Re-orientation of attention in Parkinson's disease: an extension to the vibrotactile modality

Impact of external cue validity on driving performance in Parkinson's disease

This study sought to investigate the impact of external cue validity on simulated driving performance in 19 Parkinson's disease (PD) patients and 19 healthy age-matched controls. Braking points and distance between deceleration point and braking point were analysed for red traffic signals preceded either by Valid Cues (correctly predicting signal), Invalid Cues (incorrectly predicting signal), and No Cues. Results showed that PD drivers braked significantly later and travelled significantly further between deceleration and braking points compared with controls for Invalid and No-Cue conditions. No significant group differences were observed for driving performance in response to Valid Cues. The benefit of Valid Cues relative to Invalid Cues and No Cues was significantly greater for PD drivers compared with controls. Trail Making Test (B-A) scores correlated with driving performance for PDs only. These results highlight the importance of external cues and higher cognitive functioning for driving performance in mild to moderate PD.

Attention, inhibition, and proximity to clinical onset in preclinical mutation carriers for Huntington's disease

Research in preclinical mutation carriers for Huntington's disease (HD) aims to find measures sensitive to preclinical decline. This study investigated attentional abilities in mutation carriers and noncarriers. Mutation carriers demonstrated a normal "attentional blink" during rapid serial visual presentation, normal covert visual orienting, and normal directing of attention to tactile stimuli. However, they were more likely than noncarriers to make anticipatory responses before target presentation. Additionally, those closer to estimated onset of HD demonstrated larger "inhibition of return" effects. The findings suggest potential changes in cognitive inhibition of unwanted responses, and in automatic inhibition of visual orienting, in preclinical HD.

The role of the basal ganglia in the control of automatic visuospatial attention

Cognitive impairments in patients with basal ganglia dysfunction are primarily revealed where performance relies on internal, voluntary control processes. Evidence suggests that this also extends to impaired control of more automatic processes, including visuospatial attention. The present study used a non-predictive peripheral cueing paradigm to compare and contrast visuospatial deficits in patients with Parkinson's disease (PD) with those previously revealed in patients with Huntington's disease (HD) (Fielding et al., 2006a). Compared to age-matched controls, both PD and HD patients exhibited increased distractibility or poor fixation, however only PD patients responded erroneously to cue stimuli more frequently than control subjects. All subjects demonstrated initial facilitation for valid versus invalid cues following the shorter stimulus-onset asynchronies (SOAs) and a performance decrement at the longer SOAs (inhibition of return), although there was a clear differentiation between these groups for immediate SOAs. Unlike both control and PD subjects, where IOR manifested between 350 and 1000 msec, IOR was evident as early as 150 msec for HD patients. Further, for PD patients, spatially valid cues resulted in hyper-reflexivity following 150 msec SOAs, with saccadic latencies shorter than those generated in response to un-cued targets. Thus contrasting deficits were revealed in PD and HD, emphasizing the important contribution of the basal ganglia in the control of more automatic behaviors

Temporal variation in the control of goal-directed visuospatial attention in basal ganglia disorders

A predictive central-cueing paradigm was used to compare visuospatial deficits in patients with Parkinson's (PD) and Huntington's diseases (HD), employing directionally valid and invalid visual cues over a range of stimulus onset asynchronies (SOA) to elicit a saccadic response. Compared to age-matched control groups, both PD and HD patients responded erroneously to cue stimuli more frequently, increasing significantly over longer SOAs. Both valid and invalid cues resulted in elevated latencies compared to un-cued visually guided saccades, the associated 'cost' of invalid cueing significantly greater than that for valid cueing, over all SOAs. Unlike control subjects, PD and HD patients demonstrated temporal variation with cue presentation. For PD patients, latencies following directionally invalid cues were significantly longer for intermediate SOAs, suggesting difficulty overcoming a build-up of inhibitory activity over time. No validity effect was found at 1000 ms. For HD patients, latencies for validly cued saccades with 150 ms SOAs were shorter than latencies for no-cue trials, representing a 'benefit' of valid cueing. For 500 ms SOAs latencies were comparably elevated following directionally valid and invalid cues, and for 1000 ms SOAs neither cue condition resulted in increased latencies. These findings reflect the consequence of disruption to the balance of activity over the basal ganglia facilitatory and inhibitory pathways. Imbalance in PD resulted in difficulty sustaining goal-directed behaviour, and in HD, difficulty gating inappropriate behaviour.

