Physiology and pathophysiology of cortico-basal ganglia-thalamocortical loops: theoretical and practical aspects

A new theoretical framework is used to analyze functions and pathophysiological processes of cortico-basal ganglia-thalamocortical loops and to demonstrate the hierarchical relationships between various loops. All hierarchical levels are built according to the same functional principle: Each loop is a neural optimal control system (NOCS) and includes a model of object behavior and an error distribution system. The latter includes dopaminergic neurons and is necessary to tune the model to a controlled object (CO). The regularities of pathophysiological processes in NOCSs are analyzed. Mechanisms of current functional neurosurgical procedures like lesioning and deep brain stimulation (DBS) of various basal ganglia structures and neurotransplantation are described based on proposed theoretical ideas. Parkinson's disease (PD) is used to exemplify clinical applications of the proposed theory. Within the proposed theoretical framework, PD must be considered as a disease of the error distribution system. The proposed theoretical views have broad fundamental and clinical applications.

Contributions of the prefrontal cortex and basal ganglia to set shifting

Impairments of set shifting have been associated with damage to both the prefrontal cortex (PFC) and to the basal ganglia. The purpose of these experiments was to determine whether damage to the PFC was associated with shifting impairments per se or whether any switching deficits could be attributed to a reduction of working memory capacity. In contrast, shifting impairments were expected for Parkinson patients regardless of memory load, given that these patients seem to have no cognitive deficits other than when having to shift set. To vary working memory demands, a cue to the relevant dimension (letter or shape) in an odd-man-out task was presented or withheld. Pathology to prefrontal areas associated with normal aging was not linked to shifting deficits when working memory load was reduced in a comparison of older and younger adults (Experiment 1). In contrast, set-shifting abilities were still impaired for stroke patients with prefrontal damage regardless of working memory demands (Experiment 2). Parkinson patients were relatively unimpaired on this task (Experiment 2), but began to display shifting deficits when response competition was present in the display (Experiment 3).

Dissociation of habit-learning in Parkinson's and cerebellar disease

Damage to the medial-temporal region is known to result in declarative (explicit) memory deficits but nondeclarative (implicit) memory is largely unaffected by such lesions. Earlier studies have shown that some forms of implicit learning depend on cerebellar circuits but remain preserved following affections of the basal ganglia circuits. It is unknown which forms of implicit learning persist in patients with cerebellar pathology but are affected after basal ganglia lesions. Therefore, we determined if a test sensitive for habit-learning (probabilistic classification task) resulted in normal values for patients with cerebellar disease but resulted in affected results in patients with Parkinson's disease (PD). To this end, 23 patients with PD, 16 patients with familial or idiopathic cerebellar degeneration (CD), and 20 controls were tested for habit-learning. There was no impairment of patients with CD for the early learning period but there was abnormal learning in the PD group. For a later learning period, the patients with the PD showed improved performance. We conclude that the probabilistic learning task is an implicit, nonmotor learning task which is sensitive for basal ganglia pathology but remains unaffected in the case of cerebellar pathology. Such a test may be of special interest for the detection and possible neurobehavioral treatment of cognitive and motor deficits.

