This is the first part of a title, “Humans as Superorganisms: How Microbes, Viruses, Imprinted Genes and Other Selfish Entities Shape Our Behavior” by Peter Kramer and Paola Bressan of the Department of General Psychology, University of Padua, Italy. It was published in Perspectives on Psychological Science, 10, 2015, 464-481. The only other article in this general area in the healthy memory blog is “You Have Two Brains.” That blog barely touched this topic. The authors note that psychologists and psychiatrists tend to be little aware of the science in this area, although they should be. I believe that the general public is even less aware. The objective of this blog post is to increase awareness somewhat. As you will see, it is definitely relevant.
Let us begin with brain microbes, the most instructive of the lot is Toxoplasma gondii. Sooner or later this brain microbe will infect about half or even most of us with potentially serious consequences for our mental health. Eating meat undercooked is by far the most typical, though not the only way of contracting this parasite. The infection rate is about 10% to countries with religions that promote vegetarianism, to 50% in some developed European countries, and over 70% in some parts of Africa and Latin America. The adverse consequences of this microbe are potentially reckless behavior, depression, bipolar and obsessive-compulsive disorders. It raises the probability of developing schizophrenia 2.7 times and is the largest known single risk factor, larger than any of the currently known genetic and environmental ones.
Gut microbes are for the most part beneficial. This is fortunate as there are so many of them. The human gastrointestinal tract houses up to 100 trillion microorganisms, belonging to more than 7,000 strains: collectively, these contain 10 times the number of human cells and 100 times as many genes as our genome. Each of us harbors at least 160 bacterial species, many of which are shared among us but in different proportions. It is estimated that the gastrointestinal tract contains at least 500 million neurons, it is not surprising that gut microbiota and the brain communicate to each other. Research has found that ingesting probiotics (microorganisms whose consumption provides health benefits, typically bifidobacteria and lactobacilli) that can mitigate some mood disturbances. One recent study went beyond self reports showed that probiotics modify healthy women’s brain activity in regions that control processing emotion and sensation, dampening reactions to facial expressions of anger and fear. These same brain regions are involved in anxiety disorders. When more research is done in this area, it is likely that more benefits will be found.
Brain viruses work both ways. Some viruses exploit humans, but humans are also able to exploit some viruses. Viruses exploit humans via our genes. For example, cytomegalovirus is a herpes virus that infects a majority of the world’s population. The infection is usually benign, but not always. It one large study this was not the case for 15% of the subjects who carried a particular variant of a gene involved in the stabilization of neuronal connections and in synaptic plasticity essential to learning and memory. In the carriers of this gene variant, maternal cytomegalovirus infection increased fivefold the probability of developing schizophrenia.
We humans have begun to parasitize our parasites. Some viruses are modified in the laboratory and then used to infect people to treat various genetic conditions, including those that affect the brain. In one study 16 patients with Parkinson’s disease had a modified virus, containing genes that modulate the neurotransmitter GABA, injected into their brain. Relative to a control group of 21 patients who had received a sham injection, the motor ability of the experimental group improved by about 10%—a modest, but promising start. In another study, patients with Alzheimer’s were treated with the help of a modified leukemia retrovirus that reduced degeneration. The retrovirus contained genes that induced infected cells to produce nerve growth factor; cells infected in vitro were then implanted into the patient’s brain, in a specific area that promotes cortical plasticity and memory.
Evidence is mounting that cells can be modified by the invasion of selfish entities that are not microorganisms or viruses. These foreign cells come from another human person. This topic becomes fairly technical, which will preclude further elaboration in this post. This is also the case with the topic of imprinted genes. Just be aware that all of us carry genes originally designed to produce viruses.
So there is much to be learned. Although there is much to be worried about, there is room for optimism and hope of new means of treatment,