No sequence dependent modulation of the Simon effect in Parkinson's disease

This study sought to evaluate impaired response tendencies and modulation of automatic processes in Parkinson's disease (PD), utilising a saccadic Simon task with stimulus-response (S-R) compatibility determined on the basis of cue shape. The appearance of either a circle or a square in one of two boxes presented peripherally required the generation of a leftward or rightward horizontal saccade, respectively. These goal-directed responses were considered behaviourally relevant to an examination of visuospatial performance. Although response times are typically faster when stimulus and response are spatially compatible than when they are not, sequence-dependent modulation of this effect results in large differences between S-R compatible and S-R incompatible trials when stimulus and response are spatially compatible in the preceding trial, and reduced or absent differences when stimulus and response are spatially incompatible in the preceding trial. Unlike control subjects, PD patients demonstrated significantly shorter saccadic latencies overall, compared to a baseline condition involving endogenously-driven saccades. Patients also responded erroneously to cue stimuli with greater frequency. Analyses of both saccadic latency and errors to cue demonstrated a Simon effect (relatively faster response for S-R compatible trials), irrespective of the preceding trial. This suggests impaired modulation of the Simon effect in PD, consistent with predictions of inhibitory dysfunction, or impaired episodic memory. These results demonstrate the pivotal role of the basal ganglia in the regulation of context-dependent neural activity.

Impact of internal versus external cueing on driving performance in people with Parkinson's disease

Numerous aspects of driving performance seem compromised in people with Parkinson's disease (PD). Measures of cognitive impairment consistently correlate with poor driving simulator performance in this population; however, the effects of specific cognitive difficulties on discrete aspects of driving behavior have not been investigated thoroughly. Previous studies have demonstrated that people with PD exhibit difficulties internally cueing cognitive processes. This study examined the impact of impaired internal cueing on specific driving behaviors. A simulator measured the driving behavior of 18 current drivers in the mild-to-moderate stages of PD and 18 matched controls. Participants navigated through different driving conditions where the opportunity to use internal and external cues was manipulated. People with PD exhibited difficulties using internal cues to regulate driving behavior around traffic signals and curves. Instead of using internal cues, participants with PD were more reliant on external cues to regulate driving behavior. They were also less able to adapt their driving behavior to suit driving conditions. Because all participants with PD were current drivers in the mild-to-moderate stages of the disease, findings challenge the widely-held assumption that cognitive difficulties only impact on driving performance in the moderate-to-severe stages of PD.

Orienting attention in obsessive-compulsive disorder

OBJECTIVES AND BACKGROUND

Obsessive-compulsive disorder (OCD) is characterized by recurrent obsessions and/or compulsions that affect daily functioning. This study aimed to ascertain whether OCD patients have problems in orienting attention, via the use of a vibrotactile choice reaction time task.

METHODS

Participants were required to depress a button in response to a vibration delivered to the index finger of either the right or left hand. Prior to the stimulus, one of three precues was administered: valid (precue delivered to the same hand as stimulus), invalid (precue delivered to opposite hand to stimulus), or neutral (precue delivered simultaneously to both hands).

RESULTS

Obsessive-compulsive disorder participants were overall slower and less accurate than controls. Contrary to our predictions, OCD participants did not show increased costs or benefits. However, unlike controls, patients did not show the normal pattern of faster reaction times on neutral compared with invalid precues, which may reflect a problem in inhibiting irrelevant information.

CONCLUSIONS

Both patients and controls may benefit from the provision of directed attention in tactile tasks when difficulty levels are maximal. OCD patients may have problems with inhibitory control.

