Practice-related changes in human brain functional anatomy during nonmotor learning

Practice of a novel task leads to improved performance. The brain mechanisms associated with practice-induced improvement in performance are largely unknown. To address this question we have examined the functional anatomy of the human brain with positron emission tomography (PET) during the naive and practiced performance of a simple verbal response selection task (saying an appropriate verb for a visually presented noun). As a control state, subjects were asked to repeat the visually presented nouns. Areas of the brain most active during naive performance (anterior cingulate, left prefrontal and left posterior temporal cortices, and the right cerebellar hemisphere), compared to repeating the visually presented nouns, were all significantly less active during practiced performance. These changes were accompanied by changes in the opposite direction in sylvian-insular cortex bilaterally and left medial extrastriate cortex. In effect, brief practice made the cortical circuitry used for verbal response selection indistinguishable from simple word repetition. Introduction of a novel list of words reversed the learning-related effects. These results indicate that two distinct circuits can be used for verbal response selection and normal subjects can change the brain circuits used during task performance following less than 15 min of practice. One critical factor in determining the circuitry used appears to be the degree to which a task is learned or automatic.

"Cognitive dysmetria" as an integrative theory of schizophrenia: a dysfunction in cortical-subcortical-cerebellar circuitry?

Earlier efforts to localize the symptoms of schizophrenia in a single brain region have been replaced by models that postulate a disruption in parallel distributed or dynamic circuits. Based on empirical data derived from both magnetic resonance and positron emission tomography, we have developed a model that implicates connectivity among nodes located in prefrontal regions, the thalamic nuclei, and the cerebellum. A disruption in this circuitry produces "cognitive dysmetria," difficulty in prioritizing, processing, coordinating, and responding to information. This "poor mental coordination" is a fundamental cognitive deficit in schizophrenia and can account for its broad diversity of symptoms.

COMT val158met genotype affects mu-opioid neurotransmitter responses to a pain stressor

Responses to pain and other stressors are regulated by interactions between multiple brain areas and neurochemical systems. We examined the influence of a common functional genetic polymorphism affecting the metabolism of catecholamines on the modulation of responses to sustained pain in humans. Individuals homozygous for the met158 allele of the catechol-O-methyltransferase (COMT) polymorphism (val158met) showed diminished regional mu-opioid system responses to pain compared with heterozygotes. These effects were accompanied by higher sensory and affective ratings of pain and a more negative internal affective state. Opposite effects were observed in val158 homozygotes. The COMT val158met polymorphism thus influences the human experience of pain and may underlie interindividual differences in the adaptation and responses to pain and other stressful stimuli.

Association of dopamine transporter reduction with psychomotor impairment in methamphetamine abusers

OBJECTIVE

Methamphetamine is a popular and highly addictive drug of abuse that has raised concerns because it has been shown in laboratory animals to be neurotoxic to dopamine terminals. The authors evaluated if similar changes occur in humans and assessed if they were functionally significant.

METHOD

Positron emission tomography scans following administration of [(11)C]d-threo-methylphenidate (a dopamine transporter ligand) measured dopamine transporter levels (a marker of dopamine cell terminals) in the brains of 15 detoxified methamphetamine abusers and 18 comparison subjects. Neuropsychological tests were also performed to assess motor and cognitive function.

RESULTS

Methamphetamine abusers showed significant dopamine transporter reduction in the striatum (mean differences of 27.8% in the caudate and 21.1% in the putamen) relative to the comparison subjects; this reduction was evident even in abusers who had been detoxified for at least 11 months. Dopamine transporter reduction was associated with motor slowing and memory impairment.

CONCLUSIONS

These results provide evidence that methamphetamine at dose levels taken by human abusers of the drug leads to dopamine transporter reduction that is associated with motor and cognitive impairment. These results emphasize the urgency of alerting clinicians and the public of the long-term changes that methamphetamine can induce in the human brain.

