The Effect of Spatial Working Memory Deterioration on Strategic Visuomotor Learning across Aging

Health Effects of Chronic Intermittent Hypoxia at a High Altitude among Chilean Miners: Rationale, Design, and Baseline Results of a Longitudinal Study

OBJECTIVES

This study aims to assess the health effects on mining workers of exposure to chronic intermittent hypoxia (CIH) at high- and very high-altitude mining compared with similar work at lower altitudes in Chile, and it also aims to constitute the baseline of a 5-year follow-up study.

METHODS

We designed a cross-sectional study to assess health conditions in 483 miners working at 2 levels of altitude exposure: 336 working at a very high or high altitude (HA; 247 above 3900-4400 m, and 89 at 3000-3900 m), and 147 below 2400 m. Subjects were randomly selected in two stages. First, a selection of mines from a census of mines in each altitude stratum was made. Secondly, workers with less than 2 years of employment at each of the selected mines were recruited. The main outcomes measured at the baseline were mountain sickness, sleep alterations, hypertension, body mass index, and neurocognitive functions.

RESULTS

Prevalence of acute mountain sickness (AMS) was 28.4% in the very high-altitude stratum (P = 0.0001 compared with the low stratum), and 71.7% experienced sleep disturbance (P = 0.02). The adjusted odds ratio for AMS was 9.2 (95% confidence interval: 5.2-16.3) when compared with the very high- and low-altitude groups. Motor processing speed and spatial working memory score were lower for the high-altitude group. Hypertension was lower in the highest-altitude subjects, which may be attributed to preoccupational screening even though this was not statistically significant.

CONCLUSIONS

Despite longer periods of acclimatization to CIH, subjects continue to present AMS and sleep disturbance. Compromise of executive functions was detected, including working memory at HA. Further rigorous research is warranted to understand long-term health impacts of high-altitude mining, and to provide evidence-based policy recommendations.

Cognitive and Motor Perseveration Are Associated in Older Adults

Aging causes perseveration (difficulty to switch between actions) in motor and cognitive tasks, suggesting that the same neural processes could govern these abilities in older adults. To test this, we evaluated the relation between independently measured motor and cognitive perseveration in young (21.4 ± 3.7 y/o) and older participants (76.5 ± 2.9 y/o). Motor perseveration was measured with a locomotor task in which participants had to transition between distinct walking patterns. Cognitive perseveration was measured with a card matching task in which participants had to switch between distinct matching rules. We found that perseveration in the cognitive and motor domains were positively related in older, but not younger individuals, such that participants exhibiting greater perseveration in the motor task also perseverated more in the cognitive task. Additionally, exposure reduces motor perseveration: older adults who had practiced the motor task could transition between walking patterns as proficiently as naïve, young individuals. Our results suggest an overlap in neural processes governing cognitive and motor perseveration with aging and that exposure can counteract the age-related motor perseveration.

Age Impacts the Burden That Reference Memory Imparts on an Increasing Working Memory Load and Modifies Relationships With Cholinergic Activity

Rodent aging research often utilizes spatial mazes, such as the water radial-arm-maze (WRAM), to evaluate cognition. The WRAM can simultaneously measure spatial working and reference memory, wherein these two memory types are often represented as orthogonal. There is evidence, however, that these two memory forms yield interference at a high working memory load. The current study systematically evaluated whether the presence of a reference memory component impacts handling of an increasing working memory load. Young and aged female rats were tested to assess whether aging impacts this relationship. Cholinergic projections from the basal forebrain to the hippocampus and cortex can affect cognitive outcomes, and are negatively impacted by aging. To evaluate whether age-related changes in working and reference memory profiles are associated with cholinergic functioning, we assessed choline acetyltransferase activity in these behaviorally-tested rats. Results showed that young rats outperformed aged rats on a task testing solely working memory. The addition of a reference memory component deteriorated the ability to handle an increasing working memory load, such that young rats performed similar to their aged counterparts. Aged rats also had challenges when reference memory was present, but in a different context. Specifically, aged rats had difficulty remembering which reference memory arms they had entered within a session, compared to young rats. Further, aged rats that excelled in reference memory also excelled in working memory when working memory demand was high, a relationship not seen in young rats. Relationships between cholinergic activity and maze performance differed by age in direction and brain region, reflecting the complex role that the cholinergic system plays in memory and attentional processes across the female lifespan. Overall, the addition of a reference memory requirement detrimentally impacted the ability to handle working memory information across young and aged timepoints, especially when the working memory challenge was high; these age-related deficits manifested differently with the addition of a reference memory component. This interplay between working and reference memory provides insight into the multiple domains necessary to solve complex cognitive tasks, potentially improving the understanding of complexities of age- and disease- related memory failures and optimizing their respective treatments.

