Patients with PD with VHs have substantially greater impairment of inhibitory ability than patients without VHs. These findings support interactive models of the genesis of visual hallucinations in PD.
Visual hallucinations (VHs) in Parkinson's disease (PD) can be a frequent and disturbing complication of the disease with 33% of PD patients undergoing long-term treatment experiencing VHs during the course of their illness. One line of evidence that is emerging as a possible risk factor in the occurrence of VHs is the sleep-wake cycle and sleep behavior in patients with PD. This study compared sleep patterns in a group of visually hallucinating Parkinson's patients with a group of nonhallucinating PD patients and an age-matched control group. Nocturnal sleep was assessed by actigraphy and diaries, while daytime sleepiness and function were assessed by a battery of self-rating sleep questionnaires. Compared with the control group both patient groups had more sleep-related problems and significantly altered sleep patterns, as measured by both actigraphy and sleep questionnaires. Patients who hallucinated however slept less than nonhallucinating patients and also had increased awakenings after sleep onset, reduced sleep efficiency, and increased daytime sleepiness. We propose that VHs in some PD patients may be a symptom of poor sleep and prolonged daytime sleepiness, suggesting that arousal may play a role in the genesis of the hallucination phenomenon.
Emotion, especially anxiety, has been implicated in triggering hallucinations. Sleep behaviour has also been reported to have a modest influence on the judgments that lead to hallucinatory experiences. We report an investigation on the prediction of hallucinatory predisposition which explored emotion and associated processes (stress, personality and sleep behaviour) using a questionnaire survey in a student population (N = 127). Findings indicated significant associations between perceived stress levels and sleep, with stress and being a significant predictor of the hallucinatory experience. In addition there was a predictive relationship between the proneness to hallucinate and schizotypal personality traits, characterised by the subscale of cognitive disorganisation and unusual experiences. Stress and anxiety together with personality may need to be considered in the understanding of hallucinatory experience.
The occurrences of visual hallucinations seem to be more prevalent in low light and hallucinators tend to be more prone to false positive type errors in memory tasks. Here we investigated whether the richness of stimuli does indeed affect recognition differently in hallucinating and nonhallucinating participants, and if so whether this difference extends to identifying spatial context. We compared 36 Parkinson's disease (PD) patients with visual hallucinations, 32 Parkinson's patients without hallucinations, and 36 age-matched controls, on a visual memory task where color and black and white pictures were presented at different locations. Participants had to recognize the pictures among distracters along with the location of the stimulus. Findings revealed clear differences in performance between the groups. Both PD groups had impaired recognition compared to the controls, but those with hallucinations were significantly more impaired on black and white than on color stimuli. In addition, the group with hallucinations was significantly impaired compared to the other two groups on spatial memory. We suggest that not only do PD patients have poorer recognition of pictorial stimuli than controls, those who present with visual hallucinations appear to be more heavily reliant on bottom up sensory input and impaired on spatial ability.
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