Progressive cortical synchronization of ponto-geniculo-occipital potentials during rapid eye movement sleep

Phasic events, termed ponto-geniculo-occipital potentials, appear in the brainstem, thalamus and cerebral cortex during rapid eye movement sleep. In the cat, the species of choice for ponto-geniculo-occipital studies, these field potentials are usually recorded from the lateral geniculate thalamic nucleus and visual cortex. However, the fact that brainstem cholinergic neurons play a crucial role in the transfer of ponto-geniculo-occipital potentials to the thalamus, coupled with the evidence that mesopontine tegmental neurons project to virtually all thalamic nuclei, together explain why ponto-geniculo-occipital potentials are recorded over widespread territories, beyond the visual thalamocortical system. Here we demonstrate, by means of multi-site unit and field potential recordings from sensory, motor and association cortical areas in behaving cats, that: (i) ponto-geniculo-occipital potentials appear synchronously over the neocortex; and (ii) that their cortical synchronization develops progressively from the period preceding rapid eye movement sleep by 30-90 s (pre-rapid eye movement), to reach the highest degree of intracortical coherence during later epochs of rapid eye movement sleep. We propose that the widespread coherence of cortical ponto-geniculo-occipital potentials underlies the synchronization of fast oscillations (30-40 Hz) during rapid eye movement sleep over many, functionally distinct cortical territories implicated in dreaming, as brainstem-induced ponto-geniculo-occipital-like potentials are consistently followed by such fast oscillations.