It is clear from the passage that PTSD ----.

Post-traumatic stress disorder (PTSD) is an anxiety
disorder that can develop after exposure to a terrifying
event or ordeal. While many scientific studies focus on the
molecular mechanisms for learning and memorization,
scientists need to address the “unlearning” process to
tackle PTSD. Researchers have discovered that a receptor
for glutamate, the most prominent neurotransmitter in the
central nervous system, plays a key role in the unlearning
process. They made this discovery in experiments where
they trained mice to fear a sound by coupling it with an
electric shock to the foot. They found that if, following this
fear conditioning, the mice are repeatedly exposed to the
sound without the electric shock, their fear eventually
subsides. However, mutant mice lacking the gene-coding
for metabotropic glutamate receptor 5 (mGluR5) are unable
to shake off their fear of the now harmless sound. The
researchers believe that a similar mechanism might be
perturbed in PTSD sufferers and that metabotropic
glutamate receptor 5 (mGluR5) may provide a potential
target for new therapeutic treatments.