Cognitive components of reaction time in Parkinson's disease

Connecting the dots: Sensory cueing enhances functional connectivity between pre-motor and supplementary motor areas in Parkinson's disease

People with Parkinson's disease often exhibit improvements in motor tasks when exposed to external sensory cues. While the effects of different types of sensory cues on motor functions in Parkinson's disease have been widely studied, the underlying neural mechanism of these effects and the potential of sensory cues to alter the motor cortical activity patterns and functional connectivity of cortical motor areas are still unclear. This study aims to compare changes in oxygenated haemoglobin, deoxygenated haemoglobin and correlations among different cortical regions of interest during wrist movement under different external stimulus conditions between people with Parkinson's disease and controls. Ten Parkinson's disease patients and 10 age- and sex-matched neurologically healthy individuals participated, performing repetitive wrist flexion and extension tasks under auditory and visual cues. Changes in oxygenated and deoxygenated haemoglobin in motor areas were measured using functional near-infrared spectroscopy, along with electromyograms from wrist muscles and wrist movement kinematics. The functional near-infrared spectroscopy data revealed significantly higher neural activity changes in the Parkinson's disease group's pre-motor area compared to controls (p = 0.006), and functional connectivity between the supplementary motor area and pre-motor area was also significantly higher in the Parkinson's disease group when external sensory cues were present (p = 0.016). These results indicate that external sensory cues' beneficial effects on motor tasks are linked to changes in the functional connectivity between motor areas responsible for planning and preparation of movements.

Reaching and Grasping Movements in Parkinson's Disease: A Review

Parkinson's disease (PD) is known to affect the brain motor circuits involving the basal ganglia (BG) and to induce, among other signs, general slowness and paucity of movements. In upper limb movements, PD patients show a systematic prolongation of movement duration while maintaining a sufficient level of endpoint accuracy. PD appears to cause impairments not only in movement execution, but also in movement initiation and planning, as revealed by abnormal preparatory activity of motor-related brain areas. Grasping movement is affected as well, particularly in the coordination of the hand aperture with the transport phase. In the last fifty years, numerous behavioral studies attempted to clarify the mechanisms underlying these anomalies, speculating on the plausible role that the BG-thalamo-cortical circuitry may play in normal and pathological motor control. Still, many questions remain open, especially concerning the management of the speed-accuracy tradeoff and the online feedback control. In this review, we summarize the literature results on reaching and grasping in parkinsonian patients. We analyze the relevant hypotheses on the origins of dysfunction, by focusing on the motor control aspects involved in the different movement phases and the corresponding role played by the BG. We conclude with an insight into the innovative stimulation techniques and computational models recently proposed, which might be helpful in further clarifying the mechanisms through which PD affects reaching and grasping movements.

Cortical network organization reflects clinical response to subthalamic nucleus deep brain stimulation in Parkinson's disease

The degree of response to subthalamic nucleus deep brain stimulation (STN‐DBS) is individual and hardly predictable. We hypothesized that DBS‐related changes in cortical network organization are related to the clinical effect. Network analysis based on graph theory was used to evaluate the high‐density electroencephalography (HDEEG) recorded during a visual three‐stimuli paradigm in 32 Parkinson's disease (PD) patients treated by STN‐DBS in stimulation “off” and “on” states. Preprocessed scalp data were reconstructed into the source space and correlated to the behavioral parameters. In the majority of patients (n = 26), STN‐DBS did not lead to changes in global network organization in large‐scale brain networks. In a subgroup of suboptimal responders (n = 6), identified according to reaction times (RT) and clinical parameters (lower Unified Parkinson's Disease Rating Scale [UPDRS] score improvement after DBS and worse performance in memory tests), decreased global connectivity in the 1–8 Hz frequency range and regional node strength in frontal areas were detected. The important role of the supplementary motor area for the optimal DBS response was demonstrated by the increased node strength and eigenvector centrality in good responders. This response was missing in the suboptimal responders. Cortical topologic architecture is modified by the response to STN‐DBS leading to a dysfunction of the large‐scale networks in suboptimal responders.

Transcranial direct current stimulation decreased cognition-related reaction time in older adults: A systematic review and meta-analysis

BACKGROUND

This systematic review and meta-analysis investigated the effects of transcranial direct current stimulation (tDCS) on the cognitive functions of healthy older adults by focusing on the changes in reaction time during cognitive tasks.

METHOD

A total of 31 studies qualified for this meta-analysis, and we acquired 36 comparisons from the included studies for data synthesis. The individual effect sizes were calculated by comparing the altered reaction time during the performance of a specific cognitive task between the active tDCS and sham groups. In two moderator variable analyses, we examined the potentially different effects of the tDCS protocols on the cognition-related reaction time based on the tDCS protocol used (i.e., online vs. offline tDCS) and the five cognitive domains: (a) perceptual-motor function, (b) learning and memory, (c) executive function / complex attention, (d) language, and (e) social cognition. Meta-regression analyses were conducted to estimate the relationship between demographic and tDCS parameter characteristics and the changes in reaction time.

RESULTS

The random-effects model meta-analysis revealed significant small effects of tDCS on cognition-related reaction time. Specifically, providing online tDCS significantly reduced the reaction time, and these patterns were observed during learning and memory and executive function / complex attention tasks. However, applying offline tDCS failed to find any significant reduction of reaction time across various cognitive tasks. The meta-regression analysis revealed that the effects of tDCS on the reaction time during the performance of cognitive tasks increased for the older people.

CONCLUSIONS

These findings suggest that providing online tDCS may effectively improve the ageing-induced reaction time related to specific cognitive functions of elderly people.