Distinct contribution of the cortico-striatal and cortico-cerebellar systems to motor skill learning

This review paper focuses on studies in healthy human subjects that examined the functional neuroanatomy and cerebral plasticity associated with the learning, consolidation and retention phases of motor skilled behaviors using modern brain imaging techniques. Evidence in support of a recent model proposed by Doyon and Ungerleider [Functional Anatomy of Motor Skill Learning. In: Squire LR, Schacter DL, editors. Neuropsychology of Memory. New York: Guilford Press, 2002.] is also discussed. The latter suggests that experience-dependent changes in the brain depend not only on the stage of learning, but also on whether subjects are required to learn a new sequence of movements (motor sequence learning) or learn to adapt to environmental perturbations (motor adaptation). This model proposes that the cortico-striatal and cortico-cerebellar systems contribute differentially to motor sequence learning and motor adaptation, respectively, and that this is most apparent during the slow learning phase (i.e. automatization) when subjects achieve asymptotic performance, as well as during reactivation of the new skilled behavior in the retention phase.

Posterior reversible encephalopathy syndrome: associated clinical and radiologic findings

OBJECTIVE

To identify and define clinical associations and radiologic findings of posterior reversible encephalopathy syndrome (PRES).

PATIENTS AND METHODS

Patients prospectively diagnosed as having PRES from October 1, 2005, through April 30, 2009, were pooled with retrospectively identified patients admitted from August 1, 1999, through September 30, 2005. We performed a detailed review of clinical information, including demographics, presenting symptoms, medical history, and risk factors. All patients underwent computed tomography of the brain or magnetic resonance imaging. Findings on magnetic resonance imaging were analyzed independently by 2 neuroradiologists.

RESULTS

We identified 120 cases of PRES in 113 patients (mean age, 48 years). Mean peak systolic blood pressure was 199 mm Hg (minimum-maximum, 160-268 mm Hg), and mean peak diastolic blood pressure was 109 mm Hg (minimum-maximum, 60-144 mm Hg). Etiologies of PRES included hypertension (n=69 [61%]), cytotoxic medications (n=21 [19%]), sepsis (n=8 [7%]), preeclampsia or eclampsia (n=7 [6%]), and multiple organ dysfunction (n=1 [1%]). Autoimmune disease was present in 51 patients (45%). Clinical presentations included seizures (n=84 [74%]), encephalopathy (n=32 [28%]), headache (n=29 [26%]), and visual disturbances (n=23 [20%]). In the 115 cases (109 patients) for which magnetic resonance imaging findings were available, the parieto-occipital regions were the most commonly involved (n=108 [94%]), followed by the frontal lobe (n=88 [77%]), temporal lobe (n=74 [64%]), and cerebellum (n=61 [53%]). Cerebellar involvement was significantly more frequent in patients with a history of autoimmunity (P=.008), and patients with sepsis were more likely to have cortical involvement (P<.001).

CONCLUSION

A substantial proportion of patients with PRES have underlying autoimmune conditions that may support endothelial dysfunction as a pathophysiologic mechanism. On brain imaging, the location and severity of vasogenic edema were mostly similar for the different clinical subgroups.

Modulating the experience of agency: a positron emission tomography study

This study investigated agency, the feeling of being causally involved in an action. This is the feeling that leads us to attribute an action to ourselves rather than to another person. We were interested in the effects of experimentally modulating this experience on brain areas known to be involved in action recognition and self-recognition. We used a device that allowed us to modify the subject's degree of control of the movements of a virtual hand presented on a screen. Four main conditions were used: (1) a condition where the subject had a full control of the movements of the virtual hand, (2) a condition where the movements of the virtual hand appeared rotated by 25 degrees with respect to the movements made by the subject, (3) a condition where the movements of the virtual hand appeared rotated by 50 degrees, and (4) a condition where the movements of the virtual hand were produced by another person and did not correspond to the subject's movements. The activity of two main brain areas appeared to be modulated by the degree of discrepancy between the movement executed and the movement seen on the screen. In the inferior part of the parietal lobe, specifically on the right side, the less the subject felt in control of the movements of the virtual hand, the higher the level of activation. A reverse covariation was observed in the insula. These results demonstrate that the level of activity of specific brain areas maps onto the experience of causing or controlling an action. The implication of these results for understanding pathological conditions is discussed.

