A new research paper by Prof Rony Paz of the Weizmann Institute of Science and his colleagues, published in the journal Cell, argues that humans brains are somewhat akin to modern washing machines – evolved to handle cutting-edge programming, but more vulnerable to breakdown and costly disorders.
In the paper, Paz claims that while the anatomical differences between the brains of humans and those of other primates have been fairly well documented, the non-hardware features (i.e., neural code) thereof remain to be explored.
First, the researchers enrolled a group of volunteers suffering from epilepsy who had diagnostic electrodes implanted directly into their brains to record the efficiency of “communication” between neurons in the prefrontal cortex (an evolutionarily novel structure responsible for “higher” cognitive functions) and the amygdala.
Similar electrodes were also implanted in a troop of macaque monkeys for comparison at the end of the data collection stage of the study.
For research purposes, efficient communication was defined as “that which uses the least amount of energy to transmit the maximal information – to pass on as complicated message as possible with the fewest ‘words’”, explained Raviv Pryluk, a research student in Paz’s group.
As expected, the pre-frontal cortices of both human and macaque brains were found to be more efficient than the amygdalae, which are more ancient and “primitive” regions of the brain responsible for emotional reactivity and basic “fight-or-flight” survival functions.
More interestingly, however, the same brain structures are more efficient in humans than in their primate counterparts, and the more efficient the neural code, the higher the likelihood of mental disorders.
“The lower resistance of the human amygdala to errors plays a role in exaggerated survival-like responses in inappropriate contexts, such as those we see in PTSD and other anxiety disorders,” explained Paz.
Paz and his colleagues argue that such trade-offs are characteristic of evolution more generally – various features may bestow advantages in one domain, and disadvantages in others.
If Paz and his colleagues are right, the answer to the question “Why are humans so prone to mental disorders” might be something like “Because our highly efficient brains that make us such an excellent generalist species also increase the likelihood of costly error”.