Segment difficulty in two-stroke movements in patients with Parkinson's disease

In the horizontal plane on a digitizer tablet, subjects made an elbow-extension, two-stroke movement away from the trunk to a first target and then on to a second target. If the two segments of the movement were executed in an integrative manner, the accuracy constraint on the first segment should have produced changes in kinematic features not only of that segment but also of the second segment. Two-stroke movements of ten Parkinson's disease (PD) patients and ten controls were studied to examine whether a high-accuracy constraint on the first segment influences the performance of the second, when the second target has either a high- or low-accuracy requirement. When the accuracy requirement of the second segment was low, both PD patients and controls showed that changing the first target size from large to small influenced the performance of not only the first segment but also the second segment. For the first segment, movement time, acceleration time, and deceleration time increased when moving to the small first target as compared to the large first target. The peak velocity and peak acceleration also decreased as the first target size decreased. For the second segment, similar patterns of kinematic changes in relation to the first segment were observed in all of these parameters. When the accuracy requirement of the second segment was high, the controls showed similar changes in the first and second segments in relation to the change of first target sizes. In contrast, the PD patients showed that the target size that defined the first movement mainly influenced the performance of that segment. Among kinematic parameters tested for the second segment, only acceleration time increased as the first target size decreased. Other parameters in general did not change, regardless of whether movement of the first segment was made to the small or large target. These results indicate that the two-stroke movements of PD patients showed little evidence that they were planned and organized in an integrative manner when there was a high-accuracy constraint imposed on the second segment. On the other hand, control subjects performed two-stroke movements in a manner that suggested the two segments were planned and organized together regardless of an accuracy constraint imposed.

Divergent findings regarding negative priming in Parkinson's disease: A comment on Filoteo et al. (2002) and Wylie and Stout (2002)

This commentary discusses divergent findings in 2 articles published in this issue of Neuropsychology. The studies used negative priming (NP) to probe the associations between basal ganglia function and cognition in Parkinson's disease (PD) and tested different predictions about NP in PD. Different NP tasks were used, and although the subject samples appeared to have similar clinical features, results were quite different. This commentary, written jointly by the authors of the 2 studies (J. V. Filoteo, L. M. Rilling, & D. L. Strayer, 2002; S. A. Wylie & J. C. Stout, 2002), describes a process by which their disparate results may be used to facilitate the design of new studies that may determine how specific features of NP tasks lead to different findings in PD. The results are a more systematic account of how task features, such as specific response demands, interact with the response selection processes that are implemented by the basal ganglia.

Neuroprotection by neurotrophins and GDNF family members in the excitotoxic model of Huntington's disease

Huntington's disease is a neurodegenerative disorder characterized by a selective degeneration of striatal projection neurons, which deal with choreic movements. Neuroprotective therapy could be achieved with the knowledge of the specific trophic requirements of these neuronal populations. Thus, the induction of endogenous trophic response or the exogenous administration of neurotrophic factors may help to prevent or stop the progression of the illness. Excitotoxicity has been implicated in the etiology of Huntington's disease, because intrastriatal injection of glutamate receptor agonists reproduces some of the neuropathological features of this disorder. Activation of glutamate receptors in the striatum differentially regulates the expression of neurotrophins, glial cell line-derived neurotrophic factor (GDNF), neurturin, and their receptors in the striatum and in its connections, cortex, and substantia nigra, showing a selective trophic response against excitotoxic insults. Transplantation of cells genetically engineered to release neurotrophic factors in the striatum has been used to study the neuroprotective effects of neurotrophin and GDNF family members in the excitotoxic model of Huntington's disease. Neurotrophins (brain-derived neurotrophic factor [BDNF], neurotrophin-3, and neurotrophin-4) protected striatal projection neurons against quinolinic or kainic acid treatment. However, GDNF family members showed a more specific action. Neurturin only protected gamma-aminobutyric acid (GABA)/enkephalinergic neurons that project to the external segment of the globus pallidus, whereas GDNF exerts its effects on GABA/substance P positive neurons, which project to the substantia nigra pars compacta and the internal segment of the globus pallidus. In conclusion, the trophic requirements of each population of striatal projection neurons are due to a complex interaction between several neurotrophic factors, such as neurotrophins and GDNF family members, which can be modified, in different pathological conditions. Moreover, these neurotrophic factors may be able to provide selective protection for basal ganglia circuits, which are affected in striatonigral degenerative disorders, such as Huntington's disease or multisystem atrophy.

The basal ganglia and disorders of movement: pathophysiological mechanisms

The basal ganglia are part of a neuronal network organized in parallel circuits. The "motor circuit" is most relevant to the pathophysiology of movement. Abnormal increment or reduction in the inhibitory output activity of basal ganglia give rise, respectively, to poverty and slowness of movement (i.e., Parkinson's disease) or dyskinesias.

