Thyroid hormones determine the critical period of filial imprinting in chicks - in which the young animal acquires behavioural characteristics from its parent - and subsequent learning, reports a study in Nature Communications this week. These findings provide further understanding on an already functionally diverse group of hormones.
For birds, learning occurs during the sensitive period soon after birth. Filial imprinting aids the survival of juveniles through maternal care and in the absence of its mother, the imprinting object can be replaced by a wide variety of moving objects. Koichi Homma and colleagues exposed newly-hatched chicks to plastic bricks moving along a computerised belt system, which was activated by the chick's own movement. They then investigated the molecular events that occur during the sensitive period. They find that imprinting is caused by a rapid inflow of thyroid hormone into regions of the brain that are implicated in filial imprinting and that this flow of thyroid hormone extends the sensitive period.
The authors conclude that thyroid hormone is not only important for determining the start of the sensitive period, but also lays the foundation for learning processes that occur later in development.