same time, including the activity of a singly neuron. Their monitoring was so sensitive that they could decipher the precise communications, even when the neurons appeared to be relatively quiet. With the help of a sophisticated mathematical analysis, they were able to decipher the complex conversations. Spontaneously persistent activity The neocortex spends 90% of our sleeping time in a slow wave pattern. Activity fluctuates slowly between active and dormant states, approximately once every second. The researchers focused on the brain area that has many parts; the entorhinal cortex. Neocortical activity was mirrored in the outer part of the entorhinal cortex, but the inner part of the entorhinal cortex behaved differently. The neurons remained in their active state in the inner entorhinal cortex, even when the outer part went quiet - "as if the neurons were remembering something the neocortex had recently said". The scientists called this phenomenon "spontaneously persistent activity". Furthermore, this spontaneous persistent activity made the neurons in the hippocampus become very active too. The hippocampus became quieter when the neocortex was active, however. The data the scientists collected provided them with a clear interpretation of how the "dialogue" between the different brain parts occurred. Mehta said: "During sleep the three parts of the brain are talking to each other in a very complex way. The entorhinal neurons showed persistent activity, behaving as if they were remembering something even under anesthesia when the mice could not feel or smell or hear anything. Remarkably, this persistent activity sometimes lasted for