a pavlovian model of the amygdala and its influence within the medial temporal lobe

Recent advances in neuroscience give us a better view of the innerstructure of the amygdala, of its relations with other regions in theMedial Temporal Lobe (MTL) and of the prominent role ofneuromodulation. They have particularly shed light on two kinds ofneurons in the basal nucleus of the amygdala, the so-called fearneurons and extinction neurons. Fear neurons mediate context-dependentfear by receiving contextual information from the hippocampus, whereasextinction neurons are linked with the medial prefrontal cortex (mPFC)and involved in fear extinction.The computational model of the amygdala that we describe in this paperis primarily a model of pavlovian conditioning, but its architecturealso emphasizes the central role of the amygdala in the MTL memoryprocesses through three main information flows. (i) Thalamic andhigher order sensory cortical inputs including from the perirhinalcortex are received in the lateral amygdalar nucleus, where CS-USassociations can be acquired. (ii) These associations are subsequentlymodulated, in the basal nucleus of the amygdala, by contextual inputscoming from the hippocampus and the mPFC. Basal fear and extinctionneurons indicate the currently valid association to their main targetsincluding in the MTL and the mPFC. (iii) The competition for thechoice of the pavlovian response is ultimately performed by projectionof these amygdalar neurons in the central nucleus of the amygdalawhere, beyond motor responding, a hormonal response, includingcholinergic modulation, is also triggered via the basal forebrain. Inturn, acetylcholine modulates activation in the basal nucleus andfacilitates learning in the hippocampus.Based on biologically founded arguments, our model replicates a numberof biological experiments, proposes some predictions about the role ofamygdalar regions and describes pavlovian conditioning as adistributed systemic learning, binding memory processes in the MTL.