Dopaminergic Neurotransmission in Patients With Parkinson's Disease and Impulse Control Disorders: A Systematic Review and Meta-Analysis of PET and SPECT Studies

Background: Around 30% Parkinson's disease (PD) patients develop impulse control disorders (ICDs) to D_2/3 dopamine agonists and, to a lesser extent, levodopa. We aim to investigate striatal dopaminergic function in PD patients with and without ICD.

Methods: PubMed, Science Direct, EBSCO, and ISI Web of Science databases were searched (from inception to March 7, 2018) to identify PET or SPECT studies reporting striatal dopaminergic function in PD patients with ICD (ICD+) compared to those without ICD (ICD–). Studies which included drug naïve patients, explored non-pharmacological procedures (e.g., deep brain stimulation), and those using brain blood perfusion or non-dopaminergic markers were excluded. Standardized mean difference (SDM) was used and random-effect models were applied. Separate meta-analyses were performed for dopamine transporter level, dopamine release, and dopamine receptors availability in the putamen, caudate, dorsal, and ventral striatum.

Results: A total of 238 studies were title and abstract screened, of which 19 full-texts were assessed. Nine studies (ICD+: N = 117; ICD–: N = 175 patients) were included in the analysis. ICD+ showed a significant reduction of dopamine transporter binding in the putamen (SDM = −0.46; 95% CI: −0.80, −0.11; Z = 2.61; p = 0.009), caudate (SDM = −0.38; 95% CI: −0.73, −0.04; Z = 2.18; p = 0.03) and dorsal striatum (SDM = −0.45; 95% CI: −0.77, −0.13; Z = 2.76; p = 0.006), and increased dopamine release to reward-related stimuli/gambling tasks in the ventral striatum (SDM = −1.04; 95% CI: −1.73, −0.35; Z = 2.95; p = 0.003). Dopamine receptors availability did not differ between groups. Heterogeneity was low for dopamine transporter in the dorsal striatum (I² = 0%), putamen (I² = 0%) and caudate (I² = 0%), and pre-synaptic dopamine release in the dorsal (I² = 0%) and ventral striatum (I² = 0%); heterogeneity was high for dopamine transporter levels in the ventral striatum (I² = 80%), and for dopamine receptors availability in the ventral (I² = 89%) and dorsal (I² = 86%) striatum, putamen (I² = 93%), and caudate (I² = 71%).

Conclusions: ICD+ patients show lower dopaminergic transporter levels in the dorsal striatum and increased dopamine release in the ventral striatum when engaged in reward-related stimuli/gambling tasks. This dopaminergic imbalance might represent a biological substrate for ICD in PD. Adequately powered longitudinal studies with drug naïve patients are needed to understand whether these changes may represent biomarkers of premorbid vulnerability to ICD.

Impulse Control Disorder in Parkinson's Disease: A Meta-Analysis of Cognitive, Affective, and Motivational Correlates

Background: In Parkinson's disease (PD), impulse control disorders (ICDs) develop as side-effect of dopaminergic replacement therapy (DRT). Cognitive, affective, and motivational correlates of ICD in medicated PD patients are debated. Here, we systematically reviewed and meta-analyzed the evidence for an association between ICD in PD and cognitive, affective, and motivational abnormalities. Methods: A systematic review and meta-analysis was performed on PubMed, Science Direct, ISI Web of Science, Cochrane, EBSCO for studies published between 1-1-2000 and 8-3-2017 comparing cognitive, affective, and motivational measures in PD patients with ICD (ICD+) vs. those without ICD (ICD-). Exclusion criteria were conditions other than PD, substance and/or alcohol abuse, dementia, drug naïve patients, cognition assessed by self-report tools. Standardized mean difference (SMD) was used, and random-effect model applied. Results: 10,200 studies were screened (title, abstract), 79 full-texts were assessed, and 25 were included (ICD+: 625 patients; ICD-: 938). Compared to ICD-, ICD+ showed worse performance reward-related decision-making (0.42 [0.02, 0.82], p = 0.04) and set-shifting tasks (SMD = -0.49 [95% CI -0.78, -0.21], p = 0.0008). ICD in PD was also related to higher self-reported rate of depression (0.35 [0.16, 0.54], p = 0.0004), anxiety (0.43 [0.18, 0.68], p = 0.0007), anhedonia (0.26 [0.01, 0.50], p = 0.04), and impulsivity (0.79 [0.50, 1.09], p < 0.00001). Heterogeneity was low to moderate, except for depression (I² = 61%) and anxiety (I² = 58%). Conclusions: ICD in PD is associated with worse set-shifting and reward-related decision-making, and increased depression, anxiety, anhedonia, and impulsivity. This is an important area for further studies as ICDs have negative impact on the quality of life of patients and their caregivers.

