SPONTANEOUS AND INDUCED ACTIVITY IN PYRAMIDAL UNITS

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Abstract
In the cat with intact central nervous system and without central anaesthesia, the pyramidal tract was exposed by ventral approach and the activity in single fibers of the tract recorded with metal micro-electrodes. The surface eeg from the motor area was simultaneously recorded. The surface corticogram of this preparation shows fast low voltage activity and only occasional large slow voltage waves appear in the record. The unit activity in the pyramidal tract is usually in the frequency range of 20-100/ second, without any particular grouping or pattern, and with irregular sudden discharges at higher frequency and short periods of slower activity. These variations occur unaccompanied by any change in the corticogram. In a few cases, trains of large slow waves were recorded from the cortex and the pyramidal unit activity was then synchronous with the waves. Somatic stimuli (pressure, touch, passive movements of the limbs) cause either an increase or decrease of the resting pyramidal discharge without any corresponding change of the corticogram. Stimulation of the bulbar mesencephalic and diencephalic reticular formation causes inhibition of pyramidal activity accompanied by disappearance of the large slow waves when they are present, or by no change of the fast low voltage pattern of the corticogram in the vast majority of cases. The relation of the surface cortico-gram to pyramidal activity and the site and nature of the reticular formation effects are discussed in the light of these results.