Mouse thalamocortical slices maintain synaptic connections between thalamus and cortex. When perfused with low Mg2+ medium, thalamocortical slices exhibited spontaneous thalamocortical 2-6 s long bursts of rhythmic activity every 15-30 s, which was potentiated by pentylenetetrazol and abolished by severing thalamocortical connections. These oscillations were similar in frequency and duration to normal and pathological thalamocortical rhythms in vivo. In vitro studies of these thalamocortical rhythms may prove valuable in understanding cellular factors important in rhythm generation.