FoundationalConceptsNeuroscience

a state of neural activity more akin to wakefulness than to other
stages of sleep. In addition, these REM-active neurons send signals to
the eye muscles, triggering eye movements, the hallmark feature of
REM. Finally, there is inhibition of motor output from the cortex via
the spinal cord. During REM, the sleeper’s body is relaxed, and there
is little movement, save for the eyes. If it weren't for the inhibition of
motor output, the sleeper’s body would jerk and move around quite a
bit, because the motor areas in the frontal lobes of the cerebrum are
very active during REM.
A notable aspect of REM sleep is its association with vivid dream-
ing. If someone in the REM stage of sleep is awakened, they will
generally say they were dreaming, and often dreaming quite vividly.
Perhaps 90 percent of the time this is the case. In contrast, if someone
is awakened during a NREM stage of sleep, they only infrequently re-
port dreaming vividly, perhaps 5 percent of the time. When awakened
from NREM, they might say that some kind of mental activity was
happening, some thoughts are recalled, but not the vivid sensory and
emotional experiences that one recalls in REM-stage dreams.
This strong relationship between REM sleep and vivid dreaming fits
with the robust neural activity throughout the cerebral cortex during
REM. If visual areas of the cortex are neurally activated, even if there
is no visual stimulation to the eye, one may have experiences of seeing
things. Ditto for other sensory areas. Thus, the neural activity in the
cortex during REM sleep is believed to be associated with our sensory,
motor, and emotional experiences during dreams. In vivid dreams we
see things, we hear things, we sometimes even taste and smell things.
We feel things emotionally. We have experiences of moving around,
and even moving around in ways that aren’t normally possible, like
flying.
Because of the cholinergic nature of cortical activation during REM,