Experimental neurology
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Experimental neurology · Apr 1986
Histopathologic evaluation of prolonged intracortical electrical stimulation.
Chronic stimulating microelectrodes fabricated from platinum-30% iridium (Pt-30%Ir) or activated iridium were implanted in assemblies of three in the left sensorimotor cortex of the cat and pulsed continuously at currents of 10 to 320 microA (100 to 3200 microC/cm2 X ph, 2 to 64 nC/ph) for periods of 24 h or for 23 h/day for 7 days. The microelectrodes had beveled tips with uninsulated geometric surface areas of 20 X 10(-6) cm2. Neuronal activity evoked by the focal stimulation was monitored by recording compound action potentials from the ipsilateral pyramidal tract. ⋯ Electrode dissolution appears to be best correlated with charge density and current density. Dissolution of the Pt-30%Ir microelectrode tip was observed by scanning electron microscopy at charge densities as low as 200 microC/cm2 X ph (1 A/cm2), whereas erosion of activated iridium microelectrodes occurred only at the highest charge and current densities (3200 microC/cm2 X ph, 16 A/cm2). Thus, the activated iridium electrode is superior to Pt-30%Ir for chronic stimulations, from the standpoint of electrode tip stability, because with the former, in contrast to the alloy, detectable erosion occurred only at an intensity well above that required for activation of nearby neurons.
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Experimental neurology · Apr 1986
Respiratory functions of the inferior pharyngeal constrictor and sternohyoid muscles during sleep.
We studied the respiratory activity of the inferior pharyngeal constrictor and sternohyoid muscles of the rat during non-rapid eye movement (non-REM) and REM sleep. Each animal carried chronically implanted electrodes for recording the integrated EMG activity of respiratory muscles as well as the electrocorticogram (ECoG) and postural tone (dorsal neck EMG). The latter permitted polygraphic identification of sleep states. ⋯ During REM sleep, the inferior pharyngeal constrictor and sternohyoid muscles retained their inspiratory activity. No tonic activity could be detected in either muscle. We conclude that the inferior pharyngeal constrictor and sternohyoid muscles safeguard upper airway patency in the two main sleep states.