Variable foreperiod deficits in Parkinson's disease: dissociation across reflexive and voluntary behaviors

The effect of a visual warning signal (1.0-6.5 s random foreperiod, FP) on the latency of voluntary (hand-grip) and reflexive (startle-eyeblink) reactions was investigated in Parkinson's disease (PD) patients and in young and aged control subjects. Equivalent FP effects on blink were observed across groups. By contrast, FP effects diverged for voluntary responses across groups with no effect of foreperiod duration for PD patients. The convergence of these results with findings from animal research suggests that interval-timing processes associated with higher level voluntary behaviors are dependent upon intact dopaminergic pathways, while those associated with lower level reflexive behaviors are spared in PD.     

A simple and unified approach to human voluntary movements

In his provocative article, F. Mechsner (2004) advances the thesis that human voluntary movements are subject to "psychological" or "perceptual-cognitive" control and are thus organized "without regard to efferent patterns" (p. 355). Rather than considering in detail the experiments that he proffered by way of support, the present author discusses the degree to which that supposition has appeal on the grounds of simplicity and is defined in terms that are compatible with a unified science.     

The factors that induce or overcome freezing of gait in Parkinson's disease

Freezing of gait (FoG), a transient halt in walking, is a major mobility problem for patients with Parkinson's disease (PD). This study examined the factors that induce FoG, and identified the cues and strategies that help overcome it through a postal survey of 130 PD patients. 72% reported FoG. The factors that commonly induced FoG were turning, fatigue, confined spaces and stressful situations, in addition to emotional factors. FoG was also ameliorated by various attentional and external cueing strategies. The concept of paradoxical kinesis, the potential neural substrates of such external cueing effects, and their importance for rehabilitation in PD are discussed.     

The relationship between executive function and verbal memory in Parkinson's disease

A growing body of evidence suggests that the various cognitive symptoms found in Parkinson's disease (PD) are secondary to executive dysfunction. Studies addressing this possibility for memory impairment specifically have not included measures of working memory nor have they ruled-out potential mediating variables such as overall level of cognitive impairment or depression. The purpose of this study was to include measures of these variables in determining the relationship between multiple aspects of executive function and delayed verbal recall in 32 idiopathic PD patients. Results were consistent with the original hypothesis and further suggest that working memory is a key factor in recall memory and may mediate the relationship between other executive measures and recall in PD.     

Age-related differences in postural reaction time and coordination during voluntary sway movements

The elderly are known to exhibit declines in postural control during standing and walking, however little is known about how the elderly react under time-critical and challenging postural situations. The purpose of this study was to examine age-related differences in reaction time (RT) and the pattern of temporal coordination between center of pressure (COP), trunk and head motion during voluntary postural sway movements. Healthy young (n=10; mean=24 years; SD=5 years) and elderly men (n=8; mean=75 years; SD=2 years) stood on a force plate with tri-axial accelerometers attached to the head and lower trunk. Participants were required to generate sway in the anterior-posterior (AP) or medial-lateral (ML) direction in response to an auditory cue during two different testing conditions called Static reaction and Dynamic reaction. Static reactions involved the initiation of voluntary sway in either the AP or ML direction from quiet stance. Dynamic reactions involved an orthogonal switch of voluntary sway between the AP and ML directions. Compared to the young, elderly individuals exhibited slower RT during both Static and Dynamic reaction, and smaller differences in RT and phasing between COP, trunk, and head motion. The results of this study suggest that the elderly adopted more rigid coordination strategies compared to the young when executing a rapid change in direction of whole body motion. The rigid movement strategy of the elderly was presumably generated in an effort to compensate for increased challenge to the maintenance of stability.     

Interference Effects from Observed Movement in Parkinson's Disease

Previous research has demonstrated that Parkinson's disease patients have an increased susceptibility to response conflict. In the present study, the authors investigate whether Parkinson's patients have a similar sensitivity to interference from observed movements. In all, 10 patients and 10 controls performed horizontal and vertical arm movements while watching a video of either a person performing similar movements or a moving dot. Movements were performed in the same plane (congruent) and orthogonal to the observed movement (incongruent). The off-axis variance of movements was our index of interference. Although patients tended to exhibit more off-axis variability than did controls, both groups demonstrated similar congruence effects, with greater variance in incongruent conditions. These results indicated that increased susceptibility to interference in Parkinson's disease does not extend to interference from observed movements.     

