This chapter focused on the function of neuromodulators on the hippocampal system. And it was packed with information. Acetylcholine, dopamine, norepinephrine, metabotropic glutamate receptors, GABA-B receptors, serotonin all have different effects on excitatory transmission, inhibitory transmission, spike frequency adaptation, resting membrane potential, and plasticity. By the way, all of these modulators may have different effects on each event depending on where the synapses they are modifying are located. You get the picture. Packed with information.
What I wanted to note though is how acetylcholine gates hippocampal dynamics. In the presence of new, attention-grabbing, interesting stimuli, cholinergic modulation of the hippocampus increases, such that activity at intrinsic (meaning within the hippocampus) synapses is silenced and synapses that encode the incoming sensory stream are made more active. The experience is encoded. Learning has occurred. During boring, stale, seen-that-before experiences, the intrinsic connections of the hippocampus are not silenced by acetylcholine and their activity is enhanced. It is under these conditions that information stored in the hippocampus from past experiences can be re-experienced. Remembering.
In other words, while watching you Toy Story for the first time, you likely had a serious burst of cholinergic modulation and can remember much of what happened because – oh my god – that movie was amazing. However, while watching Lost In Translation, you’ll space out and think of other things, because in this movie, nothing actually happens.