Sergio M. Pellis

The structure of skilled forelimb reaching in the rat: A proximally driven movement with a single distal rotatory component

The movements of rats trained to reach through an aperture for food pellets, located on a shelf, were videorecorded and filmed from lateral and ventral perspectives for analysis using Eshkol-Wachman Movement Notation (EWMN). Reaching was subdivided into phases of locating the food and advancing the limb to grasp the food, bringing the food to the mouth, and returning to the starting position. Further analysis of the movements comprising these acts revealed a number of novel findings. (1) Most of the first phase of the movement is produced proximally, with the limb lifted, aimed, and advanced from the shoulder. (2) After the limb is lifted from the substrate to initiate reaching, it is carried to a parasagittal position so that the long axis of the forearm is aligned along the midline of the body. This aspect of the movement aims the limb toward the target. (3) The digits are opened as the limb is advanced from the aiming position toward the food. As the paw approaches the food, pronation of the palm is accomplished by abduction of the upper arm. (4) As the limb is retracted, the digits are closed to grasp the food. As retraction ends, the paw is supinated by a rotatory movement at the wrist. This is the only distal rotatory movement. (5) The position taken by the second forelimb, as it is adducted to aid in holding the food pellet for eating, resembles the aiming posture. The results are discussed in reference to the kinematics, neural control, and the evolutionary origins of reaching in the rat and other animals. Additionally, the results provide a framework for analysis of changes in movements produced by physiological manipulations.

Play-fighting differs from serious fighting in both target of attack and tactics of fighting in the laboratory rat Rattus norvegicus

Play-fighting is often difficult to differentiate from inhibited or immature serious fighting because both may utilize many of the same behavior patterns. In the rat the two behaviors involve different targets of attack. During play-fighting, snout or oral contact is directed at the opponents nape of the neck, whereas during serious fighting, male residents mostly direct their bites at the intruders rump. Although similar to those used in serious fighting, the behavior patterns used during play-fighting are modified to achieve the different targets of attack. Even though the tactics of attack and defense appear more adult-like with increasing age, the playful targets persist well into adulthood.

Agonistic versus amicable targets of attack and defense: Consequences for the origin, function, and descriptive classification of play‐fighting

Play-fighting appears to involve the behavior patterns of attack and defense otherwise seen in serious fighting. The degree of similarity, however, depends on the body targets attacked and defended during these forms of fighting. For many taxa, including diverse mammalian families and some birds, the same targets are attacked and defended during both play-fighting and serious fighting. However, for several species of muroid rodents, the targets of play-fighting are not the same as those of serious fighting. In these cases, the tactics of attack and defense are also different. It is argued that for these muroid species the playful targets have arisen from amicable behavior (e.g., social investigation, greeting, allogrooming) rather than, as appears to be the case in so many other taxa, from agonistic behavior. These data strongly suggest that “play-fighting” has evolved from different precursors in different taxa and thus has multiple origins. Furthermore, these data have an important bearing on the universal applicability of many of the suggested functions of play-fighting and also on how such behavior is to be described and classified.

Role reversal changes during the ontogeny of play fighting in male rats : attack vs. defense

From weaning until sexual maturity, the rates at which young male rats hold each other supine during play fighting appear to become progressively asymmetrical. These changes have been previously thought to reflect an initial lack of dominance and a later development of dominance-subordinance relationships. In this paper it is shown that pairs of male rats exhibit asymmetries in playful attack and playful defense throughout development. The changes, resulting in greater asymmetry of pinning rates, are shown to result from age-dependent changes in defensive tactics; the relationship, therefore, remains constant while the form of the behavior changes. Furthermore, it is not the animals showing the highest rates of playful attack who become dominant in older ages.

Identification of the possible origin of the body target that differentiates play fighting from serious fighting in syrian golden hamsters (Mesocricetus auratus)

Play fighting in the Syrian Golden hamster Mesocricetus auratus can be distinguished from serious fighting by the targets attacked in each case. In play fighting, the animals attack and defend the cheeks and cheek pouches, whereas in serious fighting they attack and defend the rump and lower flanks. Since play typically involves the use of behaviors borrowed from other functional contexts, this paper investigates the origin of the cheek target during play fighting. Comparison of resident-intruder serious fighting with awake and anesthetized intruders does not reveal the cheek to be an inhibited target for serious attack. Similarly, analysis of social investigation and allog-rooming, while revealing the ears to be important targets, do not show the cheeks to be targets in these behaviors. Sniffing, licking, and nibbling of the cheek area appear to occur mainly during sexual encounters by males. This area, seemingly a sexual target, may be the one utilized during play fighting.

