Direct cortical responses to electric stimulation with different frequencies in chronic experiments on dogs]

Direct cortical responses (DCR) to a series of electrical stimuli with a frequency of I to 50 per second with 10 to 20 pulses in each series were studied in chronic experiments on dogs. The nature of cortical responses differed, depending on stimulation parameters. As the stimulation frequency increased, the amplitude and number of late DCR components decreased, and with further increase of frequency, the early components decreased as well. The following types of responses were revealed: recruiting, intermittent and decremental. As the stimulation frequency increased all the three types of responses could be obtained in one and the same cortical point. Recruiting was not typical of high-amplitude and multi-component DCR with a long phase of depression of initial negativity and slightly pronounced short-term subsequent facilitation, while the intermittent type of response appeared at lower frequencies than in other dogs (5 to 10 per sec). A decremental type of response was observed in all the dogs at a stimulation frequency higher than 30 per sec. The duration of the series of after-discharges to a burst of electrical pulses depended on the pattern of the DCR to a single stimulus and on the intensity and frequency of stimulation. With similar parameters of stimulation, the greater the amplitude and the longer the duration of the slow negative DCR wave, the longer the period of after-discharges following a series of stimuli.