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Biomedical subjects

Markus Kofler

Publications and source records attributed to Markus Kofler.

At least 19 recordsLinked to original sources
PubMed2007

Auditory startle reaction in primary blepharospasm.

Primary dystonia is associated with abnormal brainstem function, as shown by abnormalities of the blink reflex in blepharospasm (BSP) and of the auditory startle reaction in cervical dystonia. We examined the auditory startle reaction--a brainstem reflex elicited by an unexpected loud stimulus--in patients with primary BSP to expand knowledge on brainstem pathophysiology in primary focal dystonia. Thirteen patients with primary BSP were included and 13 age- and sex-matched healthy volunteers served as controls. Auditory startle responses (ASRs) were elicited by binaural high-intensity auditory stimuli, and reflex electromyographic activity was recorded simultaneously with surface electrodes bilaterally from masseter, orbicularis oculi, sternocleidomastoid, and biceps brachii muscles. Patients with BSP showed higher ASR probabilities (masseter, sternocleidomastoid, biceps brachii), shorter ASR onset latencies (masseter, orbicularis oculi, sternocleidomastoid), and larger ASR area-under-the-curve (masseter, sternocleidomastoid) as compared with normal controls. Habituation of ASRs did not differ significantly between patients and controls. These results corroborate previous findings of increased brainstem excitability in primary BSP but point to a different pattern of brainstem dysfunction compared to cervical dystonia, indicating that different pathophysiological mechanisms are involved in the two types of focal dystonia.

Acoustic Stimulation↗
PubMed2006

Tumors localized near the central sulcus may cause increased somatosensory evoked potentials.

OBJECTIVE: Median nerve somatosensory evoked potentials (SEPs) may be altered in patients with cerebral tumors. In rare cases cortical responses may be increased, but the significance of this finding remains unclear. METHODS: We investigated 3 patients in whom an epileptic seizure was the only neurological symptom of a cerebral tumor located near the central sulcus. We studied median nerve SEPs, motor evoked potentials in abductor digiti minimi muscle, and long-loop reflexes in abductor pollicis brevis muscle bilaterally. Two patients also underwent intraoperative neurophysiological monitoring. RESULTS: All 3 patients presented with enlarged cortical SEPs on the side of the brain tumor. The responses increased further post-operatively, and the enhancement persisted in follow-up examinations up to 6 months after surgical tumor extirpation. Intraoperative monitoring documented a substantial increase of the enlarged potential N20-P22 during tumor removal in one patient, who also presented with an exaggerated long-loop reflex on the tumor side. Transcranial magnetic stimulation revealed unremarkable motor evoked potentials in all 3 patients. CONCLUSIONS: Distinct mechanisms must be considered in order to explain both immediate and long-term changes of neuronal excitability leading to increased cortical SEPs. SIGNIFICANCE: Hyperexcitability of cortical neurons or insufficient cortical inhibitory mechanisms may be responsible for increased SEPs, which may serve as an epileptic marker in patients suffering from a tumor near the central sulcus.

Adult↗
PubMed2006

Levetiracetam suppresses long-loop reflexes at the cortical level.

Posthypoxic coma is often associated with cortical and brainstem hyperexcitability. Five months following cardiopulmonary resuscitation after myocardial infarction and ventricular arrhythmia, a 47-year-old man presented with posthypoxic cerebral dysfunction, minimal responsiveness, severe spastic-dystonic tetraparesis, and stimulus-sensitive muscle spasms upon acoustic and sensory stimulation. Neurophysiological examination revealed increased long-loop reflexes in abductor pollicis brevis muscle following median nerve stimulation at the wrist, consistent with cortical hyperexcitability. Exaggerated startle responses provided evidence of concomitant brainstem disinhibition. Levetiracetam up to 3,000 mg per day suppressed transcortical long-loop reflexes in a dose-dependent manner without concomitant suppression of the H-reflex and only mild attenuation of the startle response. The present findings suggest a suppressive effect of levetiracetam on cortical neurons in the absence of a spinal effect on monosynaptic reflexes, and thus support the drug's efficacy in posthypoxic cortical hyperexcitability.

Coma↗
PubMed2005

Startle-induced reaction time shortening is not modified by prepulse inhibition.