Trunk movement in Parkinson's disease during rising from seated position

Parkinson's disease (PD) is associated with particular difficulties rising from a seated position. Little is known about the mechanisms of sit-to-stand in this condition. We sought to define trunk movement during sit-to-stand in a group of patients with PD. Six patients and seven normal volunteers were studied using a six camera ELITE motion analysis system (BTS, Milan, Italy), which permitted data collection in the coronal, sagittal, and transverse planes. Retroreflective markers were positioned along the spine at C7, T3, T6, T9, T12, L3, and the sacrum. Whole-trunk kinematics and the movement at the six different trunk markers were recorded during rising. PD patients have a significantly greater degree of trunk flexion than controls, showing a significant increase in angular velocity of the trunk in the sagittal plane. The total range of movement of trunk rotation was significantly smaller in the PD group, but lateral movement in the trunk was greater than normal. These data suggest that patients with early PD compensate for their difficulties rising from a chair by generating greater trunk flexion at higher angular velocity, thus developing greater forward momentum. This process results in a decrease in the duration of the unstable transitional phase of sit-to-stand, allowing PD patients to reach the upright position as easily and safely as possible. Small rotational movements are an effective way to maintain the centre of mass within the base of support during sit-to-stand. This mechanism appears to be denied to the PD patients who may use increased movements in the coronal plane as an alternative strategy.

Multisensory prior entry

Despite 2 centuries of research, the question of whether attending to a sensory modality speeds the perception of stimuli in that modality has yet to be resolved. The authors highlight weaknesses inherent in this previous research and report the results of 4 experiments in which a novel methodology was used to investigate the effects on temporal order judgments (TOJs) of attending to a particular sensory modality or spatial location. Participants were presented with pairs of visual and tactile stimuli from the left and/or right at varying stimulus onset asynchronies and were required to make unspeeded TOJs regarding which stimulus appeared first. The results provide the strongest evidence to date for the existence of multisensory prior entry and support previous claims for attentional biases toward the visual modality and toward the right side of space. These findings have important implications for studies in many areas of human and animal cognition.

Effects of dopamine depletion of the dorsal striatum and further interaction with subthalamic nucleus lesions in an attentional task in the rat

The present study investigated the effects of 6-hydroxydopamine lesions of the dorsal striatum on a five choice serial reaction time task which assesses visual sustained and divided attention. Striatal dopamine loss by itself produced no deficits in accuracy on the standard form of the task, but lengthened response latencies and increased omissions and perseverative behaviour. Reducing the temporal predictability of the visual event led to impaired accuracy, contrasting with previously published effects of ventral striatal dopamine depletion. To further investigate the interactions between dopaminergic and glutamatergic systems within the basal ganglia, we have tested the effects of 6-hydroxydopamine lesions in animals bearing subthalamic nucleus lesions. Previous evidence [C. Baunez and T. W. Robbins, (1997) Eur. J. Neurosci. 9, 2086-2099] has revealed multiple deficits after bilateral lesions of the subthalamic nucleus. The present study replicated these effects. In combination with subthalamic nucleus lesions, striatal dopamine loss antagonised the increase in premature responding but did not counteract any of the other impairments. These results show the involvement of the dopaminergic nigrostriatal pathway in motor attention and arousal. Furthermore, they underline the independence of subthalamic nucleus lesion-induced effects from dopaminergic systems.

Differential clinical and motor control function in a pair of monozygotic twins with Huntington's disease

We report a pair of monozygotic Huntington's disease (HD) twins who, although sharing identical CAG repeat lengths, not only present with marked differences in clinical symptoms but also behavioral abilities as measured by our experimental procedures. Both HD twins and two healthy control subjects were tested twice over 2 years. Patient A was generally more impaired at a motor level, whereas Patient B showed greater attentional impairment; Patient B, however, showed more progressive deterioration. The control subjects' performance remained consistent over the 2-year interval. Patient A clinically had the more hyperkinetic hypotonic variant of the disease, whereas Patient B, who was the more impaired, presented with a more hypokinetic hypertonic (rigid) variant. The influences of epigenetic pre- and postnatal environmental factors should not be ignored.

Frontostriatal deficits in unipolar major depression

Recent accounts of major depression have tended to focus on dysfunction of frontothalamic-striatal reentrant circuits as a possible source of the disorder. Evidence of frontostriatal involvement in unipolar major depression from lesion and neuropsychological studies, and functional and structural imaging studies is examined. The high incidence of depressive symptomatology following left frontal and basal ganglia lesions implicate these as possible sites of dysfunction. Neuropsychological evidence indicates similar deficits in patients with major depression, perhaps with dorsolateral prefrontal deficits most prominent. Structural imaging studies report frontal and basal ganglia (BG) abnormalities particularly in cases of late-age onset depression. Resting state functional imaging studies show deficits in dorsolateral, anterior cingulate (medial frontal), and BG structures. Activation imaging studies show less consistent evidence of dorsolateral deficit, while anterior cingulate deficit is more consistently demonstrated. Variability in findings across studies may reflect differences between subtypes of depression and differences in methodology. Possible involvement of the BG in the psychomotor retardation of depression is examined. It is concluded that, while there is evidence of frontostriatal deficit in major depression, the exact nature of such deficits is uncertain. Issues such as component vs. system dysfunction need to be addressed.

