Head direction cells efference copy") preparing the network for an impending head turn. HD cells continue to fire in an organized manner during sleep, as if animals were awake. However, instead of always pointing toward the same direction—the animals are asleep and thus immobile—the neuronal "compass needle" moves constantly. In particular, during rapid eye movement sleep, a brain state rich in dreaming activity in humans and whose electrical activity is virtually indistinguishable from the waking brain, this directional signal moves as if the animal is awake: that is, HD neurons are sequentially activated, and the individual neurons representing a common direction during wake
Journal of Physical and Chemical Reference Data "Journal Citation Reports", the journal has a 2017 impact factor of 3.510. Journal of Physical and Chemical Reference Data The Journal of Physical and Chemical Reference Data is a quarterly peer-reviewed scientific journal published by AIP Publishing on behalf of the National Institute of Standards and Technology. The objective of the journal is to provide critically evaluated physical and chemical property data, fully documented as to the original sources and the criteria used for evaluation, preferably with uncertainty analysis. The editors-in-chief are Donald R. Burgess, Jr, and Allan H. Harvey. The journal is abstracted and indexed in the Science Citation