The effect of filter size on VBM analyses of DT-MRI data

Voxel-based morphometry (VBM) has been used to analyze diffusion tensor MRI (DT-MRI) data in a number of studies. In VBM, following spatial normalization, data are smoothed to improve the validity of statistical inferences and to reduce inter-individual variation. However, the size of the smoothing filter used for VBM of DT-MRI data is highly variable across studies. For example, a literature review revealed that Gaussian smoothing kernels ranging in size (full width at half maximum) from zero to 16 mm have been used in DT-MRI VBM type studies. To investigate the effect of varying filter size in such analyses, whole brain DT-MRI data from 14 schizophrenic patients were compared with those of 14 matched control subjects using VBM, when the filter size was varied from zero to 16 mm. Within this range of smoothing, four different conclusions regarding apparent patient control differences could be made: (i) no significant patient-control differences; (ii) reduced FA in right superior temporal gyrus (STG) in patients; (iii) reduced FA in both right STG and left cerebellum in patients; and (iv) reduced FA only in left cerebellum in patients. These findings stress the importance of recognizing the effect of the matched filter theorem on VBM analyses of DT-MRI data. Finally, we investigated whether one of the underlying assumptions of parametric VBM, i.e., the normality of the residuals, is met. Our results suggest that, even with moderate smoothing, a large number of voxels within central white matter regions may have non-normally distributed residuals thus making valid statistical inferences with a parametric approach problematic in these areas.

Imaging human mesolimbic dopamine transmission with positron emission tomography: I. Accuracy and precision of D(2) receptor parameter measurements in ventral striatum

Dopamine transmission in the ventral striatum (VST), a structure which includes the nucleus accumbens, ventral caudate, and ventral putamen, plays a critical role in the pathophysiology of psychotic states and in the reinforcing effects of virtually all drugs of abuse. The aim of this study was to assess the accuracy and precision of measurements of D(2) receptor availability in the VST obtained with positron emission tomography on the high-resolution ECAT EXACT HR+ scanner (Siemens Medical Systems, Knoxville, TN, U.S.A.). A method was developed for identification of the boundaries of the VST on coregistered high-resolution magnetic resonance imaging scans. Specific-to-nonspecific partition coefficient (V(3)") and binding potential (BP) of [(11)C]raclopride were measured twice in 10 subjects, using the bolus plus constant infusion method. [(11)C]Raclopride V(3)" in the VST (1.86 +/- 0.29) was significantly lower than in the dorsal caudate (DCA, 2.33 +/- 0.28) and dorsal putamen (DPU, 2.99 +/- 0.26), an observation consistent with postmortem studies. The reproducibility of V(3)" and BP were appropriate and similar in VST (V(3)" test-retest variability of 8.2% +/- 6.2%, intraclass correlation coefficient = 0.83), DCA (7.7% +/- 5.1%, 0.77), DPU (6.0% +/- 4.1%, 0.71), and striatum as a whole (6.3% +/- 4.1%, 0.78). Partial volume effects analysis revealed that activities in the VST were significantly contaminated by counts spilling over from the adjacent DCA and DPU: 70% +/- 5% of the specific binding measured in the VST originated from D(2) receptors located in the VST, whereas 12% +/- 3% and 18% +/- 3% were contributed by D(2) receptors in the DCA and DPU, respectively. Thus, accuracy of D(2) receptor measurement is improved by correction for partial voluming effects. The demonstration of an appropriate accuracy and precision of D(2) receptor measurement with [(11)C]raclopride in the VST is the first critical step toward the use of this ligand in the study of synaptic dopamine transmission at D(2) receptors in the VST using endogenous competition techniques.

Schizophrenia and cognitive dysmetria: a positron-emission tomography study of dysfunctional prefrontal-thalamic-cerebellar circuitry

Patients suffering from schizophrenia display subtle cognitive abnormalities that may reflect a difficulty in rapidly coordinating the steps that occur in a variety of mental activities. Working interactively with the prefrontal cortex, the cerebellum may play a role in coordinating both motor and cognitive performance. This positron-emission tomography study suggests the presence of a prefrontal-thalamic-cerebellar network that is activated when normal subjects recall complex narrative material, but is dysfunctional in schizophrenic patients when they perform the same task. These results support a role for the cerebellum in cognitive functions and suggest that patients with schizophrenia may suffer from a "cognitive dysmetria" due to dysfunctional prefrontal-thalamic-cerebellar circuitry.

