Functional networks in motor sequence learning: abnormal topographies in Parkinson's disease

We examined the neural circuitry underlying the explicit learning of motor sequences in normal subjects and patients with early stage Parkinson's disease (PD) using 15O-water (H2 15O) positron emission tomography (PET) and network analysis. All subjects were scanned while learning motor sequences in a task emphasizing explicit learning, and during a kinematically controlled motor execution reference task. Because different brain networks are thought to subserve target acquisition and retrieval during motor sequence learning, we used separate behavioral indices to quantify these aspects of learning during the PET experiments. In the normal cohort, network analysis of the PET data revealed a significant covariance pattern associated with acquisition performance. This topography was characterized by activations in the left dorsolateral prefrontal cortex (PFdl), rostral supplementary motor area (preSMA), anterior cingulate cortex, and in the left caudate/putamen. A second independent covariance pattern was associated with retrieval performance. This topography was characterized by bilateral activations in the premotor cortex (PMC), and in the right precuneus and posterior parietal cortex. The normal learning-related topographies failed to predict acquisition performance in PD patients and predicted retrieval performance less accurately in the controls. A separate network analysis was performed to identify discrete learning-related topographies in the PD cohort. In PD patients, acquisition performance was associated with a covariance pattern characterized by activations in the left PFdl, ventral prefrontal, and rostral premotor regions, but not in the striatum. Retrieval performance in PD patients was associated with a covariance pattern characterized by activations in the right PFdl, and bilaterally in the PMC, posterior parietal cortex, and precuneus. These results suggest that in early stage PD sequence learning networks are associated with additional cortical activation compensating for abnormalities in basal ganglia function.

The metabolic topography of essential blepharospasm: a focal dystonia with general implications

OBJECTIVE

To determine the metabolic topography of essential blepharospasm (EB).

BACKGROUND

EB is a cranial dystonia of unknown etiology and anatomic localization. The authors have used 18F-fluorodeoxyglucose (FDG) and PET with network analysis to identify distinctive patterns of regional metabolic abnormality associated with idiopathic torsion dystonia (ITD), as well as sleep induction during PET imaging to suppress involuntary movements, thereby reducing this potential confound in the analysis.

METHODS

Six patients with EB and six normal volunteers were scanned with FDG-PET. Scans were performed twice: once in wakefulness and once following sleep induction. The authors used statistical parametric mapping to compare glucose metabolism between patients with EB and control subjects in each condition. They also quantified the expression of the previously identified ITD-related metabolic networks in each subject in both conditions.

RESULTS

With active involuntary movements during wakefulness, the EB group exhibited hypermetabolism of the cerebellum and pons. With movement suppression during sleep, the EB group exhibited superior-medial frontal hypometabolism in a region associated with cortical control of eyelid movement. Network analysis demonstrated a specific metabolic covariance pattern associated with ITD was also expressed in the patients with EB in both the sleep and wake conditions.

CONCLUSION

These findings suggest that the clinical manifestations of EB are associated with abnormal metabolic activity in the pons and cerebellum, whereas the functional substrate of the disorder may be associated with abnormalities in cortical eyelid control regions. Furthermore, ITD-related networks are expressed in patients with EB, suggesting a functional commonality between both forms of primary dystonia.

Patterns of regional brain activation associated with different forms of motor learning

To examine the variations in regional cerebral blood flow during execution and learning of reaching movements, we employed a family of kinematically and dynamically controlled motor tasks in which cognitive, mnemonic and executive features of performance were differentiated and characterized quantitatively. During 15O-labeled water positron emission tomography (PET) scans, twelve right-handed subjects moved their dominant hand on a digitizing tablet from a central location to equidistant targets displayed with a cursor on a computer screen in synchrony with a tone. In the preceding week, all subjects practiced three motor tasks: 1) movements to a predictable sequence of targets; 2) learning of new visuomotor transformations in which screen cursor motion was rotated by 30 degrees -60 degrees; 3) learning new target sequences by trial and error, by using previously acquired routines in a task placing heavy load on spatial working memory. The control condition was observing screen and audio displays. Subtraction images were analyzed with Statistical Parametric Mapping to identify significant brain activation foci. Execution of predictable sequences was characterized by a modest decrease in movement time and spatial error. The underlying pattern of activation involved primary motor and sensory areas, cerebellum, basal ganglia. Adaptation to a rotated reference frame, a form of procedural learning, was associated with decrease in the imposed directional bias. This task was associated with activation in the right posterior parietal cortex. New sequences were learned explicitly. Significant activation was found in dorsolateral prefrontal and anterior cingulate cortices. In this study, we have introduced a series of flexible motor tasks with similar kinematic characteristics and different spatial attributes. These tasks can be used to assess specific aspects of motor learning with imaging in health and disease.

