Reticular formation

The core of the brainstem, where nerve cells and fibers interlace like a net. In 1949 Giuseppe Moruzzi and Horace Magoun reported that stimulating it turns the EEG into the pattern of waking.

In 1935 Frédéric Bremer in Brussels cut through the base of the cat brain in two ways. Cats cut where the brain meets the spinal cord showed signs of both sleep and waking in their EEG and their eyes. Cats cut at the level of the midbrain seemed to stay continuously asleep, even though the pathways from the ears, eyes and nose were intact^[1].

In December 1948 Moruzzi and Magoun stimulated this part of the brainstem and saw the EEG of the motor cortex go flat. They wrote in the protocol book that its activity was completely inhibited, but recording from other areas that same day they realized the note gave a distorted picture^[3]. Their 1949 paper reported that stimulating the reticular formation replaced large, slow, synchronized waves with small, fast ones, a change that looked the same as arousal by natural stimuli, and that it did not travel along any of the known sensory or motor pathways^[2].

Looking back, they recalled that a steady background of less intense activity in this upward-running system might help maintain the waking state^[3]. What was measured was a cat's EEG and behavior; awake meant that the EEG became small and fast and the animal responded to stimuli.