Recruiting responses in the cerebral cortex produced by putamen and palldium stimulation : G. Dieckmann and K. Sasaki (Frankfurt am Main, W. Germany)

Abstract

1. Field potentials in the cerebral cortex elicited by low frequency (6–10/sec) repetitive stimulation of the putamen (Put) and pallidum (Pal) were recorded by glass microelectrodes inserted at various depths in the cortex and analysed together with those evoked by stimulation of different thalamic nuclei. Surface cortical potentials recorded by a gross electrode and intracellular potential changes in cortical neurones were also provided to complement field potential analysis. 2. Stimulation of putamen or pallidum produced characteristic laminar field potentials which were similar to those elicited by stimulation of the centrum medianum (CM) nucleus in the thalamus. Superficial slow negative and deep positive potentials showed much the same time course as in a mirror image and the polarity change at 0.10–0.25 mm depth in the cortex. These profiles of field potentials indicate that putamen- and pallidum-induced potentials are pure recruiting responses in every respect. Latency of Put-induced responses was always longer than that of Pal- and CM-induced responses, the latter two being comparable. Duration was wider in the responses evoked by CM stimulation than those by Put and Pal. The optimal frequency for Put- and Pal-induced recruiting responses was 7–9/sec and the same as that for CM-induced responses in every experiment. 3. Current spread of Put and Pal stimulation to surrounding structures such as the internal capsule was outruled, since entirely different responses (augmenting responses) could be evoked in the cortex by stimulation of the internal capsule delivered through the same electrode after withdrawal of the electrodes by 1–2 mm from Put and Pal to the internal capsule. 4. The cortical area in which Put- and Pal-evoked recruiting responses were recorded was more restricted than the area for CM-induced recruiting responses and was mainly in area 6 a β. 5. The results lead us to refer to and discuss a hypothesis for the pathways of CM-induced recruiting responses that has been made on previous anatomical findings.