The oscillatory response of the electroretinogram and neuronal adaptation.

Parkinson's disease (PD) is the second most common neurodegenerative disease after Alzheimer's disease (AD). The incidence and prevalence of PD have risen rapidly during the last decades, at least partly due to the aging of the general population, as PD mainly affects persons over the age of 50 years. PD is a progressive disorder marked by aberrant protein accumulations that damage dopaminergic neurons of the substantia nigra located in the basal ganglia, resulting in parkinsonian motor symptoms. According to the Movement Disorder Society Diagnostic Criteria, the core feature of PD is slowness of movement combined with tremor and/or muscular rigidity, or both. However, PD is also a multisystem disease, and the pathological changes involve the whole nervous system causing a wide range of additional symptoms. These lesser known non‐motor symptoms of PD can precede the motor symptoms even by a decade. They include constipation, REM sleep behavior disorder, olfactory dysfunction, asymmetric shoulder pain, depression, fatigue, autonomic dysfunction and visual disturbances. There is accumulating evidence that auditory dysfunction could be a non‐motor feature or a pre‐diagnostic manifestation of PD., , , , In comparison to age‐ and sex matched controls, people with PD have higher hearing thresholds in pure‐tone average (PTA),, poorer speech discrimination and lower otoacoustic emission responses. There is emerging evidence of PD pathology involving both the peripheral and central parts of the auditory system. Sensorineural hearing loss (SNHL), which also encompasses age‐related hearing loss, is another condition the prevalence of which increases with age, rising sharply after the age of 50. SNHL is already recognized as a risk factor for cognitive impairment and there is emerging evidence that SNHL starting in midlife could also be associated with risk of PD., In the general population, hearing rehabilitation is underutilized regardless of its many known benefits, but there are very few, if any, studies on hearing rehabilitation in people with PD and the auditory dysfunction associated with PD is not yet widely recognized in clinical practice. To the best of our knowledge, it has not been studied whether diagnosed PD alters the diagnostic trajectories of hearing loss. To investigate this, we conducted a nationwide register‐based cohort study to calculate the incidence of SNHL diagnosis in relation to PD diagnosis from ten years before to ten years after PD diagnosis. Our aim was to evaluate the temporal changes in the amount of SNHL diagnoses in relation to PD diagnosis.