Absent Audiovisual Integration Elicited by Peripheral Stimuli in Parkinson's Disease

Multisensory Integration and Causal Inference in Typical and Atypical Populations

Multisensory perception is critical for effective interaction with the environment, but human responses to multisensory stimuli vary across the lifespan and appear changed in some atypical populations. In this review chapter, we consider multisensory integration within a normative Bayesian framework. We begin by outlining the complex computational challenges of multisensory causal inference and reliability-weighted cue integration, and discuss whether healthy young adults behave in accordance with normative Bayesian models. We then compare their behaviour with various other human populations (children, older adults, and those with neurological or neuropsychiatric disorders). In particular, we consider whether the differences seen in these groups are due only to changes in their computational parameters (such as sensory noise or perceptual priors), or whether the fundamental computational principles (such as reliability weighting) underlying multisensory perception may also be altered. We conclude by arguing that future research should aim explicitly to differentiate between these possibilities.

Changes in efficiencies and interactions of attentional networks in Parkinson's disease with sleep disturbance

Attention is composed of three distinct attentional networks: alerting, orienting, and executive control. Previous studies have confirmed that Parkinson's disease (PD) is associated with executive control deficits; however, the interactions among the three attentional networks and the influence of sleep disturbance in PD patients have not been investigated. Herein, the efficiencies for the three attentional networks and their interactions were evaluated using the revised attention network test. The results showed a significantly slower response and lower accuracy in the PD group than in the normal control group and a significantly slower response and lower accuracy in PD patients with sleep disturbance (PDS) than in PD patients without sleep disturbance (PDnS), which indicates a response deficit in PD and worsening in PDS. Additionally, the executive control efficiency was reduced in both PDS and PDnS, and significantly higher alerting efficiency and lower orienting efficiency were found in PDS. Furthermore, largely changed interactions and correlation patterns of attentional networks were found in PDS but not in PDnS. These results suggested that attentional networks were impaired in PD patients, particularly in those affected by sleep disturbances, and that PDS might establish special connections between attentional networks to compensate for cognitive dysfunction.

Age-Related Shifts in Theta Oscillatory Activity During Audio-Visual Integration Regardless of Visual Attentional Load

Audio-visual integration (AVI) is higher in attended conditions than in unattended conditions. Here, we explore the AVI effect when the attentional recourse is competed by additional visual distractors, and its aging effect using single- and dual-tasks. The results showed the highest AVI effect under single-task-attentional-load condition than under no- and dual-task-attentional-load conditions (all P < 0.05) in both older and younger groups, but the AVI effect was weaker and delayed for older adults compared to younger adults for all attentional-load conditions (all P < 0.05). The non-phase-locked oscillation for AVI analysis illustrated the highest theta and alpha oscillatory activity for single-task-attentional-load condition than for no- and dual-task-attentional-load conditions, and the AVI oscillatory activity mainly occurred in the Cz, CP1 and Oz of older adults but in the Fz, FC1, and Cz of younger adults. The AVI effect was significantly negatively correlated with FC1 (r² = 0.1468, P = 0.05) and Cz (r² = 0.1447, P = 0.048) theta activity and with Fz (r² = 0.1557, P = 0.043), FC1 (r² = 0.1042, P = 0.008), and Cz (r² = 0.0897, P = 0.010) alpha activity for older adults but not for younger adults in dual task. These results suggested a reduction in AVI ability for peripheral stimuli and a shift in AVI oscillation from anterior to posterior regions in older adults as an adaptive mechanism.

Age-related functional brain connectivity during audio-visual hand-held tool recognition

INTRODUCTION

Previous studies have confirmed increased functional connectivity in elderly adults during processing of simple audio-visual stimuli; however, it is unclear whether elderly adults maximize their performance by strengthening their functional brain connectivity when processing dynamic audio-visual hand-held tool stimuli. The present study aimed to explore this question using global functional connectivity.

METHODS

Twenty-one healthy elderly adults and 21 healthy younger adults were recruited to conduct a dynamic hand-held tool recognition task with high/low-intensity stimuli.

RESULTS

Elderly adults exhibited higher areas under the curve for both the high-intensity (3.5 versus. 2.7) and low-intensity (3.0 versus. 1.2) stimuli, indicating a higher audio-visual integration ability, but a delayed and widened audio-visual integration window for elderly adults for both the high-intensity (390 - 690 ms versus. 360 - 560 ms) and low-intensity (460 - 690 ms versus. 430 - 500 ms) stimuli. Additionally, elderly adults exhibited higher theta-band (all p < .01) but lower alpha-, beta-, and gamma-band functional connectivity (all p < .05) than younger adults under both the high- and low-intensity-stimulus conditions when processing audio-visual stimuli, except for gamma-band functional connectivity under the high-intensity-stimulus condition. Furthermore, higher theta- and alpha-band functional connectivity were observed for the audio-visual stimuli than for the auditory and visual stimuli and under the high-intensity-stimulus condition than under the low-intensity-stimulus condition.

CONCLUSION

The higher theta-band functional connectivity in elderly adults was mainly due to higher attention allocation. The results further suggested that in the case of sensory processing, theta, alpha, beta, and gamma activity might participate in different stages of perception.

Mental representation of the body in action in Parkinson's disease

Mixed findings characterize studies in Parkinson's disease (PD): some studies indicate a relationship between physical impairments and the ability to mentally represent the body, while others suggest spared abilities for this cognitive function. To clarify the matter, in the present study we explored the mental representations of the body in action in the same PD patients, taking also into account lateralization of symptoms and visual imagery skills. 10 PD patients with left- (lPD), 10 with right (rPD) lateralized symptoms (lPD), and 20 matched healthy controls have been recruited for the study. All patients were screened for neuropsychological impairments. To explore a more implicit component we used the hand laterality task (HLT), while the mental motor chronometry (MMC) was used to explore a more explicit one. Two control tasks, with objects instead of body parts, were administered to control for visual imagery skills. In the HLT, we detected the effects of biomechanical constraints effects in both controls and PD patients. In the latter group, importantly, this was true independently from lateralization of symptoms. In the MMC, we found the expected positive correlation between executed and imagined movements for both hands in controls only, while all PD patients, again independently form lateralization, only showed this effect for the left hand. In terms of visual imagery, only rPD patients differed from controls when asked to implicitly rotate letters, and in terms of accuracy only. However, this difference is explained by executive functions measured through the neuropsychological assessment rather than by a "pure" visual imagery impairment. In summary, our findings suggest that two different aspects of the mental representations of the body in action, one more implicit and the other more explicit, can be differently affected by PD. These impairments are unlikely explained by a basic visual imagery deficit. When present, impairments concern a higher dimension, related to motor functions and awareness, and not driven by sensory impairments, as shown by the independence of effects from physical laterality of symptoms.