Head direction cell - wikipedia.org  ## Metadata - Author: **wikipedia.org** - Full Title: Head direction cell - Category: #articles - URL: https://en.wikipedia.org/wiki/Head_direction_cells ## Highlights - **Head direction** (**HD**) **cells** are [neurons](https://en.wikipedia.org/wiki/Neuron) found in a number of brain regions that increase their firing rates above baseline levels only when the animal's head points in a specific direction ([View Highlight](https://read.readwise.io/read/01hn8ck8p32ec325y6vmgrfg44)) - HD cells continue to fire in an organized manner during sleep, as if animals were awake.[[22]](https://en.wikipedia.org/wiki/Head_direction_cell#cite_note-22) 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](https://en.wikipedia.org/wiki/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 are still active, or silent, at the same time. ([View Highlight](https://read.readwise.io/read/01hn8cxvnywjcanmwt3gtv7pcw))