Is methylphenidate like cocaine? Studies on their pharmacokinetics and distribution in the human brain

BACKGROUND

The purposes of this study were to investigate the pharmacokinetics of methylphenidate hydrochloride (Ritalin) in the human brain, to compare them with those of cocaine, and to evaluate whether cocaine and methylphenidate compete for the same binding sites.

METHODS

We used positron emission tomography to measure the temporal and spatial distribution of carbon 11 (11C)-labeled methylphenidate. These results were compared with those obtained previously for [11C]cocaine. Eight healthy male subjects, 20 to 51 years of age, were scanned with [11C]methylphenidate. Three were tested twice to assess test-retest variability, four were tested at baseline and after administration of methylphenidate, and one was tested with [11C]methylphenidate and [11C]cocaine. Two baboons were scanned to evaluate whether there was competition between cocaine and methylphenidate for the same binding sites in the brain.

RESULTS

The uptake of [11C]methylphenidate in the brain was high (mean +/- SD, 7.5% +/- 1.5%), and the maximal concentration occurred in striatum. Pretreatment with methylphenidate decreased binding only in striatum (40%). Although the regional distribution of [11C]methylphenidate, was identical to that of [11C]cocaine and they competed with each other for the same binding sites, these two drugs differed markedly in their pharmacokinetics. Clearance of [11C]methylphenidate from striatum (90 minutes) was significantly slower than that of [11C]cocaine (20 minutes). For both drugs, their fast uptake in striatum paralleled the experience of the "high." For methylphenidate, the high decreased very rapidly despite significant binding of the drug in the brain. In contrast, for cocaine, the decline in the high paralleled its fast rate of clearance from the brain.

CONCLUSION

We speculate that because the experience of the high is associated with the fast uptake of cocaine and methylphenidate in the brain, the slow clearance of methylphenidate from the brain may serve as a limiting factor in promoting its frequent self-administration.

A meta-analysis of cerebellar contributions to higher cognition from PET and fMRI studies

A growing interest in cerebellar function and its involvement in higher cognition have prompted much research in recent years. Cerebellar presence in a wide range of cognitive functions examined within an increasing body of neuroimaging literature has been observed. We applied a meta-analytic approach, which employed the activation likelihood estimate method, to consolidate results of cerebellar involvement accumulated in different cognitive tasks of interest and systematically identified similarities among the studies. The current analysis included 88 neuroimaging studies demonstrating cerebellar activations in higher cognitive domains involving emotion, executive function, language, music, timing and working memory. While largely consistent with a prior meta-analysis by Stoodley and Schmahmann ([2009]: Neuroimage 44:489-501), our results extended their findings to include music and timing domains to provide further insights into cerebellar involvement and elucidate its role in higher cognition. In addition, we conducted inter- and intradomain comparisons for the cognitive domains of emotion, language, and working memory. We also considered task differences within the domain of verbal working memory by conducting a comparison of the Sternberg with the n-back task, as well as an analysis of the differential components within the Sternberg task. Results showed a consistent cerebellar presence in the timing domain, providing evidence for a role in time keeping. Unique clusters identified within the domain further refine the topographic organization of the cerebellum.

New charts for ultrasound dating of pregnancy and assessment of fetal growth: longitudinal data from a population-based cohort study

OBJECTIVES

Correct assessment of gestational age and fetal growth is essential for optimal obstetric management. The objectives of this study were, first, to develop charts for ultrasound dating of pregnancy based on crown-rump length and biparietal diameter and, second, to derive reference curves for normal fetal growth based on biparietal diameter, head circumference, transverse cerebellar diameter, abdominal circumference and femur length from 10 weeks of gestational age onwards.

METHODS

A total of 8313 pregnant women were included for analysis in this population-based prospective cohort study. All women had repeated ultrasound assessments to examine fetal growth.

RESULTS

Charts for ultrasound dating of pregnancy, based on crown-rump length and biparietal diameter, were derived. Internal validation with the actual date of delivery showed that ultrasound imaging provided reliable gestational age estimates. Up to 92% of deliveries took place within 37-42 weeks of gestation if gestational age was derived from ultrasound data, compared with 87% based on a reliable last menstrual period. The earlier the ultrasound assessment the more accurate the prediction of date of delivery. After 24 weeks of gestation a reliable last menstrual period provided better estimates of gestational age. Reference curves for normal fetal growth from 10 weeks of gestational age onwards were derived.

