I cannot answer in a technical way, but as I am a senior I think that learning several languages at once really helps my memory in general . Switching languages and keeping the words straight can be very challenging. I speak Spanish fluently, am B2 in Portuguese B1 in Italian, and was C1 in French but stopped studying it because I have no chance of using it. I think it helps me with the aging process , slowing down memory problems plus it makes me proud of myself when I am in a class in a foreign country with all younger people and I am still one of the best in the class.

A language class is like a gym workout for the left side of our brains. As we practice a particular skill, our dendritic branches develop a healthy, fatty sheath. Think of the importance of neuroplasticity. We improve cognitive functioning by increasing the growth of synaptic connections within our neural pathways. The topic is incredibly complex and, to be sure, amazing! When I retired, learning a second language was suggested as a very effective way to keep my gray matter healthy. I guess it could be seen as a "use it or lose it" concept. With challenges such as age-related cognitive decline in our Healthcare system, learning a second language is definitely a good choice for personal development and brain health. I am a retired senior. English is my native language. I chose Spanish as a second language when I retired. I hold a Master's Degree with a major in psychology. As such, I have studied cognition to be sure. Good luck with your learning goals!