Systematic quantitative assessment of motor function in clinically isolated REM sleep behaviour disorder: A diagnostic window into early alpha-synucleinopathies

Mild motor abnormalities can herald the beginning of Parkinson´s disease but their diagnostic value is limited by multifactorial ageing-related influences on motor function. We characterized mild motor abnormalities in different motor domains by conducting a systematic motor assessment in 20 patients with clinically isolated REM sleep behaviour disorder (iRBD) without parkinsonian motor signs and 20 healthy controls. We addressed the influence of lifestyle factors and age on motor function, which needs to be distinguished from neurodegenerative motor features, and assessed the diagnostic value of innovative and established quantitative motor tests in iRBD. Patients with iRBD showed abnormalities in perceptual motor speed (falling stick test), trunk movement coordination (bend, twist and touch test) and dynamic balance (line walk test) without alterations in simple motor speed (alternate tap test), dexterity (grooved pegboard), static balance (force plate) and gait (timed up and go test). The falling stick test showed the highest diagnostic accuracy in identifying subjects with RBD (ROC-AUC 0.85, p ≤ 0.001). Multivariate analysis revealed physical activity and age as additional determinants of motor test performance. iRBD comprises a wide spectrum of mild motor abnormalities which cannot be verified by established tests for motor speed, gait and balance. The falling stick test, an innovative screening test for perceptual motor speed, provides high diagnostic potential in identifying subjects with subclinical neurodegenerative symptoms before parkinsonian motor signs become apparent. Normative data for physical activity and age need to be obtained to ensure correct interpretation of motor test results in prodromal Parkinson-related disease.

Significant cognitive decline in Parkinson's disease exacerbates the reliance on visual feedback during upper limb reaches

While upper limb reaches are often made in a feed-forward manner, visual feedback during the movement can be used to guide the reaching hand towards a target. In Parkinson's disease (PD), there is evidence that the utilisation of this visual feedback is increased. However, it is unclear if this is due solely to the characteristic slowness of movements in PD providing more opportunity for incorporating visual feedback to modify reach trajectories, or whether it is due to cognitive decline impacting (feed-forward) movement planning ability. To investigate this, we compared reaction times and movement times of reaches to a target in groups of PD patients with normal cognition (PD-NC), mild cognitive impairment (PD-MCI) or dementia (PD-D), to that of controls with normal cognition (CON-NC) or mild cognitive impairment (CON-MCI). Reaches were undertaken with full visual feedback (at a 'natural' and 'fast-as-possible' pace); with reduced visual feedback of the reaching limb to an illuminated target; and without any visual feedback to a remembered target with eyes closed. The PD-D group exhibited slower reaction times than all other groups across conditions, indicative of less efficient movement planning. When reaching to a remembered target with eyes closed, all PD groups exhibited slower movement times relative to their natural pace with full visual feedback. Crucially, this relative slowing was most pronounced for the PD-D group, compared to the PD-MCI and PD-NC groups, suggesting that substantial cognitive decline in PD exacerbates dependence on visual feedback during upper limb reaches.

Components determining the slowness of information processing in parkinson's disease

INTRODUCTION

Bradyphrenia is a key cognitive feature in Parkinson's disease (PD). There is no consensus on whether information processing speed is impaired or not beyond motor performance.

OBJECTIVE

This study aims to explore which perceptual, motor, or cognitive components of information processing are involved in the slowdown affecting cognitive performance.

METHODS

The study included 48 patients with PD (age: 63, 3 ± 8, 18; HY I-III; UPDRS 15,46 ± 7,76) and 53 healthy controls (age: 60,09 ± 12,83). Five reaction time (RT) tasks were administered to all participants. The average RT in each of the tasks and the percentage of correct answers were measured. Patients with PD were in "ON state" at the time of the evaluation. Perceptual, motor, and cognitive components were isolated by means of a series of ANCOVAs.

RESULTS

As expected, the motor component was slowed down in patients with PD. Moreover, while patients with PD showed slower RT than controls in all tasks, differences between groups did not exponentially increase with the increasing task complexity. ANCOVA analyses also revealed that the perceptual and sustained alert component resulted to be slowed down, with no differences being found in any of the remaining isolated cognitive components (i.e., response strategy-inhibition, decisional, visual search, or interference control).

CONCLUSIONS

The results revealed that slowness of information processing in PD was mainly associated with an impaired processing speed of the motor and perceptual-alertness components analyzed. The results may help designing new neurorehabilitation strategies, focusing on the improvement of perceptual and alertness mechanisms.

Program of Seven 45-min Dry Immersion Sessions Improves Choice Reaction Time in Parkinson's Disease

The study hypothesis held that in subjects with Parkinson's disease (PD), the reaction time (RT) tests of the higher cognition demand would have more readily improved under the program of analog microgravity (μG) modeled with "dry" immersion (DI). To test this hypothesis, 10 subjects with PD have passed through a program of seven DI sessions (each 45 min long) within 25-30 days, with overall μG dose 5 1/4 h. Five patients were enrolled as controls, without DI (noDI group). Simple RT (SRT), disjunctive RT (DRT), and choice RT (CRT) were assessed in four study points: before the DI program (preDI), 1 day after the DI program (postDI), 2 weeks after the DI program (DI2w), and 2 months after the DI program (DI2m). The motor time (MT) was assessed with the tapping test (TT). Additionally, signal detection time (SDT) and central processing time (CPT) were extracted from the data. Before the program of DI, the RT tests are in accordance with their cognition load: SRT (284 ± 37 ms), DRT (338 ± 38 ms), and CRT (540 ± 156 ms). In accordance with the hypothesis, CRT and DRT have improved under DI by, respectively, 20 and 8% at the study point "DI2w," whereas SRT, SDT, and MT did not change (<5% in the preDI point, p > 0.05). Thus, the program of DI provoked RT improvement specifically in the cognitively loaded tasks, in a "dose of cognition-reaction" manner. The accuracy of reaction has changed in none of the RT tests. The neurophysiologic, hormonal/neuroendocrine, behavioral, neural plasticity, and acclimation mechanisms may have contributed to such a result.

