Does essential tremor originate in the cerebral cortex?

• Published in: The Lancet (British edition) 2001-02, Vol.357 (9255), p.492-494
• Main Author: McAuley, JH
• Format: Article
• Language: English
• Subjects: Animal models; Animals; Brain; Cerebral Cortex - physiopathology; Electroencephalography; Electromyography; Essential Tremor - etiology; Extremities; Humans; Lesions; Neurological disorders; Neurology; Parkinson's disease
• ISSN: 0140-6736; 1474-547X
• DOI: 10.1016/S0140-6736(00)04036-8

In fact, the bulk of the evidence from recordings in animal models and from stereotaxic work in patients points not to the cortex but to two other potential sites for the origin of essential tremor. First, an oscillation similar to essential tremor has been shown to arise through olivocerebellar circuits.' Oscillatory activity in normal animals may result from synchronisation via cross-linking between olivary neurons mediated by gamma-aminobutyric acid.3 Perhaps in essential tremor, an amplification of this tendency, whether by a channelopathy or a specific structural synaptic defect, might result in an oscillation that becomes distributed more widely through the CNS and ultimately to the periphery as tremor. Second, the thalamus has a tendency to generate a 6 Hz range tremor through the behaviour of low threshold Ca^sup 2+^ conductances;4 the loss of normal inputs from the basal ganglia and cerebellum may release this tendency and has been proposed to result, respectively, in Parkinson's disease and cerebellar intention tremors.5 Essential tremor might arise through some other loss of input or from an abnormality of the oscillatory tendency itself. Even if tremor does not arise from the thalamus, reciprocal loop connections between thalamic nuclei and the medial thalamus may act to amplify transmitted oscillations.4 CNS loops may well turn out to be more important than CNS nuclei in generating oscillatory activity. For example, experimental lesions in various sites that might interrupt CNS loops are effective in ameliorating oscillations resembling those of essential tremor.2 The ventro-- intermediate nucleus of the thalamus is the preferred site for producing lesions stereotactically because it maximises the interruption of these loops while minimising asssociated functional deficit, rather than because it is the specific site or orgin of tremor.