Abstract
For inexperienced brains, some stimuli are more attractive than others. Human neonates and newly hatched chicks preferentially orient towards face-like stimuli, biological motion, and objects changing speed. In chicks, this enhances exposure to social partners, and subsequent attachment trough filial imprinting. Early preferences are not steady. For instance, preference for stimuli changing speed fades away after 2 days in chicks. To understand the physiological mechanisms underlying these transient responses, we tested whether early preferences for objects changing speed can be promoted by thyroid hormone 3,5,3′-triiodothyronine (T3). This hormone determines the start of imprinting’s sensitive period. We found that the preference for objects changing speed can be re-established in female chicks treated with T3. Moreover, day-1 chicks treated with an inhibitor of endogenous T3 did not show any preference. These results suggest that the time windows of early predispositions and of sensitive period for imprinting are controlled by the same molecular mechanisms.
Highlights
Experience plays a crucial role in shaping neural and behavioural development
Chicks tested on day 1 showed a significant preference for animacy (V(35) = 458, p < 0.05, d = 0.44), whereas chicks tested on day 3 did not show any preference (V(36) = 310, p = 0.72, d = 0.08)
T3- and vehicle-injected females showed a significant difference in their preferences (W(29) = 183.5, p < 0.001, d = 1.59)
Summary
Early experience effects are stronger during certain periods of development (Hensch, 2005). Lorenz (1935) used the term “critical period” to refer to the fact that rather than being available throughout the lifespan, filial imprinting is shown only during a limited period of life. This time window can be extended for a few more days when a proper stimulus is not immediately available (Bolhuis, 1991). Sensitive periods are windows of plasticity during brain development, in which experience has a powerful effect (Hensch, 2005; Dehorter and Del Pino, 2020) Being a flexible period with the characteristics of a self-terminating process (Bolhuis, 1991), imprinting is better known as a “sensitive period.” Sensitive periods are windows of plasticity during brain development, in which experience has a powerful effect (Hensch, 2005; Dehorter and Del Pino, 2020)
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