Regulation of slow potential shifts in nucleus reticularis thalami by the mesencephalic reticular formation and the frontal granular cortex.
Novel stimuli or electric stimulation of the mesencephalic reticular formation (MRF) produced large positive slow potentials (SPs) in rostral nucleus reticularis thalami (RVA) that accompanied the negative SPs known to occur in frontal cortex. SP durations (20-30 sec) were similar to the periods of unit inhibition that occur in RVA following MRF stimulation. Trains of 8 c/sec medial thalamic stimuli produced phasic negative SPs in RVA similar in duration to the intervals of unit excitation that follow each stimulus pulse. These results suggest that the polarity and duration of the SPs in RVA reflect changes in excitation of the underlying neurons. Direct activation of a specific region of RVA produced complete inhibition of visual cortex responses evoked by optic tract stimuli, a finding which suggests that RVA has an inhibitory action on the thalamus. A tone reinforced by electric shock also elicited SPs in frontal cortex (negative) and RVA (positive). In contrast to the long duration of the MRF- or novelty-elicited SPs, the durations of the conditioned SPs were phasic and were regulated by the tone--shock interval. Bilateral cryogenic blockade of the interconnections between the frontal cortex and medial thalamus abolished SPs of all origins in the frontal cortex. The blockade also abolished conditioned SPs in RVA, but did not affect the MRF-elicited ones. Thus, the subcortical SPs that accompany orienting to novel stimuli are distinct from those which occur during the higher cognitive process of conditioned expectancy and require the integrity of the mediothalamic-frontocortical system.
D000818:Animals; D002415:Cats; D003214:Conditioning, Classical / Q000502:physiology; D005071:Evoked Potentials; D005625:Frontal Lobe / Q000502:physiology*; D009433:Neural Inhibition; D009434:Neural Pathways; D009949:Orientation / Q000502:physiology; D011999:Recruitment, Neurophysiological; D012154:Reticular Formation / Q000502:physiology*; D013787:Thalamic Nuclei / Q000502:physiology*