Modeling acquisition of auditory fear in the lateral amygdala

Plasticity at auditory inputs to the dorsal part of the lateral amygdala (LAd) is required for the acquisition of auditory conditioned fear memories. Unit recordings have revealed the presence of two different cell populations in the dorsal (LAdd) and ventral (LAdv) parts of LAd (Repa et al. 2001). LAdd cells have tone responses that increase and then decrease back to habituation levels within the conditioning phase, whereas the tone responses of LAdv cells gradually increase during conditioning and persist through the extinction phase. However, the mechanisms involved in the generation of the two populations of LAd cells are unknown. Here, we analyzed the contribution of the LAd network structure to the formation of these cell types. To this end, we developed a biologically realistic LAd model that consisted of 800 principal cells and 200 interneurons differentially connected depending on their relative position, as recently reported (Samson & Pare, 2006). Moreover, the model integrated auditory and somatosensory inputs to LAd from the thalamus (to LAdd) and auditory cortex (to LAdv) and the influence of the neuromodulators norepinephrine (NE, Tully et al., 2007) and dopamine (DA, Loretan et al., 2004), which are known to be released during stress and affect the intrinsic properties of LA cells. Last, the network model used a calcium-based rule for synaptic learning.