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The authors describe preliminarily an implantable bio-stimulating device for stimulation of peripheral nerves and the central nervous system. The receiving unit is totally implantable. The system works on radiofrequency transcutaneous coupling across the skin. This new telestimulating device has a wider band width and more flexibility than units currently being used in neurosurgery. The unit is independent of coupling efficiency and is designed to accept any symmetrical or nonsymmetrical waveform within limits listed in this presentation. The unit is designed so as to provide this waveform as a constant current signal at the output of the receiver.

In 1968 BRINDLEY and LEWIN reported their implantation of an 80-elec-trode array activated by radiofrequency transmission on the visual cortex of a blind nurse (3). The pattern of phosphenes seen by this patient when the electrodes were stimulated suggested that technical refinements of this technique might enable blind persons to not only move about in their environments but even to read.

Investigators engaged in studying the effects of electrical stimulation on the blood-brain barrier (BBB) and brain usually find it necessary to fabricate the electrodes and electrode arrays required in their acute and chronic experiments. Techniques for fabricating spring-mounted, concentric and salt-bridge electrodes and electrode arrays are described in this report.

A major concern in the use of neural prostheses is whether electrical stimualtion can cause irreversible damage to neurons. The Neural Damage Model was devised to study the problem and to provide guidlines. The cerebral cortex of cats was stimulated continuously for 36 hours with balanced, biphasic waveforms. The charge per phase, charge density and current density were varied in 16 separate tests. Of these stimulus parameters the charge per phase was more closely correlatable with neuronal damage than charge density and current density. Furthermore, the findings in this study suggest that current flow is more important than electrochemical reactions in causing neural damage. Correlation between blood-brain barrier (BBB) breakdown and neuronal damage was valid only in the group of animals sacrificed immediately following stimulation. The BBB is restored within one month following electrical injury. Convulsive seizures occurred in all but one of the animals during electrical stimulation. A technique for localizing the electrode sites at autopsy and in the microscopic sections is described.

The ultrastructural response of tissues of the cat's central nervous system to chronic electrical stimulation with various parameters has been evaluated at four and a half days post stimulation. Cellular alterations included widespread cytoplasmic vacuolations, architectural derangement and disruption of plasmalemma and other membranes. Lipid inclusions and dense crystalline bodies were prominent in astrocyte-like phagocytic cells in the more severe lesions. Despite endothelial damage in brain parenchymal capillaries, significant extravasation of horseradish peroxidase was not observed. The ultrastructural damage observed following electrical stimulation varied from mild to severe. Although none of the parameters tested was found to be "safe" for clinical applications, it should be emphasized that the stimulations delivered in the present study were essentially continuous.

Acute and chronic studies of the effects of electrical stimulation on the blood-brain barrier (BBB) of the cat cerebral cortex are reported. The findings emphasize the importance of avoiding direct-coupled, monophasic waveforms in stimulating nervous tissue. Biphasic waveforms with balanced charges in each half-wave of the stimulating pulse can be used for up to 36 hours of continuous stimulation if the charge per phase (Q/ph) does not exceed 0.45 microcoulombs. Charge density (QD) is also an important parameter. When stimulating in the bipolar mode, BBB breakdown will occur first beneath the smaller electrode of the pair. Following electrical injury, the BBB will be partially restored within one week, and, with rare exceptions, be completely intact after one month.

Head injury in infants and young children may produce lesions that are relatively unique for this age group. The uniqueness is generally due to the structural immaturity of the skull, meninges and brain."Derby-hat" and diastatic fractures are common in this age group. Spurious meningoceles result from tearing of the dura which is closely adherent to the skull. The syndrome of "delayed" concussion is more commonly manifested in children. Extradural and subdural hemorrhage may develop from lacerations of the major venous sinuses. A classical extradural hematoma may occur in the absence of fracture across meningeal arterial channels. The management of patients with head injury has been improved by the more frequent use of tracheotomy, hypothermic techniques and drugs of the "lytic cocktail." Solutions of urea in 10 per cent invert sugar are administered intravenously to control cerebral edema in selected patients.

The procedure of hypophysectomy may offer some hope in metastatic carcinoma of the breast. Certainly further clinical trial is indicated. The anterior intracranial approach through the sphenoid sinus was used in eight cases. It offers a technically easier route by which to perform hypophysectomy. The immediate risk of operation does not appear to be too great. Caution must be urged against delaying this procedure until the patient is in a terminal condition.

Intractable pain in the neck and upper extremity is frequently radicular in character and mechanical in origin. Rupture of a cervical intervertebral disc is the most common cause. Diagnosis and localization are more difficult in the cervical than in the lumbar region. Pantopaque myelogram should be considered only as a mean of localization. Operation should be preceded by a thorough trial of conservative treatment.

Despite satisfactory preoperative angiographic demonstration of intracranial aneurysms, the surgeon is often confronted at operation with lesions that are unsuitable for clipping or ligating. In the experience of the authors, a rapidhardening silicone rubber preparation has served to provide an immediately effective means of confining and reinforcing the walls of certain of these lesions. The plastic barrier formed by this material envelops the aneurysm without interfering with the patency of parent vessels, thus obviating the circulatory deficits imposed by trapping measures. Three cases are presented, illustrating the techniques and principles involved.