At a very young age, monkeys respond to their mirror image. When confronted with a mirror, monkeys react as if their reflection is another monkey. They display behaviors corresponding to their species' typical social behavior repertoire, including submission, aggression, affiliation and play [1]. These behavioral responses persist over time, but are usually more frequent during the first exposure and decline thereafter [1]. Short and repetitive mirror image stimulation (MIS), rather than continuous exposition, is the most efficient way to induce a persistent behavioral response [2]. The unique features of MIS as a social stimulus present good opportunities for the study of socio-emotional behavior in primates. MIS is very pertinent because of its capacities to mimic a social encounter, and is unique in the sense that the animal has control over, and is instrumental in, producing stimulus change.

Goal
The goal of the present experiment was to design and pilot a new task using MIS to assess emotional reactivity in infant rhesus macaques.

Subjects
Eight 3-month-old male and female infant rhesus macaques (Macaca mulatta) were used.

Apparatus
A test-cage was designed specifically for this mirror task, consisting of an opaque rear wall, two wire-mesh sidewalls, and a white Plexiglas front wall containing a window closed with a one-way mirror. A guillotine door was used to expose the subject to the mirror. One video camera was affixed behind the mirror to record the monkey's facial expressions and behaviors. Another video camera was placed on one side of the cage to record the subject's location.

Procedure
The subject was introduced to the cage with the mirror masked and left for a 5-minute acclimation period. Then, a series of ten 1-minute trials was given with the mirror exposed; each trial was separated by a 15-second inter-trial interval (ITI) with the mirror hidden. Afterwards, the subject was left in the cage for a 5-minute recuperation period.

Behavioral observations and analysis
A detailed ethogram (involving a total of 50 behaviors) was defined and used to code the behavioral responses of each subject. Different categories of behaviors were coded: mirror directed behaviors, activity, location, looking behaviors, facial expressions, social behaviors, non-social behaviors, vocalizations, and self-directed behaviors.

The behavioral reactions were coded using The Observer Video-Pro. The durations and/or frequencies of each behavior were analyzed with the statistics program SPSS.

Preliminary results and conclusions
Preliminary results indicate that the first reactions of infants towards their mirror image differed strikingly between subjects. However, these reactions changed progressively, probably because the 'other monkey' displayed the same behavior as the subject. Three types of emotional reactivity to the mirror image emerged: (1) threatening becoming avoidant; (2) fearful becoming affiliative; and (3) affiliative becoming more affiliative.

More analysis is required, but this new task seems, a priori, to be effective for assessing emotional reactivity and extracting temperamental differences in young rhesus monkeys. This mirror task could thus be very useful for assessing the effects of brain lesions on emotional reactivity in primates.

References

1. Anderson, J.R.; Chamove, A.S. (1986). Primates, 27(1), 63-82.
2. Gallup, G.G. (1977). Dev. Psychobiol., 10(3), 281-284.

Paper presented at Measuring Behavior 2002 , 4^th International Conference on Methods and Techniques in Behavioral Research, 27-30 August 2002, Amsterdam, The Netherlands

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