Rapid plasticity attenuation after birth revealed by habituation in chicks

Habituation and dishabituation are two forms of experience-dependent plasticity. Habituation consists in the reduction of responsiveness to a reiterated irrelevant stimulus, whereas dishabituation is the recovery of the response to the habituated stimulus when a new one is presented. Studying the ontogeny of these processes can shed light on early organism’s plasticity and propensity to learn. In the experiments, chicks (Gallus gallus) within a running-wheel ran toward an artificial companion placed at a distance. Stop of running was the dependent variable. In Experiment 1, three groups of chicks were administered two sequences of five 250ms-bursts of white-noise, presented one hour apart, in two consecutive days at different ages (1-2-day old, 2-3-day old, or 3-4-day old). In Experiment 2, 1-day old and 3-day old chicks underwent ten 1sec-predator’s call to test for habituation, one 1sec-burst of white-noise to test for response generalization, and five 1sec-predator’s call to assess response recovery and then dishabituation. Experiment 1 showed that short-and long-term habituation appear soon after hatching. However, 1-day old chicks habituated more than 3-day old ones, indicating a greater amount of learning. Experiment 2 extended the results of Experiment 1, and demonstrated that in chicks, after hatching, the facilitating mechanisms of dishabituation appears as early as habituation.