Answer:
hippocampus
Step-by-step explanation:
Hippocampus: The term "hippocampus" is defined as one of the complex structures of an individual's brain and it is being embedded deeply inside the temporal lobe of the person. It is often considered as a vulnerable and plastic structure that generally gets damaged by a certain stimuli.
The hippocampus plays an important role in the memory and learning processes i.e, it is due to the hippocampus an individual can store information in the short-term and the long-term memory. However, explicit memory of an individual is often associated with the hippocampus.
In the question above, the given statement signifies that Lara's hippocampus wasn't fully developed by the age of eighteen months.