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At least 1,261 records · Page 70Linked to original sources
PubMed2001

Selective stimulation of cat sciatic nerve using an array of varying-length microelectrodes.

Restoration of motor function to individuals who have had spinal cord injuries or stroke has been hampered by the lack of an interface to the peripheral nervous system. A suitable interface should provide selective stimulation of a large number of individual muscle groups with graded recruitment of force. We have developed a new neural interface, the Utah Slanted Electrode Array (USEA), that was designed to be implanted into peripheral nerves. Its goal is to provide such an interface that could be useful in rehabilitation as well as neuroscience applications. In this study, the stimulation capabilities of the USEA were evaluated in acute experiments in cat sciatic nerve. The recruitment properties and the selectivity of stimulation were examined by determining the target muscles excited by stimulation via each of the 100 electrodes in the array and using force transducers to record the force produced in these muscles. It is shown in the results that groups of up to 15 electrodes were inserted into individual fascicles. Stimulation slightly above threshold was selective to one muscle group for most individual electrodes. At higher currents, co-activation of agonist but not antagonist muscles was observed in some instances. Recruitment curves for the electrode array were broader with twitch thresholds starting at much lower currents than for cuff electrodes. In these experiments, it is also shown that certain combinations of electrode pairs, inserted into an individual fascicle, excite fiber populations with substantial overlap, whereas other pairs appear to address independent populations. We conclude that the USEA permits more selective stimulation at much lower current intensities with more graded recruitment of individual muscles than is achieved by conventional cuff electrodes.

Animals↗
PubMed1998

Microelectrode recordings define the ventral posteromedial pallidotomy target.

The benefits of stereotactic ventral posteromedial pallidotomy in the treatment of Parkinson's disease have been recently rediscovered. Optimal lesion location and lesion volume, however, have yet to be determined. Micro-electrode recording and microstimulation are carried out to determine an appropriate site for the placement of electrocoagulation lesions in the medial pallidum. The cellular activity of the globus pallidus is examined for characteristic firing patterns, mean firing rates, movement-evoked activity, and presence of tremor cells, laminae, and border zones. Microstimulation allows the identification of the adjacent optic tract by reports of visual sensation and of the internal capsule by sensorimotor responses. Lesions are centred at sites in the internal segment of the globus pallidus at least 3 mm from these structures, to avoid injury to them during pallidotomy.

Brain Mapping↗
PubMed1978

Sinus node response to premature atrial stimulation in the rabbit studied with multiple microelectrode impalements.

In this study we investigated the response of the isolated rabbit sinus node to ectopic atrial premature beats elicited late in the atrial cycle. In three experiments the response of at least 45 different fibers of the sinus node was recorded, whereas, in other experiments, investigation was less extensive. In this way the spread of activation of the total pacemaker area could be mapped accurately both during spontaneous beating and the induction of ectopic atrial beats of different degrees of prematurity. We found that: (1) The conduction of an impulse from the dominant pacemaker area to the atrium during spontaneous rhythm (antegrade conduction) is slower than the conduction of an ectopic atrial impulse towards the center of the sinus node (retrograde conduction). (2) The action potential of the dominant pacemaker fibers in the sinus node is shortened because of premature activation caused by an ectopic impulse from the atrium. Late premature beats had no effect on diastolic depolarization. If the retrograde activation wave did not reach the area of the dominant pacemaker before the spontaneous discharge of these fibers, there was electrotonic influence demonstrable over a distance of about 0.5 mm. (3) Comparison of the true sinoatrial conduction time with the estimated sinoatrial conduction calculated indirectly from the length of the postextrasystolic atrial cycle revealed that, in the isolated rabbit heart, the calculated value is a serious underestimation of the true antegrade sinoatrial conduction time.

Action Potentials↗
PubMed2003

Perceptual efficacy of electrical stimulation of human retina with a microelectrode array during short-term surgical trials.