Brain Activity Underlying Muscle Relaxation

Fine motor control of not only muscle contraction but also muscle relaxation is required for appropriate movements in both daily life and sports. Movement disorders such as Parkinson’s disease and dystonia are often characterized by deficits of muscle relaxation. Neuroimaging and neurophysiological studies suggest that muscle relaxation is an active process requiring cortical activation, and not just the cessation of contraction. In this article, we review the neural mechanisms of muscle relaxation, primarily utilizing research involving transcranial magnetic stimulation (TMS). Several studies utilizing single-pulse TMS have demonstrated that, during the relaxation phase of a muscle, the excitability of the corticospinal tract controlling that particular muscle is more suppressed than in the resting condition. Other studies, utilizing paired-pulse TMS, have shown that the intracortical inhibition is activated just before muscle relaxation. Moreover, muscle relaxation of one body part suppresses cortical activities controlling other body parts in different limbs. Therefore, the cortical activity might not only be a trigger for muscle relaxation of the target muscles but could also bring about an inhibitory effect on other muscles. This spread of inhibition can hinder the appropriate contraction of muscles involved in multi-limb movements such as those used in sports and the play of musical instruments. This may also be the reason why muscle relaxation is so difficult for beginners, infants, elderly, and the cognitively impaired.

Attenuated NoGo-related beta desynchronisation and synchronisation in Parkinson's disease revealed by magnetoencephalographic recording

Parkinson’s disease (PD) is a neurodegenerative disorder characterised by motor abnormalities. Many non-demented patients with PD have cognitive impairment especially in executive functions. Using magnetoencephalographic (MEG) recording combined with event-related desynchronisation/synchronisation (ERD/ERS) analysis, we investigated cortical executive functions during a Go/NoGo task in PD patients and matched healthy subjects. PD patients had a longer reaction time in the Go condition and had a higher error ratio in both Go and NoGo conditions. The MEG analysis showed that the PD patients had a significant reduction in beta ERD during the NoGo condition and in beta ERS during both Go and NoGo conditions compared with the healthy subjects (all p < 0.05). Moreover, in the Go condition, the onsets of beta ERD and ERS were delayed in PD patients. Notably, NoGo ERS was negatively correlated with the Unified Parkinson’s Disease Rating Scale (UPDRS) score in PD patients. The present study demonstrated abnormalities in motor programming, response inhibition, and frontal inhibitory modulation in PD. Further extensive investigations are necessary to confirm the longitudinal treatment responses in PD.

Short-term temporal memory in idiopathic and Parkin-associated Parkinson's disease

In a rapidly changing environment, we often know when to do something before we have to do it. This preparation in the temporal domain is based on a ‘perception’ of elapsed time and short-term memory of previous stimulation in a similar context. These functions could be perturbed in Parkinson’s disease. Therefore, we investigated their role in eye movement preparation in sporadic Parkinson’s disease and in a very infrequent variant affecting the Parkin gene. We used a simple oculomotor task where subjects had to orient to a visual target and movement latency was measured. We found that in spite of an increased average reaction time, the influence of elapsed time on movement preparation was similar in controls and the two groups of PD patients. However, short-term temporal memory of previous stimulation was severely affected in sporadic PD patients either ON or OFF dopaminergic therapy. We conclude that the two different contributions to temporal preparation could be dissociated. Moreover, a short-term temporal memory deficit might underlie temporal cognition deficits previously observed in PD.

Multifaceted effects of noisy galvanic vestibular stimulation on manual tracking behavior in Parkinson's disease

Parkinson’s disease (PD) is a neurodegenerative movement disorder that is characterized clinically by slowness of movement, rigidity, tremor, postural instability, and often cognitive impairments. Recent studies have demonstrated altered cortico-basal ganglia rhythms in PD, which raises the possibility of a role for non-invasive stimulation therapies such as noisy galvanic vestibular stimulation (GVS). We applied noisy GVS to 12 mild-moderately affected PD subjects (Hoehn and Yahr 1.5–2.5) off medication while they performed a sinusoidal visuomotor joystick tracking task, which alternated between 2 task conditions depending on whether the displayed cursor position underestimated the actual error by 30% (‘Better’) or overestimated by 200% (‘Worse’). Either sham or subthreshold, noisy GVS (0.1–10 Hz, 1/f-type power spectrum) was applied in pseudorandom order. We used exploratory (linear discriminant analysis with bootstrapping) and confirmatory (robust multivariate linear regression) methods to determine if the presence of GVS significantly affected our ability to predict cursor position based on target variables. Variables related to displayed error were robustly seen to discriminate GVS in all subjects particularly in the Worse condition. If we considered higher frequency components of the cursor trajectory as “noise,” the signal-to-noise ratio of cursor trajectory was significantly increased during the GVS stimulation. The results suggest that noisy GVS influenced motor performance of the PD subjects, and we speculate that they were elicited through a combination of mechanisms: enhanced cingulate activity resulting in modulation of frontal midline theta rhythms, improved signal processing in neuromotor system via stochastic facilitation and/or enhanced “vigor” known to be deficient in PD subjects. Further work is required to determine if GVS has a selective effect on corrective submovements that could not be detected by the current analyses.