Feasibility of a randomized single-blind crossover trial to assess the effects of the second-generation slow-release dopamine agonists pramipexole and ropinirole on cued recall memory in idiopathic mild or moderate Parkinson's disease without cognitive impairment

Background

The aim was to assess the feasibility of a single-centre, single-blind, randomized, crossover design to explore the effects of two slow-release dopamine agonists, ropinirole and pramipexole, on cued recall in Parkinson’s disease.

As the design required a switch from the prescribed agonist (pramipexole-to-ropinirole, or ropinirole-to-pramipexole), the primary objectives were to (a) examine the efficacy of processes and procedures used to manage symptoms during the washout period and (b) to use cued recall estimates to inform a power calculation for a definitive trial.

Secondary objectives were to assess consent and missing data rates, acceptability of clinical support for the OFF sessions, experience of the OFF sessions and of agonist switching, barriers-to-participation for patients and informal caregivers.

Methods

Patients were randomized in a 1:1 ratio to two treatment arms and stabilized on each agonist for 6 weeks. The arms differed only in the sequence in which the agonists were administered. Cued recall was assessed ON medication and, following a washout period resulting in 93.75% agonist elimination, OFF medication.

Results

A total of 220 patients were screened: 145 were excluded and 75 invitations to participate were sent to eligible patients. Fifty-three patients declined, 22 consented and 16 completed the study.

There were no serious adverse events, and rates of non-serious adverse events were equivalent between the agonists.

Using the largest standard deviation (SD) of the ON–OFF difference cued recall score (inflated by ~25% to give a conservative estimate of the SD in a definitive trial) and assuming an effect of at least 10% of the observed range of OFF medication cued recall scores for either agonist to be clinically important, a main trial requires a sample size of just under 150 patients.

The consent and missing data rates were 29 and 27% respectively. The washout period and the preparation for the OFF sessions were acceptable, and the sessions were manageable. The experience of switching was also manageable. Barriers to participation included concerns about disease stability, side effects, research process, carer workload and accessibility of the information sheet.

Conclusions

This study presented challenges to recruitment both in design and execution, and while it was a major aim of the study to assess this, evaluation of these challenges provided the opportunity to explore how they could be overcome for future studies.

Trial registration

EudraCT 2012-000801-64

A deficit in familiarity-driven recognition in a right-sided mediodorsal thalamic lesion patient

OBJECTIVE

According to a still-controversial view of recognition, projections between the perirhinal cortex and the medial subdivision of the mediodorsal thalamic nucleus (mMDT) support the mnemonic processes underlying familiarity, whereas a separate extended hippocampal system is critical for the recollection of episodic details during recognition.

METHOD

In this study, we examined item recognition, familiarity, and recollection for faces and words in a patient (OG) with a right-sided lesion centered on the mMDT, which encroached on the central medial midline nucleus and may have resulted in partial disconnection of the mammillothalamic tract. On the basis of OG's neuropathology, the dual-process signal-detection (DPSD) high-threshold theory and the material-specific hypothesis of long-term memory together predicted a material-specific impairment in familiarity for novel facial memoranda, with a lesser decline in recollection of novel faces at short retention intervals. No abnormalities in either familiarity- or recollection-driven recognition of verbal memoranda were expected.

RESULTS

Comparing the performance of OG and that of a group of 10 age-, sex-, and IQ-matched healthy controls, the remember-know procedure revealed the dissociations predicted by the material-specific and DPSD hypotheses: With recognition of previously novel faces, OG showed a deficit in familiarity-driven recognition that was significantly greater than the insignificant reduction in his recollection. All components of his word recognition were, however, preserved.

CONCLUSION

A memory profile, marked by a dissociation between familiarity and recollection, fits naturally with the DPSD model and is incompatible with the idea that these kinds of memories reflect different degrees of trace strength.

Anarchic hand with abnormal agency following right inferior parietal lobe damage: a case report

Anarchic hand syndrome (AHS) is characterized by goal-directed movements performed without volitional control (agency). Different AHS subtypes have been identified; however, few studies have examined the posterior subtype. We report a case of AHS following right-hemisphere parietal damage, with left-sided somatosensory and proprioceptive impairment. Agency was examined for nonanarchic (volitional) movements performed using the anarchic hand. The patient experienced abnormal agency for movements whether motor intention and visual feedback were congruent or incongruent, but not when intention was absent (passive movement). Findings suggest a general disturbance of veridical motor awareness and agency in this case of parietal AHS.

