Impedance measurements in brain tissue of animals using microvolt signals

摘要: Abstract A technique is described for measurement of cerebral impedance with signals in the tissues 1 to 20 μv amplitude, and having a current density order 10 −13 amperes per square micron electrode surface at 1000 cycles/sec. The system will resolve cent shift resistive impedance, limited sensitivity only by input noise differential amplifier. Using chronically implanted coaxial electrodes cat both EEG measurements, certain clear consistent changes were observed, particularly dendritic layer hippocampal pyramidal cells septum, response somatic, olfactory, visual, auditory stimuli, changing physiological states consciousness, as well drug-induced during barbiturate anesthesia effects hallucinogenic agents. Certain repeatable also observed seizures. Physiological peripheral stimuli all produced transient decrease layer. Arousal from normal sleep was followed baseline towards lower impedance. Waning consciousness accompanied return higher level. Normal trains very regular sinusoidal waves septum about 3 cycles/min. During Nembutal anesthesia, there marked increase layers, pre-drug levels recovery consciousness. psychotomimetic cyclohexamine drug converse series changes. Seizures induced hippocampus septal stimulation small rapid perturbations rhythmic cycle/sec, occurring on rising baseline. Differences noted between initial seizure episodes those identical days later. possible relationship these ionic shifts volume neuronal elements (or both) glial tissue, extracellular space discussed, reference modulating influence tissue electrotonic phenomena dendrites.