Eye movement-associated discharge in brain stem neurons during desynchronized sleep.

The relationship between isolated eye movement during desynchronized sleep and unit discharge in the pontine brain stem was investigated during spontaneously occurring desynchronized sleep episodes in cats. Units histologically localized to the gigantocellular tegmental field (FTG) showed the earliest and most prominent discharge rate increases relative to eye movement onset. Inflection points for discharge rate increases of these reticular elements peaked 150-100 msec before eye movement onset and discharge maxima occurred in the time period 50 msec before and 50 msec after eye movement onset. Within the FTG there was a correlation between giant cell density and intensity of discharge rate increases relative to eye movement onset, indicating that the giant cells are the neurons that show this pattern most strongly. The exponential form of the curves of FTG inflection points and discharge maxima is compatible with self-excitation as a mechanism for recruitment in the FTG pool. Units in the central, lateral, and paralemniscal tegmental reticular fields had activity curves qualitatively similar to those of the FTG, but with less intensity of discharge rate change and shorter lead-times. The discharge pattern was quite different in the two other cell groups studied. Many units in the tegmental reticular nucleus had bursts of discharges tightly locked to eye movement onset, while pontine grey units had an irregular pattern and a low degree of phase-locking to eye movement onset. Of the neurons studied, the giant cells of the FTG best satisfy correlational criteria for eye movement generation during desynchronized sleep. These findings support the hypothesis that the FTG is part of a generator system for desynchronized sleep and may contribute directly to the elaboration of the phasic events characterizing that state.