Subthalamic nucleus stimulation in patients with a prior pallidotomy

OBJECT

A substantial number of patients with Parkinson disease (PD) who have undergone unilateral stereotactic pallidotomy ultimately develop symptom progression, becoming potential candidates for further surgical treatment. Bilateral subthalamic nucleus (STN) deep brain stimulation (DBS) has been shown to be effective in the treatment of a subset of patients with refractory PD. Microelectrode recording is performed to help localize the STN and guide final placement of the electrode. Potential alterations in physiological features of the STN after pallidotomy may complicate localization of this structure in this group of patients.

METHODS

Bilateral STN DBS surgery guided by microelectrode recording was performed in six patients who had undergone previous unilateral pallidotomies. Physiologically obtained parameters of the STN, including trajectory length, mean firing rate, cell number, and cell density were calculated. These data were compared with those from the side without prior pallidotomy within each patient, as well as with those from our series of 49 subthalamic nuclei explored in 26 patients who had not undergone prior pallidotomy but who underwent bilateral STN stimulator placement. In all patients, analysis of STN cellular activity on the side ipsilateral to the pallidotomy demonstrated a lower mean firing frequency than on the contralateral, intact side. The physiological features on the intact side were not significantly different from those found in our series of patients who had not undergone prior pallidotomy.

CONCLUSIONS

Physicians who perform STN surgery in patients with prior pallidotomy should be aware of the electrophysiological differences between the STN that had undergone pallidotomy and the one that had not, to avoid prolonging recording time to search for the typical STN. The implications of these findings for the current models of information processing in the basal ganglia are discussed.

[Cerebral MRI and evoked potentials in Wilson disease. Comparison of findings in patients with neurological follow-up]

Wilson's disease is caused by toxic copper accumulation, which leads predominantly to hepatic and basal ganglia damage. Characteristic findings in MRI and electrophysiologic examinations are described according to the occurrence of neurological symptoms. In the present study, 28 patients suffering from Wilson's disease (neurological type) were investigated. The results of MRI are compared with abnormalities of evoked potentials (BAEP, MSEP, T-VEP, MEP). All patients show hypodensities in the basal ganglial area (putamen and GI. pallidus) regularly combined with atrophy of the cerebrum and cerebellum in MRI. Signal abnormalities in the mesencephalic region (46% occurrence) and Nc. dentatus (36% occurrence) are combined with the other findings in variable patterns. Only slight changes are found in the pontine region. BAEP are disturbed in 71% of all cases and MSEP in 46%. Combined abnormalities of BAEP and MSEP were found in 39%. Pathological values occurred with a lower frequency in T-VEP (36%) and MEP (39%). The comparison of MRI findings with electrophysiological data done separately for each patient reveals no strong correlation between both methods. Individual MRI findings do not correspond with the patterns of disturbed evoked potentials and vice versa. Therefore we conclude that these methods, MRI and electrophysiological evaluation, supplement each other. Magnetic resonance imaging and electrophysiological evaluation should be performed simultaneously for therapy monitoring.

Clinical, imaging, lesion, and genetic approaches toward a model of cognitive control

The ability to suppress or override competing attentional and behavioral responses is a key component of cognitive processes. This ability continues to develop throughout childhood and appears to be disrupted in a number of childhood disorders (e.g., attention deficit/hyperactivity disorder and Tourette syndrome). At least two brain regions have been implicated repeatedly in these disorders--the frontal lobes and the basal ganglia. The common problem in cognitive control and overlap in implicated brain regions across disorders suggest a single underlying biological mechanism. At the same time, the distinct symptomatology observed across these disorders suggests multiple mechanisms are at play. This article presents converging evidence from clinical, neuroimaging, lesion, and genetic studies to provide a mechanistic model of cognitive control whereby the basal ganglia are involved in inhibition of competing actions and the frontal cortex is involved in representing the relevant thoughts and guiding the appropriate behaviors.