PURPOSE: This work is part of a feasibility assessment of a retinal prosthesis as a means to restore vision to patients with blindness caused by retinitis pigmentosa. The primary goal was to assess the concordance of the form of induced perception and the pattern of electrical stimulation of the retina, and the reproducibility of the responses. METHODS: Five volunteers with severe retinitis pigmentosa and one with normal vision were studied. A companion paper in this issue provides details on demographics, visual function, surgical methods, general stimulation strategy, and data analysis. Volunteers were awake during surgery while a 10-microm-thick, microfabricated electrode array was placed on the retina. The array was connected to extraocular current sources that delivered charges to 50-, 100-, and 400-microm-diameter electrodes. Negative control trials were randomly included. Perceptual quality was judged by the similarity between the form of stimulation and perception (i.e., accuracy) and the reproducibility of responses. RESULTS: Only 1 of 40 control tests yielded a false-positive result. On average, volunteers 3, 5, and 6 reported percepts that matched the stimulation pattern 48% and 32% of the time for single- and multiple-electrode trials, respectively. Two-point discrimination in the best cases may have been achieved in two blind subjects using (center-to-center) electrode separation of 600 and 1960 microm. Reproducibility was achieved 66% of the time in the blind subjects. By comparison, in the normal-sighted subject, perceptual form was reported accurately 57% of the time, with 82% reproducibility, and two-point discrimination may have been achieved in one trial with 620-microm electrode spacing and in two trials each with 1860- and 2480-microm electrode spacing. In subjects 5 and 6, perceptual size was inconsistently related to the charge, although relatively large differences in charge (median: 0.55 microcoulombs [microC]) between two trials produced differently sized percepts. Longer stimuli did not produce rounder percepts. CONCLUSIONS: Single percepts induced by single-electrode stimulation were relatively small, but the form of percepts, especially after multielectrode stimulation, often did not match the stimulation pattern, even in a normal-sighted volunteer. Reproducible percepts were more easily generated than those that matched the stimulation pattern.

Adult↗
PubMed2003

Methods and perceptual thresholds for short-term electrical stimulation of human retina with microelectrode arrays.

PURPOSE: To report methods for performing epiretinal electrical stimulation with microfabricated electrode arrays and determining perceptual thresholds on awake human volunteers during acute surgical trials. METHODS: Four hypotheses were tested: (1) epiretinal stimulation can be performed during acute experiments without obviously damaging the retina or degrading vision or the health of the eye; (2) perception can be obtained 50% of the time in blind patients with charge densities below published safety limits; (3) the minimal charge needed to induce perception would be higher in patients with more severe retinal degeneration; and (4) threshold charge would be lower at shorter stimulus durations. Five subjects with severe blindness from retinitis pigmentosa and one with normal vision (who underwent enucleation of the eye because of orbital cancer) were studied. Electrical stimulation of the retina was performed on awake volunteers by placing a single 250-microm diameter handheld needle electrode or a 10-microm thick microfabricated array of iridium oxide electrodes (400-, 100-, or 50-microm diameter) on the retina. Current sources outside the eye delivered charge to the electrodes. Assessment of damage was made by observing the clinical appearance of the eyes, comparing pre- and postoperative visual acuity, obtaining retinal histology in one case, and comparing perceptual thresholds with published safety limits. RESULTS: No clinically visible damage to the eye or loss of vision occurred. Even at sites removed from stimulation, histology revealed swollen photoreceptor inner and outer segments, which were believed to be nonspecific findings. Percepts could not be reliably elicited with 50-microm diameter electrodes using safe charges in one blind patient. With the two larger electrodes, only the normal-sighted patient had thresholds at charge densities below 0.25 and 1.0 millicoulombs (mC)/cm(2) for 400- and 100-microm diameter electrodes, respectively, which is one seemingly reasonable estimate of safety derived from the product of charge per phase and charge density per phase. In blind patients, thresholds always exceeded these levels, although most were close to these limits in patient 6. The range of charge density thresholds with the 400- microm electrode in blind patients was 0.28 to 2.8 mC/cm(2). The normal-sighted patient had a threshold of 0.08 mC/cm(2) with a 400-microm electrode, roughly one quarter of the lowest threshold in the blind patients. Strength-duration curves obtained in two blind patients revealed the lowest threshold charge at the 0.25- or 1.0-ms stimulus duration. CONCLUSIONS: Threshold charge densities in severely blind patients were substantially higher than that in a normal-sighted patient. Charge densities in blind patients always exceeded one seemingly reasonable estimate of safe stimulation. The potential adversity of long-term stimulation of the retina by a prosthesis has yet to be determined.