A startling auditory stimulus delivered during preparation for execution of a ballistic movement in a simple reaction time task experiment induces two effects: a startle response and a reaction time shortening (the StartReact effect). We investigated whether prepulse inhibition of the startle response is effective in suppressing either one of these effects during motor preparation. Twelve healthy volunteers were presented with seven different experimental conditions in random order: while at rest, subjects received a low intensity electrical shock on the middle finger of the left hand (Prep), a loud auditory stimulus (Start), or a combination of these two (PrepStart). While engaged in preparation for a visual simple reaction time task, they were presented with the imperative signal for execution of the reaction (React), or with any of the combinations PrepReact, StartReact, or PrepStartReact. We recorded the EMG activity from the orbicularis oculi and the sternocleidomastoid muscles to assess the startle response, and from the wrist extensor muscles to assess reaction time. The startle response was markedly reduced when Prep was presented 100 ms before Start regardless of whether the subjects were at rest or preparing for the reaction. Reaction time shortened significantly in StartReact trials with respect to React trials, and the percentage shortening was not different in trials in which Prep preceded StartReact and inhibited the startle response. The fact that prepulse inhibition of the startle response is not accompanied by modification of the StartReact effect indicates that there are separate physiological mechanisms for the two effects, an observation that has implications for further understanding of the processes underlying motor preparation for a ballistic reaction.

Adult↗
PubMed2005

Delayed anterior spinal artery syndrome following posterior scoliosis correction.

The authors report two cases of delayed post-operative anterior spinal artery syndrome (ASAS) following posterior correction with Cotrel Dubousset (CD) instrumentation for adolescent idiopathic scoliosis. Sensory pathways were continuously monitored from skin incision to awakening. In both cases intraoperative SEPs were normal and the wake-up test revealed no neurological deficit. Both patients were presented with incomplete paraplegia (no sensory impairment) three and ten hours after surgery. Without delay, both patients underwent revision surgery, and the CD instrumentation was removed. Immediately after surgery, both patients' motor power in their lower extremities improved rapidly. In cases with delayed ASAS after posterior scoliosis correction, the removal of the instrumentation system was shown to be sufficient to regain full motor recovery caudal to the level of impairment.

Adolescent↗
PubMed2005

Ipsi- and contralateral exteroceptive EMG modulation in uni- and bilaterally activated thenar muscles.

OBJECTIVE: The cutaneous silent period (CSP) is a spinal inhibitory reflex mediated by A-delta fibers. The exact underlying neural pathway, however, is unknown. This study was undertaken to investigate whether the neural circuitry mediating CSPs is wired unilaterally or whether there is evidence of influence from or upon the contralateral side. METHODS: Fifteen healthy subjects underwent bilateral CSP testing following unilateral nociceptive digit II stimulation. Surface electromyographic (EMG) recordings were obtained bilaterally from thenar muscles following unilateral recurrent nociceptive digit II stimulation while activating the ipsilateral or the contralateral or both thenar muscles against resistance. RESULTS: Nociceptive digit II stimulation evoked consistent CSPs in ipsilateral thenar muscles during voluntary contraction, while there was no consistent influence on EMG activity in contralateral thenar muscles at rest. Furthermore, nociceptive digit II stimulation did neither consistently affect EMG activity in ipsilateral thenar muscles at rest nor in contralateral thenar muscles during voluntary contraction. Finally, there was no significant difference between any CSP parameters obtained during unilateral versus bilateral muscle contraction. Occasional late excitatory EMG activity in relaxed or contracted thenar muscles resembled startle reflexes, which seem to contribute to the post-inhibition EMG-rebound. CONCLUSIONS: The present findings are consistent with unilateral wiring of the spinal circuitry mediating CSPs. SIGNIFICANCE: The essential lack of a crossed inhibitory influence of nociceptive digit II stimulation underscores the utility of CSP testing in the assessment of the A-delta fiber system in healthy subjects and patients with various pathologies.

Adult↗
PubMed2004

Influence of transcutaneous electrical nerve stimulation on cutaneous silent periods in humans.

