Exploration and motor activity in juvenile and adult rats exposed to hypergravity at 1.8 G during development: a preliminary report.

Pups from gestating rats exposed to hypergravity (1.8 G) or to normal gravity at the perinatal period were evaluated for motor activity, exploration and social interactions during juvenile and adult stages. By comparison to controls, the hypergravity group had shorter latencies before choosing a maze arm in a T-maze and a lower number of exploratory pokes in a hole board. During dyadic encounters, the hypergravity group had a lower number of self-grooming episodes and shorter latencies before crossing under the opposing rat. In contrast, no intergroup differences were observed during exploration of an elevated plus-maze and a light-dark box. These results indicate that exposure to 1.8 G during development appears to decrease exploratory tendencies in the hole board and fear-related responses in T-maze and social interaction tests.

Relationships of personality traits with performance in reaction time, psychomotor ability, and mental efficiency during a 31-day simulated climb of Mount Everest in a hypobaric chamber'.

Exposure to chronic hypoxia induces behavioral and mood disturbances and alterations in cognitive functions. We examined the relationships of personality traits, including trait-anxiety, with performance in binary visual reaction time, psychomotor ability, and mental efficiency, using the psychological database of the 'Everest-Comex 97' experiment, which consisted in a 31-day simulated climb in a hypobaric chamber from sea level to 8,848 m altitude. Analysis yielded a significant positive correlation between the climbers' mean reaction time at hypoxic conditions and preclimb scores on trait-anxiety (as assessed by Spielberger's State-Trait Anxiety Inventory) and further significant negative correlations with both Factor A (reserved-outgoing) and Factor G (expedient-conscientious) of the Cattell Sixteen Personality Factor Questionnaire. In contrast, no significant correlation was found between the climbers' mean psychomotor performance and mental efficiency with personality traits, including anxiety. These findings agree with those of previous studies: (i) anxiety could mediate stimulus-response tasks but not more complex tasks requiring strategic processes, (ii) individuals with personality traits such as 'reserved' and 'expedient' could have slight advantages in processing information on stimulus-response tasks. Limitations in study design are also discussed.

Multi-muscle control of head movements in monkeys: the referent configuration hypothesis.

It is suggested that the nervous system may specify a referent configuration (R) of the body determined by the set of the threshold joint angles at which all skeletal muscles may be silent. At the same time, electromyographic (EMG) activity and forces are generated to resist deflections of the body from this configuration. The R configuration may thus be considered an internal geometric image with which the actual body configuration (Q) is compared. Thereby the difference between the R and Q is a major factor determining the recruitment and gradation of the activity of each skeletal muscle. Control systems may produce movements by changing the R configuration according to task demands. The referent hypothesis predicts that when the R and Q configurations match each other, a global minimum in the EMG activity of all muscles involved should occur, an event most likely observed in movements with reversal in direction. To test the validity of the R hypothesis for head movements, three-dimensional kinematics and EMG activity of 14 functionally diverse neck muscles were analysed in monkeys during head rotations to and from fruit targets placed beyond the oculomotor range. Despite the functional and anatomical diversity of the neck muscles, the activity of all muscles was minimised at a reversal point of the movement trajectory, as predicted by the R hypothesis. This study thus illustrates the notion that a change in the internal geometric image of a biomechanical system may underlie movement production.

Relationships between mood states and performances in reaction time, psychomotor ability, and mental efficiency during a 31-day gradual decompression in a hypobaric chamber from sea level to 8848 m equivalent altitude.

High altitude is characterized by hypoxic environmental conditions that may induce a set of pathological disorders, known as acute mountain sickness. In addition to the physiological symptoms, exposure to high altitude may also produce adverse changes in motor skills, mental efficiency, and mood states, including anxiety. In the present study, we investigated the relationships between mood states, including anxiety, and performance changes in reaction time, psychomotor ability and mental efficiency in eight climbers participating in the 'Everest-Comex 97', a 31-day gradual decompression in a hypobaric chamber from sea level to 8848 m equivalent altitude. Tests of visual reaction time, manual dexterity, and number ordination were used; anxiety responses and mood states were assessed using the Spielberger State-Trait Anxiety Inventory (STAI) and the 'Profile of Mood States' (POMS), respectively. A significant positive correlation was found between the climbers' performance in reaction time and changes in state-type anxiety levels, suggesting that anxiety could lead to an improved reaction time. In addition, significant negative correlations were also found between the climbers' performance in psychomotor ability, mental efficiency, and reaction time, and several POMS factors, including Tension, Hostility, Confusion, and Fatigue. Overall, these data indicate, in agreement with previous studies, that anxiety may favour, or at least not alter, the processes of information of relatively simple tasks, such as reaction time, and further suggest that adverse changes in moods could modulate performance negatively.

Effects of dopaminergic agents and of an NMDA receptor antagonist on motor coordination in Lurcher mutant mice.

