ISSN:0006-8977    

DOI:10.1159/000125809

出版商:S. Karger AG    

年代:1977

数据来源: Karger

ISSN:0006-8977    

DOI:10.1159/000124597

出版商:S. Karger AG    

年代:1977

数据来源: Karger

摘要:

The objectives of several neural prostheses which are currently being investigated are discussed along with some of the principal research questions. Future neural prostheses may extend mans'' capabilities beyond that which is considered normal function.

ISSN:0006-8977    

DOI:10.1159/000124610

出版商:S. Karger AG    

年代:1977

数据来源: Karger

摘要:

A conservative requirement for ''safe'' electrical stimulation is the absence of chemical changes adjacent to the stimulating electrodes. In electrochemical terms, this means that charge transfer processes producing dissolved species must be avoided. With this restriction, the aim of this study has been to establish the maximum charge density that can be passed during each half of a biphasic stimulation pulse. Possible dissolved species resulting from faradaic reactions at the Pt/saline interface include chloride oxidation products (ClO-, ClO3-, etc.) H+ or OH- ions and Pt ions. For balanced biphasic pulses, neither Cl- oxidation nor pH shifts appear likely to constitute significant problems and the most difficult problem to avoid appears to be metal dissolution. Pt dissolution has been monitored by UV spectrophotometric analysis and, because protein interferes with the analysis, the tests were run in inorganic saline solution. Results are presented in the form of nomographs which relate Pt dissolution to the charge density per pulse and the current density. Specific recommendations for minimizing Pt dissolution include the use of platinized electrodes, the restriction of charge densities per pulse to ≤300 µC/geom cm2 of electrode surface, and preferably the use of cathodic-first biphasic puls

ISSN:0006-8977    

DOI:10.1159/000124611

出版商:S. Karger AG    

年代:1977

数据来源: Karger

摘要:

The results of evaluation of the corrosion response of Pt, Au, Rh, Ir, Pt-10% Ir and Pt-10% Rh electrodes subjected to bipolar current pulses of 0.1 and 1.0 A/geom. cm2 in a simulated neural environment are reported. The criteria for evaluation include the extent and morphology of material removal and corrosion product formation. The chemical changes on the electrode surface and in the test electrolyte are also evaluated. Modified potentiographic methods were developed which monitor interface conditions of the electrodes during chronic, long-term bi-phasic current passage. Under the test conditions established by the neural model, evaluation of the corrosion response of the candidate electrode materials shows that Rh was moderately damaged at 1.0 A/geom. cm2, while the remaining test electrodes were severely damaged at this current density. While Rh, Ir and Au exhibit corrosion resistance at 0.1 A/geom. cm2, damage to all of the test materials preclude their use in any long-term chronic neural prosthetic implant under the simulated stimulation parameters of the tests. The relative corrosion resistance of the test electrode materials is related to the adherence and coherence of the corrosion product produced on the electrode surface during the first few hundred hours of stimulation. Analysis of the voltage response of the electrodes to current passage provides a means of monitoring the nucleation and growth of the corrosion product.

ISSN:0006-8977    

DOI:10.1159/000124612

出版商:S. Karger AG    

年代:1977

数据来源: Karger

摘要:

Macaques were trained to respond to electrical excitation applied through electrodes permanently implanted within or upon striate cortex. Threshold current for the animal to detect this stimulation was highly consistent from day to day and, in the absence of tissue encapsulation of the electrodes or deliberately inflicted damage, remained stable indefinitely, 38 months in the longest case so far. Stimulating continuously for 1–8 h, however, produces an elevation of threshold, which may be permanent or temporary, depending upon a variety of conditions. A major cause of such injury is the hydrolysis commonly occurring consequent to passage of low-level currents between solutions and metal electrodes. Even when the hydrolytic reaction is eliminated by restricting the level of electrode polarization or by using capacitative stimulation with tantalum pentoxide electrodes, a rise in threshold often still occurs with protracted stimulation. With proper control in some instances, however, effective stimulation at 2–10 times the threshold level could be maintained indefinitely without apparent injury, e.g. in a blind monkey having a threshold of 290 µAthat could respond immediately to an 80 µA diminution in 580- µA,0.2-msec stimulus pulses which had been applied steadily for 1 h at

ISSN:0006-8977    

DOI:10.1159/000125575

出版商:S. Karger AG    

年代:1977

数据来源: Karger

摘要:

We have recorded from single neurons in the visual cortex of the cat while stimulating the cortical surface with the same type of electrodes and the same parameters of stimulation which have produced phosphenes in conscious man. Parameters of stimulation which will permit excitation of single cortical neurons with little risk of producing afterdischarges are described. The patterns of excitation of single neurons during surface stimulation and the effects of stimulation on neuroglial cells have also been studied. Surface stimulation also produced marked alterations in cortical excitability as tested with visually presented stimuli. Mechanisms by which single neurons are excited by surface stimulation are also considered.

ISSN:0006-8977    

DOI:10.1159/000125576

出版商:S. Karger AG    

年代:1977

数据来源: Karger

摘要:

The lateral and suprasylvian gyris of cats have been stimulated anodically by surface electrodes for a total of 40 h by biphasic square waves. Peak currents were ±6.0 mA or 1.0 mA,·to peak. Control electrodes were never stimulated. Electrode materials were low-temperature isotropic carbon and metals (Rh, Pt, Au). Reductions in tissue impedance quickly followed the onset of stimulation. The impedance change was related to stimulus current and to the incidence of motor seizures but not clearly to the electrode material. Utilizing concentric electrodes, the impedance change was not localized to the stimulating electrode – tissue interface. No protection from stimulation-associated impedance modifications was provided by the systemic administration of a material of high osmolarity (Mannitol) but the usual impedance decrease was not seen after systemic administration of a glucocortic

ISSN:0006-8977    

DOI:10.1159/000125577

出版商:S. Karger AG    

年代:1977

数据来源: Karger

摘要:

The use of implantable neural prostheses activated by radiofrequency transmission requires that the materials in the device and the stimulation techniques are not injurious to neural tissue, particularly the neurons. In this report, we discuss our experiences in the search for safe stimulation techniques. Acute and chronic experiments have been performed to evaluate electrode design and materials and to observe the effects of various stimulus protocols on the blood-brain barrier and brain. Neural tissue underlying the stimulated and control electrodes has been examined with both light and electron microscopy. Observations up to the present time indicate that the charge per phase is the most relevant stimulus parameter although the importance of charge density and current density cannot be underestimated.

ISSN:0006-8977    

DOI:10.1159/000125578

出版商:S. Karger AG    

年代:1977

数据来源: Karger

摘要:

Stimulation of the cat striate cortex with polished 1 mm2 gold, platinum, rhodium or carbon electrodes for 40 h, at 50 Hz, and 0.5 msec duration, results in tissue damage at current densities of 0.6 A/cm2. At 0.1 A/cm2 rhodium and carbon were toxic to brain. In vitro gold and platinum corroded after 1,500–2,300 h of testing in simulated cerebrospinal fluid. The materials utilized are not suitable for long-term chronic electrodes for neural prosthetic

ISSN:0006-8977    

DOI:10.1159/000125579

出版商:S. Karger AG    

年代:1977

数据来源: Karger