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The natural progression of this line of reasoning is that brain volume among humans might tell us who will become the next Einstein and who will have to copy from their neighbor on exams. However, the story isn’t so simple. After all, we reach our peak number of brain cells at a young age, but you won’t find many toddlers in a calculus class. The picture that’s emerging these days is that it’s not the sheer size of your brain, but which regions are larger, more developed or better connected. Devoting a large brain area to monitoring your heart rate won’t help you solve a Rubik’s cube.

The role of some brain structures are better understood than others. For example, the hippocampus, a small S-shaped structure that lies just inside your temples, plays a specific role in memory for facts, such as the capital of France (Paris), or events, such as what you had for breakfast (in my case, oatmeal).

Our knowledge of the hippocampus comes, in part, from a rare surgical procedure where an epileptic patient known as H.M. had a large portion of his hippocampus removed to prevent seizures. Although after the operation he suffered fewer seizures, he could no longer form new memories, such as remembering his doctors’ faces. Upon each visit, he introduced himself as if seeing them for the first time.

Completely removing the hippocampus is a drastic demonstration of the structure-function relationship, but it has only limited relevance to our own experiences with memory; it’s doubtful that you’re planning to undergo a sweeping lobotomy anytime soon. More relevant, however, are disorders such as major depression or post-traumatic stress disorder (PTSD), which will likely afflict more than one in ten people over the course of a lifetime. These disorders are characterized not just by altered emotional states, but also by deficits in memory performance. If you read off a list of words and ask someone to repeat them, a person with PTSD or depression will likely remember fewer items; this holds true even after controlling for factors like intelligence.

What might cause this drop off in memory? Imaging studies of patients with PTSD and depression reveal that part of their brain actually shrinks. They have a smaller hippocampus.

Given the fact that conditions such as PTSD are characterized by smaller hippocampi and a decline in memory, it might be important for treatments to address these deficits. Notably, patients with the worst memory performance have the most difficulty recovering.

Common treatment for both depression and PTSD include pharmacotherapy such as selective serotonin reuptake inhibitors (SSRIs). Chemically, these drugs increase serotonin levels within hours or days, presumably correcting the chemical imbalance. However, for noticeable improvement in mood and behavior, a person usually has to stay on SSRIs for up to three weeks. Might it be that the lag is due to the time it takes for the brain to begin re-growth?

In an experiment at Columbia University, a research group led by Luca Santarelli gave mice Prozac, an SSRI, and then observed the resulting changes in both behavior and cell growth in the hippocampus. After five days, before growth could take place, the mice’s behavior didn’t change. However, after a month, when new cells had formed in the hippocampus, the mice demonstrated greater motivation to get food. However, if Santarelli et al. prevented cell growth in the hippocampus using radiation, Prozac didn’t change behavior. If they used radiation on other regions of the brain besides the hippocampus, the mice’s motivation improved. Based on this finding, it seems that the behavioral effects of anti-depressants require growth in the hippocampus, which may explain why anti-depressants take up to three weeks of use before they’re effective.

For PTSD patients, treatment with an SSRI caused a significant improvement in memory. Studies looking at hippocampal growth in humans have been inconclusive, finding only modest growth of the hippocampus. However, in humans we assess size by volume measured in an MRI, not by directly examining cells to see if they’re proliferating, so it is difficult to appraise subtle changes in the hippocampus. There may be more cells, creating a denser hippocampus, but not an overall change in volume. Growth in the hippocampus may still be important for treating depression or PTSD.

The road to a high-functioning, herculean memory seems to be paved with a robust hippocampus, and PTSD and depression studies indicate that the hippocampus is dynamic and can change over time, for better or worse. It’s unclear whether SSRIs would improve memory for a healthy adult, but there is an alternative action which has shown promise as a memory enhancer. Exercise, well-documented as a stress-reliever and mood-booster, also helps improve the ability to remember words, facts and ideas. Why might this be? Following a 30-minute jog, a person has elevated levels of nerve-growth chemicals such as Brain-Derived Neurotrophic Factor (BDNF) which causes nerve cells in the hippocampus to multiply. The release of BDNF may boost both mood and memory, possibly explaining why exercise remains one of the best natural anti-depressants.

Read in Full:  http://www.psychologytoday.com/blog/you-illuminated/201002/brain-cosmetics-and-herculean-memory