Mental images across the adult lifespan: a behavioural and fMRI investigation of motor execution and motor imagery

Neural substrates of levodopa-responsive gait disorders and freezing in advanced Parkinson's disease: a kinesthetic imagery approach

Gait disturbances, including freezing of gait, are frequent and disabling symptoms of Parkinson's disease. They often respond poorly to dopaminergic treatments. Although recent studies have shed some light on their neural correlates, their modulation by dopaminergic treatment remains quite unknown. Specifically, the influence of levodopa on the networks involved in motor imagery (MI) of parkinsonian gait has not been directly studied, comparing the off and on medication states in the same patients. We therefore conducted an [H2 (15) 0] Positron emission tomography study in eight advanced parkinsonian patients (mean disease duration: 12.3 ± 3.8 years) presenting with levodopa-responsive gait disorders and FoG, and eight age-matched healthy subjects. All participants performed three tasks (MI of gait, visual imagery and a control task). Patients were tested off, after an overnight withdrawal of all antiparkinsonian treatment, and on medication, during consecutive mornings. The order of conditions was counterbalanced between subjects and sessions. Results showed that imagined gait elicited activations within motor and frontal associative areas, thalamus, basal ganglia and cerebellum in controls. Off medication, patients mainly activated premotor-parietal and pontomesencephalic regions. Levodopa increased activation in motor regions, putamen, thalamus, and cerebellum, and reduced premotor-parietal and brainstem involvement. Areas activated when patients are off medication may represent compensatory mechanisms. The recruitment of these accessory circuits has also been reported for upper-limb movements in Parkinson's disease, suggesting a partly overlapping pathophysiology between imagined levodopa-responsive gait disorders and appendicular signs. Our results also highlight a possible cerebellar contribution in the pathophysiology of parkinsonian gait disorders through kinesthetic imagery.

Do older adults perceive postural constraints for reach estimation?

BACKGROUND/STUDY CONTEXT: Recent evidence indicates that older persons have difficulty mentally representing intended movements. Furthermore, in an estimation of reach paradigm using motor imagery, a form of mental representation, older persons significantly overestimated their ability compared with young adults. The authors tested the notion that older adults may also have difficulty perceiving the postural constraints associated with reach estimation.

METHODS

The authors compared young (Mage = 22 years) and older (Mage = 67) adults on reach estimation while seated and in a more postural demanding standing and leaning forward position. The expectation was a significant postural effect with the standing condition, as evidenced by reduced overestimation.

RESULTS

Whereas there was no difference between groups in the seated condition (both overestimated), older adults underestimated whereas the younger group once again overestimated in the standing condition.

CONCLUSION

From one perspective, these results show that older adults do perceive postural constraints in light of their own physical capabilities. That is, that group perceived greater postural demands with the standing posture and elected to program a more conservative strategy, resulting in underestimation.

Effects of healthy ageing on activation pattern within the primary motor cortex during movement and motor imagery: an fMRI study

The increase in older adults over the coming decades will be accompanied by a greater burden of chronic neurological diseases affecting the motor system. The motor system adapts to maintain motor performance with the primary motor cortex (BA4) emerging as a pivotal node within this neuroplastic process. Studies of ageing often consider BA4 a homogenous area but cytoarchitectonic studies have revealed two subdivisions, an anterior (BA4a) and posterior subdivision (BA4p). Here we focus upon the effects of ageing on the involvement of BA4a and BA4p during movement and motor imagery (MI). Thirty-one right-handed healthy volunteers were recruited and screened for their ability to perform imagery (5 subjects excluded). The sample was split into an older group (n = 13, mean age 56.4 SD 9.4) and a younger group (n = 13, mean age 27.4 SD 5.3). We used an fMRI block-design (auditory-paced [1 Hz] right hand finger-thumb opposition sequence [2,3,4,5, 2...]) with MI & rest and actual movement & rest. We explored the distribution-based clustering and weighted laterality index within BA4a and BA4p. The involvement of BA4p during MI (measured with distribution-based clustering) was significantly greater in the older group (p<0.05) than in the younger group. Hemispheric balance of BA4p decreased with age during MI (Spearman rho -0.371; p<0.05), whereas that of BA4a decreased with age during actual movement (Spearman rho = -0.458 p<0.01). Irrespective of age, we found BA4 is involved during motor imagery, strengthening the rationale for its potential use in older subjects. These findings suggest that the functions of the subdivisions of BA4 are differentially affected by ageing and have implications regarding how ageing affects the cognitive processes underlying motor functions.

Mental representation for action in the elderly: implications for movement efficiency and injury risk

Recent research findings indicate that with older adulthood, there are functional decrements in spatial cognition and more specially, in the ability to mentally represent and effectively plan motor actions. A typical finding is a significant over- or underestimation of one's actual physical abilities with movement planning-planning that has implications for movement efficiency and physical safety. A practical, daily life example is estimation of reachability--a situation that for the elderly may be linked with fall incidence. A strategy used to mentally represent action is the use of motor imagery--an ability that also declines with advancing older age. This brief review highlights research findings on mental representation and motor imagery in the elderly and addresses the implications for improving movement efficiency and lowering the risk of movement-related injury.

Age-specific activation of cerebral areas in motor imagery--a fMRI study

INTRODUCTION

The objectives of this study were to study the age-specific activation patterns of cerebral areas during motor execution (ME) and motor imaging (MI) of the upper extremities and to discuss the age-related neural mechanisms associated with ME or MI.

METHODS

The functional magnetic resonance imaging technique was used to monitor the pattern and intensity of brain activation during the ME and MI of the upper extremities in 20 elderly (>50 years) and 19 young healthy subjects (<25 years).

RESULTS

No major differences were identified regarding the activated brain areas during ME or MI between the two groups; however, a minor difference was noted. The intensity of the activated brain area during ME was stronger in the older group than in the younger group, while the results with MI were the opposite. The posterior central gyrus and supplementary motor area during MI were more active in the younger group than in the older group. The putamen, lingual, and so on demonstrated stronger activation during dominant hand MI in the older group.

CONCLUSION

The results of this study revealed that the brain structure was altered and that neuronal activity was attenuated with age, and the cerebral cortex and subcortical tissues were found to be over-activated to achieve the same level of ME and MI, indicating that the activating effects of the left hemisphere enhanced with age, whereas the inhibitory effects declined during ME, and activation of the right hemisphere became more difficult during MI.