Biomedical subjects

A R Møller

Publications and source records attributed to A R Møller.

At least 73 records · Page 4Linked to original sources

PubMed1990

Recordings from human dorsal column nuclei using stimulation of the lower limb.

Responses from the surface of the dorsal column nuclei and the dorsal surface of the spinal cord were recorded using monopolar electrodes after stimulation of the lower limbs (common peroneal nerve at the knee and posterior tibial nerve at the ankle) in patients undergoing neurosurgical operations for spasmodic torticollis. Those responses were smaller in amplitude than responses to stimulation of the upper limbs (median nerve at the wrist), and the waveforms differed. The negative deflection that is prominent in the response to stimulation of the upper limbs is more variable, broader, and relatively smaller in amplitude than the response to upper limb stimulation. Another difference between responses to upper and lower limb stimulation was that multiple peaks were superimposed on the initial response to stimulation of the lower limbs, but were not as consistently seen in the responses to upper limb stimulation. The negative peak in the response from the dorsal column nuclei to lower limb stimulation was of about the same latency as the P27 peak in the far-field response (somatosensory evoked potential) to stimulation of the peroneal nerve.

Action Potentials↗

PubMed1990

Vascular compression syndrome of the eighth nerve. Clinical correlations and surgical findings.

A recently described syndrome, disabling positional vertigo (DPV), is characterized by persistent and progressive vertigo that is always associated with nausea and occasionally with vomiting; symptoms are made worse with changes in head position and are lessened with bedrest. Patients with DPV have abnormal results on vestibular testing and abnormalities in auditory nerve conduction as indicated by subtle but distinct alterations in brain stem auditory evoked potentials (BAEP). Microvascular decompression (MVD) of the vestibular nerve and, when indicated, the cochlear portion of the eighth cranial nerve has been highly successful in returning patients with DPV to normal lifestyles. Intraoperative monitoring of BAEP and auditory nerve compound action potentials have reduced the incidence of hearing loss, the major complication of MVD of the eighth nerve, to about 3 per cent. This article details the results of evaluating and treating 41 patients with DPV by MVD over a 12-month period and reports a success rate for this procedure in these patients of 73 per cent.

Humans↗

PubMed1990

Response from the inferior colliculus in the rat to tone bursts and amplitude-modulated continuous tones.

Responses from the inferior colliculus in the rat to tone bursts and bursts of broad-band noise were compared with cross-correlograms of the responses to continuous tones and noise that were amplitude modulated with pseudorandom noise. The waveform of the cross-correlograms showed great similarities with that of the evoked response, but the latency of the former showed less dependence on stimulus intensity than did the latency of the latter.

Animals↗

PubMed1989

Responses from dorsal column nuclei (DCN) in the monkey to stimulation of upper and lower limbs and spinal cord.

Responses from the dorsal surface of the exposed dorsal column nuclei (DCN) in baboons and a monkey (Macaca fascicularis) were recorded in response to electrical stimulation of the posterior tibial nerve at the ankle, the common peroneal nerve at the knee, the sciatic nerve, the spinal cord at T10, and the median nerve at the wrist. Recordings of far-field potentials from the vertex with a non-cephalic reference were made before exposing the DCN and simultaneously with recordings from the DCN. The response recorded from the DCN using a monopolar electrode to median nerve stimulation was a negative deflection (N wave) followed by a large and slow positive wave (P wave). The N wave was often preceded by a small positive deflection. The response from the median nerve to electrical stimulation of the DCN had the same latency as the initial positive peak and the initial portion of the N wave in the response from the DCN to stimulation of the median nerve, indicating that the initial positive peak was generated by presynaptic events in the DCN. The response recorded from the surface of the DCN to stimulation of the lower limbs consisted of many irregular waves followed by a large, positive deflection. Sometimes these irregular waves were superimposed on a small negative peak, and they were preceded by a positive deflection. The response from the tibial nerve to stimulation of the DCN consisted of a series of waves that had the same latency as the waves of the response from the DCN to stimulation of the tibial nerve.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1989

Response from the exposed intracranial human auditory nerve to low-frequency tones: basic characteristics.