Juvenilized play fighting in subordinate male rats

As pairs of male juvenile sibling rats that are housed together become sexually mature, they develop a dominance-subordinance relationship. These dominance relationships appear to be reflected in the play fighting of the pairmates both as juveniles and as young adults, in that the seemingly subordinate partner initiates more playful attacks at both ages. However, as adults, even though it is the subordinate that initiates more playful attacks, it is the subordinate that is pinned on his back by the partner most often. Dominant pairmates were found to switch to defensive patterns typically found in adult males. In contrast, the subordinates, when contacted on the nape, were more likely to retain the juvenile pattern of turning over to supine. Therefore, the subordinate pairmate of an adult pair of male siblings both initiates more playful attacks and defends itself in a more juvenile manner than its dominant partner, and this leads to it being pinned more frequently. This pattern of behavior by subordinate rats is suggested to function as a friendship maintenance mechanism permitting co-existence in multimale colonies.

Recovery from axial apraxia in the lateral hypothalamic labyrinthectomized rat reveals three elements of contact-righting: caphalocaudal dominance, axial rotation, and distal limb action

In earlier work, we showed that in rats, proprioceptive-tactile information is sufficient for contact-righting on the ground (from lying on one side to prone). Thus, axial rotation, starting with the shoulders and followed by the pelvis, occurs normally in labyrinthectomized animals with eyes occluded. After damage to the lateral hypothalamus, even with labyrinths intact, contact-righting is at first abolished (1-2 days postoperatively), and when it reappears, involves pushing by the hindlegs. Rostrocaudal contact-righting, involving axial rotation, takes 3-4 days to recover. If labyrinthectomy is combined with lateral hypothalamic damage, the deficit is exaggerated and recovery is greatly slowed down, now requiring 2-3 weeks. The present paper shows that during this prolonged period of recovery several transitional forms of righting are present, each produced by a different combination of limb and body axis movements. At first, axial rotation is absent, and righting is achieved only by pushing with the limbs. This is followed by a transitional form in which, even though axial rotation cannot be triggered directly by contact with the ground, it can be triggered indirectly as an allied reflex when the paw places on the ground. Eventually the body axis actively initiates the rotation to proneness (at first, in the pelvis, later in recovery, in the shoulders), with the limbs being carried. Recovery of axial rotation overlaps with the recovery of cephalic dominance, yielding complex intermediate forms of righting.

Visual modulation of vestibularly-triggered air-righting in the rat

Unlike cats, which can initiate righting in the air either with vestibular or visual input alone, the rat is dependent solely upon the labyrinths to trigger this response. We show, however, that the rat can modulate the onset and speed of its rotation according to the height above the ground from which it is dropped. In the absence of vision, rates initiate rotation with a latency of about 50 ms, irrespective of the height from which they are dropped. With vision, rats can modulate their latency to begin rotation, from about 102 ms at 50 cm, to about 39 ms at 7.5 cm. Similarly, as height of release decreases, the speed of rotation (i.e. degrees/ms) increases. Thus, in rats, even though vision cannot trigger air-righting, it does adaptively modulate this behavior as an allied reflex, increasing the likelihood that the animals will land on their feet.

Targets of attack and defense in play-fighting of the Djungarian hamster Phodopus campbelli: links to fighting and sex

Etude des cibles dattaque et de defense lors du jeu. Combat (play-fighting) chez les jeunes hamsters djungariens. Cette etude est reliee aux combats chez les adultes ainsi quau sexe

Air righting without the cervical righting reflex in adult rats

The current explanation of air righting in animals is that when falling supine in the air, labyrinthine stimulation triggers head rotation. The head rotation involves neck rotation which, via the cervical righting reflex, triggers rotation of the body. (In cats and monkeys, when the labyrinths are absent, visual stimulation when falling supine can also trigger this righting sequence.) In the present paper, a descriptive analysis of air righting in the rat shows that the shoulders rotate, carrying the unmoving head and neck passively along. Thus, for this species, labyrinthine input appears to trigger shoulder rotation directly, independently of the cervical righting reflex. This suggests that at least two physiological mechanisms exist for labyrinthine control of head rotation during air righting, one via the neck and the other via the shoulder girdle.