$520 Friday, November 11, 2005

useful range. This preconditioning approach could be used to increase therapeutic, efficacy rTMS in patient populations.

1656 Continuous Theta-Burst stimulation diminishes pain perception: a repetitive magnetic stimulation study

Antal, A :, Csifcsak, G :, Nitsche, M A a, Paulus, W ~. 1Department of Clinical Neurophysiology, Georg-August University, Gd'ttingen, Germany

Background: Pharmacoresistent pain still remains a therapeutical challenge. Continuous invasive electrical stimulation of the primary motor cortex (MI) has been introduced more than a decade ago as an effective method for reducing and alleviating chronic central and neuropathic pain. Methods: Here we apply a recently reported new method of low intensity bursts of repetitive magnetic stimulation (rTMS) at 50 Hz (called continuous theta-burst stimulation - cTBS) of the motor cortex in order to produce a long - lasting inhibitory effect on the motor cortex. 40 s of cTBS over the left M1 in healthy subjects significantly diminished A-delta fibers mediated pain perception when the contralateral hand was stimulated with a laser-beam. In accordance with the psychophysical results, the P2 component of the laser evoked potentials (LEP) that arises mostly from the anterior dngulate cortex, showed a significant decrease in amplitude when the right hand was stimulated with the laser, while the sham stimulation condition had no significant effect. Conclusioas: Non-invasive motor cortex stimulation may contribute to the understanding of the mechanisms underlying pain relief and toward a potential therapeutic benefit.

1657 Homeostatic plasticity alter itdtibition of the cortex adds to the repertoire for facilitating motor learning

Antal, A ~, BegemeieL S ~, Nitsche, M A ~, Paulus, W 1. 1Departmozt of Clinical Neurophysiology, Georg-A ugust University, Gdttingen, Germany

Background: Cortical metaplastidty or homeostatic mechanisms refer to the influence of previous general activity of a given cortical area on subsequent synaptic strengthening. The functional relevance with regard to learning and memory performance remains unclear so far. Methods: The exdtability of the primary motor cortex or the motion- sensitive visual area MY/V5 was modulated by ten minutes of anodal or cathodal transcranial direct current stimulation (tDCS) in healthy human subjects before learning of a visual tracking task. The percentage of correct tracking movements increased significantly in the early learning phase after both anodal and cathodal stimulations over both cortical areas compared to the no stimulation condition. Conclusions: The improvement of performance by prior diminution of cortical activity is in accordance with the BCM rule of homeostatic plasticity. However, the positive effects of the pre-learning excitability enhancement on the subsequent leatmng process requires an alter- native explanation. We suggest that here the BCM rule is overruled by the potency of a moderate general exdtability enhancement to bring the learning-related synaptic connections nearer to their modification threshold without influencing learning-irrelevant synapses relevantly. Titus also here the principal functional relevance of the BCM rule for the efficacy of learning is underlined, but the results alos imply that other mechanisms, such as synaptic modification threshold modula- tion, have to be taken into account.

1658 Homocystehlemia: a new risk factor for cerebral vascular diseases, dementia and migraine?

Poster Abstraets

Dnitsini S l, Tsirka E ~, Tsirka V ~, Rigopoulou S ~, DR. Michailidis K ~ . 1Neurological Department of y,d Hospital I.K.A. Panagia, Thessaloniki, Greece

Background: Since 1969 that Mc-Cully made the clinical observation, linking elevated plasma homocysteine concentrations with vascular disease a lot of epidemiological evidences and clinical studies have demonstrated the relationship between hyperhomocysteinernia with cerebral atherosderosis, dementia and migraine. Method: Woman 43 years old with positive family lfistory for vascular disease came to us because of recurrent intense episodes of migraine, dementia and transient ischemic attacks. The pathological findings included homocysteinemia, increased levels of vitamin C, low levels of vitamin BI2 and she was homozygous for the C677T polymorphism. MRI imaging revealed leukoaraiosis and the psychometric tests were pathological. Results: There are conflicting studies regarding the association of homocysteinenfia with cerebral atherosclerosis, dementia and migraine. It is generally accepted that homocysteinemia is an independent risk factor for dementia. Although it is generally accepted that homo- cysteinemia is directly related to cerebral vascular diseases it is yet to be answered whether or not induces ischemic strokes or is the result of the tissue dysfunction after the ischemic stroke. The relationslfip of homocysteinemia with migraine was adequately supported only in case of migraine with aura. Conclusion: While homocysteinemia is an independent risk factor for transient ischemic attacks and dementia it is a point of further study whether or not induces migraine.

1659 Analysis of subunits S100A1B and S100BB in comparison with the total amount of N100 in Sermn alter Cardiac A~rest

Rostn, H 1, Hall C 2, NJlsson 0 2, Rosengren, L 1. 2Department of Neurology, Sahlgrens University Hospital, Go'teborg, Sweden; 2CanAg Diagnostics, Gdteborg, Sweden

Patients who suffer a cardiac arrest have a poor prognosis. The brain is the critical organ. The neurological status must be followed for proper prognostication. Analysis of brain damage markers gives additional information of brain damage. Here we compared the release of total serum S100B with the dimer forms S100A1B and S100BB. 66 consecutive patients with out-of-hospital cardiac, arrest were included. Total S100B, S100A1B and S100BB were measured using enzyme inmmnoassays (CanAg Diagnostics AB, Sweden). The S100B assay measures the summed concentrations of S100A1B and S100BB. Outcome was measured at short term (mortality) and long term (Glasgow Outcome Scale). We observed increased levels of S I00AIB, SI00BB and total S100B respectively (day one through three) in patients deceased within 14 days compared to survivors (p < 0.001, all cases). The highest predictive values were observed for S100A1B and total S100B. The predictive values were somewhat lower for S100BB. A relation between long-term outcome according to the GOS and serum levels of S100A1B, SI00BB and total SI00B respectively was found. Patients with poor outcome had significantly higher levels of both S100A1B and S100BB days one through three. For S100A1B the level of significance was equally high on days two and three (p < 0.001) wMe for S100BB, the highest significance was obtained on day three (iJ < 0.01).

Both the homo- and the hetero-dimer forms of S 100B contribute to the total amount of SI00B released after cardiac arrest. Both are good markers of brain injury and may be used as adjunctive analyses in this patient category.

1660 Unusual presentations of eonus medullaris anti lilmn tertlfinale myxopapillary epemlymonlaS