Functional brain imaging of movement disorders

Functional brain imaging techniques such as positron emission tomography (PET) have contributed to our understanding of the pathophysiology of Parkinson's disease (PD) and other movement disorders. PET employs small amounts of positron emitting radioligands to produce quantitative measures of physiological and biochemical processes in the brain and other organs. In a PET experiment, a subject is given a compound of biological interest. The spatial and temporal distribution of the radiotracer is measured quantitatively in the course of the PET study, providing a tomographic representation of regional radioactivity concentration. In this review, we focus on the potential application of PET in the selection of suitable candidates and the assessment of surgical interventions such as pallidotomy, thalamotomy, and deep brain stimulation.

Rostral and orbital prefrontal cortex dysfunction in the manic state of bipolar disorder

OBJECTIVE

This study investigated prefrontal cortex function in the manic state of bipolar disorder.

METHOD

High-sensitivity [15O]H2O positron emission tomography and a word generation activation paradigm were used to study regional cerebral blood flow in five manic and six euthymic individuals with bipolar disorder and in five healthy individuals.

RESULTS

Decreased right rostral and orbital prefrontal cortex activation during word generation and decreased orbitofrontal activity during rest were associated with mania.

CONCLUSIONS

The data support the presence of rostral and orbital prefrontal dysfunction in primary mania. These findings, when seen in the context of the human brain lesion and the behavioral neuroanatomic literatures, may help to explain some of the neurobehavioral abnormalities characteristic of the manic state.

Radiosynthesis of [18F] N-3-fluoropropyl-2-beta-carbomethoxy-3-beta (4' methylphenyl) nortropane (FPCMT)

A synthetic procedure for the routine preparation of [18F] N-3-fluoropropyl-2-beta-carbomethoxy-3-beta-(4' methylphenyl) nortropane (18F FPCMT) has been developed. The synthesis is based on alkylation of nortropane with 18F labeled fluoropropyl tosylate. Purification of the final product was achieved by a preparative HPLC procedure using Alltech Econosil column. Separation of the desired compound was achieved and the product was clean. The radiochemical yield (without decay correction) is 4 to 5%, calculated at the end of the synthesis based on the total amount of fluorine recovered from the target. Radiochemical purity was in the range of 98 to 99%.

Reproducibility of regional metabolic covariance patterns: comparison of four populations

In a previous [18F]fluorodeoxyglucose (FDG) PET study we analyzed regional metabolic data from a combined group of Parkinson's disease (PD) patients and healthy volunteers (N), using network analysis. By this method, we identified a unique pattern of regional metabolic covariation with an expression which accurately discriminated patients from healthy volunteers. To assess the reproducibility of this pattern as a potential marker for PD, we compared the pattern's topography with that of the disease-related covariance patterns identified in three other independent populations of patients with PD and healthy individuals studied in different PET laboratories.

METHODS

The following patient populations were studied: group A (original cohort: 22 PD, 20 N; resolution: 7.5 mm full width at half maximum [FWHM]); group B (18 PD, 12 N; resolution: 4.2 mm FWHM); group C (25 PD, 15 N; resolution: 8.0 mm FWHM); and group D (14 PD, 10 N; resolution: 10 mm FWHM). Region weights for the PD-related covariance pattern (PDRP) identified in the group A analysis were correlated with those for the disease-related patterns identified in the analyses of groups B, C and D. In addition, subject scores for the group A PDRP were computed prospectively for every individual in each of the study populations. PDRP scores for PD and N within each cohort were compared.

RESULTS

The PDRP topography identified in group A was highly correlated with each of the corresponding topographies identified in the other populations (r2 approximately 0.60, P < 0.0001). Prospectively computed subject scores for the group A PDRP significantly discriminated PD from N in each population (P < 0.004).

CONCLUSION

The PDRP topography identified previously in Group A is highly reproducible across patient populations and tomographs. Prospectively computed PDRP scores can accurately discriminate patients from controls in multiple populations studied with different tomographs. Brain network imaging with FDG PET can provide robust metabolic markers for the diagnosis of PD.