Adult↗
PubMed2003

Thresholds for activation of rabbit retinal ganglion cells with an ultrafine, extracellular microelectrode.

PURPOSE: To determine electrical thresholds required for extracellular activation of retinal ganglion cells as part of a project to develop an epiretinal prosthesis. METHODS: Retinal ganglion cells were recorded extracellularly in retinas isolated from adult New Zealand White rabbits. Electrical current pulses of 100- micro s duration were delivered to the inner surface of the retina from a 5- micro m long electrode. In about half of the cells, the point of lowest threshold was found by searching with anodal current pulses; in the other cells, cathodal current pulses were used. RESULTS: Threshold measurements were obtained near the cell bodies of 20 ganglion cells and near the axons of 19 ganglion cells. Both cathodal and anodal stimuli evoked a neural response in the ganglion cells that consisted of a single action potential of near-constant latency that persisted when retinal synaptic transmission was blocked with cadmium chloride. For cell bodies, but not axons, thresholds for both cathodal and anodal stimulation were dependent on the search method used to find the point of lowest threshold. With search and stimulation of matching polarity, cathodal stimuli evoked a ganglion cell response at lower currents (approximately one seventh to one tenth axonal threshold) than did anodal stimuli for both cell bodies and axons. With cathodal search and stimulation, cell body median thresholds were somewhat lower (approximately one half) than the axonal median thresholds. With anodal search and stimulation, cell body median thresholds were approximately the same as axonal median thresholds. CONCLUSIONS: The results suggest that cathodal stimulation should produce lower thresholds, more localized stimulation, and somewhat better selectivity for cell bodies over axons than would anodal stimulation.

Action Potentials↗
PubMed2005

Thresholds for activation of rabbit retinal ganglion cells with relatively large, extracellular microelectrodes.

PURPOSE: To investigate the responses of retinal ganglion cells (RGCs) to electrical stimulation, using electrodes comparable in size to those used in human studies investigating the feasibility of an electronic retinal prosthesis. METHODS: Rabbit retinas were stimulated in vitro with current pulses applied to the inner surface with 125- and 500-mum diameter electrodes while the responses of RGCs were recorded extracellularly. RESULTS: Both short-latency (SL; 3-5 ms) and long-latency (LL; >/=9 ms) responses were observed after electrical stimulation within the receptive field of an RGC. With short, 0.1-ms current pulses, the threshold current for the SL cell response was significantly lower than that for the LL cell response. With long (10- to 20-ms) pulses, the threshold currents for the SL and LL cell responses were very similar. The threshold current for the SL cell response increased more steeply than did the LL cell response when the electrode was displaced from the point of lowest electrical threshold, either above or along the surface of the retina. Stimulation of an RGC axon outside of the cell's receptive field produced only an SL response. For 0.1-ms duration pulses, the threshold current for the axonal response was significantly higher than the threshold current for the SL cell response. At pulse durations > 1 ms, the thresholds were very similar. CONCLUSIONS: RGC responses to electrical stimulation depend on the current pulse duration and location of the stimulating electrode. For an epiretinal prosthesis, short-duration current pulses may be preferable since they result in a more localized activation of the retina.

Animals↗