CONCLUSIONS

Charts for ultrasound dating of pregnancy and reference curves for fetal biometry are presented. The results indicate that, up to 24 weeks of pregnancy, dating by ultrasound examination provides a better prediction of the date of delivery than does last menstrual period. The earlier the ultrasound assessment in pregnancy, preferably between 10 and 12 weeks, the better the estimate of gestational age.

A review of differences between basal ganglia and cerebellar control of movements as revealed by functional imaging studies

The role of the basal ganglia and cerebellum in the control of movements is unclear. We summarize results from three groups of PET studies of regional CBF. The results show a double dissociation between (i) selection of movements, which induces differential effects in the basal ganglia but not the cerebellum, and (ii) sensory information processing, which involves the cerebellum but not the basal ganglia. The first set of studies concerned motor learning of a sequence of finger movements; there was a shift of activation in the anterior-posterior direction of the basal ganglia which paralleled changes in the motor areas of the frontal cortex. During new learning, the dorsolateral prefrontal cortex and striatum (caudate nucleus and anterior putamen) were activated. When subjects had to select movements, the premotor cortex and mid-putamen were activated. With automatic (overlearned) movements, the sensorimotor cortex and posterior putamen were activated. When subjects paid attention to overlearned actions, activation shifted back to the dorsolateral prefrontal cortex and striatum. The cerebellum was not activated when subjects made new decisions, attended to their actions or selected movements. These results demonstrate components of basal ganglia-(thalamo)-cortical loops in humans. According to earlier studies in animals we propose that the basal ganglia may be concerned with selecting movements or the selection of appropriate muscles to perform a movement selected by cortical areas (e.g. premotor cortex). Secondly, a visuomotor co-ordination task was examined. In the absence of visual control over arm movements, subjects were required to use a computer mouse to either generate new lines or to re-trace lines on a computer screen. The neocerebellum (hemispheres of the posterior lobe, cerebellar nuclei and cerebellar vermis), not the basal ganglia, was more engaged when lines were re-traced (compared with new line generation). Animal experiments have shown that error detection (deviation from given lines) and correction occurs during line re-tracing but not line generation. Our data suggest that the neocerebellum (not the basal ganglia) is involved in monitoring and optimizing movements using sensory (proprioceptive) feedback. Thirdly, the relative contribution of sensory information processing to the signal during active/passive execution of a motor task (flexion and extension of the elbow) was examined; it was found that 80-90% of the neocerebellar signal could be attributed to sensory information processing. The basal ganglia were not involved in sensory information processing. They may be concerned with movement/ muscle selection (efferent motor component); the neocerebellum may be concerned with monitoring the outcome (afferent sensory component) and optimizing movements using sensory (feedback) information.

Comparison of methods for analysis of clinical [11C]raclopride studies

Five different methods for the estimation of the binding potential, a measure of Bmax/Kd, of [11C]raclopride in human striatum were compared using data from a dose ranging study of the neuroleptic CP-88,059-01. Binding potential was estimated indirectly, from distribution volumes in striatum and cerebellum, using both single- and two-tissue compartment models with a metabolite-corrected plasma curve as input function. The two-tissue compartment model was also used for a direct estimate of the binding potential. In addition, a direct estimate was obtained from the reference tissue compartment model using the cerebellum as indirect input function. Finally, an estimate of binding potential was calculated from the ratio of striatum over cerebellum counts at late times after injection. The estimates of striatum binding potential from all methods, except the direct determination using a two-tissue compartment model with metabolite-corrected plasma input function, correlated with each other. Use of an average metabolite correction resulted in only a small reduction in accuracy in this series of normal subjects. The reference tissue model provided estimates of the binding potential with the same sensitivity for detecting changes as those methods that required a metabolite-corrected plasma input function. This indicates that for routine analysis of clinical [11C]raclopride studies, no arterial cannulation is required. The range of normal values was significantly less variable with the reference tissue method than when simple striatum-to-cerebellum ratios were used.

