Contribution of Neuron Dendrites to Extracellular Sustained Potential Shifts

Abstract

This chapter discusses the contribution of neuron dendrites to extracellular sustained potential shifts. Mounting evidence suggests that extracellular sustained potential (SP) shifts are generated by depolarizations in glia cells in response to the rise in extracellular potassium activity that occurs when neighboring neurons are activated. Extracellular potassium activity increases have been shown to occur in the visual cortex in response to visual stimuli. This cortical response also occurs during barbiturate “spindle” activity and during epileptic seizures. In the spinal cord, though a close correlation exists between glial cell membrane potential and the extracellular SP, no such correlation is apparent for the neural cell membrane potential and the evoked SP. The event-related type of SP, such as the CNV in humans and its homolog in animals, differs from the potassium-glia cell type in two important aspects: (1) the event-related SP is evoked by the contextual significance of a natural or expected stimulus instead of electric activation of small afferent pathways, and (2) the event-related SP can be evoked only in the conscious brain and is always absent in the anesthetized brain.