["Inhibition of inhibition" in neurons of the cerebral cortex].

Light flashes and single electrical stimuli applied to the nucleus ventro-posterolateralis and to the LGB evoked protracted IPSPs in visual and sensorimotor cortical neurons respectively. High-frequency stimulation of the midbrain RF suppressed these IPSPs which was manifested in a shortening of the inhibitory pause and in a decrease in the amplitude of the IPSPs up to their complete elimination (disinhibition). Activation of noradrenergic pathways by stimuli applied to the locus coeruleus or to the lateral hypothalamus led to the same result. The suppression of cortical IPSPs followed by facilitation of cortical unit firing in response to thalamic or peripheral stimulation seems to be an imprortant mechanism underlying arousal.