Reaction time deficits and Parkinson's disease

Controversy surrounds the existence and nature of reaction time deficits in Parkinson's disease. Three areas of research are reviewed: the use of precues to speed movement (motor preprogramming), the effects of medication on reaction time, and simple reaction times. No evidence is found for a motor preprogramming deficit, and the presence of a parkinsonian reaction time deficit after medication withdrawal is found to be dependent upon experimental design and the withdrawal method used. Parkinson's disease is found to cause a consistent deficit in simple reaction time. A quantitative analysis of past studies reveals that a parkinsonian reaction time deficit is more likely to be present in tasks that controls can perform with a fast reaction time. This relationship between deficit and control group reaction time applies to choice, but not simple, reaction time tasks. Many studies compare patient and control choice reaction times across experimental conditions that cause control reaction time to vary. The authors of these studies should consider whether their results can be explained in terms of the simple relationship between patient reaction time deficit and control reaction time before drawing more complex conclusions from their data.

Effect of directed attention in Huntington's disease

This experiment sought to ascertain whether overt gaze (i.e., directed attention) would influence attentional performance in Huntington's disease (HD), via the use of a vibrotactile choice reaction time procedure involving biased probabilities of event occurrence. Subjects looked (i.e., direct gaze) either at the hand receiving the most (expected) vibrations, or the hand less often stimulated (the unexpected), for both crossed and uncrossed arm postures. Patients with HD showed performance advantages when directing attention (i.e., gaze) at the responding hand, especially for expected events. Patients with HD, however, were not sensitive to distributions of event probability in the uncrossed arm posture, nor when looking away from the responding hand. With the crossed arm posture, and when directing attention at the expected side, patients with HD became more sensitive to distributions of event probability. In HD, there may be a disruption of fronto-striatal circuitry on both cortical and subcortical levels which may account for impairments both in holding and shifting attention.

Brain responses to detection of right or left somatic targets are symmetrical in unilateral Parkinson's disease: a case against the concept of "parkinsonian neglect'

Signs of attentional dysfunction mimicking spatial neglect have been described both in humans with lateralised Parkinson's Disease (PD) and in animals with MPTP-related hemiparkinsonism. Such deficits have been attributed to dopamine loss in basal ganglia and cortical targets. However, in previous studies the existence of neglect was assumed from behavioural tests which needed a motor output, thus entailing interpretation ambiguities due to effects of directional hypokinesia. We recorded brain event-related potentials (ERPs) evoked by the presentation of target somatic stimuli to the affected and non-affected sides in 44 patients with unilateral or asymmetrical PD. The N2 and P3 ERP components were specifically analysed, since (a) they are triggered selectively by task-relevant, attended sensory stimuli; (b) their latency reflects stimulus evaluation time, independently from the execution of a motor response, and (c) they have proved to be abnormal in hemineglect syndromes due to focal brain lesions. Irrespective of the side (left or right) of motor symptom predominance there were no significant ERP differences to stimulation of the affected and non-affected limbs, nor was there any correlation between ERP latencies and the degree of dopamine-related motor impairment. The P3 latency was abnormally delayed in 23% of the patients, but there was no trend for abnormalities to concentrate on the affected side. This study does not confirm the existence of a significant attentional impairment toward the affected limb in lateralised PD, and suggests that previous clinical evidence of "neglect' behaviour in PD might be linked to directional hypokinesia, thus reflecting intentional, rather than attentional lateralised deficits.

