responses of normal control groups of the same age range. Although the vestibular end organ apparently is fully mature at birth, myelination within the central nervous system continues for some time, so that the vestibular reflexes of infants may not be comparable to those of adults. For this reason, it is particularly important in the evaluation of young deaf patients that their vestibular function is judged with reference to that of their age-mates. Several kinds of rotation tests, such as Baranys method, the subthreshold rotation test, and the torsion swing test, have been used to elicit vestibular responses in infants and children, perrotatory and postrotatory nystagmus being measured as an index of maturation of the vestibular system. l4 The primary result of these studies has been that the duration of nystagmus and the number of beats increase with increasing age. These rotation tests stimulate both labyrinths, hut Eviatar employed caloric stimulation of each labyrinth separately and found that vestibular responses matured over time, with patterns that correlate with gestational age and weight at birth. The present investigation had as its primary objective the longitudinal study of patients with congenital hearing impairment and delayed acquisition of gross motor function. To accomplish this, we first obtained quantitive data on the development of these skills in normal infants ,and children, along with measures of the maturation of their vestibular responses to the damped-rotation test. We then compared these data with those of congenitally deaf children, relating degree of Vestibular impairment to delay in reaching milcstones of gross motor development.

The effect of the click repetition rate on the latency of the auditory evoked brain stem response and its clinical use for a neurological diagnosis

SummaryThe effects of click repetition rate on the latency of the auditory brain stem responses (BSR) and its possible use as a clinical diagnostic tool of the brain stem disorders were investigated. When the click rate was increased, the latency of the BSR waves was prolonged. The latency of the later response components increased more than that of the earlier response components. This method was applied to the clinical cases with brain stem disorders. A case with a IVth ventricle epidermoid tumor showed a marked latency prolongation and disappearance of the waves at higher repetition rates. An explanation of the latency shift in the normal subjects and the abnormal responses of the patient to repetition rate is attempted.

Auditory brain stem responses of kernicterus infants.

Auditory brainstem evoked responses (ABRs) and behavioral audiometry in 25 infants with kernicterus were studied to determine the level of the lesion causing their hearing disorders. ABR thresholds, peak latencies of wave I and V, and interwave latency of wave V-I were measured; behavioral audiometric thresholds were determined through conditioned orientation reflex audiometry (COR). Eighty-eight per cent of infants with kernicterus who showed ABR threshold elevation with respect to age-matched normals, were found to show ABR abnormalities associated with peripheral hearing loss, and 84% of these were found to have COR threshold elevation. The ABR abnormalities were threshold elevation of wave V, prolonged latency of wave I and V, and the absence of ABRs. However, no brainstem lesion pattern was found in our cases. Our results suggested that at least some lesions which produce hearing disorders in kernicterus occur in the cochlea or auditory nerve.

Effects of deep hypothermia and circulatory arrest on the auditory brain stem responses.

ZusammenfassungDie Latenz der akustischen Hirnstammpotentiale verlängert sich mit Absinken der Körpertemperatur. Dabei ist die Latenz der späteren Komponenten mehr verlängert als die der früheren. Alle Potentiale verschwinden ab einer Körpertemperatur unter 25° C sowie bei artifizieller Unterbrechung der Blutzirkulation. Steigt die Körpertemperatur an, so werden die Latenzen erst bei Erreichen von 34° C wieder normal. Die akustischen Hirnstammpotentiale scheinen so Auskunft über die Funktion des Hirnstammes während schwerer Hypothermie zu geben.SummaryThe effects of hypothermia on auditory brain stem response (ABR) in both children with congenital heart disease undergoing cardiac surgery and cats as an animal model were investigated. The latency of the ABR waves were prolonged with decreased body temperature. The latency of the later response components were prolonged more than that of the earlier response components; all waves disappeared below 25° C and during artificial cardiac arrest. When the body temperature was raised, the later component began to reappear above 25° C; the latency of all components shortened with temperature until normal responses were obtained at 34° C. The data from both humans and cats were comparable. The ABR seems to be a useful monitor for evaluating brain stem function during deep hypothermia.

Delayed motor function and results of vestibular function tests in children with inner ear anomalies

The relation between the results of vestibular function tests and gross motor development was examined in 4 children with inner ear anomalies. CT scans demonstrated the absence of lateral semicircular canals in both ears in all 4 cases. None responded to caloric stimulation using 40 ml of icewater. In contrast, the damped rotation test elicited per-rotatory nystagmus in all cases. Per-rotatory nystagmus was provoked in only two cases by the Bárány rotation test. Development of gross motor function, especially independent walking, was more delayed in the two children in whom the Bárány rotation test failed to elicit per-rotatory nystagmus.

P300 response to tones and speech sounds after cochlear implant: A case report

P300 potentials evoked by tones and spoken words were recorded from a 20‐year‐old man with a House‐3M® single‐channel cochlear implant. Three months after cochlear implantation, there was a slight appearance of P300 response to both pure‐tone stimuli and spoken‐word stimuli; 6 months later, clearly identifiable P300 response to both pure‐tone stimuli and spoken‐word stimuli were obtained. These results are consistent with an encoding improvement for re‐establishment of information processing after auditory rehabilitation.

The progress of adrenoleukodystrophy as revealed by auditory brainstem evoked responses and brainstem histology

ZusammenfassungEin sechs Jahre altes Kind erkrankte im 5. Lebensjahr an Adrenoleucodystrophie (progressive metabolische Erkrankung des ZNS mit rapider Degeneration). Die Krankheit begann mit Dysarthrie, Schwerhörigkeit und Gangunsicherheit. Später kam es zur spastischen Paralyse, zu hochgradiger Schwerhörigkeit und Erblindung. Tod durch Atemlähmung.Während des Verlaufs wurden regelmäßig die Hirnstammpotentiale sowie die langsamen Rindenpotentiale abgeleitet. Dabei war mit fortschreitender Erkrankung eine deutliche Verminderung der Potentiale zu beobachten. Histologisch zeigten sich eine Entmyelinisierung des Hörnervs sowie Neuronenverluste im Verlauf der Hörbahn. Die Degeneration im Hirnstamm verlief dabei von rostral nach kaudal.SummarySerial studies of auditory brainstem evoked responses (ABR) and slow vertex responses (SVR) were obtained during the progress of adrenoleukodystrophy in a 6-year-old boy. This child was normal until 5 years of age. His illness began with a gait disturbance, dysarthria, and hearing difficulty. Later, spastic paralysis, serious deafness, and blindness appeared. He died of respiratory failure 2 years after the onset.The ABR was normal at onset but changed to an abnormal pattern. Initially, there was lengthening of the wave V-I interpeak interval. This was followed by the disappearance of the later components as his general condition deteriorated. At the terminal stage, only a prolonged wave I was recordable. The postmortem pathology revealed demyelination of auditory nerves and remarkable neuronal loss in the auditory pathways of the brainstem; in addition, there was a variety of extensive degeneration throughout the cerebrum, in particular the complete degeneration of the white matter with secondarily occurring ganglionic cell changes. These data suggest that degeneration of the brainstem from rostral to caudal levels occurred.