painting of a seahorse

Hippocampus means seahorse. This painting is by my friend Alex Lago, former college classmate turned artist.

Yesterday I stumbled upon this article in Science magazine. I thought it was very clever how the presence of higher levels of C14 due to the surface nuclear explosions between 1945 and 1963 helped determining that adult neurogenesis takes place in the brain. The area where this rather robust formation of new neurons takes place is the hippocampus. Quote: (…) a subpopulation of neurons renews consistently and continually, whereas another population is nonrenewing. Spalding et al. estimate that one-third of adult hippocampal neurons are turning over. This amounts to 700 new neurons added per day, for an annual turnover rate of 1.75% (or 0.004% of dentate gyrus neurons). This turnover rate was not significantly different between men and women and declined only modestly with age.

Hippocampus! I had just read about the hippocampus in Chapter 5. This is an important brain structure required for the formation of explicit memories, those that we are conscious of. Implicit memories, albeit not conscious, may be powerful and motivated by feelings, beliefs, and behaviors. Explicit memories can be semantic (facts, labels, names etc) and episodic (basically stories- more likely to contain errors, even when we think we remember them well).

The authors of the Science article state: Adult neurogenesis in this region might add a particular functionality not achievable by other types of plasticity. By staying “forever young,” the dentate gyrus could command unique solutions to computational problems only found in the brain region central to learning, memory, and many higher cognitive functions considered essential for humans.

Well, that was cool to read. I went back to Zull’s book to finish the chapter. He talks about the  connection between hippocampus and both centers of pleasure (such as basal ganglia) and the amygdala. It adds to the idea of learning framed within emotions and feelings, and how factors such as stress and PTSD can affect memories through hormones such as adrenaline and cortisol. Low levels of stress may enhance long-term memory, while chronic stress may damage the memory centers through the action of cortisol.

The final reflection is about how, at the end of the day, everything is connected. Rote memorization is helped by feelings or other associated memories, and having the memory of concrete facts or dates may help remember a story easier.