Low-frequency oscillations in human tibial somatosensory evoked potentials Oscilações de baixa freqüência no potencial evocado somato-sensitivo do nervo tibial humano

Oscillatory cerebral electric activity has been related to sensorial and perceptual-cognitive functions. The aim of this work is to investigate low frequency oscillations (<300 Hz), particularly within the gamma band (30-110 Hz), during tibial stimulation. Twenty-one volunteers were subjected to 5 Hz stimulation by current pulses of 0.2 ms duration and the minimum intensity to provoke involuntary twitch. EEG signals without (spontaneously) and during stimulation were recorded at primary somatosensory area. A time-frequency analysis indicated the effect of the stimulus artifact in the somatosensory evoked potential (SEP) frequencies up to 5 ms after the stimulus. The oscillations up to 100 Hz presented the highest relative power contribution (approximately 99%) for the SEP and showed difference (p<0.01) from the frequencies of the spontaneously EEG average. Moreover, the range 30-58 Hz was identified as the band with the highest contribution for the tibial SEP morphology (p<0.0001).<br>Oscilações da atividade elétrica cerebral têm sido associadas a funções sensoriais, de percepção e de cognição. O presente estudo objetiva investigar as oscilações de baixa freqüência, em particular da banda gama (30-110 Hz), durante estimulação do nervo tibial. Vinte e um voluntários foram estimulados com pulsos de corrente de 0,2 ms, freqüência de 5 Hz e intensidade mínima para produzir o movimento involuntário dos músculos intrínsecos do pé. Sinais EEG espontâneo e durante estimulação foram registrados na área somato-sensitiva primária. A análise tempo-freqüência indicou o efeito do artefato ao estímulo na banda de freqüência do potencial evocado somato-sensitivo (PESS) até aproximadamente 5 ms pós-estímulo. As oscilações até 100 Hz apresentaram maior contribuição relativa de potência ao PESS (aproximadamente 99%) e se mostraram significativamente diferentes (p<0,01) das freqüências da média coerente do EEG espontâneo. Além disso, a banda 30-58 Hz foi identificada como a de maior contribuição à morfologia do PESS do nervo tibial (p<0,0001)

Signaling pathways leading to ischemic mitochondrial neuroprotection

There is extensive evidence that ischemic/reperfusion mediated mitochondrial dysfunction is a major contributor to ischemic damage. However data also indicates that mild ischemic stress induces mitochondrial dependent activation of ischemic preconditioning. Ischemic preconditioning is a neuroprotective mechanism which is activated upon a brief sub-injurious ischemic exposure and is sufficient to provide protection against a subsequent lethal ischemic insult. Current research demonstrates that mitochondria are not only the inducers of but are also an important target of ischemic preconditioning mediated protection. Numerous proteins and signaling pathways are activated by ischemic preconditioning which protect the mitochondria against ischemic damage. In this review we examine some of the proteins activated by ischemic precondition which counteracts the deleterious effects of ischemia/reperfusion thereby maintaining normal mitochondrial activity and lead to ischemic tolerance