Task Feedback Processing Differs Between Young and Older Adults in Visuomotor Rotation Learning Despite Similar Initial Adaptation and Savings

Ageing has been suggested to affect sensorimotor adaptation by impairing explicit strategy use. Here we recorded electrophysiological (EEG) responses during visuomotor rotation in both young (n = 24) and older adults (n = 25), to investigate the neural processes that underpin putative age-related effects on adaptation. We measured the feedback related negativity (FRN) and the P3 in response to task-feedback, as electrophysiological markers of task error processing and outcome evaluation. The two age groups adapted similarly and showed comparable after effects and savings when re-exposed to the same perturbation several days after the initial session. Older adults, however, had less distinct EEG responses (i.e., reduced FRN amplitudes) to negative and positive task feedback. The P3 did not differ between age groups. Both young and older adults also showed a sustained late positivity following task feedback. Measured at the frontal electrode Fz, this sustained activity was negatively associated with both the amount of voluntary disengagement of explicit strategy and savings. In conclusion, despite preserved task performance, we find clear differences in neural responses to errors in older people, which suggests that there is a fundamental decline in this aspect of sensorimotor brain function with age.

Adaptation of reach action to a novel force-field is not predicted by acuity of dynamic proprioception in either older or younger adults

Healthy ageing involves degeneration of the neuromuscular system which impacts movement control and proprioception. Yet the relationship between these sensory and motor deficits in upper limb reaching has not been examined in detail. Recently, we reported that age-related proprioceptive deficits were unrelated to accuracy in rapid arm movements, but whether this applied in motor tasks more heavily dependent on proprioceptive feedback was not clear. To address this, we have tested groups of younger and older adults on a force-field adaptation task under either full or limited visual feedback conditions and examined how performance was related to dynamic proprioceptive acuity. Adaptive performance was similar between the age groups, regardless of visual feedback condition, although older adults showed increased after-effects. Physically inactive individuals made larger systematic (but not variable) proprioceptive errors, irrespective of age. However, dynamic proprioceptive acuity was unrelated to adaptation and there was no consistent evidence of proprioceptive recalibration with adaptation to the force-field for any group. Finally, in spite of clear age-dependent loss of spatial working memory capacity, we found no relationship between memory capacity and adaptive performance or proprioceptive acuity. Thus, non-clinical levels of deficit in dynamic proprioception, due to age or physical inactivity, do not affect force-field adaptation, even under conditions of limited visual feedback that might require greater proprioceptive control.

Procedural and Strategic Visuomotor Learning Deficits in Children With Developmental Coordination Disorder

Purpose: Developmental coordination disorder (DCD) is characterized by poor coordination and clumsiness in children. Subjects often show unsteady gait, frequent tripping, and difficulty holding objects. Here we evaluated the implicit and explicit motor learning capabilities of children with DCD. Method: We assessed a total of 80 children (4-12 years old). These children were divided into two groups of 40 participants each. One group with DCD diagnosis and a control group. Using a prism adaptation paradigm, we evaluated whether DCD affects procedural visuomotor adaptation. This adaptation typically occurs during the laterally displacing prism adaptation task. We contrasted these results with the performance during a reversing prism adaptation task, which mainly places demands on strategic visuomotor learning. To solve both adaptation tasks, subjects must perform the same movements, but using two completely different approaches. Results: There was a significant variable error difference between groups, confirming a motor control deficit in individuals with DCD. This group also showed significant visuomotor learning deficits in the displacing task, including less adaptation and smaller aftereffect. The analysis on the reversing task revealed a significant larger number of subjects with DCD that could not adapt, suggesting significant strategic visuomotor learning deficits in this group too. Conclusions: These results demonstrate procedural and strategic visuomotor deficits in this sample of children with DCD.