Factors influencing turning and its relationship with falls in individuals with Parkinson's disease

BACKGROUND

Falls are a major problem for people with Parkinson's disease (PD). Many studies indicate that more than 50% of people with PD have difficulty in turning that may lead to falls during daily activities. The aims of this study were to identify the relationship between turning performance and falls, and to determine the factors that influence turning performance.

METHODS

This study examined 45 patients with idiopathic PD (Hoehn and Yahr stage 1-3) using a battery of tests, including 180° turn time, balance, and muscle strength. The levels of disease severity and freezing of gait were also measured. The number of falls in the past 6 months was recorded.

RESULTS

Sixteen out of forty-five participants experienced falls in the past 6 months. A receiver operating characteristic curve showed that turn time was highly related to falls [more affected side: sensitivity = 0.81, specificity = 0.79, area under the curve (AUC) = 0.83; less affected side: sensitivity = 0.88, specificity = 0.76, AUC = 0.83]. The most important factor influencing turn time was balance ability (both sides: p = 0.000) according to the regression model. Correlations between turn time and dynamic balance were further established with reaction time, movement velocity, endpoint excursion, and maximal excursion of the LOS (limits of stability) test.

CONCLUSION

The time needed to complete a 180° turn during the SQT (step/quick turn) test is a good index to differentiate fallers from non-fallers in persons with PD. Turn time is most influenced by balance. Furthermore, balance control, especially in an anterior or sideways direction, is important for turning performance.

Quantitative electromyographic analysis of reaction time to external auditory stimuli in drug-naïve Parkinson's disease

Evaluation of motor symptoms in Parkinson's disease (PD) is still based on clinical rating scales by clinicians. Reaction time (RT) is the time interval between a specific stimulus and the start of muscle response. The aim of this study was to identify the characteristics of RT responses in PD patients using electromyography (EMG) and to elucidate the relationship between RT and clinical features of PD. The EMG activity of 31 PD patients was recorded during isometric muscle contraction. RT was defined as the time latency between an auditory beep and responsive EMG activity. PD patients demonstrated significant delays in both initiation and termination of muscle contraction compared with controls. Cardinal motor symptoms of PD were closely correlated with RT. RT was longer in more-affected side and in more-advanced PD stages. Frontal cognitive function, which is indicative of motor programming and movement regulation and perseveration, was also closely related with RT. In conclusion, greater RT is the characteristic motor features of PD and it could be used as a sensitive tool for motor function assessment in PD patients. Further investigations are required to clarify the clinical impact of the RT on the activity of daily living of patients with PD.

Differential effects of dopaminergic medication on basic motor performance and executive functions in Parkinson's disease

BACKGROUND

Patients with Parkinson's disease (PD) often show deficits in the self-initiation and selection of movements, which can be partly compensated for by external cues. We here investigated impairments in the initiation and selection of self-initiated or externally cued movements in PD. Specifically, we assessed how behavioral changes relate to medication, disease severity, and basic motor or cognitive deficits.

METHODS

Seventeen akinetic-rigid PD patients and 16 healthy controls (HC) performed a computerized motor task assessing differences between internally and externally triggered movements and reaction times. Patients performed the task twice in a randomized fashion, once with their regular dopaminergic medication and once 12h after withdrawal of medication. Additionally, all subjects underwent comprehensive neuropsychological and motor assessments.

RESULTS

Compared to HC, patients showed a significant slowing across all tasks. Furthermore, patients showed a selective deficit of movement initiation as indexed by longer reaction times when movement lateralization was internally chosen as opposed to being externally cued. This deficit correlated significantly with motor scores of the Unified Parkinson's Disease Rating Scale (UPDRS). Notably, there was no main effect of dopaminergic medication ("ON"/"OFF") on internally and externally triggered movements despite significant improvement of UPDRS and maximum finger tapping frequency in the "ON" state.

DISCUSSION

Our results suggest that disease severity in PD patients is related to disturbances in internal action initiation, selection and simple decision processes. Moreover, the data add further support to the notion that dopaminergic medication differentially affects motor and cognitive performance in PD. These findings imply that disturbances in executive functions in PD are also influenced by factors other than reduced dopaminergic activity.

Attention modulation regulates both motor and non-motor performance: a high-density EEG study in Parkinson's disease

We have previously shown that, in early stages of Parkinson's disease (PD), patients with higher reaction times are also more impaired in visual sequence learning, suggesting that movement preparation shares resources with the learning of visuospatial sequences. Here, we ascertained whether, in patients with PD, the pattern of the neural correlates of attentional processes of movement planning predict sequence learning and working memory abilities. High density Electroencephalography (EEG, 256 electrodes) was recorded in 19 patients with PD performing reaching movements in a choice reaction time paradigm. Patients were also tested with Digit Span and performed a visuomotor sequence learning task that has an important declarative learning component. We found that attenuation of alpha/beta oscillatory activity before the stimulus presentation in frontoparietal regions significantly correlated with reaction time in the choice reaction time task, similarly to what we had previously found in normal subjects. In addition, such activity significantly predicted the declarative indices of sequence learning and the scores in the Digit Span task. These findings suggest that some motor and non motor PD signs might have common neural bases, and thus, might have a similar response to the same behavioral therapy. In addition, these results might help in designing and testing the efficacy of novel rehabilitative approaches to improve specific aspects of motor performance in PD and other neurological disorders.

