Affiliations: [a] Dublin Neurological Institute at the Mater Misericordiae University Hospital, Dublin, Ireland | [b] Trinity Centre for Bioengineering, Trinity College Dublin, Dublin, Ireland | [c] School of Medicine, Trinity College Dublin, Dublin, Ireland | [d] School of Mathematical Sciences, Dublin Institute of Technology, Kevin Street, Dublin, Ireland
Correspondence to: Timothy Lynch, Dublin Neurological Institute at the Mater Misericordiae University Hospital, 57 Eccles Street, Dublin 7, Ireland. Tel.: +35 318 545 038; Fax: +35 318 545 264; E-mail: firstname.lastname@example.org
Correspondence to: Richard B. Reilly, Trinity Centre for Bioengineering, The School of Medicine and the School of Engineering, Trinity College Dublin, Ireland. Tel.: +35 318 963 393; Fax: +35 316 795 554; E-mail: email@example.com
Note:  C. Fearon and J.S. Butler contributed equally to the paper.
Abstract: Background:Sensory and perceptual disturbances progress with disease duration in Parkinson’s disease (PD) and probably contribute to motor deficits such as bradykinesia and gait disturbances, including freezing of gait (FOG). Simple reaction time tests are ideal to explore sensory processing, as they require little cognitive processing. Multisensory integration is the ability of the brain to integrate sensory information from multiple modalities into a single coherent percept, which is crucial for complex motor tasks such as gait. Objectives:The aims of this study were to: 1. Assess differences in unisensory (auditory and visual) and multisensory processing speed in people with PD and age-matched healthy controls. 2. Compare relative differences in unisensory processing in people with PD with disease duration and freezing of gait status taking into account the motor delays, which are invariably present in PD. 3. Compare relative differences in multisensory (audiovisual) processing between the PD cohort and age-matched controls. Methods:39 people with PD (23 with FOG) and 17 age-matched healthy controls performed a reaction time task in response to unisensory (auditory-alone, visual-alone) and multisensory (audiovisual) stimuli. Results:The PD group were significantly slower than controls for all conditions compared with healthy controls but auditory reaction times were significantly faster than visual for the PD group only. These relative unisensory differences are correlated with disease duration and divide the PD group by FOG status, but these factors are co-dependent. Although multisensory facilitation occurs in PD, it is significantly less enhanced than in healthy controls. Conclusion:There are significant unisensory and multisensory processing abnormalities in PD. The relative differences in unisensory processing are specific to PD progression, providing a link between these sensory abnormalities and a motor feature of PD. Sensory disturbances have previously been postulated to be central to FOG but this is the first study to predict audiovisual processing abnormalities using FOG status. The multisensory processing abnormalities are independent of disease duration and FOG status and may be a potential biomarker for the disease.