The fourth update of the rules of the procedure to determine the final, non-recoverable failure of the overall function of the cerebrum, the cerebellum and the brain stem, confirms the importance of somatosensory evoked potentials (SEP) and the early auditory evoked potentials (EAEP) for determination of irreversibility. This paper addresses the reliability and validity of the electrophysiological diagnosis, discusses the changes in the 4(th) version of the guidelines and shows up problems and sources of error in the practical application. The EAEP are valid for the irreversibility of brain death syndrome only in serial examinations or in the rare cases of sustaining wave I or wave I and II. Often an investigation is not reliable due to possible existing sound conduction disturbances or failure of all potentials before entering the clinical brain death syndrome. We therefore use the EAEP only in exceptional cases. The median nerve SEP are reliably derivable, technically simple and with few errors. There is no serial investigation required and the time required for deriving is low.

Callosal dysfunction is known to be evident in a variety of neurodegenerative and inflammatory diseases of the central nervous system. Cerebral microangiopathy (CMA) may also affect callosal pathways by chronic demyelination. The aim of the present study was to investigate callosal function with respect to the extent of CMA. Callosal function was tested by a bimanual tapping task and by analysis of the ipsilateral silent period (iSP) and the transcallosal conduction time (TCT) using transcranial magnetic stimulation. Results were correlated to the extent of CMA measured by cranial magnetic resonance imaging (cMRI) in 44 patients with CMA compared to 10 control subjects. The extent of CMA was quantified by a cMRI score. Additionally, callosal atrophy was quantified by cMRI morphometry. Frequency of pathological iSP findings or disturbed bimanual tapping was significantly correlated to a higher CMA score. Moreover, the extent of CMA was significantly correlated to the degree of callosal atrophy. It is concluded that CMA considerably affects callosal pathways, possibly by chronic demyelination of callosal fibres. As the extent of CMA and atrophy of the corpus callosum is correlated to callosal dysfunction, analysis of the iSP can be used to assess the clinical impact of CMA detected by cMRI.

The ability of the human hand to perform complex sensorimotor tasks such as tactile exploration and grasping is based on 1. exact encoding of somatosensory information by cutaneous mechanoreceptors, 2. elaborated processing of afferent signals in somatosensory relay stations and cortex fields, 3. rapid and effective interaction of sensory feedback with motor programs, and 4. different modes of sensory control, which can be switched over.

Drug Prescribing for Patients with Chronic Kidney Disease in General Practice: a Cross-Sectional Study

Evoked potentials are well established in the field of clinical neurology. Standards defining minimal requirements have been developed. For the puropse of quality control, possible errors in the measurement of EPs and in the interpretation of results have to be known. Indications to measure EPs are presented together with the assessment of frequent results.

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Animal experiments suggest that cortical sensory representations may be remodelled as a consequence of changing synaptic efficacy by timing‐dependent associative neuronal activity. Here we describe a timing‐based associative form of plasticity in human somatosensory cortex. Paired associative stimulation (PAS) was performed by combining repetitive median nerve stimulation with transcranial magnetic stimulation (TMS) over the contralateral postcentral region. PAS increased exclusively the amplitude of the P25 component of the median nerve‐evoked somatosensory‐evoked potential (MN‐SSEP), which is probably generated in the superficial cortical layers of area 3b. SSEP components reflecting neuronal activity in deeper cortical layers (N20 component) or subcortical regions (P14 component) remained constant. PAS‐induced enhancement of P25 amplitude displayed topographical specificity both for the recording (MN‐SSEP versus tibial nerve‐SSEP) and the stimulation (magnetic stimulation targeting somatosensory versus motor cortex) arrangements. Modulation of P25 amplitude was confined to a narrow range of interstimulus intervals (ISIs) between the MN pulse and the TMS pulse, and the sign of the modulation changed with ISIs differing by only 15 ms. The function describing the ISI dependence of PAS effects on somatosensory cortex resembled one previously observed in motor cortex, shifted by ∼7 ms. The findings suggest a simple model of modulation of excitability in human primary somatosensory cortex, possibly by mechanisms related to the spike‐timing‐dependent plasticity of neuronal synapses located in upper cortical layers.

INTRODUCTION:Coronary artery bypass graft surgery (CABG) using cardiopulmonary bypass (CPB) is assumed to be associated with a decline of neurocognitive functions. This study was designed to analyse the neurocognitive function of patients with coronary heart disease before and after CABG and to determine possible protective effects of oxygenator surface coating on neurological outcome.METHODS:Forty patients scheduled for selective CABG were prospectively randomized into two groups of 20 patients each according to the type of hollow-fibre membrane oxygenator used. Non-coated oxygenators (Group A) were compared to phosphorylcholine (PC)coated oxygenators (Group B). A battery of six neurological tests was administered preoperatively, 7-10 days and 4-6 months after surgery.RESULTS:One patient of Group A suffered from a perioperative stroke and died on postoperative day 3, presumably because of sudden heart failure. Two patients of Group A (10%) developed a symptomatic transitory delirious psychotic syndrome (STPT) on postoperative days 3 and 5. None of the patients of Group B had perioperative complications. The test analysis revealed a trend of declined neurocognitive function early after CABG, but did not show any difference in neurocognitive outcome between the two groups.DISCUSSION:PC coating of the oxygenators did not show any significant benefit on neurocognitive function after CABG using CPB.