Effects of moderate-volume, high-load lower-body resistance training on strength and function in persons with Parkinson's disease: a pilot study

Background. Resistance training research has demonstrated positive effects for persons with Parkinson's disease (PD), but the number of acute training variables that can be manipulated makes it difficult to determine the optimal resistance training program. Objective. The purpose of this investigation was to examine the effects of an 8-week resistance training intervention on strength and function in persons with PD. Methods. Eighteen men and women were randomized to training or standard care for the 8-week intervention. The training group performed 3 sets of 5–8 repetitions of the leg press, leg curl, and calf press twice weekly. Tests included leg press strength relative to body mass, timed up-and-go, six-minute walk, and Activities-specific Balance Confidence questionnaire. Results. There was a significant group-by-time effect for maximum leg press strength relative to body mass, with the training group significantly increasing their maximum relative strength (P < .05). No other significant interactions were noted (P > .05). Conclusions. Moderate volume, high-load weight training is effective for increasing lower-body strength in persons with PD.

Dementia in Parkinson's disease

Parkinson's disease is the second most common neurodegenerative illness diagnosed in the United States. Dementia is recognized as a common component of advanced Parkinson's disease (PD). In patients with early PD, cognitive changes occur and primarily reflect impairment in executive function. It is unknown if the early cognitive changes detected on neuropsychological testing in Parkinson's disease are predictive of the subsequent development of Parkinson's disease with dementia (PDD). Many patients with PD develop dementia characterized by a wide range of cognitive deficits distinct from those seen in Alzheimer's disease (AD). Neuropsychiatric problems frequently accompany PDD. This chapter reviews the epidemiology, clinical characteristics of early and late cognitive changes, pathology, neuroimaging, diagnosis, and treatment of PDD.

The effects of visual, auditory, and mixed cues on choice reaction in Parkinson's disease

We investigated the effects of visual, auditory, and mixed cues on complex choice reaction in people with Parkinson's disease (PD). The paradigm using a computerized task was based on a game, "paper-rock-scissors." Four types of sensory cues were employed: simple visual cues, auditory cues, visual cues with auditory distracters, and auditory cues with visual distracters. Subjects were instructed to win, draw, or even lose the games and were required to respond as soon as possible after the sensory cues. When bradykinesia was taken into account, the PD patients had slower motor reactions. Further, when asked to lose in response to auditory cues, they displayed a significant delay in cognitive processing as compared to the healthy controls (HC), with a greater delay in the presence of a visual distracter. The error rates in the PD group were significantly higher than those in the HC group. These results suggest that PD patients are more influenced in choice reaction than the HC and by visual rather than auditory cues, especially under conditions with stimulus-response incompatibility that requires overriding habitual behavior. These data may be helpful in designing effective rehabilitation programs for PD to avoid inhibition of overlearned and contextually compatible reactions with visual distracters.

Cognitive change in Parkinson disease

Parkinson disease (PD) is the most common neurodegenerative movement disorder, affecting 1 in 100 individuals over the age of 60. Dementia in the setting of PD (PDD) may be among the most debilitating symptoms associated with disease progression. Estimates of cognitive decline and dementia in PD suggest that up to 14% per year of patients over age 65 with PD will develop some cognitive impairment. Unfortunately, PDD is not well characterized and the relationship of PDD to Alzheimer disease remains unclear. PDD has been proposed as part of a spectrum with dementia with Lewy bodies, and PDD and dementia with Lewy bodies frequently coexist with Alzheimer disease. It is uncertain, however, whether there is a meaningful distinction between the different disorders. It has also been difficult to gain understanding of the interaction of motor and non-motor symptoms that affect quality of life in PD and confound cognitive and psychomotor performance. This review will examine the clinical, cognitive, neuropsychiatric features of cognitive deficits associated with PD, discuss their pathologic basis and propose avenues for future research.

Differential effects of subthalamic nucleus stimulation in advanced Parkinson disease on reaction time performance

The aim of the present study was to assess the effect of bilateral subthalamic nucleus (STN) stimulation and dopaminergic medication on speed of mental processing and motor function. Thirty-nine patients suffering from advanced Parkinson disease (PD) were operated on. Motor function and reaction time (RT) performance [simple RT (SRT) and complex RT (CRT)] were evaluated under four experimental conditions with stimulation (stim) and medication (med) on and off: stim-on/med-on, stim-on/med-off, stim-off/med-off and stim-off/med-on. In the last condition, the patients received either low medication (usual dose) or high medication (suprathreshold dose). STN stimulation improved the motor performance in the SRT and CRT tasks. Furthermore, STN deep brain stimulation (DBS) also improved response preparation as shown by the significant improvement of the RT performance in the SRT task. This effect of STN DBS on the RT performance in the SRT task was greater as compared with the CRT task. This is due to the more complex information processing that is required in the CRT task as compared to the SRT task. These data suggest that treatment of STN hyperactivity by DBS improves motor function, confirming earlier reports, but has a differential effect on cognitive functions. The STN seems to be an important modulator of cognitive processing and STN DBS can differentially affect motor and associative circuits.

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.

Association between cognitive performance and striatal dopamine binding is higher in timing and motor tasks in patients with schizophrenia

The basal ganglia have received increasing attention with regard to their role in time pacing, motor function and other components of cognition. The aim of this study was to test whether the finer the motor activity and/or time perception performance were, the higher the striatal dopamine D(2) binding would be. Single photon emission computed tomography (SPECT) with [(123)I]iodobenzamide (IBZM) was performed to measure striatal D(2) receptor densities. A battery of neuropsychological tests, including the Wisconsin Card Sorting Test (WCST), the finger tapping test (FTT), and an attention test, was performed by patients with schizophrenia. Results indicated a strong correlation between the FTT score and striatal D(2) receptor binding. Neuroleptic dosage plays an important role in the relationship between cognitive tasks and striatal dopamine receptor densities. In addition, the striatal D(2) receptor density is more significantly correlated with attentional tests that consider the time effect than those that do not. Among the three tests performed, the WCST was least significantly correlated with striatal D(2) receptor densities. A decrease in striatal dopamine D(2) receptor density seems to be associated with impaired performance on optimal timing tasks and motor processing in patients with schizophrenia.