Progressive cerebral atrophy in multiple system atrophy

Nine patients with multiple system atrophy (MSA) were studied based on MRI findings of cerebral hemispheric involvement. The age at onset was 56.4+/-8.6 (mean+/-S.D.) years, duration of illness at the first MRI study 2.1+/-1.1 years, duration of illness at the last study 9.7+/-2.6 years, and the follow-up duration 7.6+/-2.3 years. Controls were 85 neurologically intact persons (60.2+/-11.1 years age). In the MRI study, measurements of the ratio of each area to the intracranial area were performed for the cerebral hemisphere, frontal, temporal and parietal-occipital lobes. A significant progression of atrophy to under the normal limit was observed in the cerebrum, frontal and temporal lobes. Besides the typical pathological lesions in MSA, five autopsied patients revealed frontal lobe atrophy with mild gliosis, mild demyelination and glial cytoplasmic inclusions (GCIs). One of these patients showed remarkable frontal lobe atrophy with degenerative changes in the cerebral cortex. We observed the involvement of the cerebral hemisphere, especially the frontal lobe.

Impaired spatial cognition and synaptic potentiation in a murine model of human immunodeficiency virus type 1 encephalitis

Injection of human immunodeficiency virus type 1 (HIV-1)-infected human monocyte-derived macrophages (MDMs) into the basal ganglia of severe combined immunodeficient mice recapitulates histopathologic features of HIV-1 encephalitis (HIVE). Here, we show that the neural damage in HIVE mice extends beyond the basal ganglia and is associated with cognitive impairment. Morris water maze tests showed impaired spatial learning 8 d after MDM injection. Moreover, impaired synaptic potentiation in the hippocampal CA1 subregion was demonstrated at 8 and 15 d. By day 15, post-tetanic, short-term, and long-term potentiation were reduced by 14.1, 29.5, and 45.3% in HIVE mice compared with sham-injected or control animals. Neurofilament (NF) and synaptophysin (SP) antigens were decreased significantly in the CA2 hippocampal subregion of HIVE mice with limited neuronal apoptosis. By day 15, the CA2 region of HIVE mice expressed 3.8- and 2.6-fold less NF and SP than shams. These findings support the notion that HIV-1-infected and immune-competent brain macrophages can cause neuronal damage at distant anatomic sites. Importantly, the findings demonstrate the value of the model in exploring the physiological basis and therapeutic potential for HIV-1-associated dementia.

Interictal and ictal EEG activity in the basal ganglia: an SEEG study in patients with temporal lobe epilepsy

PURPOSE

The interictal and ictal EEG activity in the basal ganglia in patients with temporal lobe epilepsy were studied during invasive EEG monitoring.

METHODS

Eight epilepsy surgery candidates, each with a proven mesiotemporal seizure-onset zone, participated in the study. We used two invasive EEG methods to determine the seizure-onset zone. In both methods, diagonal electrodes were targeted into the amygdalohippocampal complex via a frontal approach and were passed through the basal ganglia with several leads. We analyzed 16 partial epileptic seizures, four of which became secondarily generalized.

RESULTS

No epileptic interictal or ictal discharges were noticed in the basal ganglia. The interictal activity in the basal ganglia was a mixture of low-voltage beta activity and medium-voltage alpha-theta activity. When the ictal paroxysmal activity remained localized to the seizure-onset zone, the activity of the basal ganglia did not change. The spread of epileptic activity to other cortical structures was associated with the basal ganglia EEG slowing to a theta-delta range of 3-7 Hz. This slowing was dependent on the spread of ictal discharge within the ipsilateral temporal lobe (related to the investigated basal ganglia structures); alternatively, the slowing occurred in association with the regional spread of ictal activity from the mesiotemporal region to the temporal neocortex contralaterally to the investigated basal ganglia. Secondary generalization was associated with a further slowing of basal ganglia activity.

CONCLUSIONS

The basal ganglia do not generate specific epileptic EEG activity. Despite the absence of spikes, the basal ganglia participate in changing or reflect changes in the distribution of the ictal epileptic activity.

