Boguslaw P. Gorny

The impairments in reaching and the movements of compensation in rats with motor cortex lesions: an endpoint, videorecording, and movement notation analysis

Reaching for food by rats, with the limb contralateral to limb area motor cortex damage, was analyzed using end-point scores, videoanalysis, and Eshkol-Wachmann Movement Notation (EWMN). End point results from groups of rats with small, medium, and large lesions showed reaching success and amount of food grasped per reach decreased with increases in lesion size. Videoanalysis and EWMN showed that the impairments were attributable to: (1) an inability to pronate the paw over the food by abduction of the upper arm, and (2) an inability to supinate the paw at the wrist to orient the food to the mouth. There were no obvious impairments in locating food using olfaction, in positioning the body in order to initiate a reach, or in clasping the digits to grasp food. There were only mild impairments in lifting, aiming, and advancing the limb. In rats with medium and large lesions, loss of pronation and supination were compensated for by a variety of whole body movements. These findings are discussed in reference to neural and behavioral mechanisms underlying recovery of function and the contribution of the motor cortex to skilled movements in the rat and other species.

Skilled reaching in rats and humans: evidence for parallel development or homology

Forelimb reaching by the rat is used as a paradigm for the experimental study of neural control, plasticity, and recovery of function after injury, in the expectation that results are generalizable to humans. The present study was done to compare rat to human reaching movements. The movements of both species were videorecorded and subjected to frame-by-frame analysis using Cartesian (spatial and velocity) and Eshkol-Wachman Movement Notation (EWMN) systems. The component movements of reaching, their sequence and velocity profiles, and their topography were similar in the two species. Both species also displayed more supination and lengthened grasping times when reaching for small as opposed to large objects. Both rats and humans moved the limb medially using the upper arm to aim it when they were required to reach through an aperture but in a free reaching test only rats continued to aim the limb. Human movements were characterized by greater blending of movement components, more variability, and independent digit use. Arguments are presented that the similarities and differences in rat and human reaching are not trivially accounted for by limb and task similarities. The many similarities in the movements of the two species provide evidence for at least parallel development or perhaps even homology.

Arpeggio and fractionated digit movements used in prehension by rats.

Although it is well known that rats can use one limb to reach for and retrieve food, the way that the paw and digits are used to grasp the food has not been described. Using results obtained from a high speed videorecording procedure, the present study describes how small and large pieces of food are located by the paw and grasped with the digits in a reaching task. As the rat pronates a paw over food, the tips of digits 5 through 2 are successively placed and spread over the target area in an arpeggio movement. The target area is then palpated by downward movements of the palm. If food is not present, the paw is withdrawn without grasping. If food is contacted, the food is manipulated and grasped by the digits with grasp patterns that depend upon food size. Large food pellets are contacted with the pad of digit 3 and then grasped between digits 3 and 4. Small food pellets are first contacted with pad of digit 4 and are grasped between digits 4 and 5. Digit 5 can be partially flexed medially so that the food is held in a modified power grip between digits 4 and 5. The results show that rats use a whole paw movement to position the digits in an arpeggio fashion and they use fractionated digit movements to grasp food. The results are discussed in relation to the possible comparative and anatomical significance of the movements.

The Defensive Strategies of Foraging Rats: A Review and Synthesis

Foraging rats (Rattus norvegicus) are vulnerable to, and must protect themselves from, two kinds of threat. Conspecifics will attempt to steal their food and they themselves will be subject to predation. To safeguard their food and themselves they are able to call upon a surprising number of strategies and defensive maneuvers. This paper summarizes their defensive strategies, the stimulus features of their surroundings that modify these strategies, and the cognitive processes that they use to evaluate their susceptibility to threat. Their strategies are discussed both as antecedents of human behavior and in relation to their relevance in understanding brain function.

Postprandial scanning by the rat (Rattus norvegicus): The importance of eating time and an application of "warm-up" movements.

