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Monkeys Show Spontaneous Mirror Self-Recognition After Learning Precise Instrumental Mirror Use

Feb 14, 2017     Email"> PrintText Size

Self-awareness is a form of higher intelligence that can be revealed by mirror self-recognition in humans. Testing mirror self-recognition (MSR) has become the main approach to examining the existence of self-recognition in animals, and only a few species have passed this test.

In the standard face mark test for demonstrating MSR, an odorless nonirritant dye is placed on the face of the subject (without the subject’s awareness) that can only be seen in the mirror. Humans and several species of great apes could pass the test by touching the dye mark after looking at themselves in the mirror. However, whether failing the MSR test is a result of the lack of an animal’s self-recognition ability or the inadequacy of the mirror test remains controversial. 

A recent study conducted by researchers at Dr. GONG Neng’s team from the Non-human Primate Facility of the Institute of Neuroscience of Chinese Academy of Sciences demonstrated that monkeys showed spontaneous MSR behaviors after learning precise visual-proprioceptive association for mirror images. This work was published in PNAS.

Dr. GONG Neng's team in a previous study reported such MSR behaviors in monkeys after several weeks of visual-somatosensory association training, by applying an irritant laser light on the monkey’s face in front of the mirror.

In this study, researchers designed a new training strategy in which the monkey was only trained to use the mirror as an instrument to find hidden objects. They trained head-fixed monkeys seated in front of a mirror to touch, with spatiotemporal precision, a laser pointer light spot on an adjacent board that could only be seen in the mirror (Fig. A).

After several weeks of training, when the same laser pointer light spot was projected to the monkey’s face, a location not used in training, all three trained monkeys successfully touched the face area marked by the light spot in front of a mirror (Fig. B). All trained monkeys passed the standard face mark test for MSR both on the monkey chair and in their home cage. Importantly, distinct from untrained control monkeys, the trained monkeys showed typical mirror-induced self-directed behaviors in their home cage, such as using the mirror to explore normally unseen body parts (Fig. B). 

In this study, visual-proprioceptive training of rhesus monkeys to precisely locate objects outside the body has resulted in self-directed behaviors in front of a mirror. This work may shed light on the neural basis of MSR and self-awareness. It further suggests that the failure to demonstrate MSR in animals could be attributed to the lack of the ability in visual-proprioceptive association for the mirror images, rather than the absence of bodily self-consciousness.

Figure: (A) Visual-proprioceptive association training; (B) Mirror-induced self-directed behaviors. (Image by GONG Neng’s team)

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(Editor: LIU Jia)

Contact

GONG Neng

Institute of Neuroscience

Phone:
E-mail: ngong@ion.ac.cn

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