Brain Network Segregation and Glucose Energy Utilization: Relevance for Age-Related Differences in Cognitive Function

The human brain is organized into segregated networks with strong within-network connections and relatively weaker between-network connections. This "small-world" organization may be essential for maintaining an energetically efficient system, crucial to the brain which consumes 20% of the body's energy. Brain network segregation and glucose energy utilization both change throughout the lifespan. However, it remains unclear whether these processes interact to contribute to differences in cognitive performance with age. To address this, we examined fluorodeoxyglucose-positron emission tomography and resting-state functional magnetic resonance imaging from 88 participants aged 18-73 years old. Consistent with prior work, brain network segregation showed a negative association with age across both sensorimotor and association networks. However, relative glucose metabolism demonstrated an interaction with age, showing a negative slope in association networks but a positive slope in sensorimotor networks. Overall, brain networks with lower segregation showed significantly steeper age-related differences in glucose metabolism, compared with highly segregated networks. Sensorimotor network segregation mediated the association between age and poorer spatial cognition performance, and sensorimotor network metabolism mediated the association between age and slower response time. These data provide evidence that sensorimotor segregation and glucose metabolism underlie some age-related changes in cognition. Interventions that stimulate somatosensory networks could be important for treatment of age-related cognitive decline.

Age-related reduction in motor adaptation: brain structural correlates and the role of explicit memory

The adaption of movement to changes in the environment varies across life span. Recent evidence has linked motor adaptation and its reduction with age to differences in "explicit" learning processes. We examine differences in brain structure and cognition underlying motor adaptation in a population-based cohort (n = 322, aged 18-89 years) using a visuomotor learning task and structural magnetic resonance imaging. Reduced motor adaptation with age was associated with reduced volume in striatum, prefrontal, and sensorimotor cortical regions, but not cerebellum. Medial temporal lobe volume, including the hippocampus, became a stronger determinant of motor adaptation with age. Consistent with the role of the medial temporal lobes, declarative long-term memory showed a similar interaction, whereby memory was more positively correlated with motor adaptation with increasing age. By contrast, visual short-term memory was related to motor adaptation, independently of age. These results support the hypothesis that cerebellar learning is largely unaffected in old age, and the reduction in motor adaptation with age is driven by a decline in explicit memory systems.

Can patients with cerebellar disease switch learning mechanisms to reduce their adaptation deficits?

Systematic perturbations in motor adaptation tasks are primarily countered by learning from sensory-prediction errors, with secondary contributions from other learning processes. Despite the availability of these additional processes, particularly the use of explicit re-aiming to counteract observed target errors, patients with cerebellar degeneration are surprisingly unable to compensate for their sensory-prediction error deficits by spontaneously switching to another learning mechanism. We hypothesized that if the nature of the task was changed-by allowing vision of the hand, which eliminates sensory-prediction errors-patients could be induced to preferentially adopt aiming strategies to solve visuomotor rotations. To test this, we first developed a novel visuomotor rotation paradigm that provides participants with vision of their hand in addition to the cursor, effectively setting the sensory-prediction error signal to zero. We demonstrated in younger healthy control subjects that this promotes a switch to strategic re-aiming based on target errors. We then showed that with vision of the hand, patients with cerebellar degeneration could also switch to an aiming strategy in response to visuomotor rotations, performing similarly to age-matched participants (older controls). Moreover, patients could retrieve their learned aiming solution after vision of the hand was removed (although they could not improve beyond what they retrieved), and retain it for at least 1 year. Both patients and older controls, however, exhibited impaired overall adaptation performance compared to younger healthy controls (age 18-33 years), likely due to age-related reductions in spatial and working memory. Patients also failed to generalize, i.e. they were unable to adopt analogous aiming strategies in response to novel rotations. Hence, there appears to be an inescapable obligatory dependence on sensory-prediction error-based learning-even when this system is impaired in patients with cerebellar disease. The persistence of sensory-prediction error-based learning effectively suppresses a switch to target error-based learning, which perhaps explains the unexpectedly poor performance by patients with cerebellar degeneration in visuomotor adaptation tasks.