A positron emission tomographic study in spontaneous migraine

BACKGROUND

Functional brain imaging in acute migraine has proved challenging because of the logistic problems associated with an episodic condition. Since the seminal observation of brainstem activation in migraine, there has been only a single case substantiating this finding.

OBJECTIVE

To test the hypothesis that brainstem activation could be detected in migraine and to refine the anatomic localization with higher-resolution positron emission tomography than previously used.

DESIGN

Using positron emission tomography with radioactive water (H(2)15O), we studied acute migraine attacks occurring spontaneously. Five patients underwent imaging in ictal and interictal states, and the differences were analyzed by means of statistical parametric mapping.

SETTING

Tertiary referral center.

PATIENTS

Six volunteers with episodic migraine were recruited from advertisements in migraine newsletters. One patient was excluded because of use of preventive medication.

MAIN OUTCOME MEASURE

Brainstem activation during migraine state vs interictal state.

RESULTS

Two patients had a typical migrainous aura before the onset of the headache. All of the attacks studied fulfilled standard diagnostic criteria for migraine. Comparing the migraine scans with interictal scans, there was significant activation in the dorsal pons, lateralized to the left (small volume correction, P = .003). Activation was also seen in the right anterior cingulate, posterior cingulate, cerebellum, thalamus, insula, prefrontal cortex, and temporal lobes. There was an area of deactivation in the migraine phase also located in the pons, lateralized to the right.

CONCLUSIONS

Our findings provide clear evidence of dorsal pontine activation in migraine and reinforce the view that migraine is a subcortical disorder modulating afferent neural traffic.

Alterations of benzodiazepine receptors in type II alcoholic subjects measured with SPECT and [123I]iomazenil

OBJECTIVE

Alterations in cortical benzodiazepine receptor density have been described in postmortem and in vivo studies of alcoholic subjects. The authors attempted to replicate these findings using single photon emission computed tomography and the benzodiazepine receptor radiotracer [123I]iomazenil.

METHOD

They measured the distribution volume of benzodiazepine receptors in 11 recently detoxified patients with type II alcoholism and 11 healthy comparison subjects. The tracer was given as a bolus followed by a continuous infusion to achieve sustained binding equilibrium at the benzodiazepine receptors. Data were analyzed by using a region of interest method (regions of interest were identified on coregistered magnetic resonance imaging scans) and by a pixel-by-pixel method (distribution volume maps were analyzed with statistical parametric mapping for between-group differences).

RESULTS

The region of interest analysis revealed that alcoholic patients had significantly lower benzodiazepine distribution volume than comparison subjects in the frontal, anterior cingulate, and cerebellar cortices. Statistical parametric mapping revealed two large excursions in which the distribution volume in alcoholic patients was significantly lower than in comparison subjects: the anterior cingulate, extending into the right middle frontal gyrus, and the left occipital cortex.

CONCLUSIONS

Benzodiazepine receptor distribution volume is significantly lower in several cortical regions and the cerebellum in alcoholic subjects than in healthy comparison subjects. These results are consistent with previous reports and might indicate either a toxic effect of alcoholism on benzodiazepine receptors or a vulnerability factor for developing alcoholism.

Cerebellar contributions to motor timing: a PET study of auditory and visual rhythm reproduction

The perception and production of temporal patterns, or rhythms, is important for both music and speech. However, the way in which the human brain achieves accurate timing of perceptual input and motor output is as yet little understood. Central control of both motor timing and perceptual timing across modalities has been linked to both the cerebellum and the basal ganglia (BG). The present study was designed to test the hypothesized central control of temporal processing and to examine the roles of the cerebellum, BG, and sensory association areas. In this positron emission tomography (PET) activation paradigm, subjects reproduced rhythms of increasing temporal complexity that were presented separately in the auditory and visual modalities. The results provide support for a supramodal contribution of the lateral cerebellar cortex and cerebellar vermis to the production of a timed motor response, particularly when it is complex and/or novel. The results also give partial support to the involvement of BG structures in motor timing, although this may be more directly related to implementation of the motor response than to timing per se. Finally, sensory association areas and the ventrolateral frontal cortex were found to be involved in modality-specific encoding and retrieval of the temporal stimuli. Taken together, these results point to the participation of a number of neural structures in the production of a timed motor response from an external stimulus. The role of the cerebellum in timing is conceptualized not as a clock or counter but simply as the structure that provides the necessary circuitry for the sensory system to extract temporal information and for the motor system to learn to produce a precisely timed response.

