Figure 1.

Schematic of coronal brain section to illustrate potential pathways of focal to bilateral seizure spread. A, Neuronal lamination of right (R) and left (L) premotor cortex is illustrated by numerals 1 to 6, interconnected by the corpus callosum (CC, large arrow). Left and right ventral lateral (VL) nuclei of the thalamus are shown. B, Cobalt (Co²⁺) produces a seizure focus (star). Seizure activity reaches the left motor cortex and right VL quickly and simultaneously but arrives at the left VL but only after a long delay (dashed line). Cutting the CC prevents the bilateral spread of ictal activity. Suppression of VL via chemogenetic or optogenetic techniques decreases seizure amplitude and duration, confirming that the thalamus modulates (“amplifies”) focal seizure expression.