[Is the afferent auditory message modulated by the cortex?]. / Le message afférent auditif est-il modulé par le cortex?

An eventual modulation of the afferent auditory message by the cortex is the subject of this study. To test this hypothesis, clicks (10 Hz, 100 microseconds) of white noise of 40 and 70 dB Hl were sent alternatively into the ears of normally hearing volunteers, while the brainstem evoked potentials were recorded. The subjects were asked to focus or relax their attention on one or other ear. Thirty subjects aged less than 25 years (15 men and 15 women) with normal hearing level, were split into two groups. The first group was asked to focus first on the more strongly stimulated ear (70 dB), the second group on the more weakly stimulated one (40 dB). Each subject received (1) without any instruction about attention: 40 dB on the left ear (L), 70 dB on the right ear (R); 40 dB then 70 dB bilateral; (2) 2 runs with 40 dB on the L and 70 dB on the R focussing on the most or less strongly stimulated ear; (3) a run without instruction with 70 dB on the L and 40 dB on the R, and (4) two runs with 70 dB on the L and 40 dB on the R focussing enough on the more or less strongly stimulated ear. On the evoked potentials simultaneously recorded, amplitudes and latencies of the pikes were measured and compared. From these experiments, the following elements were obtained. (1) The measured potentials were always caused by ipsilateral stimuli. (2) Focussing on left or right ear was not equivalent. (3) A gender difference appeared in the brainstem auditory responses. (4) Preferential attention paid to the left ear was more efficient than to the right one. (5) Attention can alter the whole nervous pathway with considerable lengthening of O-I, O-III, O-V, III-V, I-V but not I-III latencies. The III wave amplitude generally decreased on the side where attention was focussed while V waves seemed not to vary. These first results indicate that a cortico-efferent pathway stimulated by the attention plays a role in the auditory responses modifying the afferent message. These effects were not the same among the side focussing attention and among sex.

[Lateral efferent system and evoked auditory potentials. Response in tinnitus]. / Système efférent latéral et potentiels évoqués auditifs. Réponse des porteurs d'acouphènes.

The effects of ipsi- or contralateral masking have been studied in 45 normal hearing subjects and in 49 tinnitus patients. With normal subjects, ipsilateral masking during auditory stimulation involves--in opposition to contralateral masking which does not alter any latencies--a significant lengthening of all the latencies in the brainstem, except that of the first wave (right and left), and a significant decreasing of the amplitudes of the waves I L and R. It was important to know whether the lengthening of the latencies in the brainstem--which we suppose to be due to the stimulation of the lateral efferent system--was not in fact due to a preferential stimulation of the auditory cells from the basis of the cochlea. Yet experiments have shown that continuous masking of 40 dB at 750 Hz or 4000 Hz added to stimulation, involved no significant modification of the latencies in normal subjects. Therefore the lengthening of the latencies obtained with white noise masking, belonged to an other sphere. The second problem concerned the responses of tinnitus patients. Ipsilateral masking in white noises does not alter any latencies in the patients' brainstem. They seem to have lost the possibility of reacting to any additional noise coming from the outside. As we have already noticed, their latencies before masking were different from those of normal subjects. With masking the patients, latencies remained unchanged whereas the latencies of normal subjects lengthened and caught up the patients. To conclude, we suppose the lateral efferent system can be explored by the adjunction of white noise masking, ipsilateral to the stimulation. The expected response is a lengthening of interpeak I-V latency, without any modification of the latency of the first wave. Tinnitus patients generally do not have that type of response to white noise masking. Their lateral efferent system may not be operating.

[Can the efferent auditory system be explored via early evoked potentials? Preliminary results in normal hearing subjects and people with tinnitus]. / Le système efférent auditif peut-il être exploré par les potentiels évoqués précoces? Premiers resultats chez le normal et les porteurs d'acouphènes.

