Behavioral adaptation in neonatal chicks following embryonic vestibular system rearrangement.

Micro-surgery was performed on chick embryos during the second day of incubation (45-50 hours). Either one otocyst was removed or was rotated 180 degrees and reimplanted. The chicks' behavior was studied for 1-13 weeks after hatching. The unilateral loss or rearrangement of vestibular (and auditory) input led initially to abnormal behavior patterns, usually consisting of poor righting reflexes, deficits in locomotion, balance and pecking accuracy, and a pronounced head nystagmus. However, in every case, these abnormalities were corrected within a few days after hatching, so that the operated animals became almost indistinguishable from normal controls. Histological evidence confirmed the extent of the loss of the vestibular and auditory structures and nuclear amalgams. The observed capacity of the neonatal chick to adapt to this sensory loss or disorientation is a rather rare example of infraprimate behavioral adjustment or modifiability, contrasting with the frequent demonstrations of behavioral rigidity in lower forms.