Defective cortical drive to muscle in Parkinson's disease and its improvement with levodopa

We recorded whole-scalp magnetoencephalographic (MEG) signals simultaneously with surface electromyographic (EMG) activity from eight patients with Parkinson's disease after withdrawal and reinstatement of treatment with levodopa. Variations were seen in the coherence between the forearm extensor EMG and the MEG signal originating near or in the hand region of the primary motor cortex. As a group, the parkinsonian patients withdrawn from levodopa showed a reduction in the coherence at 15-30 Hz and 35-60 Hz, and a further three untreated patients had abnormally strong MEG-EMG coherence at 5-12 Hz compared with when medicated or with eight healthy age-matched control subjects. We conclude that the basal ganglia have a specific effect on the temporal organization of motor cortical activity during voluntary tonic contraction. Abnormalities in this aspect of basal ganglia function may directly contribute to bradykinesia and weakness in Parkinson's disease.

Evidence of thalamic disinhibition in patients with hemichorea: semiquantitative analysis using SPECT

OBJECTIVES

Hemichorea sometimes occurs after lesions that selectively involve the caudate nucleus, putamen, and globus pallidus. Some reports have hypothesised that the loss of subthalamic nucleus control on the internal segment of the globus pallidus, followed by the disinhibition of the thalamus may contribute to chorea. However, the pathophysiology is poorly understood. Therefore, clinicoradiological localisation was evaluated and a comparison of the haemodynamic status of the basal ganglia and thalamus was made.

METHODS

Six patients presenting with acute onset of hemichorea were assessed. Neuroimaging studies, including MRI and SPECT examinations in addition to detailed biochemical tests, were performed. A semiquantitative analysis was performed by comparing the ratio of blood flow between patients and normal controls. In addition, the ratio of perfusion asymmetry was calculated as the ratio between each area contralateral to the chorea and that homolateral to the chorea. The comparison was made with a two sample t test.

RESULTS

The causes of hemichorea found consisted of four cases of acute stroke, one non-ketotic hyperglycaemia, and one systemic lupus erythematosus. Brain MRI indicated lesion sites in the contralateral putamen, globus pallidus, caudate nucleus, and subthalamic nucleus. A significant decrease in the ratio of blood flow in the basal ganglia contralateral to the chorea and a significant increase in the thalamus was found when comparing the perfusion asymmetries, which were calculated as the ratio of cerebral blood flow (CBF) for each region to that in the homolateral occipital area (p<0.05).

CONCLUSION

An alteration in CBF in both the contralateral thalamus and basal ganglia reflect the loss of pallidal inhibitory input from the pallidum to the thalamus. This change in CBF may be one of epiphenomena, which implicates an occurrence of hemichorea in humans.

Separating storage from retrieval dysfunction of temporal memory in Parkinson's disease

Dysfunction of the basal ganglia and the brain nuclei interconnected with them leads to disturbances of movement and cognition exemplified in Parkinson's disease (PD) and Huntington's disease, including disordered timing of movements and impaired time estimation. Previous research has shown that whereas striatal damage in animals can result in the loss of temporal control over behavior, dopaminergic deregulation in the human striatum associated with PD distorts the memory for time. Here we show a dissociation between deficits in storage (writing to) and retrieval (reading from) temporal memory processes. Both are dysfunctional in PD and sensitive to treatment with dopaminergic agents, but produce dissimilar distortions. When time intervals are stored in memory while the subjects are dopamine depleted, the process is slowed, leading to overestimation of two different time intervals. Conversely, when retrieval occurs in a dopamine-depleted state, interference or coupling occurs between two remembered time intervals, producing overestimation of the shorter and underestimation of the longer one. Whether those two separable patterns of dysfunction in storing and retrieving temporal memories rely on distinct neural networks within the basal ganglia and/or their cortical targets remains to be answered by future research.

