Transmission of burst responses through slices of rat cerebral cortex.

1. Slices of rat's forebrain, 400 micron thick, have been cut and maintained in a bath perfused with warm oxygenated Krebs solution. Records were made with extracellular micropipettes of the neural responses to local stimulation of the cortex itself or the underlying white matter. 2. Single stimuli at either of these sites could produce an all-or-nothing burst response among nearby neurones. This response usually lasted 0.2-0.5 s during which repetitively discharging cortical units could be recorded at all cortical depths. 3. This burst response was transmitted from the stimulated point across the cortex in all directions with a velocity of roughly 0.1 m s-1. 4. Complete recovery of excitability among neurones generating the burst response took about 10 s. 5. Removal of Ca2+ from the perfusate prevented transmission of this response, as did a high concentration of Mg2+ or 160 mg/100 ml of ethanol. 6. Propagation of the burst response was not dependent upon the integrity of the underlying white matter; it required only that any 20% of the cortical thickness was intact and undamaged. 7. In coronal sections of brain the response could be transmitted from one hemisphere to the other provided that the corpus callosum was intact.