The use of masking in brainstem auditory evoked potential technic remains one of the important issue regarding the evaluation of different auditory control systems. Brainstem auditory evoked response wave form latencies and amplitudes have been studied on 14 normal hearing subjects. On one hand the contralateral masking which theoretically stimulates the medial contralateral efferent bundle did not modify the responses. On the other hand, the ipsilateral masking stimulating the lateral bundle reduced the amplitude of wave I and lengthened the latency of interwave I to V. The same protocol has been applied to 21 tinnitus patients. In these subjects before masking, the waves amplitude was lower and inter wave I-V latency was lengthened. The ipsilateral did not modify the responses as in the normal population. Comparing brainstem responses obtained in masking and no masking condition offers the possibility of evaluating the lateral efferent system function but we can conclude that the contralateral masking is of no use studying the medial system and that dysfunctions of the lateral efferent system could be one mechanism responsible for tinnitus.

[Modification of precocious evoked auditory potential amplitudes observed in tinnitus]. / Modifications des amplitudes des potentiels évoques auditifs précoces observées dans les acouphènes.

Brainstem evoked response audiometry has been performed in 139 patients complaining of tinnitus, unilateral or bilateral. Amplitudes of I, III, V waves and the amplitude relations I/III, I/V, III/V have been compared with those obtained in a normal population (n = 20). Amplitudes of waves I and III decreased according to their localization: decrease of left I and III for left tinnitus, decrease of left I and right III for right tinnitus, and for I and III both left and right for bilateral tinnitus. Recording of brainstem evoked response before any therapeutical treatment, especially study of amplitudes, could therefore provide information an localization of tinnitus.

[Auditory evoked potentials in distinguishing between peripheral and central tinnitus]. / Potentiels évoqués auditifs dans la distinction entre acouphènes périphériques et centraux.

Brainstem evoked response audiometry has been performed in 164 patients complaining of tinnitus, unilateral or bilateral. The latency of every wave and the latency between the peak of every wave have been compared with those obtained in a normal population (n = 57). The latency of the first wave is increased significantly at the same side of the tinnitus. But I-V latency is shorter at the side of the tinnitus. When this increase is absent, the I-V latency is prolonged the side of the tinnitus. It is possible to differentiate between tinnitus of peripheral origin and that of central origin, although the existence of unilateral deafness is constant. The same results have been obtained in the deaf patients with bilateral symmetric deafness, in accordance with Maurizi et al., 1985.

[Effects of nicotine on precocious evoked auditory potentials of the rat in the presence or absence of endogenous serotonin]. / Effets de la nicotine sur les potentiels évoqués auditifs précoces du rat, en présence ou en l'absence de sérotonine endogène.

In the rat, nicotine bitartrate (100 micrograms/kg) by intraperitoneal route provokes modifications of the brain stem auditory evoked potentials. These changes are complex: a) decrease of the amplitude of waves IV and V, probably by fixation on nicotinic type receptors, neuronal serotonin stores being normal; b) increase of the amplitude of waves I, I' and II, more important when endogenous stores are depleted; c) increase in the latency of these waves when serotonin stores are normal.

[Study by auditory evoked potentials of the efficacy of transcutaneous electric stimulation in the treatment of tinnitus]. / Etude par les potentiels évoqués auditifs de l'efficacité de l'électrostimulation transcutanée dans le traitement des acouphènes.

Thirty patients complaining about tinnitus were treated by transcutaneous tragal electrical stimulation. The effect of this treatment has been evaluated by BASR recordings before and after treatment. Taking into account the subjective results three groups are described. The first one (10 patients) is relieved of tinnitus. In second and third group the symptoms still exist, whatever the electrode's position (anode or cathode in tragal position). When BASR are studied before the electrical stimulation no inter-subjects difference can be found. After stimulation, the left delta I-V latency is significatively lengthened, and the wave I latency is shortened in the first group. The study of the two other groups do not reveal any difference between the pre- and the post- stimulation evaluation. So the BASR appears to be a good predictive tool for tinnitus suppression by electrical stimulation.

[Gastroduodenal electric activity, in situ, during anesthesia and recovery. Study in chronic electrode-carrying rats]. / Etude de l'activité électrique gastroduodénale, in situ, au cours de l'anesthésie et du réveil. Etude chez le rat porteur d'électrodes chroniques.