The cutaneous silent period (CSP) is a spinal inhibitory reflex mediated by A-delta fibers. Ten healthy subjects underwent assessment of the effect of high-frequency transcutaneous electrical nerve stimulation (TENS) on the CSP. Surface electromyographic (EMG) recordings were obtained from thenar muscles following recurrent nociceptive digit II stimulation. Group average CSP duration was shortened relative to baseline recordings following 15 min of TENS. The amount of exteroceptive EMG inhibition was slightly increased due to a concomitant suppression of transcortical long-loop reflexes, which may be present within the CSP. Thus, TENS exerts an influence on both inhibitory and excitatory circuits involved in protective reflexes. These effects are likely mediated at the spinal segmental level through TENS-associated presynaptic inhibition of nociceptive A-delta fibers. The findings are in agreement with a known opiate-insensitive mechanism of TENS at the spinal level, and a previously reported insensitivity to fentanyl of CSPs.

Adult↗
PubMed2004

Nociceptive EMG suppression in triceps brachii muscle in humans.

OBJECTIVE: Inhibitory spinal reflexes in human hand muscles mediated by cutaneous afferents (=cutaneous silent periods, CSPs) serve to protect the hand from injury. Proximal muscles are included in a complex protective pattern implementing both excitatory and inhibitory reflexes. METHODS: We investigated the functional organization of CSPs in the triceps brachii muscle (TB) - the prime elbow extensor - assessing different stimulus intensities and elbow positions. Thirteen healthy subjects underwent recurrent electrical index finger tip stimulation with different intensities while volitionally activating TB against resistance. The rectified and averaged electromyogram (EMG) was recorded from TB with surface electrodes while the elbow joint was held in full flexion, full extension, and at an angle of 90 degrees. RESULTS: Digit II stimulation resulted in distinct CSPs in TB. Increasing stimulus intensities caused a more profound EMG suppression. Different elbow positions had a significant influence on CSP onset and end latency, and duration. CONCLUSIONS: The present findings are consistent with a functional organization of protective reflexes in the proximal human upper limb across several metameric segments. Spinal inhibitory neurons serving to rapidly suppress basic muscle synergies may compete with neural circuitry involved in postural control.

Adult↗
PubMed2004

Interside comparison of cutaneous silent periods in thenar muscles of healthy male and female subjects.

OBJECTIVE: The cutaneous silent period (CSP) is a spinal inhibitory reflex mediated by A-delta fibers. To date, no data are available about normal interside differences. METHODS: Twenty healthy subjects underwent comparison of CSPs in the dominant and non-dominant hand. Surface electromyographic (EMG) recordings were obtained from thenar muscles on either side following ipsilateral recurrent nociceptive digit II stimulation. RESULTS: Group average CSP onset and end latency, CSP duration, and the magnitude of EMG suppression were not significantly different between both sides. Regression analysis revealed powerful correlations between individual CSP parameters of dominant and non-dominant hands. Calculated upper normal limits of maximum interside differences were 17% for CSP onset latency, 14% for CSP end latency, 22% for CSP duration, and 45% for the index of suppression. CSP parameters in right-handed subjects did not differ significantly from those in left-handed subjects. Female subjects tended to have shorter CSP onset latencies, longer CSP duration, and a smaller index of suppression, resulting in a larger overall suppression. CONCLUSIONS: CSPs prove to be robust nociceptive cutaneomuscular reflexes with little side-to-side difference. SIGNIFICANCE: The presented normative values of interside differences enable a more thorough comparison with patient data in various conditions.

Adult↗
PubMed2003

Cutaneous silent periods in intramedullary spinal cord lesions.