Zerebrale mikroangioangiopathische Veränderungen sind im höheren Lebensalter häufig. Diese Veränderungen können zu Symptomen eines pure motor stroke, Gangstörungen (lower body parkinsonism) oder kognitiven Defiziten führen. Eine Korrelation zwischen kognitiver Dysfunktion, Atrophie des Corpus callosum (CC) und white mattter lesions konnte gezeigt werden. Transkallosale motorische Bahnen spielen eine wichtige Rolle für die Präzision bimanueller Bewegungen. Ziel der Studie war die Untersuchung der funktionellen Integrität des CC bei Patienten mit ZM mittels fokaler transkranieller Magnetstimulation (fTMS).

Clinicopathologic evidence suggests differential involvement of cortex and corpus callosum (CC) in various disorders presenting with a parkinsonian syndrome. We tested the hypothesis of whether neurophysiologic and morphometric assessments of CC as surrogate parameters of cortical involvement could be helpful in differential diagnosis of parkinsonian disorders. The integrity of CC was assessed neurophysiologically by measuring the ipsilateral silent period (iSP) evoked by transcranial magnetic stimulation (TMS) in a total of 25 patients with idiopathic parkinsonian syndromes (IPS), corticobasal ganglionic degeneration (CBD), progressive supranuclear palsy (PSP), or multiple system atrophy (MSA). Additionally, morphometric analyses of magnetic resonance imaging (MRI) measurements of CC was carried out in all patients. iSP was abnormal in all 5 CBD and all 5 PSP patients, whereas it was intact in all 10 IPS patients and all 5 MSA patients. Among various MRI parameters of CC, testing between different groups revealed a significant difference only for measurements of the middle part of the truncus. CBD and PSP patients exhibited a significant atrophy as compared with control subjects. These data suggest impairment of callosal integrity in patients with CBD and PSP. iSP measurements may be a useful clinical neurophysiologic test in differential diagnosis of patients with parkinsonian syndromes. © 2004 Movement Disorder Society

Neuronale Dysfunktionen von Kortex und Hirnstamm spielen für die Pathophysiologie der Migräne eine entscheidende Rolle. Funktionelle bildgebende Verfahren (fMRT), Perfusionsmessungen und elektrophysiologische Untersuchungsverfahren wie EEG und MEG, multimodal evozierte Potenziale, ereigniskorrelierte Potenziale und Reflexuntersuchungen haben bei Migränepatienten eine Vielzahl von auffälligen und teilweise widersprüchlichen Befunden erbracht. Diese hängen vom Zeitpunkt der Untersuchung innerhalb des Migränezyklus (interiktual, Aura, Kopfschmerzphase) und zum Teil vom Migränetyp (Migräne mit oder ohne Aura) ab. Dysfunktionen von Filter- und Schutzmechanismen, die das ZNS regulär vor einem exzessiven sensorischen Informationsfluss abschirmen, besitzen wahrscheinlich für die Auslösung von Migräneattacken eine große Bedeutung. In konkurrierenden Modellvorstellungen werden eine neuronale Hyperexzitabilität im ZNS, aber auch eine kortikale Hypoexzitabilität als Prädispositionsfaktoren für Migräneattacken propagiert.

Paired associative stimulation (PAS) refers to a paradigm consisting of slow-rate repetitive low-frequency median nerve stimulation combined with transcranial magnetic stimulation (TMS) over the contralateral motor cortex. This protocol has been shown to induce plastic changes of excitability in the human motor cortex. Its principles of design were shaped after associative long-term potentiation (LTP) in experimental animals, a cellular mechanism likely to be relevant for learning and memory. PAS-induced changes of cortical excitability share a number of physiological properties with LTP. Of particular importance is the fact that the sign of PAS-induced changes of the size of amplitudes of the motor evoked potentials (MEPs) depends on the exact interval between the afferent and the magnetic pulse during the intervention. A number of observations suggest that PAS-induced excitability changes may have functional significance. PAS-induced plasticity may contribute to elucidating the pathogenesis of neurological disorders where neuroplasticity is thought to have a pathogenetic role. Finally, PAS-induced plasticity may itself have therapeutic potential.

Hypermotorisches Verhalten bei Kindern mit ADHD lässt sich unter anderem als vermehrte Fazilitierung oder verminderte Inhibition motorischer Prozesse auffassen. Kürzlich konnten wir zeigen, dass der mit transkranieller Magnetstimulation (TMS) untersuchte inhibitorische Parameter der ipsilateralen Silent Period (iSP) bei Kindern mit ADHD gegenüber Kontrollen eine verlängerte Latenz und eine reduzierte Dauer aufweist [1]. Hier wurde der Einfluss einer Medikation mit Methylphenidat auf die bei ADHD-Kindern veränderte iSP untersucht.

Objectives: The use of cardiopulmonary bypass (CPB) is assumed to be associated with a decline of cognitive functions. The possible protective effects of oxygenator surface coating remains still unknown.

Neuronal dysfunctions of the cortex and brainstem play a major role in the pathophysiology of migraine. Functional brain imaging (fMRI), perfusion measurements and electrophysiological investigations such as EEG and MEG, multimodal evoked potentials, event-related potentials and reflex measurements have revealed many abnormal and even contradictory findings. These depend on the investigation time within the migraine cycle (interictual, aura and acute headache) and partly on the migraine subtype (migraine with or without aura). Dysfunctions of filter mechanisms protecting the brain from an overflow of sensory input might play a crucial role in inducing migraine attacks. Competing pathophysiological models suggest neuronal hyperexcitability within the CNS, but also hypoexcitability of the cerebral cortex as predisposing factors in migraine.