State Dependent Activity in Thalamocortical Cells
Extracellular recordings (Part A) of thalamocortical cells in the cat LGNd during the transition from sleep to waking by McCarley et al. at Harvard University revealed that during sleep the neurons repetitive bursts of 3-5 action potentials, while waking or REM (rapid-eye movement) sleep (when dreams are most vivid), the neurons generate repetitive, single spike activity.
Similarly, Hirsch et al., in France, discovered (Part B) through intracellular recordings from these neurons during these state transitions, that the membrane potential of the cell depolarized considerably in the transition from slow wave sleep to waking or REM sleep. During periods of EEG-synchronization (slow wave sleep), bursts of action potentials are generated on top of slow and broad spikes. However, in the transition to the waking or REM-sleep state, the membrane potential depolarized and these slow spikes disappeared and were replaced with repetitive, single spike activity.
We have investigated these pronounced changes in activity generation through the use of in vitro slice techniques