Bioelectrical impedance analysis (BIA) for body composition has been based on the volume conductor model that results in the mathematical relationship Ht2/R approximately FFM, where Ht is body height, R is whole body resistance or impedance, and FFM is fat-free mass. Although this relationship exists in the human subject, its strength and usefulness have been subject to conflicting reports. This study reassessed the theory and methodology of BIA and describes a new technique for measuring segmental impedance that may resolve some major limitations associated with the current whole body impedance methodology. By use of data from 200 adult subjects, a new theory and methodology for BIA were developed in four steps: 1) a rationale was presented for replacing the Ht2/R model by one based on electrical resistivity, 2) a practical six-electrode technique for segmental BIA that uses only peripheral electrode sites was described, 3) prediction equations for fat weight based on the new segmental BIA technique were developed, and 4) prediction equations for fat distribution, a potential new use of impedance methodology, were developed using a new measure of fat distribution, the impedance index.

Understanding of the electrophysiologic principles of radiofrequency lesion making is necessary to ensure reliable results in surgical procedures using this technique. A radiofrequency lesion is produced by tissue electrocoagulation. lts method of formation and factors affecting heat generation and loss are discussed. Guidelines for making radiofrequency lesions, based on electrophysiologic principles, are outlined.

A prospective review of 75 of 190 parkinsonian patients undergoing unilateral thalamotomy was displayed with a computer graphics technique examining three equal consecutive groups from the pre-, early, and late L-dopa eras. Histograms for average function and scattergrams of individual patient''s performance preoperatively and up to 2 years postoperatively were prepared. No ipsilateral effects or consistent iatrogenic deterioration of any function were identified. 2 years after surgery, 82% had no tremor in the contralateral fingers or hand and 7% had almost no tremor; contralateral tremor elsewhere was infrequent. Rigidity and manual dexterity improved less strikingly, the latter only reflecting abolition of tremor; locomotion, speech, facial movement and handwriting did not improve. There was no mortality, but 8% had persistent significant complications. VIM thalamotomy remains the treatment of choice for severe drug-resistant parkinsonian tremor.

1. Responses suggesting activation of the vestibular system, elicited by electrical stimulation of the human thalamus during 22 routine stereotaxic neurosurgical procedures, were examined in a retrospective study to determine the possible existence of vestibulothalamo-cortical projections in man. 2. Such responses were most frequently described as sensations of movement through space and were associated with two distinct vestibulothalamic projections: a) an anterior relay was situated ventral to the medial lemniscus, passing lateral to the red nucleus and dorsal to the subthalamic nucleus prior to terminating in the nucleus ventrointermedius (Vim) (comparable to VPLo in primates); b) a posterior relay associated with the auditory pathway (lateral lemniscus and brachium of the inferior colliculus) projected to the medial geniculate body. 3. The production of sensations of motion in conscious patients by stimulating areas that are similar to those reported constituting vestibulothalamic pathways in cats and primates implies a distinct primary sensory cortical projection for processing information from the vestibular receptors pertaining to the recognition of spatial movements.

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