Variability in the characteristics of pontogeniculooccipital spikes during paradoxical sleep.

An important criterion for identifying paradoxical sleep is the presence of a peculiar waveform recorded in the pons, lateral geniculate body, and visual cortex during that sleep state. These waveforms, termed PGO waves, have long been viewed as having large and constant amplitudes, an initial negative deflection in the visual cortex, and not being dependent on the levels of background illumination. Waveforms recorded during wakefulness have different characteristics, and these have been used to differentiate the waking state from paradoxical sleep. The present study demonstrated that most PGO waves have highly variable amplitudes during paradoxical sleep and that only a small fraction conform to the stereotypic wave characteristics of constant and large amplitudes and the presence of initial negative deflections. These findings argue against the criteria commonly used to differentiate PGO waves during paradoxical sleep from the eye movement potentials recorded in wakefulness.