The responses recorded from the exposed intracranial portion of the eighth nerve in man with normal hearing to short bursts of low-frequency tones (500, 1000, and 1500 Hz) consist of two components; these two components can be separated by adding and subtracting, respectively, the responses to tonebursts of opposite polarity. Subtracting the responses to tones of opposite polarity reveals a waveform that resembles the sinusoidal waveform of the stimulus (frequency-following response = FFR), while adding the responses to tones of opposite polarity reveals a slow component, the waveform of which is more variable than the frequency-following component. The initial deflection of the slow component of the response to 1000 Hz and to 1500 Hz is a positive peak followed by a slow, negative deflection, and the response to 1500-Hz tonebursts often shows a clear off-response. The slow component of the response to 500-Hz tones often has an initial negative peak followed by a slow, positive or negative wave. The temporal relationship between the stimulus tone and the frequency-following component changes only slightly when the intensity of the sound is changed, whereas the latency of the slow potential decreases with increasing stimulus intensity. The FFR can be masked by noise, and the results of masking with highpass-filtered noise indicate that the frequency-following response may be generated at a location on the basilar membrane that is tuned to a frequency that is higher than that of the stimulus tone.

Auditory Pathways↗

PubMed1989

Responses from the exposed human auditory nerve to pseudorandom noise.

Whole-nerve responses to lowpass-filtered noise (2.5 kHz) and broadband click stimuli were recorded from the exposed intracranial portion of the eighth nerve in patients with normal hearing who were undergoing neurosurgical operations to relieve vascular compression of cranial nerves V, VII, and VIII. Cross-correlograms between the response and the noise showed a large degree of individual variation. When noise of 95 dB SPL was used, the correlograms in some patients had a large peak that represented a positive correlation between a negative nerve potential and the rarefaction phase of the sound and that peak could usually be identified at a delay that was close to the latency of the main negative peak in the response to high-intensity broadband click sounds (3.0-3.5 ms). The amplitude of these components decreased when the sound intensity was decreased, and, at stimulus intensities below 80 dB, the correlograms became dominated by components at longer delays. In other patients, peaks of a similar amplitude appeared in the cross-correlograms between delays of 2 and 12 ms in the entire range of sound intensities that were studied (65-105 dB SPL). In all patients the location of the peaks was little affected by the stimulus intensity in the range studied. All reproducible peaks that appeared at delays longer than 2.8 ms shifted towards longer delays when the recording electrode was moved from a location near the porus acusticus to a more central location (near the brainstem) on the exposed intracranial portion of the eighth nerve, indicating that components at longer delays than 2.8 ms result from propagated neural activity in the auditory nerve. It is assumed on the basis of the results that these correlograms are measures of phase-locking of neural activity to a complex stimulus sound (noise).

Acoustic Stimulation↗

PubMed1989

Does intraoperative monitoring of auditory evoked potentials reduce incidence of hearing loss as a complication of microvascular decompression of cranial nerves?

During a 14-month period, 129 individuals underwent 140 operations for microvascular decompression to relieve hemifacial spasm, disabling positional vertigo, tinnitus, or trigeminal neuralgia at our institution. Seven patients were operated upon twice on the same side and 4 were operated upon on both sides at different times. In each case, the brainstem auditory evoked potentials were monitored intraoperatively by the same neurophysiologist. In 75 of these operations, compound action potentials were also recorded from the exposed 8th nerve. Comparison of speech discrimination scores before the operation and at the time of discharge showed that at discharge, discrimination had decreased in 7 patients by 15% or more and increased in 4 patients by 15% or more, in 2 patients by as much as 52%. Essentially similar results were obtained when preoperative speech discrimination scores were compared with results obtained from the 87 patients who returned for a follow-up visit between 3 and 6 months after discharge. Only one patient lost hearing (during a second operation to relieve hemifacial spasm). Another patient (also operated upon to relieve hemifacial spasm) suffered noticeable hearing loss postoperatively, but had recovered nearly normal hearing by 4 months after the operation. Nine patients had an average elevation of the hearing threshold for pure tones in the speech frequency range (500 to 2000 Hz) of 11 dB or more at 4 to 5 days after the operation; 8 of these had fluid in their middle ears that most likely contributed to the hearing loss. Threshold elevations occurred at 4000 Hz and 8000 Hz in 19 and 29 ears, respectively.

Audiometry, Evoked Response↗

PubMed1988

Effects of cerebellar retractions on the cochlear nerve: an experimental study on rhesus monkeys.