Quantitative brain FDG/PET studies using dynamic aortic imaging

Positron emission tomography (PET) measurements of cerebral glucose utilization using 18F-fluorodeoxyglucose (FDG) are a useful tool in the investigation of localized brain function in normal and disease states. A major impediment to the application of FDG/PET in clinical investigation has been the need for arterial blood sampling to quantify cerebral glucose metabolism (CMRGlc). Qualitative studies, though informative in a variety of clinical settings, are of limited value for research applications and do not utilize the inherent quantitative nature of PET. We present a novel PET technique employing a whole-body PET tomograph with abdominal aortic imaging from 0 to 30 min as an alternative to arterial blood sampling to obtain the input function for cerebral metabolic rate calculations. Two or three arterial samples taken during the 10-45 min period were used to scale and extend the blood curve and the brain was imaged from 35-55 min post-injection. We performed 12 studies in which both arterial blood sampling and aortic scans were obtained. We found the correlation of global metabolic rates (GMR) when comparing the two techniques to be extremely high (R2 = 0.99). This suggests that the use of dynamic aortic imaging is less invasive and a viable alternative to arterial blood sampling in quantitative FDG/PET imaging.

Positron emission tomographic studies in restless legs syndrome

We studied six restless legs syndrome (RLS) patients with [F18]fluorodeoxyglucose (FDG) positron emission tomography (PET). We also studied four of these same patients with [F18]fluorodopa (FDOPA) PET. The patients' FDG and FDOPA PET scans were compared with those from age-matched healthy control subjects. No significant differences between the two groups were found for any regional blood flow values derived from the FDG scans or for any binding constants derived from the FDOPA scans. These results suggest that any abnormal resting brain metabolic activity or putative presynaptic dopaminergic defect in RLS is likely either to be so subtle that it is below the threshold for ready detection by PET or that it is located in an area of neural tissue inaccessible to the current scanner. No substantial defect is likely to involve the dopaminergic nigrostriatal axis.

Nervous system dysfunction in Waldenström's macroglobulinemia: response to treatment

A patient presented with a peripheral neuropathy and was found to have Waldenstrom's macroglobulinemia with high serum titers of antibodies to myelin-associated glycoprotein. He developed parkinsonism that was poorly responsive to levodopa. He failed conventional therapy and was treated with autologous bone marrow transplantation, which resulted in improvement of the neuropathy but not his parkinsonism. Critical cytoreduction in the B-cell clone may be necessary for improvement of the neuropathy of Waldenstrom's macroglobulinemia.

The metabolic anatomy of tremor in Parkinson's disease

OBJECTIVE

To identify regional metabolic brain networks related specifically to the presence of tremor in PD.

BACKGROUND

The pathophysiology of parkinsonian tremor is unknown. Because tremor in PD occurs mainly in repose, we used resting state PET with 18F-fluorodeoxyglucose (FDG) to identify specific metabolic brain networks associated with this clinical manifestation.

METHODS

We studied two discrete groups of eight PD patients with and without tremor using FDG/PET. Both patient groups were matched for gender, age, and Unified Parkinson Disease Rating Scale ratings for akinesia and rigidity. Ten normal volunteer subjects served as controls.

RESULTS

Network analysis with the Scaled Subprofile Model was performed in two steps. 1) We computed the expression of the PD-related pattern (PDRP) identified by us previously in each of the PD patients and control subjects. Although PDRP subject scores were abnormally elevated in the combined PD cohort (p < 0.005), these values did not differ in the PD patient groups with and without tremor (p = 0.36). 2) We used SSM to analyze the data from the combined PD cohort comprising both patient groups. We found that PD patients with tremor were characterized by increased expression of a metabolic network comprising the thalamus, pons, and premotor cortical regions. Subject scores for this pattern were elevated in the tremor group compared with the atremulous patient group and the normal control group (p < 0.005).

CONCLUSIONS

The findings suggest that PD patients with tremor are characterized by distinct increases in the functional activity of thalamo-motor cortical projections. Modulation of this functional anatomic pathway is likely to be the mechanism for successful interventions for the relief of parkinsonian tremor.

Dopamine transporter imaging with fluorine-18-FPCIT and PET

Fluorinated N-3-fluoropropyl-2-beta-carboxymethoxy-3-beta-(4-iodophenyl) nortropane (FPCIT) has been synthesized as a dopamine transporter ligand for PET studies. We evaluated the regional brain uptake and the plasma metabolism of [18F]-FPCIT.

METHODS

PET studies were conducted on 7 normal subjects and on 10 patients with Parkinson's disease. After the [18F]-FPCIT injection (4.4+/-1.8 mCi), dynamic scans were acquired over 100 min. Plasma metabolite analysis was performed using high-performance liquid chromatography (HPLC).

