Relationships between electrically induced slow negative potentials and changes in extracellular potassium concentrations in cerebral cortex of the cat.

Experiments were carried out on cats under deep nembutal anaesthesia. Local cortical stimulation evoked both a slow negative potential (SNP) and an increase in extracellular potassium ([K+]o) which were maximal in the upper cortical layers. The decline in the K(+)-potential in deeper layers was slower than in the upper ones so that with time [K+]o became equal in upper and deeper layers. No SNP was recorded at that time, perhaps explaining why K(+)-potential decay is of longer duration than the SNP. Transcallosal stimulation also evoked an SNP but gave a lesser difference in delta [K+]o in upper and deeper layers. The lower amplitude of the SNP evoked by transcallosal stimulation may be due to these circumstances. These data could clarify the mechanism of correlation disturbance between SNPs and K(+)-potentials in the cerebral cortex.