Analysis and microelectronic design of tubular electrode arrays intended for chronic , multiple single - unit recording from captured nerve f bres

The paper discusses proposals for recording multiple single-unit potentials from nerve fibres that become captured in an array of tube electrodes. Capturing may be through regeneration. of cut fibres or by placement of dissected filaments into grooves which are then covered. The factors contributing to signal-to-noise ratios obtainable with this type of electrode are discussed. The design, construction and bench-test results are given for an electrode array in which thin-film microelectronic techniques are used to build a densely packed, flexible, 3-dimensional electrode array consisting of a bundle of plastic tubes with flat metal contacts at midtube. Keyword s-Chronic recording, Microelectrode arrays, Neurophysiology Introduction and increase the signal-to-noise ratios obtainable THE DIFFICULTIES of adapting the classical metal extracellularly. microelectrode to chronic recording are legion, nerves tGuTH3 1956) as well as the particularly when multiple, closely spaced probes nerve of lower vertebrates and are desired. The electrodes are fragile, their electrical SPERRY, 1963) will regenerate if cut and re-establish and physical properties inconsistent, and their functional connections. MARKS found that perimanipulation and positioning quite tedious. 'Floatpheral nerve bundles of bullfrogs (1969) and rats ing' microelectrodes (SALCMAN and BAK, 1973) (personal communication) will regenerate through improve chronic-recording stability, but it is still Sponges and tubes of various metals and ~lastics, not possible to guarantee holding a single unit for although rat sciatic nerve fibres appear to be more than a day or so. somewhat limited in their ability to fill densely a ideally, to maximise the number of information narrow tube, because of the more rapid proliferchannels and minimise the intrusion on the nervous ation of Schwann cells. Mammalian and amphibian system, it would be desirable to have several neurons C.n.S. fibres appear either Or to simultaneously present on each of several channels. regenerate rather than cuts With high signal-to-noise ratios and stable or only 1972 a, b, c, and d) . However, c.n.s. fibres have been slowly changing waveforms, one could make use of Seen to slide spontaneously into deep, narrow grooves any of several waveform analysers and separators (25 X 5 ~ m ) in inert plastic implants (unpublished). previously described (KENT, 1971; SCHMIDT, 1971; Recently, IVIANNARD et a[. (1974) constructed a GLASER and MARKS, 1968). An attempt to achieve tubular regeneration electrode by mechanical such a data stream was made by GER~TEW and drilling through silver wires embedded in Epon. CLARK (1964) who designed a single electrode with Their array of 10 such tubes, 1 0 0 ~ m in diameter multiple exposed metal patches, but their design and 700 Pm long, success full^ recorded 50 to 150 PV suffers the usual problems of discretemicroelectrodes, multiunit potentials from regenerated Xenopus i plus an additional signal-to-noise attenuation sciatic motor fibres. caused by averaging signals over several patches. This paper analyses the neuronal and electrode In this paper, we explore previously proposed parameters that are theoretically important in techniques for achieving a solution to these problems recording from nerve fibres in tubes and describes a by capturing nerve fibres in tubes, either by allowing fabrication technique for regeneration tube arrays them to regenerate through tubes (MARKS, 1969) which appears to be adaptable to a variety of or by inserting them into grooves which are subelectrode approaches. The difficulties in hand sequently sealed (HOFFER et a/., 1973; BRINDLEY, manufacture of electrode arrays, as well as the 1972). This configuration has certain inherent inherent limitations of geometry and packing of properties which should both stabilise spatial discrete wires, has led us to develop techniques of relationships between electrodes and nerve fibres thin-film microelectronics in constructing arrays of tubular electrodes. Such techniques are beginning to Firslreceived5lhDecember1975andinfinalform16th June 1976 find Uses in neurophysiology for both in V ~ V O Medical & Biological Engineering & Computing March 1977 195