Apomorphine delays simple reaction time in Parkinsonian patients

BACKGROUND

Parkinsonian patients have difficulty in the preparation and execution of movements, which translate into delayed performance of simple reaction time (SRT) paradigms.

OBJECTIVE

To examine short-term effects of an acute subcutaneous injection of the dopamine agonist apomorphine on the results of a SRT task.

METHODS

We studied a SRT paradigm in 26 non-fluctuating idiopathic Parkinsonian patients, before and 30, 60, 90 min after administration of apomorphine.

RESULTS

The reaction time (RT) was significantly delayed after apomorphine injection. We found no significant change in movement time (MT).

CONCLUSION

Delay of RT and the lack of response of MT to apomorphine administration may result from the sedative effects of apomorphine, overstimulation of postsynaptic dopaminergic receptors with subsequent inhibition of prefrontal cholinergic neurotransmission, and at least partial binding of apomorphine to presynaptic dopaminergic autoreceptors, which cause inhibition of locomotor activity. We suggest that future studies testing the capacity for reaction in Parkinsonian patients should consider the exact timing of the delivery of dopamine substituting drugs prior to the test.

Differential response in choice reaction time following apomorphine based on prior dopaminergic treatment

Choice reaction time (CRT) paradigms demonstrated deficits in the preparation and execution of movements in patients with Parkinson's Disease (PD). Predominantly these trials did not consider an influence of acute and long-term dopaminergic substitution. Objective was to determine the acute effect of apomorphine on the response to a repeatedly performed CRT task. We repeatedly executed the CRT paradigm before and after subcutaneous apomorphine injection in previously treated, untreated and long-term dopamine substituted PD patients, who took placebo. No significant change of CRT and movement time (MT) appeared in PD patients with chronic dopaminergic drug intake after apomorphine injection. CRT and MT both significantly worsened in untreated PD patients. Placebo application induced no significant alteration. Binding of apomorphine to presynaptic autoreceptors with subsequent sedation or inhibition of locomotor activity hypothetically explain our results in before untreated PD patients. Previous long-term dopaminergic substitution may cause a certain tolerance to this phenomenon.

Attentional resource and processing speed limitations during sentence processing in Parkinson's disease

Several studies have suggested that patients with Parkinson's disease (PD) have sentence comprehension difficulty in part because of their limited executive resources. However, these assessments confound the executive resources contributing to sentence comprehension with the resources needed for task performance. In the present study, we used a word detection technique that minimizes task demands in order to evaluate attentional and processing speed resources during the comprehension of simple sentences without subordinate clauses and sentences containing subject-relative and object-relative center-embedded subordinate clauses. We found that PD patients have poor sensitivity to phonetic errors embedded in unbound grammatical morphemes, regardless of the clausal structure of the sentence, suggesting difficulty attending to grammatical morphemes. We also found that PD patients are significantly slowed in their sensitivity to phonetic errors in content words embedded in object-relative center-embedded sentences. Slowed sensitivity to content words in object-relative sentences was correlated with timed executive measures of planning. On a traditional measure of comprehension, these PD patients were impaired for sentences containing object-relative center-embedded clauses compared to sentences with subject-relative center-embedded clauses, and comprehension of object-relative sentences was correlated with executive measures. Our findings are consistent with the claim that limited executive resources for strategic attention and processing speed contribute to the sentence comprehension difficulties of PD patients.

A role of the basal ganglia in movement: the effect of precues on discrete bi-directional movements in Parkinson's disease

The effect of a precue on improving movement initiation (i.e., reaction time; RT) is well understood, whereas its influence on movement execution (i.e., movement time; MT) has rarely been examined. The current study investigated the influence of a directional precue (i.e., left vs. right) on the RT and MT of simple and discrete bi-directional movements in a large sample of Parkinson's disease patients and healthy control participants. Both patients and controls were tested twice, with testing sessions separated by 2 hours. Patients were tested first following an overnight levodopa withdrawal and again after they had taken their medication. Both patients and controls demonstrated a significant RT improvement when information was provided in advance. MT in both healthy participants and medicated patients was, however, slower with the provision of advance information, while unmedicated patients showed no significant MT effects. These results suggest that while the basal ganglia may not be involved in motor program selection, they may dynamically modulate movement execution.

Correlation of reaction time in and out of the functional MR unit

RATIONALE AND OBJECTIVES

The authors performed this study to determine whether reaction times (RTs) recorded in the functional magnetic resonance (MR) imaging environment reflect the performance of the patient outside the imaging room.

MATERIALS AND METHODS

Fifteen healthy control subjects (mean age, 61.6 years) performed a simple reaction time (SRT) task outside the MR magnet and a visuomotor response time task inside the magnet with use of block-design and event-related paradigms. For both behavioral and functional MR imaging tests, subjects tapped the right index finger upon the appearance of a visual cue. The mean RTs for out-of-magnet and functional MR imaging paradigms were compared. Results. There was a statistically significant difference in RTs between block-design and single-event paradigms (t = 3.458, P < .004). The RT values during functional MR imaging and SRT tasks did not show significant differences (.65 < P < .7, paired t test). However, no correlation was found in RT values between event-related (p = -0.004, P = .15) or block-design (p = 0.03, P = .13) paradigms and SRT data. With the block-design functional MR imaging paradigm, the RT was significantly faster (P < .0003) at the beginning of the session than the end, illustrating the effect of anticipation.

