Brain-first versus body-first Parkinson's disease: a multimodal imaging case-control study.

Parkinson's disease is characterized by the presence of abnormal, intraneuronal α-synuclein aggregates, which may propagate from cell-to-cell in a prion-like manner. However, it remains uncertain where the initial α-synuclein aggregates originate. We have hypothesized that Parkinson's disease comprises two subtypes. A brain-first (top-down) type, where α-synuclein pathology initially arises in the brain with secondary spreading to the peripheral autonomic nervous system; and a body-first (bottom-up) type, where the pathology originates in the enteric or peripheral autonomic nervous system and then spreads to the brain. We also hypothesized that isolated REM sleep behaviour disorder (iRBD) is a prodromal phenotype for the body-first type. Using multimodal imaging, we tested the hypothesis by quantifying neuronal dysfunction in structures corresponding to Braak stages I, II and III involvement in three distinct patient groups. We included 37 consecutive de novo patients with Parkinson's disease into this case-control PET study. Patients with Parkinson's disease were divided into 24 RBD-negative (PDRBD-) and 13 RBD-positive cases (PDRBD+) and a comparator group of 22 iRBD patients. We used 11C-donepezil PET/CT to assess cholinergic (parasympathetic) innervation, 123I-metaiodobenzylguanidine (MIBG) scintigraphy to measure cardiac sympathetic innervation, neuromelanin-sensitive MRI to measure the integrity of locus coeruleus pigmented neurons, and 18F-dihydroxyphenylalanine (FDOPA) PET to assess putaminal dopamine storage capacity. Colon volume and transit times were assessed with CT scans and radiopaque markers. Imaging data from the three groups were interrogated with ANOVA and Kruskal-Wallis tests corrected for multiple comparisons. The PDRBD- and PDRBD+ groups showed similar marked reductions in putaminal FDOPA-specific uptake, whereas two-thirds of iRBD patients had normal scans (P < 10-13, ANOVA). When compared to the PDRBD- patients, the PDRBD+ and iRBD patients showed reduced mean MIBG heart:mediastinum ratios (P < 10-5, ANOVA) and colon 11C-donepezil standard uptake values (P = 0.008, ANOVA). The PDRBD+ group trended towards a reduced mean MRI locus coeruleus: pons ratio compared to PDRBD- (P = 0.07, t-test). In comparison to the other groups, the PDRBD+ group also had enlarged colon volumes (P < 0.001, ANOVA) and delayed colonic transit times (P = 0.01, Kruskal-Wallis). The combined iRBD and PDRBD+ patient data were compatible with a body-first trajectory, characterized by initial loss of cardiac MIBG signal and 11C-colonic donepezil signal followed by loss of putaminal FDOPA uptake. In contrast, the PDRBD- data were compatible with a brain-first trajectory, characterized by primary loss of putaminal FDOPA uptake followed by a secondary loss of cardiac MIBG signal and 11C-donepezil signal. These findings support the existence of brain-first and body-first subtypes of Parkinson's disease.

Evaluation of the noradrenergic system in Parkinson's disease: an 11C-MeNER PET and neuromelanin MRI study.

