Investigating visual misperceptions in Parkinson's disease: A novel
behavioral paradigm.
Shine JM, Halliday GH, Carlos M, Naismith SL, Lewis SJ.
Mov Disord. 2012 Apr; 27(4):500-5
Barbara Borroni and Enrico Premi, University of Brescia, Italy. F1000
Neurological Disorders
23 Apr 2012 | Technical Advance, New Finding
I found this article interesting because it applies a novel behavioral
paradigm to study visual misperceptions and hallucinations in
Parkinson's disease (PD). This novel approach allows an objective
analysis of these behavioral disturbances, pointing to a potential
involvement of attentional networks as a pathophysiological basis for
these symptoms.
Advanced stages of PD are frequently characterized by behavioral
disturbances with altered perception, generally referred as
'hallucinations'. Even if this clinical symptom has a clear-cut medical
definition, it is generally used as a sort of umbrella term in PD.
Different mechanisms have been proposed, considering conditions
correlated with a more peripheral perceptual impairment (i.e.
Charles-Bonnet syndrome) but also a pathological role for rapid eye
movement sleep (REM)-like sleep imagery in the awake status.
Furthermore, different neuroimaging studies (either functional or
structural) explored the anatomical correlation of visual
hallucination/misperceptions in PD, showing frontal and temporal
involvement (more related with a complex circuitry impairment rather
than a series of focal lesions behind the symptoms).
In this work, Shine et al., taking into account the recent theoretical
developments in the physiopathology mechanisms {1} on an impaired
attentional control network, proposed a bistable percept paradigm (BPP)
to quantify visual misperceptions in PD patients. In this task, patients
processed visual stimuli (single images and bistable percepts) and the
number of uncorrected responses (misperceptions and missed images) was
recorded. PD patients with an high error score presented more
neuropsychiatric symptoms (like visual misperceptions and
hallucinations), more self-reported sleep behavior disorders (RBD) and a
poorer performance on Trail Making Test B-A, as an index of attentional
set shifting. These results suggested that PD patients with visual
hallucinations, despite an intact visual imagery and spatial perception
processing, were impaired regarding object perception and recognition
memory. As recently described {1}, the impairment of the attentional
network (correlated with executive functions) may explain visual
misperceptions and hallucinations in PD.
The strength of the study is surely the utilization of the BPP as an
objective tool to study misperceptions and hallucinations in PD
patients. This theoretical framework, integrated with functional
neuroimaging study, could elucidate the neuroanatomical basis of these
behavioral disturbances in PD patients, also contributing to a better
understanding of brain functioning.
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