Imprintability of Newly Hatched Domestic Chicks on an Artificial Object: A Novel High Time-Resolution Apparatus Based on a Running Disc

Abstract

In filial imprinting, newly hatched chicks repeatedly approach a conspicuous object nearby and memorize it, even though it is an artificial object instead of their mother hen. Imprinting on an artificial object in a laboratory setting has a clear sensitive period from post hatch days 1–3 in the case of domestic chicks. However, the establishment of imprintability are difficult to investigate because of the limitations of the behavioral apparatus. In this study, we developed a novel behavioral apparatus, based on a running disc, to investigate the learning processes of imprinting in newly hatched domestic chicks. In the apparatus, the chick repeatedly approaches the imprinting object on the disc. The apparatus sends a transistor-transistor-logic signal every 1/10 turn of the disc to a personal computer through a data acquisition system following the chick’s approach to the imprinting object on the monitor. The imprinting training and tests were designed to define the three learning processes in imprinting. The first process is the one in which chicks spontaneously approach the moving object. The second is an acquired process in which chicks approach an object even when it is static. In the third process, chicks discriminate between the differently colored imprinting object and the control object in the preference test. Using the apparatus, the difference in the chicks’ behavior during or after the sensitive period was examined. During the sensitive period, the chicks at post hatch hour 12 and 18 developed the first imprinting training process. The chicks at post hatch hour 24 maintained learning until the second process. The chicks at post hatch hour 30 reached the discrimination process in the test. After the sensitive period, the chicks reared in darkness until post hatch day 4 exhibited poor first learning process in the training. Thus, this apparatus will be useful for the detection of behavioral changes during neuronal development and learning processes.

Temporal hampering of thyroid hormone synthesis just before hatching impeded the filial imprinting in domestic chicks

“…Imprinting training and tests were conducted 30 h after hatching. These methods are similar to those in the study performed by Aoki et al, 2022a . (B) In one session of training, a movie, 20 s long, was repeatedly played on the monitor 180 times for 1 h. In the training movie, a yellow imprinting object appeared for 12 s. The object was static for the first 4 s, then repeatedly turned clockwise and anti-clockwise with artificial sounds for 6 s. After the object stopped moving, it remained static again for the last 2 s. A trial of 20 s was divided into five periods (4 s each) to analyze the performance of the chicks during training.…”

“…We used the running disc-based behavioral apparatus (25 cm in diameter) used in a previous study ( Aoki et al, 2022a ). The imprinting object was displayed on a thin-film transistor monitor (refresh rate: 56–75 Hz; size: 213 mm × 160 mm; type: LCM-T102AS, Logitec Corp., Tokyo, Japan).…”

“…The imprinting training was performed as described by Aoki et al (2022a) , and briefly outlined as follows: Two sessions (Training one and 2) were conducted at 1-h intervals at P1 and 30 h after hatching ( Figure 1A ). One training session involved playing a movie (20 s long) 180 times for 1 h ( Figure 1B ).…”

“…We recently developed a running disc-based behavioral apparatus to analyze the imprinting learning process ( Aoki et al, 2022a ). This apparatus records the approach behavior toward the imprinting object in milliseconds.…”

“…This indicates that the chicks proceeded stepwise from the first to the third imprinting learning process. At 30 h post-hatching, the chicks reached the third learning process, but the chicks before that age remained in the first or second learning processes ( Aoki et al, 2022a ). We think that this apparatus is useful for evaluating the effects of temporal thyroid hormone decrease caused by exposure to MMI during the pre-hatch period on the learning processes in imprinting after hatching.…”