Damage to the dorsomedial thalamic nucleus, central lateral intralaminar thalamic nucleus, and midline thalamic nuclei on the right-side impair executive function and attention under conditions of high demand but not low demand

This study reports a patient, OG, with a unilateral right-sided thalamic lesion. High resolution 3T magnetic resonance imaging revealed damage to the parvicellular and magnocellular subdivisions of the dorsomedial thalamus (DMT), the central lateral intralaminar nucleus (also known as the paralamellar DMT), the paraventricular and the central medial midline thalamic nuclei. According to the neuropsychological literature, the DMT, the midline and intralaminar thalamic nuclei influence a wide array of cognitive functions by virtue of their modulatory influences on executive function and attention, and this is particularly indicated under conditions of low arousal or high cognitive demand. We explored this prediction in OG, and compared his performance on a range of low and high demand versions of tests that tapped executive function and attention to a group of 6 age- and IQ-matched controls. OG, without exception, significantly under performed on the high-demand attention and executive function tasks, but performed normally on the low-demand versions. These findings extend and refine current understanding of the effects of thalamic lesion on attention and executive function.

Recollection deficiencies in patients with major depressive disorder

Neuropsychological research suggests that recognition memory (RM) and recall memory are impaired in patients with a major depressive disorder or a dysphoric mood state. This study examines the proposal that abnormalities in recollection (a form of recall) result from a breakdown in frontal strategic memory processes involved in encoding and retrieval, and executive functions linked to reality monitoring, planning, problem-solving, reasoning and decision-making. We investigated two predictions arising from this theory. Firstly, patients diagnosed with a major depressive disorder (MDD) will display a dissociation between (deficient) recollection and (preserved) familiarity. Secondly, if recollection impairments are indicative of a breakdown in prefrontal strategic memory processes which are dependent, at least in part, on executive processes, then an explicit correlational approach predicts that recollection will be positively associated with the severity of executive dysfunction in MDD patients. The remember/know paradigm was used to investigate RM for words and neutral faces in 16 MDD patients and 16 healthy volunteers, matched for age, gender and estimates of premorbid IQ. Measures of executive function included working memory, reasoning and decision-making. Applying the Dual Process Signal Detection interpretation of the remember/know data, the MDD group displayed significant impairments in RM and recollection rates for both verbal and neutral facial memoranda. In contrast, familiarity-aware rates were preserved. There was no evidence of executive dysfunction in the patient group, and little evidence that recollection rates correlated with executive function. Furthermore, a single process signal detection approach suggested that the MDD patients displayed a reduction in sensitivity for RM and remember rates but not know responses. The criteria for detecting studied from unstudied items, and remembering from knowing, were the same in both patient and healthy control groups. Taken together, these findings are consistent with the view that MDD is marked by a decline in RM, which is underpinned by an impairment in recollection rather than familiarity processes. The extent to which the recollection deficiencies arise from disruption of strategic memory and executive processes requires further investigation.

Effect of disease severity and dopaminergic medication on recollection and familiarity in patients with idiopathic nondementing Parkinson's

The effect of disease severity and dopaminergic medication on the assessment of familiarity and the recollection of episodic details during recognition in nondementing idiopathic Parkinson's is uncertain. Some studies have reported familiarity as deficient in mild Parkinson's yet others have found it intact even in moderate Parkinson's. Recollection has been found to be both preserved and deficient in mild and moderate Parkinson's. The extent to which these conflicting findings are explained by disease severity or dopaminergic medication or a combination of the two is uncertain, as all studies assessed patients in a medicated state, and disease severity has not always been consistently reported. Twelve patients with mild Parkinson's and 11 with moderate Parkinson's (medicated Hoehn and Yahr mean: 2.1 and 3.2, respectively), completed matched versions of a yes/no recognition memory test in a medicated and unmedicated condition (termed ON and OFF, respectively). Twenty-one matched healthy volunteers also completed both memory tasks in 2 separate sessions (termed Blue and Green, respectively). In the ON/Green condition, the moderate Parkinson's recollection performance was significantly poorer than the healthy volunteers and mild Parkinson's. By contrast, recognition memory and familiarity measures in both Parkinson's group were relatively spared. In the OFF/Blue condition, the moderate Parkinson's recollection was impaired, but only in relation to the healthy volunteer set. There were no significant differences in recollection performance between the mild and moderate Parkinson's groups. Again, recognition memory and familiarity measures in both Parkinson's group were relatively spared. Further analyses showed the moderate patients' recollection rates to be significantly poorer ON-medication compared to OFF. These findings are discussed in relation to the staging of disease progression on medial temporal areas which separately support recollection and familiarity, and the putative effects the different classes of dopaminergic drugs may have on these areas.

