Basal Ganglia Thalamus Research Articles

Pathophysiology of chorea and bradykinesia in Huntington's disease

This article reviews the neurophysiological abnormalities described in Huntington's disease. Among the typical features of choreic movements are variable and random patterns of electromyographic (EMG) activity, including cocontraction of agonist and antagonist muscles. Studies of premotor potentials show that choreic movements are not preceded by a Bereitschaftspotential, therefore demonstrating that choreic movement is involuntary. Early cortical median-nerve somatosensory-evoked potentials have reduced amplitudes and the reduction correlates with reduced glucose consumption in the caudate nucleus. Long-latency stretch reflexes evoked in the small hand muscles are depressed. These findings may reflect failed thalamocortical relay of sensory information. In Huntington's disease, the R2 response of the blink reflex has prolonged latencies, diminished amplitudes, and greater habituation than normal. These abnormalities correlate with the severity of chorea in the face. Patients with Huntington's disease perform simple voluntary movements more slowly than normal subjects and with an abnormal triphasic EMG pattern. Bradykinesia is also present during their performance of simultaneous and sequential movements. Eye movements show abnormalities similar to those seen in arm movements. In Huntington's disease, arm movement execution is associated with reduced PET activation of cortical frontal areas. Studies using transcranial magnetic stimulation show that patients with Huntington's disease have normal corticospinal conduction but some patients have a prolonged cortical silent period. Bradykinesia results from degeneration of the basal ganglia output to the supplementary motor areas concerned with the initiation and maintenance of sequential movements. The coexisting hyperkinetic and hypokinetic movement disorders in patients with Huntington's disease probably reflect the involvement of direct and indirect pathways in the basal ganglia-thalamus-cortical motor circuit.

Delayed Unilateral Post-Traumatic Tremor: Localization Studies Using Single-Proton Computed Tomographic and Magnetic Resonance Spectroscopy Techniques

We present the case of a 46-year-old former U.S. Marine who developed unilateral dystonic tremor responsive to anticholinergic medications 13 years after contralateral, combat-induced head trauma. Although conventional neuroimaging techniques showed normal brain anatomy, single-proton computed tomographic scans demonstrated hypometabolism ipsilateral to the area of old trauma. Proton echoplanar spectral imaging demonstrated decreased signal in this same area on creatine imaging, which normalized on anticholinergic medication. Choline imaging on medication showed a signal void in the clinically suspected basal ganglia-thalamus region. We believe that these results indirectly suggest a trans-synaptic origin of the patient's movement disorder.

Analysis of tissue and arterial blood temperatures in the resting human forearm. 1948.

Analysis of tissue and arterial blood temperatures in the resting human forearm. 1948.

Subcortical Input to the Smooth and Saccadic Eye Movement Subregions of the Frontal Eye Field inCebusMonkey

We have recently identified two functional subregions in the frontal eye field (FEF) of the Cebus monkey, a smooth eye movement subregion (FEFsem) and a saccadic subregion (FEFsac). The thalamic input to these two subregions was studied and quantified to gain more information about the influence of the cerebellum and basal ganglia on the oculomotor control mechanisms of the cerebral cortex. A recent study using transneuronal transport of virus demonstrated that there are neurons in the basal ganglia and cerebellum that project to the FEFsac with only a single intervening synapse (Lunch et al., 1994). In the present study, we concentrated on the thalamic input to the FEFsem to define possible basal ganglia-thalamus-cortex and cerebellum-thalamus-cortex channels of information flow to the FEFsem. We localized the functional subregions using low threshold microstimulation, and retrogradely transported fluorescent tracers were then placed into the FEFsem and FEFsac. The neurons that project to the FEFsem are distributed in (1) the rostral portion of the ventral lateral nucleus, pars caudalis, (2) the caudal portion of the ventral lateral nucleus, pars caudalis, (3) the mediodorsal nucleus, (4) the ventral anterior nucleus, pars parvocellularis, and (5) the ventral anterior nucleus, pars magnocellularis. In contrast, the large majority of neurons that project to the FEFsac are located in the paralaminar region of the mediodorsal nucleus. The FEFsac and FEFsem thus each receive neural input from both basal ganglia-receiving and cerebellar-receiving cell groups in the thalamus, but each receives input from a unique combination of thalamic nuclei.

