The high-impedance electrodes required to record single unit activity16 are particularly sensitive to noise, especially when they are long enough for human subcortical recording.25 Furthermore, stimulation through high-impedance electrodes produces high current density at the electrode tip which, by causing electrolysis and breakdown of insulation at the tip, interferes with subsequent recordings through the same microelectrode (FA Lenz, et al., unpublished data). For these reasons, recording and stimulation are often performed by using a single low-impedance electrode2,25 which is not capable of discriminating the activity of single units.
A microelectrode is described which has tougher insulation, relatively low impedance, and a fine tip, and which can be used repeatedly for stimulation and reliable recordings of both evoked potentials and single unit activity during stereotaxic operations. A simple method for on-line histogram analysis of single unit activity is also outlined.
We thank M. Teofilo, A. Suran, and H. H. Nguyen-Huu for technical assistance.
Donaldson IML: The properties of some human thalamus units. Some new observations and a critical review of the localization of thalamic nuclei. Brain 96:419–4401973Donaldson IML: The properties of some human thalamus units. Some new observations and a critical review of the localization of thalamic nuclei. Brain 96:
Ranck JB Jr: Which elements are excited in electrical stimulation of mammalian central nervous system: a review. Brain Res 98:417–4401975Ranck JB Jr: Which elements are excited in electrical stimulation of mammalian central nervous system: a review. Brain Res 98:
Micro-forge manufactured by Technical Products International, St. Louis, Missouri.
Tubing manufactured by Vita Needle Corp., Needham, Massachusetts; Kapton poly-imide sleeve manufactured by Niemad Industries, New York, New York.
Epoxylite manufactured by Epoxylite of Canada Ltd., Fort Erie, Ontario, Canada.
Microdrive manufactured by David Kopf Instruments, Tujunga, California.
This research was supported by the PSI Foundation, Toronto, Ontario, Canada, the Parkinson's Foundation of Canada, and the Medical Research Council (Canada).