Age related differences in the strategies used by middle aged adults to solve a block design task.

In the present study, it was proposed to investigate the effects of aging on the strategies used to solve a block design task and to establish whether these strategies may be associated with differential patterns of ability. Two groups of subjects, 30 young adults (aged 20-35 years) and 30 middle-aged adults (aged 45-60 years) were set a computer version of the Kohs task and a battery of tests. An age-related decrease in fluid intelligence (Gf) and visual-spatial ability (Gv) was observed, along with the fact that most of the older subjects used a global strategy rather than a synthetic one. On the other hand, while continuing to use strategies of the analytic type, the older subjects looked more frequently at the model and scored high on crystallized intelligence (Gc). These findings are discussed from two different points of view: the theory of hierarchical stimuli and the hypothesis that metacognitive ability, which is thought to rely on Gc, may increase with age, and thus compensate for the loss of Gf and Gv.

Basal ganglia and supplementary motor area subtend duration perception: an fMRI study.

Brain imaging studies on duration perception usually report the activation of a network that includes the frontal and mesiofrontal cortex (supplementary motor area, SMA), parietal cortex, and subcortical areas (basal ganglia, thalamus, and cerebellum). To address the question of the specific involvement of these structures in temporal processing, we contrasted two visual discrimination tasks in which the relevant stimulus dimension was either its intensity or its duration. Eleven adults had to indicate (by pressing one of two keys) whether they thought the duration or the intensity of a light (LED) was equal to (right hand) or different from (left hand) that of a previously presented standard. In a control task, subjects had to press one of the two keys at random. A similar broad network was observed in both the duration-minus-control and intensity-minus-control comparisons. The intensity-minus-duration comparison pointed out activation in areas known to participate in cognitive operations on visual stimuli: right occipital gyrus, fusiform gyri, hippocampus, precuneus, and intraparietal sulcus. In contrast, the duration-minus-intensity comparison indicated activation of a complex network that included the basal ganglia, SMA, ventrolateral prefrontal cortex, inferior parietal cortex, and temporal cortex. These structures form several subnetworks, each possibly in charge of specific time-coding operations in humans. The SMA and basal ganglia may be implicated in the time-keeping mechanism, and the frontal-parietal areas may be involved in the attentional and mnemonic operations required for encoding and retrieving duration information.

Does cerebral activity change in middle-aged adults in a visual discrimination task?

The purpose of this study was to assess changes in cerebral activity in middle-aged adults (MA: 50 years) compared to young adults (YA: 20 years). Subjects had to compare the duration or the intensity of a visual stimulus with a previously memorized standard. Evoked potentials were recorded, and a dipole model (obtained from PET data on young adults) was applied for fitting late-latency components. MA performance was poorer than YA performance. Task-specific ERP late components were found (P3 in intensity, CNV in duration), but P3 had a lower amplitude and CNV was less frontal in MAs compared to YAs. The activity of the dipoles that generate late components - cuneus in the intensity task, right frontal in the duration task, and anterior cingulate in both tasks-was less ample or less peaked in MAs than in YAs. This study characterizes neurobiological effects of aging that may already be visible during midlife.

ERPs and PET analysis of time perception: spatial and temporal brain mapping during visual discrimination tasks.

ERPs were recorded from 12 subjects performing duration and intensity visual discrimination tasks which have been previously used in a PET study. PET data showed that the same network was activated in both tasks [P. Maquet et al., NeuroImage 3:119-126, 1996]. Different ERP waveforms were observed for the late latency components depending on the dimension of the stimulus to be processed: frontal negativity (CNV) for the duration task and parieto-occipital positivity (P300) for the intensity task. Using BESA software, the sources were first modelled with a "PET dipolar model" (right prefrontal, right parietal, anterior cingulate, left and right fusiforms). To obtain a better fit for ERPs recorded in each task, two sources (cuneus, left prefrontal area) had to be added. Consistently with PET findings, dipole modelling indicates that duration and intensity dimensions of a visual stimulus are processed in the same areas. However, ERPs also reveal prominent differences between the time course of the dipole activations for each task, particularly for sources contributing to the late latency ERP components. In the intensity task, dipoles located in the cuneus, the anterior cingulate, and the left prefrontal area yield largest activity within the P300 interval, then activity diminishes rapidly as the stimulus ends, whereas in the duration task, the cuneus and anterior cingulate are still active several hundred milliseconds following stimulus offset. Moreover, in the duration task, the activity of the right frontal dipole parallels the CNV waveform, whereas in the intensity task, this dipole is largely inactive. We assume that the right frontal area plays a specific role in the formation of temporal judgments.