OBJECTIVE: The neurophysiological assessment of intramedullary spinal cord lesions has been unsatisfactory. Previous studies in patients with syringomyelia suggest that testing of cutaneous silent periods (CSPs) may be useful to assess centromedullary lesions. METHODS: The authors studied nine patients with intramedullary spinal cord lesions of different etiologies. Eight patients with cervical lesions presented with hypalgesia, hypothermesthesia, or pain in at least one upper extremity; five of them had also upper limb weakness or sensory impairment. One patient with a thoracic lesion had normal upper limb function. The authors recorded CSPs in abductor pollicis brevis muscle following digit II and digit V stimulation. Somatosensory evoked potentials (SEPs) were obtained following median and tibial nerve stimulation. Motor evoked potentials (MEPs) were obtained in biceps brachii, abductor digiti minimi and tibialis anterior muscles following transcranial magnetic or electrical stimulation. RESULTS: CSP abnormalities were found in all patients with cervical lesions, but not in the patient with a thoracic lesion. Cortical median nerve SEPs had normal latencies in all patients, while tibial nerve SEPs, upper limb MEPs, and lower limb MEPs were delayed in five patients each. In one patient, abnormal CSP were the only neurophysiological finding. CSP abnormalities were associated with hypalgesia and hypothermesthesia in 95% of the studies. CONCLUSION: Upper extremity CSP testing is a sensitive neurophysiological technique for the assessment of cervical intramedullary lesions. In particular, abnormal CSPs are highly associated with spinothalamic dysfunction.

Adult↗
PubMed2003

Auditory startle response in cervical dystonia.

The excitability of brainstem neurons is abnormally enhanced in patients with cervical dystonia (CD), but the extend of such abnormality is not known. We examined whether patients with CD showed abnormalities in the auditory startle response (ASR), a brainstem reflex elicited by an unexpected loud stimulus. Thirteen patients with CD were investigated 3 months after botulinum toxin treatment. Thirteen healthy volunteers served as controls. ASRs were elicited by binaural high-intensity auditory stimuli. Reflex electromyographic (EMG) activity was recorded simultaneously with surface electrodes bilaterally from masseter, orbicularis oculi, sternocleidomastoid, and biceps brachii muscles. We found that ASR onset latencies were similar for patients and controls. CD patients had significantly lower ASR probabilities than controls (P = 0.007). ASR area under the curve was significantly smaller in CD patients (P = 0.017). Similar to controls, patients showed a significant habituation of ASR (P < 0.001, each); however, CD patients showed a prolonged tonic or phasic EMG activity after the initial ASR that was not observed in controls. Normal latencies and recruitment pattern indicate a preserved organization of intrinsic neural pathways mediating ASR in CD. Reduced ASR probability and magnitude as well as prolonged EMG activity after the proper startle response corroborate and extend previous findings on brainstem dysfunction in CD.

Adult↗
PubMed2003

Preserved cutaneous silent periods in severe entrapment neuropathies.

Noxious digital nerve stimulation during isometric contraction of hand muscles leads to transient suppression of the electromyographic activity, the so-called cutaneous silent period (CSP), which is mostly due to a spinal reflex mediated by A-delta fibers. We investigated two patients with carpal tunnel syndrome (CTS) and two patients with ulnar entrapment at the elbow (UNE), in whom routine sensory conduction studies failed to document afferent fiber continuity across the lesion site. In three patients, motor nerve conduction studies and electromyography failed to demonstrate intact efferent fibers. Noxious stimulation of digit II elicited distinct CSPs in ulnar-innervated hand muscles in both patients with CTS, and stimulation of digit V evoked CSPs in median-innervated hand muscles in both UNE patients. The presence of a CSP can only be explained by preserved A-delta fibers crossing the respective lesion site. Thus, preserved CSPs may serve to document residual nerve continuity in severe entrapment neuropathies when fast-conducting fibers are so compromised that their continuity cannot be detected by standard electrodiagnostic techniques.

Action Potentials↗
PubMed2003

Exaggerated auditory startle responses in multiple system atrophy: a comparative study of parkinson and cerebellar subtypes.