Relationships between movement initiation times and movement-related cortical potentials in Parkinson's disease

Movement-related cortical potentials recorded from the scalp reveal increasing cortical activity occurring prior to voluntary movement. Studies of set-related cortical activity recorded from single neurones within premotor and supplementary motor areas in monkeys suggest that such premovement activity may act to prime activity of appropriate motor units in readiness to move, thereby facilitating the movement response. Such a role of early stage premovement activity in movement-related cortical potentials was investigated by examining the relationship between premovement cortical activity and movement initiation or reaction times. Parkinson's disease and control subjects performed a simple button-pressing reaction time task and individual movement-related potentials were averaged for responses with short compared with long reaction times. For Parkinson's disease subjects but not for the control subjects, early stage premovement cortical activity was significantly increased in amplitude for faster reaction times, indicating that there is indeed a relationship between premovement cortical activity amplitude and movement initiation or reaction times. In support of studies of set-related cortical activity in monkeys, it is therefore suggested that early stage premovement activity reflects the priming of appropriate motor units of primary motor cortex, thereby reducing movement initiation or reaction times.PsycINFO classification: 2330; 2520; 2530     

The effects of voluntary movements on auditory-haptic and haptic-haptic temporal order judgments

In two experiments we investigated the effects of voluntary movements on temporal haptic perception. Measures of sensitivity (JND) and temporal alignment (PSS) were obtained from temporal order judgments made on intermodal auditory-haptic (Experiment 1) or intramodal haptic (Experiment 2) stimulus pairs under three movement conditions. In the baseline, static condition, the arm of the participants remained stationary. In the passive condition, the arm was displaced by a servo-controlled motorized device. In the active condition, the participants moved voluntarily. The auditory stimulus was a short, 500Hz tone presented over headphones and the haptic stimulus was a brief suprathreshold force pulse applied to the tip of the index finger orthogonally to the finger movement. Active movement did not significantly affect discrimination sensitivity on the auditory-haptic stimulus pairs, whereas it significantly improved sensitivity in the case of the haptic stimulus pair, demonstrating a key role for motor command information in temporal sensitivity in the haptic system. Points of subjective simultaneity were by-and-large coincident with physical simultaneity, with one striking exception in the passive condition with the auditory-haptic stimulus pair. In the latter case, the haptic stimulus had to be presented 45ms before the auditory stimulus in order to obtain subjective simultaneity. A model is proposed to explain the discrimination performance.     

Personality traits that distinguish you and me are better memorized

Female participants described themselves via desirable and undesirable traits that they possessed or lacked. For each trait, they then received feedback informing them whether they were similar to, or different from a female target. After a distracting task, participants received a recognition test and completed a recall test of the traits. The traits that allowed the participant to be differentiated from the target (because they were applicable to one but not the other) were best recognized and recalled. Undesirable traits were better recognized than desirable ones. However, the picture of the target emanating from the recall data presents her in a very desirable way. The results are discussed within a pragmatic framework. ©1997 John Wiley & Sons, Ltd.     

Postural and focal inhibition of voluntary movements prepared under various temporal constraints

Large disturbances arising from the moving segments (focal movement) are commonly counteracted by anticipatory postural adjustments (APAs). The aim of this study was to investigate how APAs – focal movement coordination changes under temporal constraint. Ten subjects were instructed to perform an arm raising movement in the reactive (simple reaction time) and predictive (anticipation–coincidence) tasks. A stop paradigm was applied to reveal the coordination. On some unexpected trials, a stop signal indicated to inhibit the movement; it occurred randomly at different delays (SOA) relative to the go signal in the reactive task, and at different delays prior to the focal response initiation in the predictive task. Focal movement was measured using contact switch, accelerometer and EMG from the anterior deltoid. APAs were quantified using centre of pressure displacement and EMG from three postural muscles. The inhibition rates as a function of the SOA produce psychometric functions where the bi-serial points allow the moment of the motor "command release" to be estimated. Repeated measures ANOVAs showed that APAs and focal movement were closely timed in the reactive task but distinct in a predictive task. Data were discussed according to two different models of coordination: (1) hierarchical model where APAs and focal movement are the results of a single motor command; (2) parallel model implying two independent motor commands. The data clearly favor the parallel model when the temporal constraint is low. The stop paradigm appears as a promising technique to explore APAs – focal movement coordination.     

