New York:The specialised nerve cells in our brain that are responsible for emotional memory also play an important role in fear learning, say researchers. The team from Mount Sinai Health System in New York City set out to identify the synaptic connections between brain's inhibitory cells called parvalbumin-interneurons (PV-INs), sensory pathways and neighbouring principal neurons in a brain region involved in detecting and responding to dangerous situations. They found that the sparse but potent population of PV-INs in the amygdala region of the brain influence fear memory encoding -- the process responsible for persistent reactions to trauma-associated cues. Stimuli encountered during a traumatic event can elicit strong emotional reactions long after the threat has subsided. These emotional memories are thought to be encoded through changes in the neural connections or synapses, within the basolateral amygdala that provide outputs to other brain areas, controlling the so-called "fight or flight" response. "Our study is the first to show that this default silencing may, in part, be attributable to a sparse population of inhibitory PV-INs," said Roger Clem from Mount Sinai. "The complex anatomy of these cells may allow them to function like master regulators on a hair trigger, springing into action to suppress their neighbours when they detect even the slightest sensory perturbation," Clem added. To investigate whether fear learning alters PV-IN properties and their silencing effect on surrounding neurons, the researchers introduced fear conditioning in a mouse model, pairing an auditory tone with a subsequent aversive foot shock. They found that when animals acquire a fear memory, the suppressive influence of PV-INs is relieved, allowing the fear system to respond more vigorously during a "fight-or-flight" response. The study was published recently in the journal Neuron.