RESULTS

Plasma HPLC revealed two peaks corresponding to unmetabolized [18F]-FPCIT and a polar metabolite. The fraction of the parent compound decreased rapidly to 25% at 25 min. Fluorine-18-FPCIT showed a striatum-to-occipital ratio (SOR) of 3.5 at 90 min postinjection. The ratio of striatal-to-occipital distribution volume (DVR) was calculated directly by using a mean tissue-to-plasma efflux constant for occipital cortex obtained in 10 subjects (ki=0.037 min(-1)). DVR measures determined with and without plasma input function were correlated (r=0.98, p < 0.0001). In normal subjects, a significant age-related decline of DVR was observed both for caudate and putamen, corresponding to a 7.7% and 6.4% decline per decade, respectively (r > 0.85, p < 0.01). Both DVR and SOR correctly classified early-stage Parkinson's disease patients with comparable accuracy (p < 0.0001). Age-corrected DVR values correlated negatively with the Uniform Parkinson's Disease Rating Scale composite motor ratings (r=0.66, p < 0.05).

CONCLUSION

The tracer characteristics are compatible with a high-affinity, reversible ligand. FPCIT/PET demonstrated age-related decline in dopamine transporter binding in normal subjects as well as significant reductions in patients with idiopathic Parkinson's disease, which correlates with the disease severity.

Cerebral glucose metabolism in women with panic disorder

OBJECTIVE

This study was undertaken to clarify earlier inconsistent findings in brain metabolic topography in panic disorder patients at rest.

METHOD

Positron emission tomography (PET) with [18F]fluorodeoxyglucose was used to determine cerebral metabolic activity in six female patients with a DSM-III-R diagnosis of panic disorder and in six healthy female volunteers. All patients with panic disorder were medication free and were sensitive to lactate infusion.

RESULTS

A significant increase in glucose metabolism was found in the left hippocampus and parahippocampal area of the panic disorder subjects in comparison with that found in the healthy subjects. In addition, a significant decrease in metabolism was found in the right inferior parietal and right superior temporal brain regions of the panic disorder subjects in comparison with that of the normal subjects. There was no significant correlation between scores for the severity of panic disorder or for the severity of lactate-induced panic attack and the quantified PET abnormality.

CONCLUSIONS

These data provide further support for the hypothesis of an abnormal brain metabolism in the hippocampal and parahippocampal area in individuals with panic disorder and also suggest other areas of aberrant brain metabolism in this disorder.

Functional brain networks in DYT1 dystonia

Early-onset idiopathic torsion dystonia (ITD) is an autosomal dominant hyperkinetic movement disorder with incomplete penetrance, associated with a 3 base-pair deletion in the DYT1 gene on chromosome 9q34. To determine the metabolic substrates of brain dysfunction in DYT1 dystonia, we scanned 7 nonmanifesting and 10 affected DYT1 carriers and 14 normal volunteers with [18F]fluorodeoxyglucose and positron emission tomography. We found that DYT1 dystonia is mediated by the expression of two independent regional metabolic covariance patterns. The first pattern, identified in an analysis of nonmanifesting gene carriers was designated movement free (MF). This abnormal pattern was characterized by increased metabolic activity in the lentiform nuclei, cerebellum, and supplementary motor areas. The MF pattern was present in DYT1 carriers with and without clinical manifestations and persisted in DYT1 dystonia patients in whom involuntary movements were suppressed by sleep. The second pattern, identified in an analysis of affected gene carriers with sustained contractions at rest, was designated movement related (MR). This pattern was characterized by increased metabolic activity in the midbrain, cerebellum, and thalamus. The expression of the MR pattern was increased in waking DYT1 patients with sustained dystonia, compared with DYT1 carriers who were unaffected or who had dystonia only on action, as well as normal controls. MR subject scores declined significantly with sleep in affected DYT1 patients but not in normal controls. These findings indicate the penetrance of the DYT1 gene is considerably greater than previously assumed. ITD is mediated through the interaction of functional brain networks relating separately to gene status and to abnormal movement.

Cognitive functioning after pallidotomy for refractory Parkinson's disease

BACKGROUND

Earlier approaches to pallidotomy for refractory Parkinson's disease had significant complication rates. More recent approaches show fewer complications, but the effect of pallidotomy on cognition is unclear. The current study was conducted to examine the neuropsychological effects of unilateral pallidotomy.

