Acetylcholine modulates neuronal circuits during behavior
The neuromodulator acetylcholine plays a key role in the coordination of attention and learning. Using a combination of recently developed techniques like optogenetics, two-photon imaging and genetic targeting of cell types, neuroscientists uncovered important mechanisms regarding the function of acetylcholine in adjusting neuronal circuit dynamics during behavior. Rogier Poorthuis, Leona Enke and Johannes Letzkus, all from the Max Planck Institute for Brain Research, reviewed recent data and concluded that acetylcholine can enhance sensory processing by rapid and differential recruitment of special types of neocortical interneurons that in turn disinhibit pyramidal neurons. This disinhibition might increase the gain of pyramidal neuron responses during attentive behavior and learning.
The data show that electrical stimulation and physiological recruitment of the basal forebrain can activate interneurons, small inhibitory neurons that control pyramidal neuron activity, in a fast way via cholinergic signaling. Hence acetylcholine can rapidly convey information to neocortex about the behavioral state of the animal. Interestingly, acetylcholine activates especially those interneurons that are connected to other interneurons and thus disinhibit pyramidal neurons, thereby boosting sensory responses.
The disinhibitory motif is seen with different processes in the brain, such as locomotion and learning. In addition, it is recruited in parallel in different sensory areas. Hence, acetylcholine might enhance sensory processing during learning and attentive behavior through a common disinhibitory motif. Disinhibition seems to be an attractive mechanism to increase sensory responses during learning and active behavioral states since it is permissive for strong activation of pyramidal neurons by sensory input, but does not cause firing in itself. In addition, disinhibition can increase the gain of pyramidal neuron responses without affecting stimulus selectivity.