Lurcher mutant mice, characterized by an ataxic gait and olivocerebellar degeneration, were evaluated for motor coordination in the coat-hanger test after peripheral injections of two doses of dextromethorphan, a noncompetitive N-methyl-D-aspartate receptor antagonist, L-dopa/carbidopa, and SKF 77434, a dopamine D1 receptor agonist. There was an improvement in the distance traveled on the suspended horizontal string after 25 and 50 mg/kg of dextromethorphan and 37.5 mg/kg of L-dopa/carbidopa, but not after SKF 77434. None of the drugs reduced movement times or increased latencies before falling. These results indicate that NMDA receptor antagonism or stimulation of some dopaminergic mechanisms partially improve genetically determined cerebellar ataxia in mice.

Performance of visually triggered wrist movements task in monkey: an application of information theory to evaluate deficits following unilateral substantia nigra pars reticulata lesion.

On the basis of an information theory approach, visual-motor efficiency (VME) was analyzed during pointing movement tasks in rhesus monkeys. This application was used to evaluate deficits in the ability to perform pointing movements as well as to chart the progress of the monkey during the chronic stage recovery period following unilateral lesion of the medial part of the substantia nigra pars reticulata. This unilateral lesion produced slight but significant chronic contralateral head roll tilt associated with body turning and induced profound modification of the VME at the beginning of the chronic stage of the symptomatology. Recovery developed in the following weeks, leading to a 3-fold increase in VME. However, at the end of the test (4 weeks postoperative), performance remained sub-normal: a decrease of 20-30% when compared to the control.

Muscular after-contraction and ongoing postural reactions in standing and sitting humans.

Muscular after-contraction (MA-C) and the ongoing postural reaction of the body was studied in standing and sitting subjects in two visual situations: eyes open or closed. EMG of trapezius and latissimus dorsalis and 3D kinematic recordings of the left scapula were analysed. The release of the long-lasting sustained isometric contraction at the level of the scapula produced a muscular after-contraction consisting of involuntary muscular contraction associated with a trunk movement similar to the unroll of a spiral. The unroll of the spiral is in the opposite direction when we compare the standing and sitting situations. We suppose that the muscular after-contraction reveals the activity of central tonigenic structures in evoking involuntary trunk movements in humans and stresses the importance of the initial postural situation (standing or sitting) and the visual condition in the characteristics of these involuntary movements.

Neurobehavioral evaluation of lurcher mutant mice during ontogeny.

Lurcher mutant mice were compared to normal littermate controls for body weight, body righting, negative geotropism, sensorimotor coordination (rotating grid, wire suspension, rotorod), and visuomotor coordination requiring swimming toward a pole during postnatal (P) days 0-30. Lurcher mutants had a lower body weight on P20-P30 and were slower before performing the complete body righting response on P13-P30. Because of postural instability during the negative geotropism test, lurcher mutants turned quicker up the slope than normal mice. The mutants fell sooner from the rotating grid on P11-P14, from the horizontal wire on P15-P16, and from the rotorod on P14-P30. Lurcher mutants were also slower before swimming to the pole or climbing to the top of the pole and were inferior in pole climbing height on P22-P30. These results indicate test-selective and time-selective neurobehavioral deficits during ontogeny in a spontaneous cerebellar mutant.

Dorsal striatal lesions in rats. 1: Effects on exploration and motor coordination.

Rats with small dorsal striatal lesions were compared to sham-operated controls in a series of test measuring their exploratory behavior in a T-maze, a hole-board, and an elevated plus-maze. Motor coordination was evaluated in the inclined grid and in the square bridge tests and grip strength in the wire suspension test. The rats with dorsal striatal lesions were not impaired in the motor coordination tests, the grip strength test, nor in spontaneous alternation. By contrast, an increase of emergence latencies in the elevated plus-maze and a reduction of motor activity in the hole-board confined space during the early part of testing were observed in rats with dorsal striatal lesions. These results are ascribed to a lesion-induced situation-specific increase in inhibition.

Dorsal striatal lesions in rats. 2: Effects on spatial and non-spatial learning.

Rats with small electrolytic lesions of the dorsal striatum were evaluated in acquisition of spatial learning, sensorimotor learning, and a straight runway food approach response and its extinction. No differences were detected between rats with dorsal striatal lesions and sham-operated controls during acquisition of hidden and visible trials in the Morris water maze. Neither was an intergroup difference observed during acquisition of the rotorod test of motor coordination. Lesioned rats were not impaired in running for a food reward, but their running latencies on day 2 of extinction were lower than those of controls, an indication of perseveration. These results indicate that perseverative responding may occur in dorsal striatal lesioned rats in the absence of spatial or sensorimotor defects.

Effect of group size on social organization in rats with restricted access to food.

In groups of rats subjected to a experimental design in which access to the feeder was made difficult, a behavioural differentiation developed. Some rats brought back food pellets to the cage (carrier rats) while the others stayed in the home cage (noncarrier rats). We compared the social organization underlying the adoption of these roles in groups of three and six rats. Reducing group size increased the incidence of carrier rats, leading to a smaller number of differentiated groups. However, differentiated groups seemed to adapt to the situation in the same way as the groups of six rats. In both cases, carriers could be distinguished from noncarriers by their way of obtaining food and by how food possession stopped. Moreover, behavioural variables generally exhibited better stability in small groups and noncarrier/carrier rat relations were more extensive, resulting in more typical organization. The potential use of such groups for pharmacological studies is discussed.