The conductivity of the human skull: Results of in vivo and in vitro measurements

The conductivity of the human skull was measured both in vitro and in vivo. The in vitro measurement was performed on a sample of fresh skull placed w ithin a saline environment. For the in vivo measurement a small current was passed through the head by means of two electrodes placed on the scalp, Th e potential distribution thus generated on the scalp was measured in two su bjects for two locations of the current injecting electrodes, Both methods revealed a skull conductivity of about 0.015 boolean OR /m. For the conduct ivities of the brain, the skull and the scalp a ratio of 1:1/15:1 was found . This is consistent with some of the reports on conductivities found in th e literature, but differs considerably from the ratio 1 :1/80:1 commonly us ed in neural source localization. An explanation is provided for this discr epancy, indicating that the correct ratio is 1:1/15:1.