CONCLUSION

Functional MR imaging RTs must be used to determine the correlation between subjects' performance and the volume of brain activation in a functional MR imaging experiment. The effect of anticipation should be minimized, which could best be achieved by using event-related paradigms.

Delay of simple reaction time after levodopa intake

BACKGROUND

Parkinsonian patients (PP) have deficits in the preparation and execution of movements. It is generally accepted that PP show delayed performance of simple reaction time (SRT) paradigms due to impaired response preprogramming. To date, no trial considered putative effects of dopaminergic substitution on SRT performance in PP.

OBJECTIVES

To determine short-term effects of acute levodopa intake and impact of long-term dopaminergic substitution on the results of a SRT task.

METHODS

We repeatedly performed a SRT paradigm in previously untreated- and treated PP, taken off medication for at least 12 h, before and after intake of levodopa/benserazide and in PP, who received placebo.

RESULTS

Reaction time significantly increased and movement time did not change after levodopa intake. Placebo application showed no effects.

CONCLUSIONS

Levodopa delayed cognitive processing and/or behaviour. Sedative effects of levodopa and/or dopamine overflow in prefrontal regions with subsequent cholinergic dysfunction hypothetically caused this phenomenon.

Choice reaction time after levodopa challenge in parkinsonian patients

Various types of choice reaction time paradigms demonstrated deficits in the preparation and execution of movements in parkinsonian subjects. These studies showed controversial results, since they included parkinsonian individuals being: (i) previously untreated; (ii) off; or (iii) on anti-parkinsonian medication. Moreover, these trials do not take into consideration the acute effects of levodopa administration. Objective of this study was to determine the effect of long-term dopaminergic substitution therapy within a standardized levodopa challenge test in combination with a repeatedly performed choice reaction time task in parkinsonian individuals. Parkinsonian participants consisted of previously untreated, so-called "de-novo" patients and of individuals, who were chronically substituted with dopaminergic drugs, but were taken off medication for at least 12 h. All participants took 250 mg levodopa/benserazide after assessment of baseline data. Then we repeatedly measured choice reaction- and movement time within the next 90 min. No significant change of the assessed task data appeared in the "de-novo" group, but reaction- and movement time significantly shortened in previously treated subjects. Sedative effects of levodopa and/or dopaminergic overstimulation hypothetically explain the results of the previously untreated patients, whereas long-term dopaminergic substitution therapy hypothetically causes tolerance to these phenomena in treated parkinsonian individuals. Future studies on parkinsonian subjects should discuss their results on the basic pathophysiology or basal ganglia dysfunction in the light of a putative impact of long-term anti-parkinsonian drug therapy.

A neuropsychological comparison of demented and nondemented patients with Parkinson's disease

The strength and sensitivity of neuropsychological test findings in patients with Parkinson's disease (PD) was reviewed using meta-analytic principles to provide a basis of comparison of deficits in nondemented and demented patients with PD. The review revealed significant relationships among duration of disease, physical disability, and cognitive impairment in nondemented patients, and qualitative and quantitative differences in the pattern of neuropsychological test impairments between nondemented and demented patients with PD. The disparate profiles of neuropsychological impairment in nondemented and demented patients may indeed reflect disease progression in keeping with the significant clinical correlations in nondemented patients. That is, as the duration of the disease endures, it appears that performance on tasks of delayed recall deteriorates first, followed by performance on measures of manual dexterity, cognitive flexibility, and abstraction.

Sentence processing in Parkinson's disease

Parkinson's disease (PD) is a neurodegenerative condition that is associated with the depletion of dopamine (DA)-containing neurons in specific brain regions. This article reviews one consequence of this defect-sentence comprehension difficulty in nondemented patients with PD. The first section describes the pattern of cognitive deficits seen in patients with PD, focusing specifically on their difficulties with language processing. Subsequent sections relate the profile of cognitive impairments in PD to studies investigating compromised DA metabolism in fronto-striatal brain regions. The findings suggest that the sentence comprehension deficit in PD is due in large part to limitations in the strategic distribution of cognitive resources such as selective attention that contribute to the processing of complex material. The physiological basis for this deficit appears to be associated with the disruption of a fronto-striatal cerebral network that is compromised following degradation of the DA projection system.

The use of advance information for motor preparation in Parkinson's disease: effects of cueing and compatibility between warning and imperative stimuli

The ability of 13 Parkinsonian patients and 11 age-matched control subjects to process and use two components of the information given prior to a voluntary movement was studied using reaction time (RT) tasks. This advance information about the direction of a pointing movement was given using a double stimulation paradigm with an auditory warning signal (WS) which occurred prior to a visual imperative signal (IS). The first component of the information was given by the WS at the beginning of each trial, and the second component was the WS-IS compatibility during series of trials. The subjects were tested with three RT paradigms: a cued simple (CS) task, a cued choice (NC) task, and a priming choice (P) task. The results show that the normal subjects used both the lateral cue and the WS-IS compatibility to shorten their RTs, whereas the Parkinsonian patients were able to use the lateral warning signal, but their ability to use the degree of compatibility stimuli was impaired. These data suggest that when dealing with lateral cues in a RT task, Parkinsonian patients have no difficulty in identifying a stimulus and selecting the appropriate response, but that this is no longer so in the case of stimulus compatibility. This impairment may be due to attentional disorders involving a dysfunction affecting the medial premotor system, which includes the basal ganglia and may be responsible for the feedforward movement control deficits associated with Parkinson's disease.