Cerebellar retractions were performed in the cerebellopontine (CP) angle of rhesus monkeys to study the relationship between changes in brainstem auditory evoked potentials (BAEP) and/or compound action potentials (CAP) from the cochlear nerve, and morphological changes in the cochlear nerve in order to investigate the nature of cochlear nerve injuries caused by this surgical procedure. The changes in the BAEP and/or CAP from the cochlear nerve that were seen during cerebellar retraction were similar to those seen in human patients during operation. After completion of each experiment the temporal bones were prepared for histological examination. Hemorrhages often developed at the fundus of the internal auditory canal as a direct result of cerebellar retraction. These hemorrhages were located at the area cribrosa, where the branches of the internal auditory artery penetrate the cribriform plate. As the hemorrhages appeared to be due to avulsion rupture of these branches, they were considered to be the probable cause of the sudden loss of all the components of the auditory responses. The cochlear nerve fibers, especially those at the basal turn of the cochlea, avulsed simultaneously at the area cribrosa in most cases.

Action Potentials↗

PubMed1988

Use of pseudorandom noise in studies of auditory evoked potentials.

The extent to which sensorineural systems such as the auditory system are nonlinear depends on the type of stimulus that is used, and the part of the system from which recordings are made. An estimate of the first-order Wiener kernel of the evoked response from the inferior colliculus to amplitude-modulated tones and noise was obtained by cross-correlating the response with the same pseudorandom noise as was used to amplitude modulate the sounds that were used as stimuli, in order to characterize the linear portion of the system. The shape of these cross-correlograms resembled the potentials evoked to short bursts of the unmodulated tones and noise. The degree of nonlinearity in the response to amplitude-modulated tones and noise was determined, and information about the type of nonlinearity was obtained using the inverse-repeat feature of the pseudorandom noise. Recordings both from the surface and from deep in the nucleus of the inferior colliculus revealed nonlinearities that were predominantly of an even order, but the magnitude of the nonlinearities depended on what stimulus was used, the stimulus intensity, and from which neural structure the recording was made.

Acoustic Stimulation↗

PubMed1988

Injuries to the auditory nerve: a study in monkeys.

The effect of traction injury to the eighth nerve on the compound action potentials (CAPs) recorded from the exposed nerve in response to tonebursts and click sounds was compared to responses elicited by continuous tones and noise that were amplitude-modulated with pseudorandom noise. Responses to the continuous sounds were presented in the form of cross-correlograms between the averaged response, with the averager locked to the periodicity of the noise and one period of the noise. While the wave form of these cross-correlograms was similar to the wave form of the response to the same, but unmodulated, stimulus when presented in short bursts when the nerve was intact, these two measures changed in different ways as a result of slight injury to the nerve. Thus, the N1 peak of the CAP in response to clicks and tones or noisebursts became prolonged when the nerve was stretched, while the first peak in the cross-correlograms was essentially unchanged. The second peak in the cross-correlogram was obliterated, but the N2 peak in the CAP was clearly present, although attenuated. More severe injury resulting in a nearly total conduction block, however, produced similar changes in the CAPs and cross-correlograms.

Acoustic Stimulation↗

PubMed1988

Responses from the brainstem at the entrance of the eighth nerve in human to contralateral stimulation.

Recordings were made from the exposed eighth nerve (N VIII) and the lateral brainstem near the root entry zone of N VIII to contralateral click stimulation in patients undergoing microvascular decompression operations to relieve hemifacial spasm or trigeminal neuralgia. Similar recordings were made in patients undergoing operations to remove acoustic tumors using a retromastoid approach to the cerebellopontine angle. The waveform of the response that was recorded using a monopolar electrode placed on the intracranial portion of the eighth nerve was similar to the potentials recorded from the lateral surface of the brainstem near the entrance of the eighth nerve, and consisted of a positive deflection with a latency of about 4 ms, and sometimes a second and smaller positive peak with a slightly shorter latency than that of peak V in the BAEP could be seen in such recordings. It was concluded that the potentials are generated in brainstem structures, most likely the cochlear nucleus. It is assumed that when the potentials are recorded from the exposed eighth nerve, the nerve passively conducts the activity from the active structure to the recording site. The latency of the main positive peak in these potentials does not bear any direct relationship to any identifiable component of the farfield evoked potentials when these potentials are recorded from the vertex or the earlobe of the stimulated ear and a noncephalic reference is used. It seems likely that the potential is generated by fibers that originate in cells in the cochlear nucleus on the stimulated side, and that the initial positivity reflects the termination of these fibers in the cochlear nucleus on the side from which the recording is made.

Brain Stem↗

PubMed1988

[Cochlear nerve injuries caused by manipulations in cerebellopontine angle: Part I. Electrophysiological and morphological study in dogs].

