Abstract
As a part of the study to elucidate the influence of exteroceptive stimulation on the excitability of the brainstem reticular formation in the presence of flash stimuli, the effect on the recruiting response was investigated in the rabbit and the following observed.1) The amplitude of the recruiting response appearing in the cerebral cortex EEG increased, on stimulation of the nucleus centrum medianum, nucleus reticularis and nucleus ventralis anterior (VA), belonging to the diffuse thalamocortical projection system, by 8Hz when the soft contact lens (CL) or the hard CL was attached in the absence of the flash stimulus.2) The amplitude of this recruiting response was suppressed and decreased when the soft CL or hard CL was attached in the presence of the flash stimulus.3) The amplitude of this recruiting response increas ed when tlhe flash stimulus was given. This finding indicates that the suppression of the recruiting response by the flash stimulus when the CL is attached is not due to the flash stimulus alone.4) The rate of change in the amplitude of the re cruiting response with of the soft CL and the hard CL was analyzed quantitatively by determination of the wave pattern using the digital computor (Nihon Kohden ATAC-201). In the absence of the flash stimulus, an increase in amplitude of the recruiting response of an average of +23% (soft CL) and +45% (hard CL)respectively while in the presence of the flash stimulus, there was an average decrease of 15% (soft CL) and 18% (hard CL), respectively. The rate of change in amplitude with the flash stimulus alone averaged +18%. These results sugget that t he previously reported decrease in excitability of the brainstem reticular formation on attachment of the CL in the absence of the flash stimulus and the increase in the presence of the flash stimulus can be attributed to a rise in indirect suppression (in the absence of the flash stimulus) and a decrease in indirect suppression (in the presence of the flash stimulus) via the diffuse thalamocortical projection system.
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