Pathological involvement of the noradrenergic locus coeruleus occurs early in Parkinson's disease, and widespread noradrenaline reductions are found at post-mortem. Rapid eye movement sleep behaviour disorder (RBD) accompanies Parkinson's disease and its presence predicts an unfavourable disease course with a higher propensity to cognitive impairment and orthostatic hypotension. MRI can detect neuromelanin in the locus coeruleus while 11C-MeNER PET is a marker of noradrenaline transporter availability. Here, we use both imaging modalities to study the association of RBD, cognition and autonomic dysfunction in Parkinson's disease with loss of noradrenergic function. Thirty non-demented Parkinson's disease patients [16 patients with RBD and 14 without RBD, comparable across age (66.6 ± 6.7 years), sex (22 males), and disease stage (Hoehn and Yahr, 2.3 ± 0.5)], had imaging of the locus coeruleus with neuromelanin sensitive MRI and brain noradrenaline transporter availability with 11C-MeNER PET. RBD was confirmed with polysomnography; cognitive function was assessed with a neuropsychological test battery, and blood pressure changes on tilting were documented; results were compared to 12 matched control subjects. We found that Parkinson's disease patients with RBD showed decreased locus coeruleus neuromelanin signal on MRI (P < 0.001) and widespread reduced binding of 11C-MeNER (P < 0.001), which correlated with amount of REM sleep without atonia. Parkinson's disease with RBD was also associated with a higher incidence of cognitive impairment, slowed EEG activity, and orthostatic hypotension. Reduced 11C-MeNER binding correlated with EEG slowing, cognitive performance, and orthostatic hypotension. In conclusion, reduced noradrenergic function in Parkinson's disease was linked to the presence of RBD and associated with cognitive deterioration and orthostatic hypotension. Noradrenergic impairment may contribute to the high prevalence of these non-motor symptoms in Parkinson's disease, and may be of relevance when treating these conditions in Parkinson's disease.

Decreased intestinal acetylcholinesterase in early Parkinson disease: An 11C-donepezil PET study.

OBJECTIVE: To investigate systemic levels of acetylcholinesterase in early Parkinson disease (PD) with 11C-donepezil PET, a potential marker of parasympathetic innervation. METHODS: This was a cross-sectional study with 19 patients with early-stage PD (disease duration 1.5 ± 0.6 years) and 16 age-matched controls who had clinical assessments, olfaction tests, and 11C-donepezil PET to measure acetylcholinesterase density in peripheral organs. RESULTS: The patients with PD showed significantly reduced 11C-donepezil uptake in the small intestine (-14%, p = 0.018), colon (-22%, p < 0.001), and kidneys (-14%, p = 0.028). No difference in myocardial or pancreatic acetylcholinesterase levels was seen. CONCLUSION: We found significantly decreased 11C-donepezil signal in the intestine and kidneys of patients with early PD, suggesting that parasympathetic denervation is present early in the disease course.

Deep brain stimulation reveals emotional impact processing in ventromedial prefrontal cortex.

We tested the hypothesis that modulation of monoaminergic tone with deep-brain stimulation (DBS) of subthalamic nucleus would reveal a site of reactivity in the ventromedial prefrontal cortex that we previously identified by modulating serotonergic and noradrenergic mechanisms by blocking serotonin-noradrenaline reuptake sites. We tested the hypothesis in patients with Parkinson's disease in whom we had measured the changes of blood flow everywhere in the brain associated with the deep brain stimulation of the subthalamic nucleus. We determined the emotional reactivity of the patients as the average impact of emotive images rated by the patients off the DBS. We then searched for sites in the brain that had significant correlation of the changes of blood flow with the emotional impact rated by the patients. The results indicate a significant link between the emotional impact when patients are not stimulated and the change of blood flow associated with the DBS. In subjects with a low emotional impact, activity measured as blood flow rose when the electrode was turned on, while in subjects of high impact, the activity at this site in the ventromedial prefrontal cortex declined when the electrode was turned on. We conclude that changes of neurotransmission in the ventromedial prefrontal cortex had an effect on the tissue that depends on changes of monoamine concentration interacting with specific combinations of inhibitory and excitatory monoamine receptors.

Attention, emotion, and deactivation of default activity in inferior medial prefrontal cortex.

Attention deactivates the inferior medial prefrontal cortex (IMPC), but it is uncertain if emotions can attenuate this deactivation. To test the extent to which common emotions interfere with attention, we measured changes of a blood flow index of brain activity in key areas of the IMPC with positron emission tomography (PET) of labeled water (H(15)2O) uptake in brain of 14 healthy subjects. The subjects performed either a less demanding or a more demanding task of attention while they watched neutral and emotive images of people in realistic indoor or outdoor situations. In the less demanding task, subjects used the index finger to press any key when a new image appeared. In the more demanding task, subjects chose the index or middle finger to press separate keys for outdoor and indoor scenes. Compared to the less demanding task, in a global search of all gray matter, the more demanding significantly lowered blood flow (rCBF) in left IMPC, left and right insula, and right amygdala, and significantly raised blood flow in motor cortex and right precuneus. Restricted searches of rCBF changes by emotion, at coordinates of significant effect in previous studies of the medial prefrontal and temporal cortices, revealed significant activation in the fusiform gyrus, independently of the task. In contrast, we found no effect of emotional content in the IMPC, where emotions failed to override the effect of the task. The results are consistent with a role of the IMPC in the selection among competitive inputs from multiple brain regions, as predicted by the theory of a default mode of brain function. The absent emotional interference with the deactivation of the default state suggests that the inferior prefrontal cortex continued to serve the attention rather than submit to the distraction.

