In the article linked by Better Aging, they claim that “The findings from recent studies show that just one or two servings of dark chocolate may boost memory, improve cognition, strengthen the immune system and uplift your mood. The studies, from Loma Linda University in California, found brain activity increased in various regions of the brain 30 minutes after consumption of 48 grams of chocolate (about the size of a candy bar) that was 70% cocoa and 30% organic cane sugar.” They suggest that 70% cacao (organic cocoa beans) enhances neuroplasticity, (the ability of the brain to form and reorganize synaptic connections, especially in response to learning or experience or following injury - The Oxford Dictionary). They also claim that ‘A second study from the university found eating 48 grams of chocolate every day for a week boosted the genes responsible for white blood cell activation and increased the expression of genes involved in neural signaling and sensory perception.”
Harvard Health released an article noting that places where chocolate consumption is the highest also have the highest number of Nobel Peace Prize recipients. This is just an interesting fact, but there could definitely be a correlation there. This article references a study done by PubMed.
https://www.health.harvard.edu/blog/your-brain-on-chocolate-2017081612179
PubMed released a study in which they analyzed the flavonoids found in cocoa. They found that they can exert cardiovascular benefits as well as attention span and memory retention. The administering of cocoa ingestion can lead to extreme benefits for at-risk patients. “Cocoa flavanols administration could also enhance normal cognitive functioning and exert a protective role on cognitive performance and cardiovascular function specifically impaired by sleep loss, in healthy subjects”.
https://pubmed.ncbi.nlm.nih.gov/28560212/
The Cleveland Clinic provides some data on how much chocolate and what kind of chocolate is the most optimal for brain stimulation. “Peart says a recommended dark chocolate serving size is between one and two ounces, which is about 30 to 60 grams. That’s a bigger amount of chocolate than you might think. For example, one ounce is the equivalent of three thin squares of chocolate broken off from a bigger bar. Dark chocolate is also best savored slowly — a little goes a long way.” They say that although dark chocolate is rich in antioxidants and flavonoids, it is still high in calories and fat, so it should be enjoyed in moderation. It can be incorporated into any diet but shouldn’t be eaten excessively. They also recommend, “Start by having 50% dark chocolate and then move up to 65% and then 70% and work your way up.”
https://health.clevelandclinic.org/dark-chocolate-health-benefits
A study performed by the University of Illinois compiled 18 non-smoking, healthy adults and administered the cocoa in two rounds, the first containing flavonol-rich cocoa and the second containing processed cocoa with very little flavonols. Neither the participants or the researchers knew which kind of cocoa was ingested first. After two hours, the participants who had consumed the flavonol-rich cocoa. “Most of the participants had a stronger and faster brain oxygenation response after exposure to cocoa flavanols than they did at baseline or after consuming cocoa lacking flavanols, the researchers found. The levels of maximal oxygenation were more than three times higher in the high-flavanol cocoa versus the low-flavanol cocoa, and the oxygenation response was about one minute faster”.
https://health.clevelandclinic.org/dark-chocolate-health-benefits
I will mark this as misleading because the claim states that chocolate is "the" brain food, which is not necessarily true, but studies do prove that it can be helpful for brain connectivity.