Choreoathetosis, hypothyroidism, and pulmonary alterations due to human NKX2-1 haploinsufficiency

The occurrence of neurological symptoms and developmental delay in patients affected by congenital hypothyroidism (CH) has been attributed to the lack of thyroid hormone in the developing CNS. Accordingly, after the introduction of neonatal screening programs for CH, which allowed early and adequate treatment, an almost normal outcome for most CH patients could be achieved. However, a few patients did not reach this favorable outcome despite early and adequate treatment. Here we describe five patients with variable degrees of CH who suffered from choreoathetosis, muscular hypotonia, and pulmonary problems, an association of symptoms that had not been described before this study. Since this clinical picture matched the phenotype of mice targeted for deletion of the transcription factor gene Nkx2-1, we investigated the human NKX2-1 gene in these five patients. We found heterozygous loss of function mutations in each of these five patients, e.g., one complete gene deletion, one missense mutation (G2626T), and three nonsense mutations (2595insGG, C2519A, C1302A). Therefore, the unfavorable outcome in patients with CH, especially those with choreoathetosis and pulmonary symptoms, can be explained by mutations in the NKX2-1 gene rather than by hypothyroidism. Moreover, the association of symptoms in the patients with NKX2-1 mutations points to an important role of human NKX2-1 in the development and function of thyroid, basal ganglia, and lung, as already described for rodents.

Ictal hyperperfusion patterns according to the progression of temporal lobe seizures

OBJECTIVE

To investigate ictal hyperperfusion patterns during semiologic progression of seizures, the authors performed SPECT subtraction in 50 patients with temporal lobe epilepsy (TLE).

METHODS

The patients were categorized into five groups according to semiologic progression during ictal SPECT (Group 1 had aura only; Group 2 had motionless staring with or without aura; Group 3 had motionless staring and then automatism with or without aura; Group 4 had motionless staring and then dystonic posturing with or without aura and automatism; and Group 5 had motionless staring, automatism, then head version and generalized seizures with or without aura and dystonic posturing).

RESULTS

In Group 1, three patients showed ipsilateral temporal hyperperfusion and two had bilateral temporal hyperperfusion with ipsilateral predominance. In Group 2, three patients (42.9%) showed bilateral temporal hyperperfusion with unilateral predominance and four patients (57.1%) revealed insular hyperperfusion of epileptic side. In Group 3, 15 patients (88.2%) showed bilateral temporal hyperperfusion with unilateral predominance and 12 patients (70.6%) revealed insular hyperperfusion. In Group 4, 11 patients (84.6%) showed basal ganglia hyperperfusion on the opposite hemisphere to the side of the dystonic posturing. In Group 5, there were multiple hyperperfusion areas in the frontal, temporal, and basal ganglia regions. However, the injection times of radiotracer in five groups were relatively short and similar.

CONCLUSIONS

The semiologic progression in TLE seizures were related to the propagation of hyperperfusion from ipsilateral temporal lobe to contralateral temporal lobe, insula, basal ganglia, and frontal lobe. Not only the radiotracer injection time but also semiologic progression after the injection was important to determine hyperperfusion pattern of ictal SPECT.

[Rapid-eye-movement sleep disorders in Parkinson's disease]