OBJECTIVE: Auditory startle responses (ASRs) have recently been reported to be exaggerated in cranial and peripheral nerve supplied muscles of patients with multiple system atrophy (MSA). ASRs displayed increased probability, amplitude and duration, shorter onset latency, and reduced habituation in comparison with healthy subjects. In order to investigate whether certain ASR features may differentiate MSA subtypes, the authors studied ASRs in 21 MSA patients (olivopontocerebellar type, MSA-C: n = 8, striatonigral type, MSA-P: n = 13), and 17 age-matched normal controls. METHODS: ASRs were elicited by binaural high-intensity auditory stimuli which differed randomly in tonal frequency and intensity (250 Hz, 90 db; 500 Hz, 105 db; 750 Hz, 105 db; 1000 Hz, 110 db normal hearing level), presented through tubal insert phones. Reflex electromyographic activity was simultaneously recorded with surface electrodes from masseter, orbicularis oculi, sternocleidomastoid, biceps brachii, abductor pollicis brevis, rectus femoris, tibialis anterior, and soleus muscles. RESULTS: Eighteen MSA patients (86%) had exaggerated ASRs as compared to normal subjects. At group level, indices of ASR disinhibition including increased ASR probability (in extremity muscles), shortened onset latency, and enlarged response magnitude were significantly more marked in MSA-P as compared to MSA-C patients. ASR probability showed habituation in normal subjects, less in MSA-P. and none in MSA-C patients. Three MSA-patients had no ASRs except in orbicularis oculi muscle. CONCLUSIONS: Although absent ASRs may occur in some MSA patients, most of them exhibit exaggerated ASRs. This finding may reflect disinhibition of lower brainstem nuclei due to the degenerative disorder. ASRs were significantly more disinhibited in MSA-P versus MSA-C. suggesting involvement of different neural structures in the two MSA-subtypes.

Acoustic Stimulation↗
PubMed2003

Functional organization of exteroceptive inhibition following nociceptive electrical fingertip stimulation in humans.

OBJECTIVE: To investigate the functional organization of inhibitory spinal reflexes mediated by cutaneous afferents (=cutaneous silent periods, CSPs) in order to assess differential strategies used by the human spinal cord to inhibit movement in upper limb muscles within the same myotome. METHODS: Twenty healthy subjects underwent assessment of the effect of electrical finger-tip stimulation with different intensities on voluntarily contracting hand muscles. The rectified and averaged electromyogram (EMG) was recorded with surface electrodes placed over abductor pollicis brevis (APB), abductor digiti minimi (ADM), and first dorsal interosseous (FDI) muscles following recurrent digit II and digit V stimulation. RESULTS: Finger-tip stimulation resulted in a series of inhibitory and excitatory EMG responses in all 3 hand muscles. Stimulus intensity exerted a significant influence on various CSP parameters (probability, onset and end latency, duration, index of suppression). CSPs were most pronounced in APB following digit II and, somewhat less, following digit V stimulation. FDI and ADM differed in CSP onset latency following digit II stimulation, and in the overall amount of suppression following digit V stimulation, despite being supplied by the same nerve and the same myotome. Excitatory long-loop reflexes seemed to be suppressed by increasing stimulus intensities, yet they interfered with CSPs, even when using noxious stimulation, in FDI following digit II stimulation, and in both ADM and FDI following digit V stimulation. CONCLUSIONS: The findings are consistent with the presence of an inhibitory neural circuitry within the human spinal cord which can rapidly restrain distinct muscle synergies. Neurophysiology indicates a more functional - task-related - organization of protective reflexes in the human upper extremity, rather than a merely metameric - anatomically based - order of activation of this neuronal circuitry.

Adult↗
PubMed2002

"Occupational backache" - surface electromyography demonstrates the advantage of an ergonomic versus a standard microscope workstation.

Musculoskeletal symptoms such as low back pain, neck pain, and tension headache are reported by up to 80% of professional personnel involved in daily microscope work. Yet, in striking contrast to the high prevalence of complaints, there is a general unawareness of this issue both in those suffering, and those ordering and designing microscopes. We intend to call attention to this underestimated work-related health hazard and to demonstrate a potential means of prevention. We obtained repeated surface electromyographic (EMG) recordings from the most strained neck, upper limb, and back muscles in 12 healthy volunteers while they were operating a near-to-ergonomic prototype workstation and a conventional microscope, respectively. Mean EMG activity was reduced in all recorded muscles when operating the ergonomic workstation compared to the standard microscope. This improvement became more distinct with sustained work, and was most pronounced in those muscles displaying the highest degree of activity while using the standard microscope. We demonstrate the usefulness of surface EMG recordings to show the advantage of an ergonomically tailored and individually adjustable microscope workstation over a standard microscope. The former allows the operator to maintain a more physiological posture, and may thus prevent the development of cumulative musculoskeletal disorders during prolonged microscope-related work.

Adult↗