Neural Circuits and Fear Conditioning
The processing of auditory input involves a complex neural network involving multiple regions of the brain. In particular, the amygdala has been noted as an integrative center in memory, decision making, and emotional response to auditory stimuli.
Recently, Yang et al. (2016) examined neural circuits underlying auditory fear conditioning (e.g., sound conditioned with shock) involving the lateral amygdala. Previous studies have shown that the auditory cortex is required for auditory fear learning and that fear conditioning induces rapid and long-term changes in neural responses and dynamic in the auditory cortex. However, the specifics of this modification remain elusive.
To study the process Yang et, al. utilized tracing methods with electron microscopy to identify projections from the lateral amygdala to the auditory cortex. The auditory fear conditioning process was specific to increase in connectivity (newly formed synaptic boutons) between the lateral amygdala and auditory cortex. However, there were no changes in neural connectivity from the medial geniculate body of the thalamus. Silencing of the lateral amygdala neurons (using drugs called DREADDs) resulted in significantly reducing the fear response of the animal. However, this does not appear to work in the other direction: blocking the pathway from the auditory cortex to the amygdala does not prevent auditory fear conditioning.
The authors do not discuss clinical applications, but the findings bring to thought applications to tinnitus, hyperacusis, misophonia, and other sound sensitivities.
Yang Y, Dan-qian L, Wei H, Juan D, Yangang S, Yi Z, Mu-ming P. (2016) Selective synaptic remodeling of amygdalocortical connections associated with fear memory. Neuroscience (September 5).