We observed the movements of rats (Rattus norvegicus) after they had eaten food pellets of various size or hardness. With rooted hindlegs, they made head scans, with vibrissae in contact with the substrate, that began over the area below where they had eaten and then expanded to include almost the entire area surrounding their body. Scanning was not contingent on the presence of dropped food. It occurred when rats ate on a screen through which any dropped crumbs could fall. It also occurred when rats were trained to find food at a location distant to where they ate. Although the duration of scanning increased in proportion to the size of food consumed, when eating time was varied, using food items of similar size but different hardness, scanning increased in proportion to eating time. Postprandial scans resemble the exploratory (warm-up) movements that bridge transitions from immobility to locomotion. We propose that a subset of the movements of warm-up are co-opted in this postprandial period. It is likely that in natural foraging situations they are useful for food searching. The results suggest that although the motor system may be conservative in the number of actions that it can produce, diversity is achieved by applying fundamental patterns to many uses.

Making two movements at once: Impairments of movement, posture, and their integration underlie the adult skilled reaching deficit of neonatally dopamine-depleted rats

Adult rats depleted bilaterally of dopamine in infancy display a profound impairment in skilled forelimb use in reaching for food. This impairment was investigated using end-point measures of reaching success, movement analysis, and kinematic measures. The rats made few successful reaches in either an easy or a difficult reaching test. Their reaches were characterized by many attempts in which trajectories of the limb were irregular and the movements were slow. Their lack of success was related in part to an impairment in making component movements of the reach, including aiming, pronating, grasping, and supinating the paw and in releasing the food pellet. It was also related to an inability to adjust posture as the limb was voluntarily moved toward the food. The results are consistent with the hypotheses that the basal ganglia, including its dopamine innervation, is important for enabling voluntary movements and postural adjustments and perhaps also the simultaneous performance of two movements at the same time.

Dopamine and skilled limb use in the rat: more severe bilateral impairments follow substantia nigra than sensorimotor cortex 6-hydroxydopamine injection

The experiments examined the suggestion that the dopaminergic (DA) projection to the motor cortex are involved in the motor impairments that follow complete hemitelencephalic DA depletions. The neurotoxin, 6-hydroxydopamine (6-OHDA), was injected unilaterally into the sensorimotor cortex (MCtx), the ventral tegmental area (VTA), or into the substantia nigra pars compacta (SN) of rats trained to reach for food with either forelimb. The SN injections produced large (greater than 95%) unilateral striatal dopamine (DA) depletions and severe bilateral impairments in limb use. VTA and MCtx injections did not produce impairments in limb use or severe depletions of cortical DA. An effective test of the contribution of cortical DA to skilled limb use must await a more effective technique for producing selective cortical DA depletion. Nevertheless, the results suggest that the severe impairments of skilled forelimb use that follow hemitelencephalic DA depletions may stem primarily from depletion of the nigrostriatal DA projection.

Impaired dodging in food-conflict following fimbria-fornix transection in rats: a novel hippocampal formation deficit

It is well known that damage to the hippocampal formation (Ammons horn, dentate gyrus, fimbria-fornix, and other pathways) produces impairments in spatial navigation and in certain forms of learning. Lesions within these structures have also been reported to produce some motor impairments, but the nature of these impairments is less understood. The present study examined the effects of fimbria-fornix lesions on food wrenching and dodging, social interactions that occur when one rat attempts to steal food from a conspecific, who in turn attempts to protect the food by an evasive movement. Lesion effectiveness was confirmed histologically and electrophysiologically, by the loss of hippocampal rhythmical slow-wave activity (RSA or theta), and by changes in open field behavior (increased open field behavior, less thigmotaxis and more defecation). Analysis of the social interaction indicated when an eating control rat was approached by a conspecific that was attempting to steal its food, it prevented the theft by dodging, a rapid lateral maneuver involving forequarter turning and stepping with the rear limbs. Rats with fimbria-fornix lesions were significantly impaired in dodging and so were more likely to lose their food to the robber. This novel deficit in motor behavior is discussed in relation to contemporary theories of hippocampal function and it is suggested that the deficit may be caused by an inability of the fimbria-fornix damaged animals to disengage attention from eating in order to initiate an evasive movement to protect food. The finding of this novel deficit underscores the importance of considering both loss as well as release phenomena in the analysis of hippocampal formation function.