Dual thalamoamygdalar routes control emotional behavior
Constantly changing environment requires behavioral adaptation to promote survival. Behavioral responses to external threatening stimuli require precise sensory processes as well as an appropriate brain state to drive plasticity in the amygdala circuit. Amygdala is responsible for the formation and recall of associative fear memories and can help to quickly select adequate threat responses. However, the source of the sensory and arousal-related information in the amygdala as well their effect on the amygdalar activity and thus, on the behavioral responses remain elusive. We identified two, genetically identified thalamic cell classes which compose the major thalamo-amygdala routes. While neurons in the medial thalamus were found to be responsible for setting the arousal levels in the brain, a certain lateral thalamic population was identified to carry fear-related multimodal (sensory + affective) information. Conveying these signals to the amygdala with high efficacy and short latency, both thalamic pathways were able to control the firing pattern of the amygdala neurons and thus, the formation of associative fear memories. Furthermore, the activity of the latter thalamic cells showed plasticity to environmental (conditioned) stimulus, which changes were necessary for signal discrimination. Thus, roles of these two thalamo-amygdala populations in emotional processes go beyond the concept of simple sensory relays. Altogether, parallel thalamic routes to the amygdala provide complex information that can shape the adequate affective behavioral responses in a dangerous situation.