We present a model for the attentional neuromodulation of decision and selection processes. The model assumes that phasic responses in the brain nucleus Locus Coeruleus modulate, via the transmission of norepinephrine, the synaptic efficiency of neural circuits, at specific (stimulus and task dependent) time intervals. The model is applied first, to a task of perceptual choice, simulating attentional fluctuations and accounting for a series of behavioral and neurophysiological data. Second, the flexibility of information processing, whereby the parameters of the local circuits are modified online, is illustrated in the application of the model to a task of selection from short-term memory.