Kinematic gait parameters for older adults with Parkinson's disease during street crossing simulation

Safe street crossing is important for older adults' social inclusion. We assessed gait kinematic adaptation under different simulated street crossing conditions in older adults with Parkinson's disease (PD) and made comparisons with older adults without PD to understand how PD interferes in outdoor task performance, helping in the development of strategies to reduce road traffic accident risk. In 20 older adults without PD (control group – CG) and 20 with PD (GPD), we assessed usual gait (C1), gait during street crossing simulation (C2), and gait during reduced-time street crossing simulation (C3). Velocity, step length, and step, swing, stance, and double support time were analyzed. Spatiotemporal differences in gait between groups and conditions were analyzed. The GPD walked 16% slower in C1 and 12% slower in C2 and C3 than the CG. GPD also took 11% shorter steps in C1 and 9.5% shorter steps in C2. The double support time was 8.5% greater in C1. In intragroup comparisons, there were significant differences in all gait conditions. The CG showed increased velocity (C2 15% > C1; C3 13% > C2; C3 26% > C1), step length (C2 8% > C1; C3 5% > C2; C3 13% > C1), and swing time (C2 2% > C1; C3 3.7% > C2; C3 6% > C1), and decreased step time (C2 7.5% < C1; C3 8% < C2; C3 15% < C1), stance time (C2 1.3% < C1; C3 2.5% < C2; C3 3.6% < C1), and double support time (C2 6.3% < C1; C3 10.5% < C2; C3 16% < C1). GPD showed increased velocity (C2 19% > C1; C3 13.5% > C2; C3 29.7% > C1), step length, (C2 6% > C1; C3 7% > C2; C3 16% > C1), and swing time (C2 3% > C1; C3 3% > C2; C3 5.5% > C1) and decreased step time (C2 10.3% < C1; C3 7.7% < C2; C3 17% < C1), stance time (C2 1.7% < C1; C3 1.7% < C2; C3 3.4% < C1), and double support time (C2 7% < C1; C3 9.5% < C2; C3 16% < C1). Kinematic changes observed in the intergroup comparison show that participants with PD had lower velocity in all conditions. However, per the intragroup results, both participants with and without PD managed to significantly modify gait variables to attempt to cross the street in the given time. It is necessary to assess whether this increases fall risk by exposing them to road traffic accidents.     

Source memory in Parkinson's disease

Three experiments (ns = 14 per group) are reported which investigated the ability of Parkinson patients to remember the characteristics of conditions under which a memory was acquired. In Exp. 1, subjects were required to indicate for each item in a recognition memory test whether it was spoken by Experimenter 1 or by Experimenter 2 (external-external source memory). In Exp. 2, subjects had to indicate for each item whether it was generated by themselves or by the experimenter (internal-external source memory). In Exp. 3, subjects had to judge whether an item was generated by themselves in saying or in thinking (internal-internal source memory). We found that patients with Parkinson's disease were not impaired in the previous two kinds of source memory (Exp. 1 and 2) but were impaired in internal-internal source memory (Exp. 3) relative to the age-matched control groups. In addition, both groups' performance could be improved when given distinctive cues, i.e., perceptual cues in Exp. 1 and different-domain cues in Exp. 2. These results suggest that the availability of cues was critical for Parkinson's disease in source memory. Finally, the result of Exp. 2 also showed generation effects for patients with Parkinson's disease. The generation effect refers to better memory of information by people when they had to produce it, e.g., producing associates to a word, compared with memory of information given to them.     

The influence of eye-gaze and arrow pointing distractor cues on voluntary eye movements

We investigated Ricciardelli et al.'s (2002) claim, that the tendency for gaze direction to elicit automatic attentional following is unique to biologically significant information. Participants made voluntary saccades to targets on the left or the right of a display, which were either congruent or incongruent with a centrally presented distractor (eye-gaze or arrow). Contrary to Ricciardelli et al., for both distractor types, saccade latencies were slower, and participants made more directional errors, on incongruent than on congruent trials. Moreover, a cost-benefit analysis showed no difference between the two distractor types. However, latencies for erroneous saccades were faster than correctly directed saccades for the eye-gaze distractors, but not for the arrow distractors.     

