A Lee

Reality monitoring and visual hallucinations in Parkinson’s disease

Between 8 and 40% of Parkinson disease (PD) patients will have visual hallucinations (VHs) during the course of their illness. Although cognitive impairment has been identified as a risk factor for hallucinations, more specific neuropsychological deficits underlying such phenomena have not been established. Research in psychopathology has converged to suggest that hallucinations are associated with confusion between internal representations of events and real events (i.e. impaired-source monitoring). We evaluated three groups: 17 Parkinsons patients with visual hallucinations, 20 Parkinsons patients without hallucinations and 20 age-matched controls, using tests of visual imagery, visual perception and memory, including tests of source monitoring and recollective experience. The study revealed that Parkinsons patients with hallucinations appear to have intact visual imagery processes and spatial perception. However, there were impairments in object perception and recognition memory, and poor recollection of the encoding episode in comparison to both non-hallucinating Parkinsons patients and healthy controls. Errors were especially likely to occur when encoding and retrieval cues were in different modalities. The findings raise the possibility that visual hallucinations in Parkinsons patients could stem from a combination of faulty perceptual processing of environmental stimuli, and less detailed recollection of experience combined with intact image generation.

Visual and spatial symptoms in Parkinson’s disease

The interaction of visual/visuospatial and motor symptoms in Parkinsons disease (PD) was investigated by means of a 31-item self-report questionnaire. The majority of 81 non-demented patients reported problems on non-motor tasks that depended on visual or visuospatial abilities. Over a third reported visual hallucinations, double vision and difficulty estimating spatial relations. Freezing of gait was associated with visual hallucinations, double vision and contrast sensitivity deficits. Visual strategies frequently were employed to overcome freezing. The results underscore the importance of investigating visual and visuospatial impairments in PD and their relation to motor symptoms, in order to help patients develop successful compensatory strategies.

Impairments of mental rotation in Parkinson's disease

It is controversial whether parkinsonian patients are impaired on visuospatial tasks. In the present study, patients and normal control subjects judged whether pairs of wire-frame figures in different orientations were the same or different. The orientation difference between the figures was either in the picture plane (around the z-axis, or two-dimensional) or in depth (around the y-axis, or three-dimensional). Reaction times and error rates were measured. For the two-dimensional task, there were no significant differences in errors between the two groups, though Parkinsonian subjects were significantly slower to respond than the control group. In the three-dimensional task, patients had a different pattern of reaction times from the controls and made significantly more errors, which were systematic at large angular differences. The results suggest a visuospatial deficit in Parkinsons disease, which reflects problems in some aspect of the perception of extra-personal space.

Evidence from a line bisection task for visuospatial neglect in left hemiparkinson's disease.

The perception of extrapersonal space in Parkinsons disease was examined with two line bisection tasks. One was a conventional pencil and paper test, the line bisection section of the Behavioural Inattention Test. In the other, the stimuli were displayed on a large (2x2.4 m) screen and varied in length (48-480 mm) and also in location on the screen (left, centre and right). They were presented at two viewing distances (0.6 and 1.5 m). Subjects remotely adjusted the position of a cursor until it appeared to bisect the stimulus line, using two push-buttons, one in each hand. The PD participants (n=18) had a marked asymmetry of motor symptoms. They were divided into two groups, those with predominantly left-sided motor symptoms (LPD, n=9), and those with predominantly right-sided motor symptoms (RPD, n=9). The control group (n=9) were all right-handed. No significant differences between the groups were found on the BIT bisection task. In contrast, when the stimuli were presented on the screen, LPD subjects showed a significant rightward bias in their settings of the cursor, particularly for lines on the left and centre of the screen, which was greater, the longer the stimulus line. The RPD group bisected lines slightly to the left, in common with the control group (pseudo-neglect). In a second experiment, Parkinsonian subjects repeated this task, but with the buttons reversed between the hands, so that the cursor was moved to the left by the right hand, and vice versa, but the pattern of results was the same as in the first experiment. The data suggest a small but reliable neglect in left hemiparkinsons disease, which is contralateral to the non-dominant (and probably worse affected) hemisphere. The dissociation between the response and the bisection error suggests a visuospatial impairment in LPD.

Disruption of estimation of body-scaled aperture width in Hemiparkinson's disease.

A group of patients with left-sided symptoms of Parkinsons disease (LPD) was compared with a group of patients with right-sided symptoms (RPD) and with a group of healthy age-matched controls on body-scaled judgements of aperture width. Participants judged whether or not they would fit through a life-sized schematic doorway shown on a large screen. A staircase technique was used to find the door width for which 50% of the judgements were positive. The ratio between this measure and the width of the participants body at the shoulders (the aperture to shoulder - A/S ratio) was calculated. The A/S ratio was approximately 1.5 in the LPD group, approximately 0.9 in the RPD group, and approximately 1.1 in the control group, suggesting that the visual representation of the doorway (or that of its relationship to perceived body-size) is compressed in LPD (and perhaps expanded in RPD). The A/S ratios were invariant with viewing distance (0.6 or 1.5 m), the contrast polarity of the display (white on dark, or vice versa) and the doorway surround (blank, or vertical or horizontal stripes). The findings are discussed with reference to the neural representation of external space and of the body, and to the motor problems of Parkinsons disease.

Dopamine and the representation of the upper visual field: evidence from vertical bisection errors in unilateral Parkinson's disease.

It has been suggested that dopamine is an important neurotransmitter in the brain mechanisms which represent the upper visual field. This idea was tested with a vertical line bisection task in unilateral Parkinsons disease. Stimuli of a range of lengths were presented on a large screen in three positions (left, centre and right) and at two viewing distances (0.6 and 1.5m). The patients, who were compared with a group of normal age-matched controls, comprised 16 sufferers from predominantly unilateral disease, 8 with more severe left-sided symptoms (LPD) and 8 with more severe right-sided symptoms (RPD). The LPD group consistently set the bisecting cursor below the midpoint of the stimulus lines, and their bisection error became larger as the length of the line increased. In contrast, the controls set the cursor above the midpoint of the line, an error which also increased with line length. The settings of the RPD group were similar to those of the controls. The results suggest altitudinal neglect in left unilateral PD, and support the hypothesis of dopaminergic involvement in the coding of upper visual space, with the proviso that the perceptual component of this involves the right hemisphere in humans.

Measuring Brain Signals to Evaluate the Role of Creativity in Interceptive Human Movement

Human movement involves executive control and cognition. Elite sports require development of this expertise together with the physical conditioning. This research explores the role of creativity in developing mental skills in sports from a computational neuroscience perspective. Future direction of the research will aim to study the role of creativity on performance in the case of cricket batting. Here we present a review of the methods and the preliminary results on brain source estimation analysis on a number of sample dataset. A roadmap for future theoretical and experimental evaluation procedure is discussed as well.