During the past 10 years, there has been an increasing interest in the study of rapid-eye-movement (REM) sleep in neurodegenerative diseases and more particulary in Parkinson's disease (PD). This interest is justified by the strong association observed between these diseases and REM sleep behavior disorder (RBD). In the first section of this paper, a critical review of the literature on the presence of REM sleep disorders in PD is presented. Studies that show an association between PD and RBD are reviewed. Studies that report the presence of other REM sleep disorders in PD (short latency, abnormal length and/or proportion of REM sleep, increasing occurrence of hallucinations) are then discussed. Limitations of the criteria proposed by Rechtschaffen et Kales (1968) for the quantification of REM sleep are also presented. Some authors believe that dopaminergic (DA) agents used in the treatment of PD (levodopa, bromocriptine, pergolide, pramipexole and selegiline) could be a responsable factor for the occurence of REM sleep disorders observed in this disease. The literature concerning the impact of these DA agents on human REM sleep is therefore critically reviewed. It is concluded that DA agents cannot explain on their own the presence of REM sleep disorders in PD. Other causes, among which the disturbance of some neurochemical systems linked to the neuropathological process of the disease, must be considered in order to explain these REM sleep disorders. In the second section of this paper, we present the different pathophysiological hypotheses proposed to explain REM sleep disorders in PD, such as a dysfunction of the cholinergic, noradrenergic, serotonergic, dopaminergic or GABAergic neurons. Emphasis is placed on the role of cholinergic neurons of the pedunculopontine and laterodorsal tegmental nuclei, structures shown to be particularly impaired in PD. Neurophysiological, neuroanatomical and neuropharmacological studies demonstrate that these neurons are strongly implicated in the different REM sleep parameters (muscular atonia, electroencephalographic desynchronisation, ponto-geniculo-occipital spikes). Finally, future research directions are proposed.

Neuroengineering models of brain disease

The techniques of computational simulation have begun to be applied to modeling neurological disease and mental illness. Such neuroengineering models provide a conceptual bridge between molecular/cellular pathology and cognitive performance. We consider models of Alzheimer's disease, Parkinson's disease, and schizophrenia. Each of these diseases involves a disorder of neuromodulation coupled with underlying neuronal pathology. Parallels arising between these models suggests that a common set of computational mechanisms may account for functional loss across a spectrum of brain diseases. In particular, we focus on attractor-based network dynamics and how they arise from neural architectures, on mechanisms for linking sequences of attractor states and their role in cognition, and on the role of neuromodulation in controlling these processes. These studies suggest new approaches to understanding the forebrain circuits underlying cognition, and point toward a new tool for dissecting the pathophysiology of brain disease.

Neuropsychiatry of the basal ganglia

This review aims to relate recent findings describing the role and neural connectivity of the basal ganglia to the clinical neuropsychiatry of basal ganglia movement disorders and to the role of basal ganglia disturbances in "psychiatric"' states. Articles relating to the relevant topics were initially collected through MEDLINE and papers relating to the clinical conditions discussed were also reviewed. The anatomy and connections of the basal ganglia indicate that these structures are important links between parts of the brain that have classically been considered to be related to emotional functioning and brain regions previously considered to have largely motor functions. The basal ganglia have a role in the development and integration of psychomotor behaviours, involving motor functions, memory and attentional mechanisms, and reward processes.

Rhythmic movement disorder: polysomnographic study and summary of reported cases

Rhythmic movement disorder (RMD) is classified as a sleep-wake transition disorder. However, some RMD patients show rhythmic movements during rapid-eye-movement (REM) sleep, during which muscle activity is completely absent. In order to determine the sleep stages in which episodes of RMD occur, we investigated two children with RMD by means of polysomnography, and also summarized the polysomnographic reports on patients with RMD. We also quantified the REM sleep atonia in our patients using the tonic and phasic inhibition indices (TII and PII). In addition, to examine the involvement of the basal ganglia in RMD patients, we studied the frequency of gross movements (GMs) during sleep in each sleep stage. Both patients showed rhythmic movements in all sleep stages, i.e. including REM sleep. Few rhythmic movements occurred during sleep-wake transition periods. Both patients showed normal TII and PII scores as well as a normal pattern for the sleep stage-dependent modulation of GMs during sleep. Eighteen of the 33 reported RMD patients, including ours, experienced episodes during REM sleep, while the other 15 patients had no episodes during REM sleep. Among the 18 patients who had episodes during REM sleep, eight experienced the episodes exclusively during REM sleep. It is unlikely that the neuronal mechanisms that underlie RMD episodes were the same in the 15 patients who had no RMD episodes during REM sleep and the eight who had them only during REM sleep. We propose that RMD can be divided into several subgroups according to the differences in the underlying neuronal mechanisms.