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.

Reaction time responding in rats

The use of reaction time has a great tradition in the field of human information processing research. In animal research the use of reaction time test paradigms is mainly limited to two research fields: the role of the striatum in movement initiation; and aging. It was discussed that reaction time responding can be regarded as "single behavior", this term was used to indicate that only one behavioral category is measured, allowing a better analysis of brain-behavior relationships. Reaction time studies investigating the role of the striatum in motor functions revealed that the initiation of a behavioral response is dependent on the interaction of different neurotransmitters (viz. dopamine, glutamate, GABA). Studies in which lesions were made in different brain structures suggested that motor initiation is dependent on defined brain structures (e.g. medialldorsal striatum, prefrontal cortex). It was concluded that the use of reaction time measures can indeed be a powerful tool in studying brain-behavior relationships. However, there are some methodological constraints with respect to the assessment of reaction time in rats, as was tried to exemplify by the experiments described in the present paper. On the one hand one should try to control for behavioral characteristics of rats that may affect the validity of the parameter reaction time. On the other hand, the mean value of reaction time should be in the range of what has been reported in man. Although these criteria were not always met in several studies, it was concluded that reaction time can be validly assessed in rats. Finally, it was discussed that the use of reaction time may go beyond studies that investigate the role of the basal ganglia in motor output. Since response latency is a direct measure of information processing this parameter may provide insight into basic elements of cognition. Based on the significance of reaction times in human studies the use of this dependent variable in rats may provide a fruitful approach in studying brain-behavior relationships in cognitive functions.

Differential diagnosis of the major progressive dementias and depression in middle and late adulthood: a summary of the literature of the early 1990s

There is a preponderance of research on the neuropsychology of the various dementias. There are also direct comparisons between two or more dementias available in the literature. This paper sought to summarize the most recent literature, primarily from 1990 through mid-1996, including recent reviews of the literature from previous decades. The purpose was to provide, in one location, a summary of neuropsychological (i.e., cognitive, motor, and psychiatric) characteristics of major noninfectious, progressive dementias and depression of middle and late adulthood. It is hoped that this review, particularly a summary table provided, will serve as a guide in the differential diagnosis of the dementias by clinicians. In addition to Alzheimer's disease, vascular dementias, Parkinson's disease, Lewy body dementia, Huntington's disease, and frontal lobe dementia, the impact of depression on cognitive functioning is covered given the frequency with which neuropsychologists are asked to differentiate depression from primary dementia.

Psychomotor slowing, negative symptoms and dopamine receptor availability--an IBZM SPECT study in neuroleptic-treated and drug-free schizophrenic patients

Anhedonia and psychomotor slowing in schizophrenia have been attributed to a dysfunction of dopaminergic neurotransmission. To differentiate between disease and drug-induced negative symptoms, we examined eight drug-free and eight neuroleptic-treated schizophrenic patients. Positive and negative symptoms and extrapyramidal side effects were assessed using standardized rating scales (PSAS, AMDP, SANS). 'Reaction time' and 'motor speed' were measured using a computer-aided system and striatal dopamine D2/D3 receptor availability was assessed using [I-123]IBZM SPECT. Psychomotor reaction time, parkinsonism, affective flattening and avolition were increased in treated patients relative to the untreated cohort and were negatively correlated with dopamine D2/D3 receptor availability. Significant positive correlations were found between parkinsonism and affective flattening and between psychomotor slowing and avolition. Positive symptoms were not significantly associated with striatal IBZM binding. These findings support the hypothesis that neuroleptic-induced dopamine D2/D3 blockade in the striatum can mimic certain negative symptoms, such as affective flattening and avolition, and indicates that psychomotor testing may be helpful in differentiating between disease and drug-induced negative symptoms.

Event-related potentials in parkinsonian patients under auditory discrimination tasks

Seventeen non-demented idiopathic medicated Parkinsonian patients and 17 age- and education-matched controls participated in auditory discrimination tasks. The study aimed at revealing the differences in their ability for auditory information processing. Series comprising 1000 Hz and 800 Hz tones were used as stimuli. The accuracy in the tones' discrimination was determined by means of counting the high tone or recording a binary sensomotor reaction. The results based on the mean group values of event-related potential components show that the Parkinsonian patients had lower amplitude for the exogenous N1 and endogenous P3 components of the evoked responses. In the sensomotor task series the patients had longer N2 latency than controls. In the counting series the patients recognized the tones well and gave an exact count but during the sensomotor task they had longer reaction time, more erroneous answers and depressed P3. The data show differences in the information processing between the two groups and reveal cognitive impairment in the Parkinsonian patients.

The neurobiological basis of movement initiation

Simple reaction time (RT) is defined as the elapsed time between presentation of a single stimulus and onset of movement. In choice RT, there are at least two stimuli, requiring two distinct responses. The neurobiological basis of RT in humans has mostly been evaluated in patients with Parkinson's disease or cerebellar disease. Lesion studies in animals have assessed the different contributions of various subregions of the basal ganglia and the cerebellum. There is a prolongation of simple RT and in some cases of choice RT in Parkinson's disease. Both simple and choice RT are susceptible to modulation by brain dopamine levels. However, such is not invariably the case, attesting to the contribution of non-dopaminergic neurons in the sensori-motor slowing found in Parkinson's disease. An increase in simple RT and in choice RT are found in patients with cerebellar atrophy. The initiation of fast ballistic movements is associated with the dentate efferent system. This system is modulated by dopaminergic and glutamatergic pathways to the striatum.

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.