Classical conditioning in a chimpanzee fetus

Nobuyuki Kawai1), Naoki Horimoto2), Seiichi Morokuma2), Chisato Douke3), Masayuki Tanaka3), Masaki Tomonaga3), and Tetsuro Matsuzawa 3)
1) Nagoya University, Japan, 2) Kyushu University, Japan, 3) Kyoto University, Japan

From the viewpoint of social transmission of knowledge, representation of events is important. Because all information to be transmitted include representations. Animals represent various events in environment. One of the simplest and robust demonstration of the usage of representations in animals is classical conditioning. Classical conditioning is acquired even by invertebrates and by young human infant as early as two days old. So far, however, conditioning of fetus in human and non-human primates has never assessed.
We investigated whether a conditioning is possible in a chimpanzee fetus. The conditioning started at 201 days gestational age (GA). To exclude the possibility of pseudo-conditioning, two kinds of pure tone was employed as conditioned stimuli, with the one tone (500 Hz) always followed by an unconditioned stimulus (US), while another (1000 Hz) was never followed by the US. The US was a vibroacoustic stimulation (VAS) of 80 Hz (110 Gal) upon mother's abdomen. The conditioning was carried out once in a week until 216 days GA by monitoring the fetus movements with ultrasonographic technique. Thereafter, it was conducted in almost everyday until labor at 233 days GA. There was no differential responding to both tones during embryo period. After delivery, however, the infant showed exaggerated responding to the tone of 500 Hz, but not to the tone of 1000 Hz, when the infant was tested by the two tones on the next day, 33rd, and 58th after birth. The amount of response, calculated by vocal and body movements, increased from right after the birth to the age of two month. Another chimpanzee infant of four month, which did not experience any conditioning, did not show any apparent response to the both tones.
These results strongly suggest that the chimpanzee fetus could distinguish the two tones, and establish conditioning at least after at 201 days GA, but the association was not expressed right after birth and required several days or a month to yield apparent behaviors.

 

KAWAI, Nobuyuki
Graduate School of Human Informatics,
Nagoya University
Furo-cho, Chikusa-ku, Nagoya, 464-8601, Japan
kawai@info.human.nagoya-u.ac.jp