Activity of Common Marmosets (Callithrix jacchus) in Limited Spaces: Hand Movement Characteristics Andrzej W. Przybyszewski, Sripad Sosale, and Avi Chaudhuri McGill University The increasing popularity of marmoset monkeys (Callithrix jacchus) in anatomical, behavioral, and electrophysiological studies has called for a detailed analysis of their natural behavior within limited spaces. In the present study, the authors analyzed hand movements during horizontal and vertical progressions in a cylinder. The trajectory of each hand covered the entire cylinder floor during horizontal progressions and the entire cylinder wall during vertical progressions. Different marmosets have different patterns of hand movement. The average maximum angle of hand movements for all marmosets during horizontal and vertical progressions oscillates, although the average over time is constant and similar for both hands, whereas head movements during horizontal progressions become smaller with successive progressions. Another observed difference between rats and monkeys was in the size of head and hand movements at the beginning of each experimental session. During the 1st horizontal progression, all marmosets moved their heads to a greater extent than their hands. This sequential head and hand movement is referred as bistable behavior. The bistable pattern of motor behavior, which was also observed in successive progressions, may be derived from an inherent fear of predators or exploratory interest of a novel environment. Keywords: motor behavior, visual inspection, exploration, bistability, lateralization A major trend in brain research over the past decade has been to focus on pathological changes caused by illness or injury and how such changes can elevate our understanding of the mechanisms underlying regeneration and plasticity of the central nervous sys- tem. In an increasingly aging society, there are a growing number of people that show age-related pathological behavior with unknown or idiopathic etiologies. One example in terms of motor move- ments is apraxia. The widely accepted definition of apraxia is a “disorder of skilled movement not caused by weakness, akinesia, deafferentation, abnormal tone or posture” (Heath, Westwood, Roy, & Young, 2002; Heilman, Schwartz, & Geschwind, 1975; Liepmann, 1900). The riddle of apraxia arises from the observation that occurrence of abnormal movements depends on the condition of testing (De Renzi & Lucchelli, 1988). As such, clear protocols need to be developed in terms of animal models. A first step toward establishing an animal model for apraxia and other motor disorders would, however, require a more precise understanding of motor function in freely moving normal animals. The common marmoset (Callithrix jacchus) is becoming in- creasing popular as a primate model of freely moving behavior. The primary and higher sensory brain structures related to vision, audition, and somatosensory functions have been well mapped (Bendor & Wang, 2005; Dias, Robbins, & Roberts, 1996; Kru- bitzer & Kaas, 1990; McLoughlin & Schiessl, 2006; Rosa & Tweedale, 2000). Marmosets live in hierarchical groups that per- mit behavioral studies to include social interactions, interanimal communication, group relationships, learning, imitation, and par- enting behavior (De Renzi & Lucchelli, 1988; MacDonald, Spetch, Kelly, & Cheng, 2004; Ross & French, 2004; Steenhuis & Bryden, 1989). Furthermore, their small size and relative ease of mainte- nance make them an increasingly attractive species for behavioral and neurobiological research. From a neurobiological perspective, marmoset monkeys also offer certain advantages. Recent efforts at understanding neuro- plastic changes at both physiological and molecular levels have sparked considerable excitement after reported findings that sen- sory deafferentation initiates neural activation from surrounding cortical sites (Florence, Taub, & Kaas, 1998; Huffman & Kru- bitzer, 2001; Jain, Catania, & Kaas, 1997; Pons et al., 1991). A key advantage with marmosets is that their unfolded cortex permits easier access for anatomical and physiological studies. Experimen- tal models of apraxia or motor dysfunction can therefore be ex- plored with greater ease in this species in addressing mechanistic features of neuroplastic cortical reorganization (Fang, Jain, & Kaas, 2002). We recently have documented similarities in marmoset and rat exploratory behavior in a cylinder test through a comparison of head movements in both species (Gharbawie, Whishaw, & Whishaw, 2004; Przybyszewski, Sosale, & Chaudhuri, 2006). However, rats rely more on olfactory and tactile cues for their exploratory behavior, whereas primates are more reliant on vision for guiding motor behavior. Thus, our prior findings of a similarity between the two species in terms of head movements are counter- Andrzej W. Przybyszewski, Sripad Sosale, and Avi Chaudhuri, Depart- ment of Psychology, McGill University, Montreal, Quebec, Canada. This work was supported by a research grant to Avi Chaudhuri from the Natural Sciences and Engineering Research Council of Canada. Correspondence concerning this article should be addressed to Andrzej Przybyszewski, Department of Psychology, McGill University, 1205 Dr Penfield Avenue, Montreal, QC H3A 1B1 Canada. E-mail: przy@ego.psych.mcgill.ca Journal of Comparative Psychology Copyright 2007 by the American Psychological Association 2007, Vol. 121, No. 3, 332–344 0735-7036/07/$12.00 DOI: 10.1037/0735-7036.121.3.332 332