Low-resolution brain electromagnetic tomography revealed simultaneously active frontal and parietal sleep spindle sources in the human cortex

Analyses of scalp-recorded sleep spindles have demonstrated topographically distinct slow and fast spindle waves. In the present paper, the electrical activity in the brain corresponding to different types of sleep spindles w as estimated by means of low-resolution electromagnetic tomography. In its new implementation, this method is based on realistic head geometry and sol ution space is restricted to the cortical gray matter and hippocampus. In m ultichannel all-night electroencephalographic recordings, 10-20 artifact-fr ee 1.25-s epochs with frontally, parietally and approximately equally distr ibuted spindles were marked visually in 10 normal healthy subjects aged 20- 35 years. As a control condition, artifact-free non-spindle epochs 1-3 s be fore or after the corresponding spindle episodes were marked. Low-resolutio n electromagnetic tomography demonstrated, independent of the scalp distrib ution, a distributed spindle source in the prefrontal cortex (Brodmann area s 9 and 10), oscillating with a frequency below 13 Hz, and in the precuneus (Brodmann area 7), oscillating with a frequency above 13 Hz. In extremely rare cases only the prefrontal or the parietal source was active. Brodmann areas 9 and 10 have principal connections to the dorsomedial thalamic nucle us; Brodmann area 7 is connected to the lateroposterior, laterodorsal and r ostral intralaminar centrolateral thalamic nuclei. Thus, the localized cort ical brain regions are directly connected with adjacent parts of the dorsal thalamus, where sleep spindles are generated. The results demonstrated simultaneously active cortical spindle sources whi ch differed in frequency by approximately 2 Hz and were located in brain re gions known to be critically involved in the processing of sensory input, w hich is in line with the assumed functional role of sleep spindles. (C) 200 1 IBRO. Published by Elsevier Science Ltd. All rights reserved.