Cognitive deficit in hippocampal-dependent tasks in Werner syndrome mouse model

Mammalian aging is often characterized by metabolic disturbances, cognitive declines and DNA repairs deficiency, but the underlying molecular mechanisms are still not well understood. Alterations in DNA repair can significantly exacerbate aging. Mammalian neuronal cells which accumulate unrepaired DNA damage over time could potentially lead to brain functions disorders. Focusing on the ATP-dependent RecQ-type DNA helicase, an enzyme involved in repair of double strand DNA, a mouse model of Werner syndrome (WS) had been proposed as a model of accelerated aging. Until now, no study has investigated the impact of this premature aging syndrome on learning and memory. Spatial memory and cognitive flexibility are particularly affected by the aging process in both men and rodents. Studies have shown that aged mice exhibited similar performance than young adult mice on non-hippocampus dependent memory whereas their performances were decreased in hippocampus-dependent tasks. In this study, we have submitted 3, 5 and 8 month-old WS mice to several behavioral paradigms to evaluate hippocampus-dependent (spatial object location, Morris water maze and fear conditioning) and non hippocampus-dependent (object recognition) memories. No effect on the locomotion activity and anxiety level has been observed in adult WS mice. Interestingly, the 8 month-old WS mice exhibit long-term memory impairment similar to aged mice, suggesting that adult WS mice do develop some aspects of cognitive aging.

The prescriptions from Shenghui soup enhanced neurite growth and GAP-43 expression level in PC12 cells

Background

Shenghui soup is a traditional Chinese herbal medicine used in clinic for the treatment of forgetfulness. In order to understanding the prescription principle, the effects of “tonifying qi and strengthening spleen” group (TQSS) including Poria cocos (Schw.) Wolf. and Panax ginseng C.A.Mey and “eliminating phlegm and strengthening intelligence” group (EPSI) composed of Polygala tenuifolia Willd., Acorus calamus L. and Sinapis alba L from the herb complex on neurite growth in PC12 cells, two disassembled prescriptions derived from Shenghui soup and their molecular mechanisms were investigated.

Methods

Firstly, CCK-8 kit was used to detect the impact of the two prescriptions on PC12 cell viability; and Flow cytometry was performed to measure the cell apoptosis when PC12 cells were treated with these drugs. Secondly, the effect of the two prescriptions on the differentiation of PC12 cells was observed. Finally, the mRNA and protein expression levels of GAP-43 were analyzed by RT-PCR and western blot, respectively.

Results

“Tonifying qi and strengthening spleen” prescription decreased cell viability in a dose-dependent manner, but had no significant effect on cell apoptosis. Meanwhile, it could improve neurite growth and elevate the mRNA and protein expression level of GAP-43. “Eliminating phlegm and strengthening intelligence” prescription also exerted the similar effects on cell viability and apoptosis. Furthermore, it could also enhance cell neurite growth, with a higher expression level of GAP-43 mRNA and protein.

Conclusion

“Tonifying qi and strengthening spleen” and “eliminating phlegm and strengthening intelligence” prescriptions from Shenghui soup have a positive effect on neurite growth. Their effects are related to the up-regulating expression of GAP-43.

Electronic supplementary material

The online version of this article (doi:10.1186/s12906-016-1339-y) contains supplementary material, which is available to authorized users.