Microengineered interfaces with the nervous system

The results from early work suggested that selective recordings could be made with small recording sites spaced 40 μm apart, and possibly less; the authors are presently engaged in attempting to quantify the effect various probe design parameters (site size, positioning, etc.) have on recording performance. A number of problems are also highlighted. Under-etched films at the probe tip damaged tissue during insertion, and this was probably made worse by the coarse mechanical micromanipulator used. Power-line (50 Hz) interference was also present, although this could be reduced to an acceptable level by taking appropriate grounding precautions. In addition, the amplifier gains had to be calibrated after an experiment, meaning that they could not be varied throughout the experiment. These problems have been addressed. The probe fabrication procedure has been modified, and fabrication of new probes is in its final phase at Southampton. In addition, a hydraulic micromanipulator has been purchased. A 5-channel headstage amplifier is being produced using surface mount technology, and it appears (from prototype studies) that this combined with the large steel micromanipulator stage will reduce 50 Hz interference below the level of other noise sources in the instrumentation. This will enable the elimination of the 50 Hz notch filter (which caused significant distortion to the signal), and the extension of the lower 3 dB point of the band-pass filter down to 10 Hz (so that small signals from slower small diameter fibres may be better detected). The new instrumentation has been designed with close tolerance components, and a switchable (stepped) gain selection. A computer system (PC with a high-speed I/O card) has been purchased for data acquisition, and software for this has been written in LabVIEW. Initial evaluation of the data will still be based on spike amplitude, however later evaluation can be based on other techniques (e.g. template matching/cross correlation techniques)