Arousal Theory

Abstract

The single most ubiquitous construct in neuroscience is that of arousal or activation and no brain system contributes more to these functions than the mesencephalic reticular formation. This diffusely projecting neural network originating in the midbrain determines the activation or arousal level of higher-level brain regions ipsilateral to the side activated by electrical stimulation. This system receives sensory information, including ambient lighting and sound levels, altering the sensitivity or the intensity of information conveyed through the primary sensory projection pathways extending through the thalamic relays and onto the primary projection cortices for each modality. Thus, arousal levels, as witnessed initially through behavioral activation and cage activity and later through cortical desynchrony of the electroencephalogram, may be altered directly as a function of ambient sensory conditions. In turn, this activating system appears to be regulated through the descending influences of the frontal lobes.