Why are some Parkinson disease patients unaware of their dyskinesias?

OBJECTIVE

To test the hypothesis that anosognosia for dyskinesias in Parkinson disease (PD) results from a failure to detect discrepancies between intended and actual movement.

BACKGROUND

PD patients often complain of drug-induced dyskinesias (involuntary movements) less than their carers. This remarkable unawareness is an example of anosognosia (ie, unawareness of deficits associated with an illness). A better understanding of anosognosia for dyskinesias in PD is important to understand the impact of the illness and side effects of treatment.

METHODS

The ability to detect a discrepancy between intended movement and visual feedback about actual movement was investigated in 6 PD patients with anosognosia for dyskinesias, 11 nonanosognosic PD controls with dyskinesias, and 22 healthy volunteers, using a mirror to reverse the expected visual consequences of an executed movement.

RESULTS

Nonanosognosic PD patients and healthy volunteers rated mirror-reversed movement as significantly stranger than normal movement (P=0.024 and <0.001, respectively), whereas PD patients with anosognosia for dyskinesias did not (P=0.375).

CONCLUSIONS

The findings support our proposal, in that PD patients with anosognosia for dyskinesias do not report mirror-reversed movement (in which intentions and visual feedback conflict) as feeling distinct from normal movement.

Reality monitoring in anosognosia for hemiplegia

Anosognosia for hemiplegia (AHP) is a lack of awareness about paralysis following stroke. Recent explanations use a 'forward model' of movement to suggest that AHP patients fail to register discrepancies between internally- and externally-generated sensory information. We predicted that this failure would impair the ability to recall from memory whether information is internally- or externally-generated (i.e., reality monitor). Two experiments examined this prediction. Experiment 1 demonstrated that AHP patients exhibit a reality monitoring deficit for non-motor information (i.e., perceived vs. imagined drawings), whilst hemiplegic controls without anosognosia (nonAHP) perform like age-matched healthy volunteers (HVs). Experiment 2 explored if this deficit occurs when AHP patients discriminate performed, imagined, or observed movement. Results showed impaired reality monitoring for movements in AHP and nonAHP patients relative to HVs. Findings suggest that reality monitoring processes not directly related to movement, together with a failure to reality monitor movements, contribute to the pathogenesis of AHP.

Short Article: Effect of Click Trains on Duration Estimates by People with Parkinson's Disease

Patients with a diagnosis of Parkinson's disease and age- and IQ-matched controls estimated the duration of short 500-Hz tones (325–1,225 ms), on trials where the tone was either preceded by 3 s of 5-Hz clicks, or presented without clicks. The click manipulation had been shown in earlier studies with student participants to make verbal estimates longer. Patients were tested both on and off their dopaminergic medication, and controls were also tested in two sessions. Verbal estimates were markedly and significantly longer on trials with clicks than on those without clicks for both the patients and the controls, but there were no significant performance differences between patients or controls, nor between the on and off medication sessions in the patients. The study shows that a manipulation of subjective time, which has had small but consistent effects in student participants, also affects timing in patients and adds to a growing body of evidence that timing in patients with Parkinson's disease may in many cases have the same characteristics as those of neurologically intact control groups.

Bilateral dorsolateral thalamic lesions disrupts conscious recollection

In an earlier study we disputed the claim that the mediodorsal thalamic nucleus is critical for familiarity. We reported patient (QX) who showed a severe deficit in conscious recollection, and behavioural problems (disinhibition, emotional lability) with relative sparing of familiarity-aware memory following a left mediodorsal thalamic lesion. More recent MR imaging has revealed that QX's lesions are more extensive than previously reported and involve both dorsolateral thalamic nuclei, and whilst there is evidence of left mediodorsal thalamic damage, it is not the main focus of damage. This paper reports a full analysis of QX's thalamic pathology alongside a more detailed investigation of his recognition memory, using yes/no and forced-choice procedures, and executive function. The results revealed impairments in yes/no recognition and conscious recollection rates of famous, artist and unknown names. In addition to the previously noted behavioural disinhibition and emotional lability, a deficit in spontaneous planning ability was evident on the Zoo Map Test (subtest of the Bahavioural Assessment of the Dysexecutive Syndrome). Forced-choice recognition, familiarity estimates and remote memory showed higher levels of preservation. The findings indicate that the dorsolateral thalamus is part of the extended hippocampal circuit which is causally critical only for recall and conscious recollection of complex associations rather than for the more automatic processes linked with novelty detection.