Monoaminergic modulation of emotional impact in the inferomedial prefrontal cortex.

People assess the impact of emotionally loaded images differently. We define this impact as the average difference between individual ratings of standardized "pleasant" and "unpleasant" images. To determine the neuroanatomical correlate of a hypothetical interaction between emotional impact and cerebral excitability, we first determined the individual effect on cerebral blood flow of a pharmacological challenge with the monoamine reuptake inhibitor clomipramine in nine healthy volunteers. In a later, independent, session the nine volunteers rated pleasant, neutral, and unpleasant images of the standard Empathy Picture System on a scale from +3 to -3. We then used regression analysis to identify sites in the ventromedial prefrontal cortex at which the two separately acquired measures, blood flow change and emotional impact of images, correlated significantly. The regression analysis identified a locus in Brodmann's area 11 of the inferomedial prefrontal cortex (IMPC) at which these two separate measures had significant inverse correlation. Thus, under the specific circumstance of positron emission tomography (PET) of a pharmacological challenge, a key region of the inferomedial prefrontal cortex underwent deactivation in proportion to a separately rated emotional impact of a stimulus. We propose a specific pharmacodynamic mechanism that explains the correlation between the emotional impact and the effect of a serotonin-noradrenaline reuptake inhibitor on cerebral blood flow.

STN-stimulation in Parkinson's disease restores striatal inhibition of thalamocortical projection.

To test the hypothesis that deep brain stimulation of the subthalamic nucleus (STN) restores the inhibitory output to the striatothalamocortical loop in Parkinson's disease, we obtained functional brain images of blood flow in 10 STN-stimulated patients with Parkinson's disease. Patients were immobile and off antiparkinsonian medication for 12 h. They were scanned with and without bilateral STN-stimulation with a 4-h interval between the two conditions. The order of DBS stimulation (ON or OFF) was randomized. Stimulation significantly raised regional cerebral blood flow (rCBF) bilaterally in the STN and in the left nucleus lentiformis. Conversely, flow declined in the left supplementary motor area (BA 6), ventrolateral nucleus of the left thalamus, and right cerebellum. Activation of the basal ganglia and deactivation of supplementary motor area and thalamus were both correlated with the improvement of motor function. The result is consistent with the explanation that stimulation in resting patients raises output from the STN with activation of the inhibitory basal ganglia output nuclei and subsequent deactivation of the thalamic anteroventral and ventrolateral nuclei and the supplementary motor area.

As time goes by: temporal constraints on emotional activation of inferior medial prefrontal cortex.

To investigate the influence of stimulus duration on emotional processing, we measured changes of regional cerebral blood flow (rCBF) in 14 healthy subjects who viewed neutral or emotional images presented for 3 or 6 s. Presentation for 3 s reproduced the previous result of higher rCBF in inferior medial prefrontal cortex (IMPC) during neutral than emotional stimulation. Six-second presentation reverted this relationship, with activity in IMPC being higher during emotional stimulation. Prolonged stimulus presentation attenuated the rise of rCBF associated with emotions in left parietal cortex and cerebellar hemisphere. We speculate that the different rCBF during neutral and emotional stimulation for 6 s is a consequence of attention divided between the emotional stimuli and their associations. Thus, prefrontal activity rises when a cognitive task accompanies emotional stimulation because several cognitive processes compete for attention. The IMPC may serve the mechanism of attention underlying the concept of a default mode of brain function, selecting among competitive inputs from multiple brain regions rather than just processing emotions. The results emphasize the importance of implicit cognitive processing during emotional activation, however, unintended.