Crossed cerebellar diaschisis. Further studies

To investigate further the topographical, clinical and temporal correlates of crossed cerebellar diaschisis (CCD) after supratentorial stroke, 55 patients suffering from a single unilateral ischaemic stroke in the carotid artery territory were studied with the quantitative oxygen-15 steady-state technique and positron tomography. Fourteen patients had one or more follow-up studies, contributing a total of 72 studies. The phenomenon of CCD, defined by depressed oxygen consumption in the contralateral cerebellum, was statistically significant in 58% of the studies. It was more prominent when the supratentorial infarct involved the internal capsule or the cortical mantle extensively, consistent with the hypothesis that it results from destruction of the corticopontocerebellar fibres. Although CCD was associated with the presence of hemiparesis, it also occurred in patients without hemiparesis and was not seen in all those with hemiparesis, suggesting that destruction of the pyramidal tract is neither necessary nor sufficient to induce CCD. Finally, CCD tended to persist over long periods of time after a stroke, pointing towards a transneuronal degeneration possibly akin to crossed cerebellar atrophy as a likely explanation for CCD. Nevertheless, CCD could be seen within hours of a stroke and sometimes disappeared within a few days, suggesting a temporal continuum between early, potentially reversible functional hypometabolism (diaschisis) and irreversible degeneration.

Positron emission tomographic imaging of the dopamine transporter with 11C-WIN 35,428 reveals marked declines in mild Parkinson's disease

Parkinson's Disease (PD) is characterized by a selective loss of nigrostriatal dopaminergic neurons that results in a marked reduction of dopaminergic nerve terminals in the striatum. Recently, 11C-WIN 35,428, a cocaine analogue that specifically labels the dopamine transporter, was developed and can be used to label dopaminergic nerve terminals in vivo by positron emission tomography. In healthy control subjects, binding of 11C-WIN 35,428 is highest in the striatum. In addition, 2 symmetrical focal areas of low binding were observed in the midbrain. The cerebellum functioned as an appropriate region for nonspecific binding. The binding of 11C-WIN 35,428 in patients with PD (Hoehn-Yahr II) was compared with that in healthy control subjects by using the (region-cerebellum)/cerebellum ratio for data acquired 34 to 82 minutes after injection. In control subjects, this ratio varied, at approximately 2, in the striatum. In patients with PD, binding in the posterior putamen was reduced by 78%, whereas the anterior putamen and the caudate nucleus showed a reduction of 59 and 39%, respectively. The reduction in 11C-WIN 35,428 binding was highest in the midbrain (84%). The high specific/nonspecific binding ratio and the pronounced reduction in binding in mild PD may permit detection of even earlier stages of PD or presymptomatic individuals with dopaminergic cell loss.

Localization of a cerebellar timing process using PET

We used positron emission tomography (PET) to localize a cerebellar timing function. Six healthy volunteers estimated time differences by comparing a test interval (defined by two tones) with a standard interval. In the timing condition, subjects lifted their right index finger if the test interval was shorter and their right middle finger if it was longer than the standard interval. In the control condition, the two intervals were identical and subjects had to alternate between lifting their index and middle fingers. We examined regional cerebral blood flow (rCBF) using the standard C15O2 inhalation technique. Comparison of control and rest conditions revealed significant increases of rCBF during the control condition in the inferior parts of the ipsilateral cerebellar hemisphere, reflecting finger movements. Comparison of timing and control conditions showed additional activations of the cerebellar vermis and hemispheres bilaterally during the timing condition, reflecting the cerebellar timing process. We conclude that the cerebellum is involved in time-critical perception ("timing"). This nonmotor task can be separated from a motor task (finger movement).

