Chronic brain ischemia in the monkey assessed by somatosensory evoked potentials and local blood flow measurements

Physiological changes occurring in experimentally induced chronic ischemic areas of the brain in monkeys have been investigated by measuring local cerebral blood flow (lCBF) and recording somatosensory evoked potentials (SEPs) to median nerve stimulation in the cortex and thalamus (VPL). Ischemia was produced by occlusion of the middle cerebral artery (MCA). Its development was followed for weeks in the unanesthetized monkey. SEPs in VPL and cortex were shown to be useful indicators of neuronal activity in the course of brain ischemia. The most reliable parameters were found to be the amplitude of components P10, P12 and P20 of the cortical SEP, generated around the central sulcus. The relationship between the changes in spontaneous recovery of the SEPs, lCBF and behavioral signs, in the course of time, revealed characteristic patterns. Different components of the cortical SEP provide useful information on the localization of the ischemic cortical area. In addition, the amplitude of the VPL SEP may also change significantly after the occlusion of the MCA. Clear evidence for the phenomenon of diaschisis in terms of SEPs, was found in only one animal. An analysis of the relationship between lCBF and the amplitude of the SEPs showed that cortical SEPs could be measured at local CBF levels as low as 15 ml/100 g X min. The relationship between lCBF and cortical SEP amplitude was approximately linear in the range from about 60 ml/100 g X min down to 15 ml/100 g X min.