The spatial parameters encoded by hamsters during exploration: a further study.

The information used by hamsters while reacting to a spatial change after habituation of exploration was analysed. In our previous work, animals had the opportunity to explore a circular open field containing four different objects, for two sessions. During the third session, when the locations of two objects were exchanged, hamsters re-explored selectively the exchanged objects. The present study, relying on the same procedure, examined the possibility that subjects' detection of the change relied on an egocentric strategy, i.e., that hamsters were using the pattern formed by the horizontal alignment of the objects as seen from the location at which they were introduced into the field. Therefore, in Experiment 1, the placement of the subjects at the beginning of the test session was different from that used on previous sessions. Most hamsters still displayed a reaction to the object displacements, although their reactions were not selectively directed to the exchanged objects. Experiment 2 revealed that, when the subjects were placed at a different location at the beginning of each session, the change in object locations was not detected. Lastly, Experiment 3 showed that removing the only available extra-apparatus visual cue did not prevent hamsters from selectively reacting to the displaced objects. These results are discussed with respect to the notion that during exploration hamsters encode local views of the environment, which ultimately leads to the building up of overall cognitive maps after they have been given sufficient exploration.

Akathisia, motility, and locomotion in healthy volunteers.

Apomorphine (10 micrograms/kg subcutaneously with oral domperidone 10 mg), oral sultopride (50 mg), and placebos were given to nine normal volunteers, using a Latin-square design and double-blind procedures. A battery of tests was applied before the dose, and after the dose after time lapses of 15, 45, 90, 105, 120, and 180 min. Spatiotemporal and dynamic gait parameters, gait stability, and modulations remained unchanged with all three treatments. Apomorphine induced repeated yawning in all subjects. Akathisia was observed in four of nine subjects with sultopride. Sultopride was associated with drowsiness and sleepiness on visual analog scales. Akathisia may be related to decreased dopaminergic activity in the prefrontal cortex and mesocortical dopamine system blockade. The imbalance between mesocortical and nigrostriatal dopaminergic systems might explain the fact that sultopride in our experiment modified spontaneous behavior but not volitional behavior. Thus, it is possible to discriminate between two types of increased motor activity, and motility must be distinguished from locomotor activity.

Slowness in elderly gait.

The aim of this research was to better understand how gait slows with age. We analyzed the kinematic parameters of locomotion (velocity, stride length, cycle duration, swing and double support durations), and their interrelationships both in the slowing process due to aging and in intentional modulations of velocity. The experiments were carried out on a group of 67 elderly adults (aged 60 to 80+) walking with a free gait and a fast gait. This group was compared to a young population in equivalent situations. The results show that the main characteristics of the elderly gait are the shortening of strides and the increasing of the double support phase. However, these properties seem to be due to the slowness of the elderly gait more than to more specific alterations affecting this population since identical features were also observed in the slow gait of the young subjects. Furthermore, the ability to intentionally modulate velocity observed in this study was not altered by aging. These results suggest that elderly gait can be said to be normal if one takes the velocity into account.

Short-term and long-term habituation of exploration in rats, hamsters and gerbils.

Short-term (within-session) and long-term (between-session) habituation of exploratory behavior was studied in rats, hamsters and gerbils. Subjects were observed in an open field containing four different objects during three 15-min sessions with an 8-14 h interval between each session. Their exploratory activity was measured by the numbers of contacts they made with these objects. The three species differed from each other in both their long-term and short-term habituation of exploration. Rats showed disrupted between-session habituation because of an important initial burst of activity at the beginning of each session. In contrast, hamsters and gerbils displayed between-session habituation, but within-session habituation occured during the first session only. These results are discussed in relation both to the adaptive value of exploration, and to the natural habitat of each species.