The effect of anaesthesia (sodium pentobarbital, two various doses) was studied in the rat with chronic gastric and duodenal electrodes. Gastric and duodenal electrical activity was recorded in pre- and peranesthesia period. All rhythmic slow and fast components are slowed in the same condition of time when an important decrease of central temperature is observed (external controlled temperature 22 degrees C). Gastric slow wave (650 microV, frequency normal level 5.6 c/min) decreases about 40% in 180 min. The waking arise after 5h30, 1h30 before the complete recuperation of the previous rhythm. For half dose conditions, gastric slow wave frequency decreases about 30% in 30 min; waking up occurs in 90 min. Gastric emptying complex observed previously. Is only observed during 20-30 min of the initial period of the anaesthesia at 50 mg/kg, and throughout the anaesthesia at 25 mg/kg.

[Effect of nicotine on auditory functions in the rat, studied by electrocochleography and auditory evoked potentials of the brain stem]. / Effet de la nicotine sur les fonctions auditives du rat, exploré par électrocochléographie et potentiels évoqués auditifs du tronc cérébral. Travail préliminaire.

The rôle of nicotine (100 micrograms/kg) on brainstem auditory evoked responses (FFP) and electrocochleography (EcoG) in rats anaesthetized with pentobarbital has been studied. Each component of FFP and EcoG was analysed in terms of its latency and amplitude. Nicotine failed to produce any significant changes in the latencies of the FFP and EcoG components. Nicotine after 30 min increases significantly the amplitude I, I', II and III, of the FFP components, and decreases no significantly IV and V components. These finding suggests the presence of muscarinic and nicotinic effect of nicotine, in the mediation of the brainstem auditory pathway.

[Long-term gentamicin ototoxicity in the rat: research on retro-cochlear involvement by study of evoked auditory potentials of the brain stem]. / Ototoxicité à long terme de la gentamicine chez le rat: recherche d'une atteinte rétro-cochléaire par l'étude des potentiels évoqués auditifs du tronc cérébral.

Four groups of rats treated with single (50 mg/kg and 200 mg/kg) or multiple (3 X 200 mg/kg and 5 X 200 mg/kg) doses of gentamycin were studied over a 6-month period and compared with a control group. At 50 mg/kg no significant changes were observed. Significant signs of intoxication were observed at 200 mg/kg doses and at multiple doses. A significant lengthening of the latencies with changes in amplitude and a transitional increase in the auditory threshold were observed as early as the end of treatment. This was followed by a phase of amplitude decrease, a rise in auditory threshold and a decrease in latencies which remains unexplained.

[Relation between the electrical and mechanical activity of the stomach. In situ study of the anesthetized rat]. / Relations entre l'activité électrique et la motricité de l'estomac. Etude in situ chez le rat anesthésié.

The relations between the electrical and mechanical activity of the corpus and the antrum have been studied by means of several microelectrodes and enterographic transducer under binocular control (X 5) in anaesthetized rats (pentobarbital Na, 4 mg/kg). The recording period starts from 30 min after the onset of anaesthesia. This time corresponds to the release of the post operative inhibitions. Several rhythms of slow components have been in evidence thanks to a long time constant (5 sec): the dominant component with his frequency 4.04 +/- 1.06 c/min (n = 302 values). This frequency increases (5.11 +/- 1.3 c/min) during the antropyloric evacuation. Other rhythmic components of smaller amplitude (less than 200 microV) and frequency ranging between 7-16 c/min have been seen in quiescent conditions. In contractile state, the incidence of such rhythms decreases. The weakest manifestations of mechanical activity consist of small rhythmic variations of volume, the frequency corresponding to the main gastric rhythm of 4.5 c/min; however any spiking activity is observed. The second step of activity is the peristalsis (speed: 1 mm/sec), the circular contractility is accompanied by small spikes (less than 200 microV) in short salves. The third step is marked by the antral contraction with an important volume of variation, spike bursts of greater amplitude and biphasic slow wave are recorded. The antral activity is followed by a break of the main rhythm activity during 20 sec. These activities appear as a result from a structuration of local oscillators of relatively high frequency, in this species.