METHODS

Neuropsychological testing was performed on patients with medically refractory, predominantly unilateral Parkinson's disease at baseline and after unilateral ventral pallidotomy (n=28) or after an equivalent period without surgery in control patients (n=10).

RESULTS

Pallidotomy patients showed no significant changes from baseline to retesting relative to the control group for any measure. Across all of the tests administered, only five of the surgery patients showed a significant decline, and of these five none declined on more than one test. Depression did not relate to preoperative or postoperative cognition. The pallidotomy group showed a significant improvement in motor functioning and activities of daily living whereas the control group did not. These measures were not associated with the neuropsychological test scores at baseline or retest.

CONCLUSIONS

Stereotactic unilateral ventral pallidotomy does not seem to produce dramatic cognitive declines in most patients.

Differential diagnosis of parkinsonism with [18F]fluorodeoxyglucose and PET

The clinical differentiation between typical idiopathic Parkinson's disease (IPD) and atypical parkinsonian disorders (APD) is complicated by the presence of signs and symptoms common to both forms of parkinsonism. Metabolic brain imaging with [18F]fluorodeoxyglucose (FDG) and positron emission tomography (PET) may be a useful adjunct in differentiating APD from IPD. To explore this possibility, we studied 48 parkinsonian patients suspected as having possible APD because of a deteriorating response to dopaminergic treatment, the development of autonomic dysfunction, or both. A group of 56 patients with likely IPD served as control subjects. We used quantitative FDG/PET to measure regional rates of cerebral glucose use in IPD and APD patients. We used discriminant analysis to categorize IPD and APD patients based on their regional metabolic data. We found that a linear combination of caudate, lentiform, and thalamic values accurately discriminated APD from IPD patients (p < 0.0001). Significant metabolic abnormalities were present in the striatum and the thalamus of 36 of 48 (75%) APD patients. Our findings show that measurements of regional glucose metabolism can be used to discriminate patients with suspected APD from their counterparts with classic IPD. FDG/PET may be a useful adjunct to the clinical examination in the differential diagnosis of parkinsonism.

[11C]raclopride-PET studies of the Huntington's disease rate of progression: relevance of the trinucleotide repeat length

We used [11C]raclopride and positron emission tomography (PET) to assess the relationship between striatal dopamine D2 receptor binding, trinucleotide repeat number (CAG), and subject age in 10 asymptomatic and 8 symptomatic carriers of the Huntington's disease (HD) mutation. In both preclinical and symptomatic gene carriers, we found significant correlations between CAG repeat length and the ratio of percent loss in striatal D2 receptor binding divided by age. In accord with neuropathological studies, we obtained an intercept at 35.5 CAG repeats in the symptomatic HD patients. Nonetheless, we noted that the slopes of the correlation lines differed significantly for the presymptomatic and symptomatic cohorts. These PET results support the notion that the HD disease process is a function of trinucleotide length and age, and that the development of clinical signs and symptoms is associated with CAG repeat lengths greater than 35.5. However, our analysis also suggests that striatal degeneration may proceed in a nonlinear fashion. These findings have implications for the design of neuroprotective strategies for the treatment of HD.

Brain lactate and N-acetylaspartate in pediatric AIDS encephalopathy

Two children with acquired immunodeficiency syndrome (AIDS) and progressive encephalopathy underwent MR spectroscopy before and after antiretroviral therapy. Initial MR spectroscopy of the basal ganglia region showed decreased N-acetylaspartate (NAA)/creatine (Cr) and a lactate peak. After therapy, there was improvement in NAA/Cr and an absence of the abnormal lactate peak. We suggest that decreased NAA/Cr in AIDS is reversible, that brain lactate might correlate with inflammation, and that MR spectroscopy can be useful in treatment trials.

Asymmetric predominantly ipsilateral blepharospasm and contralateral parkinsonism in an elderly patient with a right mesencephalic cyst

A 66-year-old woman presented with a 3-year history of predominantly right-sided blepharospasm and a 1-year history of progressive predominantly left-sided hemiparkinsonism manifested by a left upper extremity resting tremor and left-sided bradykinesia. Magnetic resonance imaging of the brain revealed a large right mesencephalic cyst with mass effect. Positron emission tomography revealed bilateral striatal hypometabolism consistent with nigrostriatal dopaminergic dysfunction. The association of predominantly ipsilateral blepharospasm and predominantly contralateral hemiparkinsonism is very rare, and its association with a posterior fossa space-occupying lesion has been reported only once. This is the second report of such an association and the first description of adult-onset symptomatology.