A cognitive neuropsychological and psychophysiological investigation of a patient who exhibited an acute exacerbated behavioural response during innocuous somatosensory stimulation and movement

We report findings from a cognitive neuropsychological and psychophysiological investigation of a patient who displayed an exacerbated acute emotional expression during movement, innocuous, and aversive somatosensory stimulation. The condition developed in the context of non-specific white matter ischaemia along with abnormalities in the cortical white matter of the left anterior parietal lobe, and subcortical white matter of the left Sylvian cortex.

Cognitive neuropsychological assessment revealed a pronounced deficiency in executive function, relative to IQ, memory, attention, language and visual processing. Compared to a normal control group, the patient [EQ] displayed a significantly elevated skin conductance level during both innocuous and aversive somatosensory stimulation. His pain tolerance was also significantly reduced. Despite this, EQ remained able to accurately describe the form of stimulation taking place, and to rate the levels of pain intensity and pain affect.

These results suggest that EQ’s exaggerated behavioural response and reduced pain tolerance to somatosensory stimulation may be linked to cognitive changes, possibly related to increased apprehension and fear, rather than altered pain intensity or pain affect per se.

Investigation of conscious recollection, false recognition and delusional misidentification in patients with schizophrenia

BACKGROUND

Recognition memory (RM) is impaired in patients with schizophrenia, as they rely largely on feelings of familiarity rather than conscious recollection. It has been suggested that this abnormality may reflect a breakdown in strategic memory processes involved in both encoding and retrieval. By studying 2 patients with false recognition (FR; patient C.T.) and delusional misidentification (DM; patient B.C.), and a group of psychotic control patients, we examined proposals that FR and DM exist on a continuum of increasingly severe impairment in strategic memory function.

METHODS

Executive function, autobiographical memory and verbal and facial RM were assessed using standard neuropsychological tests and the remember/know paradigm.

RESULTS

The psychotic control group displayed a significantly reduced reliance on remember judgements and compensatory elevation in know judgements on both RM tasks compared with the normal control group. Patient B.C. also followed this trend, but in a much more pronounced manner. In contrast, patient C.T. displayed a qualitatively different performance profile, which was marked by an increased dependence on remember responses.

CONCLUSIONS

We have presented evidence which support proposals that a breakdown in strategic memory and executive dysfunction are more pronounced in DM than FR. However, the small sample size precludes any firm conclusions being drawn.

Recognition memory abnormalities in asymptomatic biological parents of a patient with schizophrenia

BACKGROUND

Recognition memory dysfunction has been frequently reported in schizophrenic populations, and has been linked with the development of delusions and thought disorder. A range of neuropsychological abnormalities have also been documented in the biological asymptomatic relatives of patients with schizophrenia; however, recognition memory has not been one of them.

AIM

This study was carried out in order to investigate: (i) verbal and facial recognition memory in terms of accuracy and false alarm rates; and (ii) contributions from the episodic and semantic memory systems to recognition memory, in the biological asymptomatic parents of a reported schizophrenic patient and a set of male and female psychotic controls.

RESULTS

Gender differences failed to emerge between the psychotic controls on any of the recognition measures (discrimination accuracy, response bias, hit and false alarm rates, 'remember' and 'know' recognition memory decisions). However, there was evidence of recognition dysfunction in the female relative, and to a lesser extent, in the male. Both parent's recognition memory performance profiles were marked by a pathologically elevated false alarm rate, and an increased dependence 'remember' judgements, i.e. input from the episodic memory system, to drive recognition memory decisions.

CONCLUSIONS

These findings are discussed in the context of models of episodic and semantic memory impairment in schizophrenia.

Contribution of the left dorsomedial thalamus to recognition memory: a neuropsychological case study

This study reports a patient with a unilateral left thalamic lesion which was centred on the dorsomedial thalamic nucleus. Cognitive neuropsychological assessment revealed a severe impairment in verbal memory and symptoms of executive dysfunction, in the presence of relatively intact visual and facial recognition, working memory, praxis, language and IQ. Verbal and visual recognition memory were investigated using the remember-know paradigm. The results indicated a profound impairment in recollection-driven verbal recognition memory. These results are discussed in the context of the role of the dorsomedial thalamic nucleus in recognition memory, and functional models of memory.