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
Evolution of the cochlea Evolution of the cochlea Cochlea is Latin for “snail, shell or screw” and originates from the Greek word κοχλίας "kohlias". The modern definition, the auditory portion of the inner ear, originated in the late 17th century. Within the mammalian cochlea exists the organ of Corti, which contains hair cells that are responsible for translating the vibrations it receives from surrounding fluid-filled ducts into electrical impulses that are sent to the brain to process sound. This spiral-shaped cochlea is estimated to have originated during the early Cretaceous Period, around 120 million years ago. Further, the auditory innervation of the spiral-shaped cochlea