I get what your therapist is talking about... and maybe there is just confusion or like you say, they're a bit enthusiastic about how they relate some things. Synapses degrade as we age, and they eventually severe themselves, however, evidence supports slowing such things, and further evidence supports new growth by maintain mental functioning. Like I said... neurologists seem to struggle with the exact specifics of what our brain does, and does not do... because they keep finding new things all the time. We know very little about the brain, and that they seem to agree on.
In the last 10 years PTSD has gone from a chemical imbalance, to the amygdala is the cause of PTSD, to the hippocampus, to the pre-frontal cortex. Neurology shows from scans that all seem to be aspects of PTSD, yet no one is the answer, and right now, they really don't know exactly where PTSD holds up in the brain. Then you have evidence to support that it could be the entire brain, as our neurons store memory (brain is basically a big muscle) and memory is even stored in other body parts (know for a long time due to organ transplants, just still not understood).
You could then scrap all of that above, and start again, because the above information is still theoretical, as they keep finding changes, adding, removing, exploring and trying to understand the brain and complex organ that is the human body. It is my understanding that based on the ratio of learning, i.e. it took a hundred years to learn a couple percent of the human body, then 50 to learn a whole bunch of the body, the ratio from memory calculates we should crack a whole lot knowledge on the human body by 2030.
I don't know the right name, but basically the perpetual velocity of learnt knowledge on a graph, it goes slow for a long period, then sharply rises over a short period, as once learning is achieved, further learning accumulates faster.