A comparison between the effect of intentional modulations and the action of L-dopa on gait in Parkinson's disease.

The aims of the present study were to analyze how L-Dopa allows parkinsonian patients to increase their gait velocity and to compare these L-Dopa-induced modifications with those achieved by consciously attempting to walk as fast as possible (intentional modulations). The 'intentional modulations' of velocity were also compared with those of healthy elderly subjects. The results showed that parkinsonian patients walked more slowly, with shorter strides and shorter durations of swing phase, and longer durations of stance and double support phases, although no differences were observed for cycle duration. The mechanisms involved in increasing gait velocity were found to differ according to whether this was achieved through the action of L-Dopa, or by intentional increases in velocity. Intentional increases in velocity were greater than those caused by the effect of L-Dopa. The patients, however, used efficient strategies to increase their velocity when under the influence of L-Dopa. As L-Dopa leads to a ceiling effect on stride length, the patients can increase their velocity by modifying the cycle to such an extent that it compensates for the limitation in stride length. This strategy effectively increases velocity, despite the L-Dopa ceiling effect. The effects of L-Dopa on locomotion and, more generally, on motor control aspects are discussed.

Dopa-sensitive and dopa-resistant gait parameters in Parkinson's disease.

Quantitative analysis of gait was performed in 20 parkinsonians before and 1 h after the acute administration of L-Dopa in order to discriminate between the Dopa-sensitive and the Dopa-resistant kinematic gait parameters. The stride length and the kinematic parameters (swing velocity, peak velocity) related to the energy were Dopa-sensitive. The improvement of the bent forward posture by L-Dopa may explain the stride length increase. Temporal parameters (stride and swing duration, stride duration variability), related to rhythm, were Dopa-resistant. Experimental data argue for the importance of force control in maintaining the posture. The stride length variability, possibly related to the variability of force production shown to exist in parkinsonians was not significantly improved by L-Dopa. In Parkinson's disease different hypotheses might explain the inexorable aggravation of gait disorders along the course of the disease: (1) an advancing disorder of coordination between postural control and locomotion, (2) if some gait parameters like stride length and kinematic parameters are Dopa-sensitive, the others are Dopa-resistant and thus may involve other mechanisms than dopamine deficiency.

Quantitative analysis of gait in Parkinson patients: increased variability of stride length.

Analysis of the spatio-temporal and kinematic parameters of locomotion recorded in 21 parkinsonian patients compared to 58 normal elderly subjects showed significant differences in all the recorded parameters. However the relationship between these parameters was preserved, as was the basic locomotor pattern. The variability of stride length, more marked in parkinsonian patients, increased as a function of the clinical stages of Hoehn and Yahr. This index could be useful in assessing the course of the disease in patients.

Unintentional modulations of human gait by optical flow.

Visual whole-field motion is known to trigger motor responses which minimize retinal slip (VOR, OKN and control of balance). In locomotion, however, the retinal slip is utilized to control the velocity and direction of displacement. The present experiment was aimed at determining how the velocity of optical flow affects the regulation of locomotion. Unintentional modulations in velocity, stride length and cadence were analyzed using a task in which artificial optical flow gave the subjects the impression they were walking at a different speed than they actually were. Slight but systematic modifications in locomotion were observed: experimental variation of the optical flow resulted in a decrease in stride length. None of the subjects were aware of this decrease, despite the fact that their muscular and articular afferences provided them with supraliminal information. Although visual flow velocity is usually a direct consequence of walking velocity, experimental modifications of visual flow were found here to cause unintentional modulations in locomotor parameters (stride length and cadence) more than in their product (velocity).

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.

[A new method of quantitative analysis of parkinsonian gait: report of 6 patients]. / Une nouvelle méthode d'analyse quantitative de la marche du parkinsonien: illustration sur 6 patients.

A simple quantitative method of gait analysis in parkinsonism is presented. In this method, spatial and temporal parameters (stride length and duration, stance duration and double support duration) and cinematic parameters (velocity) were evaluated. A pilot trial performed in 6 patients highlighted the pathological aspect of the parkinsonian gait as compared to the gait of healthy elderly subjects. A significant degradation (reduced speed, diminished stride length, short duration of the double support stage) was noted, even when parkinsonians were compared with the oldest of the control subjects.