Cochlear nerve injuries caused by manipulations in the cerebellopontine angle were electrophysiologically and morphologically investigated using dogs. Compression injuries were developed at the portions of the cochlear nerves that were directly retracted by a retractor. The blood vessels supplying the cochlear nerve trunk easily ruptured and the Schwann-glial junctions of the cochlear nerve were separated, due to traction force derived from the manipulations in the CP angle. From these results, some technical points to preserve hearing during CP angle surgery were discussed.

Action Potentials↗

PubMed1988

[Cochlear nerve injuries caused by manipulations in cerebellopontine angle: Part II. An electrophysiological and morphological study in rhesus monkeys].

Cochlear nerve injuries caused by the manipulations in the cerebellopontine angle were electrophysiologically and morphologically investigated in rhesus monkeys. The brainstem auditory evoked potentials and/or the compound action potentials recorded from the intracranial portions of the cochlear nerve so often deteriorated due to cerebellar retractions. In these cases, the morphological changes were often verified at the most distal portions of the cochlear nerves at the fundus of the internal auditory canal (area cribrosa): the cochlear nerve fibers were pulled out from the bony foramina at the area cribrosa and the branches of the internal auditory artery were also avulsed and ruptured. Sudden loss of the auditory evoked potentials was occasionally experienced during cerebellar retractions in the monkeys as occurred in human CP angle surgery. In these cases, massive hemorrhages were found at the area cribrosa. This indicates that sudden loss of hearing function during CP angle manipulations is caused by vascular accident of the internal auditory artery. It was emphasized that the operative procedures should be done with the operative direction toward the cochlea and that the operative procedures away from the cochlea should be avoided, because they may effect traction force on the cochlear nerve.

Action Potentials↗

PubMed1987

Recording compound action potentials from the optic nerve in man and monkeys.

Compound action potentials were recorded from the optic nerve in patients undergoing neurosurgical operations and in rhesus monkeys. The stimuli were short light flashes delivered by light-emitting diodes that were bonded to plastic contact lenses positioned on one or both eyes, and potentials were recorded simultaneously from electrodes placed on the scalp. Potentials recorded from the optic nerve in man have an initial small positive deflection, with a latency of about 45 msec, followed by a negativity with a latency of 60-70 msec. The wave form depends on the recording site on the optic nerve and, occasionally, oscillations with a frequency around 100 Hz were seen in the responses from the optic nerve. There was considerable individual variation in the shape and size of the recorded potentials, but most potentials recorded simultaneously from an electrode placed on Oz with a reference electrode on the forehead appeared as positive deflections with latencies of about 80 msec and, occasionally, with a small positivity with a latency of about 45 msec. Compound action potentials recorded from the optic nerve near the ocular globe in the rhesus monkey in response to similar light flashes appeared as negative deflections with latencies of about 17 msec. The potentials recorded at the chiasm appeared as initial positive deflections, with the latency of the earliest peak being about 35 msec, on which oscillations with frequencies of about 100-150 Hz occasionally could be seen. The recordings from electrodes placed on the scalp (Cz-Oz and Cz-shoulder) in the monkey showed a positive peak with a latency of about 65 msec.(ABSTRACT TRUNCATED AT 250 WORDS)

Action Potentials↗

PubMed1987

Auditory evoked potentials to continuous amplitude-modulated sounds: can they be described by linear models?

The responses from the round window of the cochlea and the surface of the cochlear nucleus to continuous tones and noise that were amplitude-modulated with pseudorandom noise were studied. The responses were averaged with the averager locked to the periodicity of the pseudorandom noise, and the cross-correlation between the averaged responses and one period of the pseudorandom noise was computed. The degrees of non-linearities in the responses were estimated by comparing the response of a linear model that had this cross-correlogram as its impulse response and the physiological response. The root mean square (RMS) value of the histograms increases as a function of the stimulus intensity and reaches a peak at 40-60 dB above threshold, above which intensity it decreases. The non-linear component of the response increases monotonically with sound intensity in the range from threshold to 60-70 dB above threshold. The pseudorandom noise was of the inverse-repeat type, and when even-order non-linearities were canceled by subtracting the latter half of the responses to one period of the pseudorandom noise from the first half a much closer agreement with the model responses was obtained, indicating that the non-linearities were mainly of even order. It was concluded that the non-linearities of the responses may have been caused by an unequal response to increases and decreases in stimulus intensity.

Acoustic Stimulation↗

PubMed1987

Hemifacial spasm: ephaptic transmission or hyperexcitability of the facial motor nucleus?