Covert orienting of attention in the rat and the role of striatal dopamine

Attention can be directed to a location in the absence of overt signs of orienting, a phenomenon termed "covert orienting." The ability to orient attention covertly has been well documented in humans, but recent progress has been made with the operational definition of the processes involved in covert orienting. Reaction times to visual targets are quickened when attention is drawn to the location of the subsequent target, and processes such as disengagement, maintenance, and movement of attention can be dissociated by using this method. The possible involvement of striatal dopamine in covert orienting is disputed, with conflicting reports of deficits in covert orienting in patients with Parkinson's disease. To examine the significance of dopamine in the striatum in attentional processes, a test of covert orienting, analogous to that used in humans, was devised for the rat. Unilateral dopamine-depleting lesions of the striatum resulted in increases in mean reaction times contralateral to the side of the lesion, but reaction times did not change differentially as a function of the requirements to maintain, disengage, or shift attention. These findings add additional support to the hypothesis that the deficit that appears as hemineglect observed after striatal damage reflects a motor impairment rather than damage in neural systems underlying mechanisms for directing attention.

Simon effect and attention in Parkinson's disease: a comparison with Huntington's disease and Tourette's syndrome

Patients with hyperkinetic basal-ganglia disorders (Huntington's disease, HD; and Tourette's syndrome, TS) have difficulty with spatially incongruent stimulus-response configurations, the Simon effect, and with inhibiting inappropriate responses in a conditionality paradigm. However Parkinson's disease (PD) patients with hypokinetic basal-ganglia disorder show normal (for their age) conditionality and congruency effects, probably because the task is extremely sensitive to aging and PD patients are typically older than HD and TS individuals. Overall, HD patients were by far the most affected, reflecting the likely greater involvement of the caudate (with its predominantly cognitive role) than the putamen; the latter structure, with a predominantly motor involvement, is the more affected in PD.

Advance information and movement sequencing in Gilles de la Tourette's syndrome

Tourette's syndrome is a chronic neurological disorder manifested by involuntary motor tics and vocalisations. Because the basal ganglia have been implicated in the pathology underlying Tourette's syndrome, the present two procedures, both involving sequential movements, sought to determine the extent to which patients with Tourette's syndrome were reliant on, and could utilise different levels of advance information. Patients with Tourette's syndrome were found to be more reliant than controls on external visual cues to execute rather than to initiate a motor programme. When there was a high level of reduction in advance information--that is, a visual pathway to be followed was extinguished well in advance of each successive movement--executions progressively slowed as the sequence was traversed. Similarly, if no advance information was provided before each move, movement execution was slower than that of controls. The movement initiation times of patients with Tourette's syndrome were, however, similar to those of controls, as were their movement execution times when advance visual information was available. It seems that patients with Tourette's syndrome, like parkinsonian patients who are known to have a basal ganglia disorder, require external sensory cues to sequence a motor programme effectively. The present study found evidence consistent with the hypothesis that patients with Tourette's syndrome, like patients with Parkinson's disease, may be dysfunctional in internal switching mechanisms. Alternatively, with limited visual guidance, patients with Tourette's syndrome, regardless of medication or depression state, may require more time to plan and programme each next submovement, and under such conditions may require external visual cues to direct attention effectively to given targets. Although the underlying pathogenesis is still speculative, it is concluded that there is much to support the notion that Tourette's syndrome may stem from abnormalities of the major pathways between the basal ganglia and the frontal lobes.

Auditory selective attention is impaired in Parkinson's disease--event-related evidence from EEG potentials

Selective attention refers to the ability to focus on one channel of information in the presence of distracting other channels. For the visual modality, results on impairments of selective attention have been conflicting in patients with idiopathic Parkinson's disease (PD). Independent of possible interferences from visual or movement disturbances selective attention can be measured as the so-called 'processing negativity' (PN) using auditory evoked potentials. Therefore, auditory selective attention with the PN was measured in 14 patients with PD and 16 control subjects. Subjects had to attend to tones presented to one ear (i.e. to press a button to occasionally presented longer tones) and ignore tones presented to the other ear. Tones were presented at a rate of 1/s ('slow') or 2/s ('fast'). PN was measured as the difference of the potentials evoked by attended minus ignored standard tones. PN was significantly smaller in the PD patients than in the controls with slow presentation. There was no difference between both groups with fast presentation. PN remained unchanged when patients had a 12-h withdrawal of their usual anti-Parkinsonian drug therapy. PD patients and controls did not differ in their P3 component evoked in the usual 'oddball' task nor in the mismatch negativity evoked by the occasionally longer tones in the PN task. The results provide evidence for an impairment of auditory selective attention that is specific for patients with PD (i.e. independent of the P3 component).