Sub-second functional imaging by electrical impedance tomography

Functional imaging of the human brain using electrical impedance tomography (EIT) is reported, where the measurement data were collected over a period of 308 ms. Initiation of the measurement sequence occurred at times ranging from 70 to 740 ms after administration of visual or auditory stimuli to two volunteers. The reconstructed images of conductivity change due to individual visual stimulus events correspond with anatomical regions known to be involved in visual sensory processing and the processing of cognitive reflexes. We propose that the mechanism enabling this EIT imaging capability is concerned with synaptic effects upon local conductivity of bulk brain tissue, which is supported by the observations of Klivington and Galambos. In turn, the sensitivity of EIT to this effect is much greater than previously expected, due to the high conductivity of in-vivo skull.