Hemifacial spasm is a rare disorder that is caused by a blood vessel cross-compressing the facial nerve near the nerve's entry into the brain stem. Electrical stimulation of one branch of the facial nerve on the affected side in patients elicits a response from muscles that are innervated by another branch. Intraoperative recording of this abnormal muscle response, together with measurements of conduction times in parts of the facial nerve, in earlier studies have shown evidence that the cross-transmission of antidromic activity that causes this response occurs central to the site of vascular compression of the facial nerve. In this study we show that in rare circumstances during microvascular decompression operations, a small EMG potential precedes the regular abnormal muscle response. This early response has a latency that is equal to the sum of the conduction times of the portions of the facial nerve that would have been involved if the cross-transmission had occurred at the site of vascular compression of the facial nerve, and it may thus be a result of ephaptic transmission in the nerve at that location. Thus, cross-transmission of antidromic activity can indeed occur in the facial nerve at the site of compression, although we have observed this early potential in only 3 of more than 50 patients who were operated upon for hemifacial spasm; further, in those three patients it occurred only for a short time and only during surgical manipulation of the facial nerve. In view of the fact that this early response occurs only after the nerve has been manipulated, and because it is of such small magnitude, it seems unlikely that such cross-transmission (ephaptic transmission) at the site of the vascular compression plays a direct role in generating the spasm and the antidromic activity that spreads from one branch of the facial nerve to another.

Electric Conductivity↗

PubMed1987

Signs of hemifacial spasm created by chronic periodic stimulation of the facial nerve in the rat.

We show in this paper that daily electrical stimulation of the facial nerve near its entrance to the brain stem in rats results in abnormalities in the electromyographic response of the facial muscles that resemble those seen in patients with hemifacial spasm. After about 4 weeks of daily electrical stimulation of the facial nerve for 1 min/day, stimulation of the temporal branch of the facial nerve resulted in an abnormal EMG response from the mentalis/orbicularis oris muscles, consisting of an initial deflection with a latency of about 6 ms, followed by a burst of EMG activity lasting 10 to 50 ms. We found such "lateral spread" of antidromic activity in all 10 rats that were subjected to chronic stimulation, but not in normal rats and not in rats that had electrodes implanted but which had not been stimulated. Measurements of neural conduction times suggest that the location of the cross transmission that gives rise to this lateral spread response is central to the site where the facial nerve exits the brain stem, probably in the facial motor nucleus. We take these results to support the hypothesis that chronic stimulation of the facial nerve can change the facial nucleus in such a way that it becomes hyperactive, and cross transmission between neurons that are innervating different facial muscles is facilitated.

Animals↗

PubMed1987

Stimulus properties influencing the responses of inferior colliculus neurons to amplitude-modulated sounds.

The temporal pattern of the responses of neurons in the inferior colliculus of the anesthetized rat were studied using continuous tone or noise carrier signals, amplitude modulated by pseudorandom noise. Period histograms of the responses, cross-correlated with the pseudorandom noise, gave an estimate of the unit's impulse responses to modulation. The amplitude-modulation rate transfer function (MTF) was obtained by Fourier transforming the correlograms. At sound levels within approximately 15 dB of the unit threshold, the MTFs were near lowpass functions between 6 and 200 Hz but became more bandpass-like as the intensity was increased. There was a steep decline in the response to modulation at modulation frequencies above 200 Hz for all stimulus intensities. For the bandpass-type MTFs the greatest modulation of the discharge pattern occurred at modulation frequencies between 10 and 200 Hz with a maximum in the distribution of MTF peak values between 100 and 120 Hz. There was no consistent relationship with characteristic frequency of either the position of the MTF peak or the high-frequency cutoff of the MTF. The cross-correlograms obtained at high stimulus intensities (30-60 dB above threshold) often showed a negative peak, representing a decrease in the probability of firing in response to intensity increments in the stimulus, and denoting a nonmonotonic rate-intensity function. The MTFs for units responding to amplitude-modulated broadband noise were often flatter in the low frequency region than those generated with tone carriers at corresponding intensities. For some units addition of a broadband noise background to the modulated tone changed the response characteristic of the MTF from bandpass to lowpass and shifted the MTF peak to a lower modulation frequency. The results demonstrate that although neurons in the inferior colliculus are selectively sensitive to the modulation frequency of dynamic stimuli, the response characteristics are not invariant, but instead are closely dependent on the conditions under which the modulation is presented.

Acoustic Stimulation↗