Tag Archives: dreams

REM sleep and saccades

When we sleep we pass through a cycle of types of sleep. One of these types is REM (rapid eye movement) sleep and if we are awqkened during REM sleep we report dreaming. During REM sleep movement of the body is suppressed (except of sleep-walkers). Only the eyes are moving under the eye lids. These eye movements resemble the regular rapid movement of the eyes from one fixation to another when awake, called saccades.

A recent paper (Thomas Andrillon, Yuval Nir, Chiara Cirelli, Giulio Tononi, Itzhak Fried. Single-neuron activity and eye movements during human REM sleep and awake vision. Nature Communications, 2015; 6: 7884 DOI: 10.1038/ncomms8884) compares REMs and saccades. The research was carried out on epileptic patients being prepared for surgery by having electrodes implanted deep in the brain for 10 days. In this case there were 9 patients with electrodes in the medial temporal lobe. The MTL is thought of as a bridge between vision and imagining visual scenes on the one hand and memory on the other. As well as recording activity from neurons, the researchers also recorded movement of the eye muscles and conventional EEC from various parts of the scalp.

They found the REMs and saccades were very similar in their pattern of activity in the brain. This says something very interesting about consciousness. When the eyes move in a saccade there is saccadic suppression of the information arriving via the optic nerve from the eyes. There are signals arriving and they affect brain activity but they do not register in consciousness; the gap in visual information is also hidden from consciousness. We are, in affect, as when watching a movie, viewing a series of still images and creating a continuous effect. So saccades are associated with creating a continuous effect from a train of discrete, discontinuous signals. (At least that is one theory.)

The type of dreaming that is associated with REM sleep can be seen as a very similar process, a form of consciousness that is cut off from actual sensory input and from control of skeletal muscles. The purpose of these dreams is unclear but it probably involves some aspect of memory processing. So perhaps the dreams are a series of discontinuous images divided by REMs, leaving no trace of the gaps during the eye movement, as in awake consciousness.

But why would the eye movement by required to create the conscious process during sleep? Perhaps it drives it, or controls it, or times its components, or perhaps it is not required but cannot be eliminated. What interesting questions! They may help to understand conventional consciousness as well as dreams.

Here is the abstract: “Are rapid eye movements (REMs) in sleep associated with visual-like activity, as during wakefulness? Here we examine single-unit activities (n 1⁄4 2,057) and intracranial electroencephalography across the human medial temporal lobe (MTL) and neocortex during sleep and wakefulness, and during visual stimulation with fixation. During sleep and wakefulness, REM onsets are associated with distinct intracranial potentials, reminiscent of ponto-geniculate-occipital waves. Individual neurons, especially in the MTL, exhibit reduced firing rates before REMs as well as transient increases in firing rate immediately after, similar to activity patterns observed upon image presentation during fixation without eye movements. Moreover, the selectivity of individual units is correlated with their response latency, such that units activated after a small number of images or REMs exhibit delayed increases in firing rates. Finally, the phase of theta oscillations is similarly reset following REMs in sleep and wakefulness, and after controlled visual stimulation. Our results suggest that REMs during sleep rearrange discrete epochs of visual-like processing as during wakefulness.