Experimental Performance of Steel and Platinum Electrodes with Chronic Monophasic Stimulation of the Brain

Cortical Histopathology following Stimulation with Metallic and Carbon Electrodes; pp. 142–157

“…These findings arc not in agreement with histological stud ies of nervous system damage with depth electrodes [36] or short-term surface stimulation of cortex [11]. However, research on chronic stimu lation supports the present findings since there is greater cortical damage at the ultrastructural level with CF using a roughened platinum elec trode of 1 mm'-gcom surface area chronically at 0.6 A/geom cm- [1], The type of wave form (monophasic vs. biphasic) also affects the blood brain barrier [25,28] and results in differences in tissue damage [II,36], It is difficult to compare the histological damage shown in the for mer studies since the times, methods, and parameters of stimulation vary. The electrode construction and types of electrode material also dif fer between experiments.…”

“…The stimulation pathologies correlated with the changes in stimula tion wave sequence are interesting [11,25,36]. If the stimulation elec trode (0.6 A/crn-) had the initial phase of the biphasic wave as positive (AF), the tissue damage that results is the loss of one cortical layer less than for CF.…”

“…The gold and platinum electrodes appear to be 'safe' electrodes at 0.1 A/'cm-' current density which is at the lower limit of stimulation required to produce a visual 'phosphene' or auditory '311010116' [3-6, 10, 11]. Al though the lower current density results in little tissue damage [10,11,36], this level is loo low for consistent threshold or suprathreshold stim ulation. However, with the reliable production of phosphenes at 0.6 A/cm-there is loss of cortical layers.…”

“…When depth electrodes are utilized the histological changes due to stimu lation following implantation arc not apparent [29]. Electrode implanta tion and stimulation result not only in histopathological alterations of tissue but in changes in respiratory enzymes, neuroglial alkaline phos phatase activity and other phosphate-releasing enzymes over time [29], Short stimulation times result in less damage than longer stimulation times utilizing surface or indwelling electrodes [1,11,28,36]. Not only are there dura-arachnoid-connective tissue encapsulation differences due to time of stimulation, but also the effects on the nervous system tissue increase over time.…”

Cerebral Tissue Response to Electrode Implantation

“…Recently electrode implantation alone has been shown to influence certain functional and behavioral patterns (Boast et al, 1976;Herzetal., 1974;Persson & Hansson, 1976;Robinson et al, 1975;Wetzel et al, 1969). Boast et al, (1976) have suggested that these changes might be related to hemodynamic alterations due to the hemorrhagic and traumatic influence of the implantation method.…”