A positron emission tomography study of essential tremor: evidence for overactivity of cerebellar connections

The origin of essential tremor is unknown. Animal models have suggested that the inferior olivary nucleus may act as a tremor generator. We used positron emission tomography to study changes in regional cerebral blood flow associated with involuntary postural tremor and passive wrist oscillation in patients with essential tremor. Activation due to voluntary wrist oscillation and arm extension without tremor was studied in normal control subjects. The essential tremor group had bilaterally increased cerebellar blood flow at rest (without tremor) compared with the control group. Involuntary postural tremor was associated with further bilateral cerebellar activation, and also contralateral striatal, thalamic, and sensorimotor cortex activation. Voluntary wrist oscillation, maintained arm extension without tremor, and passive wrist oscillation were all associated with significant ipsilateral rather than bilateral cerebellar activation. We conclude that essential tremor is associated with increased bilateral cerebellar activity both at rest and during tremor.

Cerebellothalamocortical connectivity regulates penetrance in dystonia

Dystonia is a brain disorder characterized by sustained involuntary muscle contractions. It is typically inherited as an autosomal dominant trait with incomplete penetrance. While lacking clear degenerative neuropathology, primary dystonia is thought to involve microstructural and functional changes in neuronal circuitry. In the current study, we used magnetic resonance diffusion tensor imaging and probabilistic tractography to identify the specific circuit abnormalities that underlie clinical penetrance in carriers of genetic mutations for this disorder. This approach revealed reduced integrity of cerebellothalamocortical fiber tracts, likely developmental in origin, in both manifesting and clinically nonmanifesting dystonia mutation carriers. In these subjects, reductions in cerebellothalamic connectivity correlated with increased motor activation responses, consistent with loss of inhibition at the cortical level. Nonmanifesting mutation carriers were distinguished by an additional area of fiber tract disruption situated distally along the thalamocortical segment of the pathway, in tandem with the proximal cerebellar outflow abnormality. In individual gene carriers, clinical penetrance was determined by the difference in connectivity measured at these two sites. Overall, these findings point to a novel mechanism to explain differences in clinical expression in carriers of genes for brain disease.

Association of abnormal cerebellar activation with motor learning difficulties in dyslexic adults

BACKGROUND

In addition to their impairments in literacy-related skills, dyslexic children show characteristic difficulties in phonological skill, motor skill, and balance. There is behavioural and biochemical evidence that these difficulties may be attributable to mild cerebellar dysfunction. We wanted to find out whether there was abnormal brain activation when dyslexic adults undertook tasks known normally to involve cerebellar activation.

METHODS

Brain activation was monitored by positron emission tomography in matched groups of six dyslexic adults and six control adults as they carried out either a prelearned sequence or learned a novel sequence of finger movements.

FINDINGS

Brain activation was significantly lower (p<0.01) for the dyslexic adults than for the controls in the right cerebellar cortex and the left cingulate gyrus when executing the prelearned sequence, and in the right cerebellar cortex when learning the new sequence.

INTERPRETATION

The results provided direct evidence that, for this group of dyslexic adults, the behavioural signs of cerebellar abnormality reflect underlying abnormalities in cerebellar activation.

Consensus Paper: Cerebellum and Social Cognition

The traditional view on the cerebellum is that it controls motor behavior. Although recent work has revealed that the cerebellum supports also nonmotor functions such as cognition and affect, only during the last 5 years it has become evident that the cerebellum also plays an important social role. This role is evident in social cognition based on interpreting goal-directed actions through the movements of individuals (social "mirroring") which is very close to its original role in motor learning, as well as in social understanding of other individuals' mental state, such as their intentions, beliefs, past behaviors, future aspirations, and personality traits (social "mentalizing"). Most of this mentalizing role is supported by the posterior cerebellum (e.g., Crus I and II). The most dominant hypothesis is that the cerebellum assists in learning and understanding social action sequences, and so facilitates social cognition by supporting optimal predictions about imminent or future social interaction and cooperation. This consensus paper brings together experts from different fields to discuss recent efforts in understanding the role of the cerebellum in social cognition, and the understanding of social behaviors and mental states by others, its effect on clinical impairments such as cerebellar ataxia and autism spectrum disorder, and how the cerebellum can become a potential target for noninvasive brain stimulation as a therapeutic intervention. We report on the most recent empirical findings and techniques for understanding and manipulating cerebellar circuits in humans. Cerebellar circuitry appears now as a key structure to elucidate social interactions.