Case report: Primary malignant rhabdoid tumour of the brain

A 2-year-old Omani boy presented with a one week history of headache and vomiting. On examination he had a right third cranial nerve palsy but normal fundi. His haemoglobin showed evidence of sickle cell trait. A lumbar puncture was carried out and showed a normal CSF. The patient was then transferred to our hospital for a computed tomography (CT) scan. Scans pre and post-contrast (Figs 1 & 2) revealed a well marginated, lobulated hyperdense mass that enhanced with contrast. It involved the left temporal and parietal lobes, extended into the deep frontal lobe and the thalamic-basal ganglia regions. No cystic change or calcification was seen. There was vasogenic oedema of the white mat ter posterolaterat to the mass and marked compression of the ipsilateral ventricle with midline shift to the contralateral side. No bone destruction was seen. The clinical diagnosis at this stage was a sarcoma or a glioma with unusual ly high attenuation. A craniotomy was performed. I n spite of the enhancement noted on CT, the mass was surprisingly hypovascular, greyish-white in colour with soft consistency and was attached to the dura. It did not extend through the dura and was not related to any muscle. The mass was resected as far as possible. Microscopic examination showed tumour tissue rich in undifferentiated cells with round to oval nuclei, vesicular nuclei, nucleoli and mitotic activity. Some cells had ample eosinophylic cytoplasm, and the turnout was initially thought to be a rhabdomyosarcoma. Fur ther examination with special stains showed focal keratin positivity, diffuse vimentin positivity but no synaptophysin positivity (Fig. 3), and this suggested that it was a malignant rhabdoid tumour. Ultrasound of the abdomen was then carried out to find a primary site. The kidneys were found to be normal. Radiation therapy was given two weeks after surgery, but the boy died two mon ths after presentation. Post-mortem examination was not carried out. examination it has the appearance of a rhabdomyosarcoma, but further light microscopic, immunohistochemical and ultrastructural data provides evidence that malignant rhabdoid tumour should be classed as a separate neoplasm. The histogenesis remains a source of speculation and it is now considered unrelated to Wilms tumour or rhabdomyosarcoma [3]. The tumour found in our patient had a morphology and immunohistochemical profile matching that described in malignant rhabdoid tumour. It was vimentin positive and keratin positive for groups of cells and negative for desmin and myoglobin [3], unlike the rhabdomyosarcoma which should show reactions with antibodies against glial fibrillary acid protein, neurofilament or synaptophysin. A hyperdense lesion on CT as in this case could be a childhood meningioma (sarcoma) especially with its dural base. The CT appearance then is a uniform intrinsic increased density lesion, accompanied by flecks of calcification. The tumour is generally well circumscribed, rounded, ovoid or lobulated and enhances with contrast uniformly. Metastases are usually multiple.

Neurobiologia do parkinsonismo: I. substratos neurais e neuroquímica dos gânglios basais

Movement disorders, in general, are characterized by a breakdown in the integrated coordination of posture and motion by multiple brain and muscular systems. In the expression of parkinsonism, in particular, critical and altered structures such as substantia nigra, appear to be related to the cortex-basal ganglia and thalamus-basal ganglia sub-circuits.

Factors that affect the uptake of ammonia by the brain: the blood-brain pH gradient

The brain uptake index (BUI) for [13N]ammonia was measured in 7 areas of the rat brain at 8 different pH values ranging from 6.58 to 7.73. When the regional BUI was plotted as a function of the pH of the test bolus, a significant linear correlation was found for each region (P < 0.001). The highest slope was observed in the thalamus-basal ganglia complex (0.392 ± 0.018) (S.D.), and the lowest in the ventral pons (0.143 ± 0.011). These studies indicate that the brain-blood pH gradient plays a major role in determining the forward flux of ammonia from the blood into the brain in the physiological pH range. Regional differences in the slope may be due to metabolic factors. This pH effect may be important in clinical conditions characterized by hyperammonemia such as hepatic encephalopathy, and in the interpretation of [13N]ammonia emission tomographic images of the brain.