Well, if you have half a mind, you have a whole hippocampus. It’s the part of the brain in charge of long-term memory (Where are the car keys?) and spatial relations (Will this car fit into that parking space?). It’s shaped like a horseshoe and straddles both of the brain’s hemispheres. It works like a book’s index, where it consolidates new memories and helps to retrieve them later on. It’s the search engine of the brain. Depending on the perceived importance of a task or episode, learning and remembering may require only a single exposure, after which the memory trace either disappears or consolidates into the long-term cache.
Neuroscientists use rats and mice in their investigations. This is an intriguing proposition to non-scientists, who are not aware that all mammalian hippocampi tend to work the same way. The anatomy, physiology and genetics of mice and rats are strikingly similar to humans’, where 95% of their genome is shared. Rats are the subjects of study because they mature quickly and have brains large enough to make observations easy. About the only part of the brain that separates us from rats is the prefrontal cortex with its higher-level thought processes, such as setting goals, reminiscing, and inhibiting irrelevant functions.
To exemplify the parallels, scientists exposed rats to environments that were enriched, standard or impoverished. Later, their brains were examined, finding that the structures of the enriched had more and longer dendrites, which afford more opportunity for learning and memory. Post-mortem brain tissue of college-educated humans was compared with that of lesser-educated humans, also finding more and longer dendrites, leading to the conclusion that brain changes—multiplying connections—occur in response to a complex environment (Jacobs, 1993) (Diamond, 1972, 2001).
Diets high in saturated fats and refined sugars may cause changes in the brain that fuel the overconsumption of foods that make people gain weight. Such cerebral alterations happen in spite of the mental stimulation that encourages positive brain development. In this vicious cycle lies a possible explanation why obesity is so hard to overcome—the brain says to keep eating while blocking thoughts of self-control. Lab rats offered unlimited access to a high-energy diet (high-fat/high-calorie) fared much worse in memory tests than their cohorts fed the opposite, indicating to researchers a change in functionality of the hippocampus (Davidson, 2012). In effect, they “forgot” to stop eating. It appears that saturated fats and refined sugars interfere with messages that tell you when to rein it in. Diet-induced obesity has such deleterious effects on the hypothalamus that more time becomes necessary to learn new tasks and more errors occur along the way (Valladolid-Acebes, 2011).
Excess energy intake, especially if combined with a sedentary lifestyle, is associated with a number of conditions that include cardiovascular disease, insulin resistance/diabetes, and some cancers. But this elevated risk of cognitive decline in later life is something that can be contained with conscious effort. Public health messages have decried the scourge of obesity for a time, but have never made known its association with mental dilapidation (Sabia, 2009). For those memories maintained by the hippocampus, the edge goes to people of normal weight (Nilsson, 2009).
Neural plasticity refers to the change in structure, function and organization of neurons in response to new learning experiences, where nerve connection are added based on outside stimuli, as mentioned earlier. Some researchers have reported sex differences in response to high-fat and high-sucrose diet, where females are less vulnerable to its impact (Hwang, 2010). This relative immunity from cognitive compromise does little for connubial bliss. We need to note, though, that some types of learning and memory may be affected by diet more than others. For example, memory retention but not acquisition may suffer. We also know that sugar intake has an effect on triglycerides, the reduction of which could reduce cognitive impairment while improving cardiac health. That may be worth a look.
There is considerable data from animal studies and somewhat more limited data from human studies to support the premise that excess energy intake drives cognitive dysfunction and disrupts neural plasticity. Because of individual differences—genetics, exercise, lifestyle—it’s not likely that science can make recommendations about the ideal energy intake, although an upper limit of 2200 calories for men and 2000 calories for women has been proposed. Meanwhile, exercise is recognized as a major factor in mediating the adverse effect of sloppy diet on cognitive wherewithal (van Praag, 2009), followed by increase in social interaction or engaging in challenging activities such as some hobbies afford (Bennett, 2006). So, now when you watch what you eat, watch what you eat. Eating to live is not the same as living to eat.
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