Stimulation of subthalamic nucleus inhibits emotional activation of fusiform gyrus.

In patients with Parkinson's disease, deep brain stimulation of the subthalamic nucleus is known to impair their ability to correctly identify facial expressions of negative emotions. This difficulty exists only when the stimulator is active. The reason for the impairment is unknown. To test the hypothesis that the stimulation itself is responsible, we used positron emission tomography to compare functional activations of brain regions in nine patients with Parkinson's disease treated with surgically implanted electrodes into both subthalamic nuclei, and 22 healthy volunteers. Both groups viewed images with neutral or emotional content from Aarhus University's standard Empathy Picture System () with 360 images of people in pleasant, unpleasant or neutral real-life situations, presenting either the situations or close-ups of the facial expressions of the people involved. Both groups, the patients with stimulation OFF and the healthy volunteers, had raised regional blood flow rates (rCBF) in the right fusiform gyrus when they viewed emotionally expressive faces compared to neutral faces. With stimulation turned on, this response was significantly inhibited in the patients because of a raised rCBF at baseline during the neutral faces. Stimulation of the STN did not alter fusiform reaction to emotionally pregnant scenes; nor did healthy volunteers and patients react differently to these stimuli regardless of stimulation status. Also, STN stimulation raised the emotional activation of the anterior cingulate and lowered the activity of the putamen. The findings suggest that the stimulation of the subthalamic nucleus interferes with the integration of specific neocortical networks involved in the recognition of facial expressions.

Serotonin modulation of cerebral blood flow measured with positron emission tomography (PET) in humans.

To develop a method to measure the dynamic response of the serotonin system in vivo, the effects of intravenously administered citalopram (the most selective of the serotonin reuptake inhibitors) or clomipramine on cerebral blood flow (CBF) were evaluated. CBF was measured with positron emission tomography (PET) in 27 normal subjects scanned under baseline conditions and, on the same day, after an intravenous (IV) infusion of placebo, citalopram, or clomipramine using a randomized, double-blind design. The main effects of the drugs on blood flow occurred in the thalamus, hypothalamus, and cingulate cortex. Compared to placebo, clomipramine reduced blood flow in the mediodorsal and ventral lateral nuclei of the thalamus, whereas citalopram reduced blood flow in the pulvinar nucleus and the hypothalamus. Compared to clomipramine, citalopram decreased blood flow in the cingulate cortex. The findings support previous reports showing acute central effects of citalopram and clomipramine on regional serotonergic functions measured by PET. Acute side effects may, however, require that care is taken in the selection of experimental designs for future PET studies using IV administration of these antidepressants.

Emotional valence modulates activity in the posterior fusiform gyrus and inferior medial prefrontal cortex in social perception.

Previous studies have shown that during the presentation of emotionally loaded visual stimuli, activity increases in the visual and limbic cortices. This study focuses on empathic reactions induced by presenting pictures of situations and facial expressions from a "third party" point of view only. We measured regional changes in blood flow (rCBF) in nine healthy subjects while they were looking at neutral, positive, or negative emotional pictures of low (facial expressions) and high (persons in real-life situations) social complexity. A significant rCBF increase occurred in the right posterior fusiform gyrus during presentation of emotional pictures of both low and high social complexity. We also observed an interaction between emotionality and social complexity in the left inferior occipital gyrus for situations, where emotionality produced a significantly larger rCBF increase for situations than faces. No significant rCBF changes were observed in the amygdala or other parts of the limbic system. A significant rCBF decrease was found in the right inferior medial prefrontal cortex during presentation of the emotional pictures. This is discussed with respect to the "default mode of the brain" theory. We suggest that there is a neural network in the posterior fusiform and inferior occipital gyrus specialized in identifying emotionally important visual clues. Messages from this and other areas converge to the medial prefrontal cortex, to be evaluated in terms of relevance for attention. We believe that this is a crucial part of a network used in normal empathic reactions and social interactions.