The relationship between contrast sensitivity, gait, and reading speed in Parkinson's disease

Parkinson's disease (PD) results in reduced walking speed and visual difficulties, including difficulty reading (Davidsdottir, Cronin-Golomb, & Lee, 2005). PD is characterized by a reduction in dopamine, which is instrumental in determining a person's contrast sensitivity (CS). This study assessed the relationship between CS, gait (step length and walking speed), and reading speed in 18 non-demented PD volunteers with normal acuity. We found that CS correlated with walking speed (r = .57, p = .01), step length (r = .53, p = .02), and reading speed (r = .54, p = .02). Visual acuity (which has not been tied to dopamine in the same way) correlated with reading speed (r(s) = -.65, p = .004), but not with gait measures. We also assessed the contribution of age, education, and cognitive status (Shipley Institute of Living Scale) to these variables. We conclude that CS and age both play an important role in determining gait in PD, while reading speed is related to both acuity and CS, but not age.     

Impulse-control disorders in Parkinson's disease

Parkinson's disease is a neurodegenerative disorder characterized by bradykinesia, rigidity, postural instability, and resting tremor. Increasingly, Parkinson's disease has been associated with a broad spectrum of non-motor symptoms, such as olfactory loss, sleep disorders, autonomic dysfunction, cognitive impairment, psychosis, depression, anxiety, and apathy. In addition, a minority of Parkinson's disease patients develop compulsive behaviors while receiving dopamine-replacement therapy, including medication hoarding, pathological gambling, binge eating, hyperlibidinous behavior, compulsive shopping, and punding. These behaviors may result in psychosocial impairment for patients and therapeutic challenges for clinicians. This article reviews the anatomic substrates, behavioral spectrum, associated factors, and potential treatments for dopamine-replacement therapy-related compulsions in Parkinson's disease.     

Emotional dysfunction in Parkinson's disease

In addition to motor symptomatology, idiopathic Parkinson's disease is characterized by emotional dysfunction. Depression affects some 30 to 40 percent of Parkinson patients and other psychiatric co-morbidities include anxiety and apathy. Neuropsychological and neuroimaging studies of emotional dysfunction in Parkinson patients suggest abnormalities involving mesolimbic and mesocortical dopaminergic pathways. There is also evidence suggesting that the interaction between serotonin and dopamine systems is important in the understanding and treatment of mood disorders in Parkinson's disease. In this review we discuss the neuropsychiatric abnormalities that accompany Parkinson's disease and describe their neuropsychological, neuropharmacologic, and neuroimaging concomitants.     

Motor excitability is reduced prior to voluntary movements in children and adolescents with Tourette syndrome

Tourette syndrome (TS) is a neuro‐developmental disorder characterized by the occurrence of motor and vocal tics: involuntary, repetitive, stereotyped behaviours that occur with a limited duration, often typically many times in a single day. Previous studies suggest that children and adolescents with TS may undergo compensatory, neuroplastic changes in brain structure and function that help them gain control over their tics. In the current study we used single‐pulse and dual‐site paired‐pulse transcranial magnetic stimulation (TMS), in conjunction with a manual choice reaction time task that induces high levels of inter‐manual conflict, to investigate this conjecture in a group of children and adolescents with TS, but without co‐morbid Attention Deficit Hyperactivity Disorder (ADHD). We found that performance on the behavioural response‐conflict task did not differ between the adolescents with TS and a group of age‐matched typically developing individuals. By contrast, our study demonstrated that cortical excitability, as measured by TMS‐induced motor‐evoked potentials (MEPs), was significantly reduced in the TS group in the period immediately preceding a finger movement. This effect is interpreted as consistent with previous suggestions that the cortical hyper‐excitability that may give rise to tics in TS is actively suppressed by cognitive control mechanisms. Finally, we found no reliable evidence for altered patterns of functional inter‐hemispheric connectivity in TS. These results provide evidence for compensatory brain reorganization that may underlie the increased self‐regulation mechanisms that have been hypothesized to bring about the control of tics during adolescence.     

Visual aiming movements in Alzheimer's disease

This study examined whether AD affects the control of pointing movements. Sixteen older adults with probable AD and 10 age-matched healthy adults pointed at targets varying in size (3 and 7 mm in diameter) and located at three positions (at the midline and 33 degrees to the left and right). Results revealed the patients exhibited longer movement time, lower peak velocity and more time in deceleration, although they exhibited effects of target size and location comparable to the healthy controls. AD, then, would appear to slow down movement without affecting the motor system's ability to respond to task demands.