Groucho Marxism

The human brain is an incredibly complex organ. Nonetheless we usually imagine that our brains remain roughly static over time. A recent article in New Scientist argues that this view is incorrect. According to the conception outlined there, our brains our dynamic systems which transform continuously over the course of our lifetimes. In this blog post I will summarize some of the points put forward in this article. We begin by asking a seemingly innocuous question: When does adulthood begin? This question is notoriously difficult to answer scientifically. Legally of course, adulthood arrives at a specific time, typically at age 18 or 21 in most countries. But neurologically speaking things aren’t so straightforward as there isn’t an exact moment that the brain flips from a juvenile to adult state.

Until around a decade ago, neuroscientists tended to assume that the brain fully develops around age 25 for most people. More recently, researchers have attempted to zero in on a more accurate number by looking at the development of brain structures. In childhood the brain has many neural connections which get pruned down during adolescence to make the brain more efficient. It should be possible in theory to pinpoint the moment when these structures top being pruned and define this as the point at which adulthood is reached. Unfortunately it is extremely difficult to do that in practice. Therefore, rather than asking when the brain starts looking like an adult’s, perhaps instead we should ask when it starts behaving like one.

By analyzing the executive function of the brain – that is, the mental skills that allow us to plan, focus attention, remember instructions, and juggle multiple tasks successfully – researchers at the University of Minnesota have estimated that adulthood arrives much earlier than previously assumed, at around age 20. However given the complexity of the brain it may be misguided to fixate on this one particular function. Other researchers at the University of Cambridge have attempted to get a broader view by mapping brain development over the entire human lifespan. They found that the brain undergoes four major shifts, around ages 9, 32, 66, and 83. This suggests that the brain continues to refine itself far beyond the legal age of adulthood.

Despite this lack of consensus, what is clear is that the brain is not fully developed at age 18, the legal age for adulthood in many countries. In particular, frontal lobe networks that are involved in impulse control tend to develop far later. This explains why younger people are less more risk-averse than older people (they are far more likely to be involved in a driving accident, for example). The lack of consensus on when adulthood occurs makes clear that whereas legal, medical, and social systems need an exact definition of adulthood, neurology cannot provide one. The idea that there isn’t a clear point at which childhood ends and adulthood begins is something I think we all understand intuitively, even if we don’t always like to admit it.

Another time of life when peoples’ brains go through a transformation is during pregnancy. At this time the brain remodels itself to allow a mother to more effectively to care for her baby. Scientific consensus around this has undergone a profound shift in the past decade, and it is now understood that the brain begins to change from the earliest stages of pregnancy. The most striking changes occur in the default mode network, a system involved in self-reflection, planning, and emotional and social cognition. These changes are what enable the mother to immediately bond with her child. Evidence indicates that parenthood alters fathers’ brains too. It is unclear how long these changes last, but what is clear is that the parental brain seems to come with durable improvements in cognition.

The obvious explanation for this is that the challenges of parenting force the brain to work harder, thereby building up cognitive improvement. It is difficult to test this hypothesis scientifically due to the many confounding factors involved. Whatever the explanation, there are many studies which suggest that parenthood has a positive impact on the brain. Interestingly, the research points to a upside down U-shaped relationship between number of children and cognitive impact. Apparently having four or more children can actually increase the risk of degenerative neurological conditions such as Alzheimer’s. (Perhaps the brain just gives up at that point.) For better or worse, having children clearly leaves an indelible mark on us.

In a previous blog post I argued that the ‘self’, as usually understood – a core identity which remains constant and does not change over time – is an illusion. This view is in line with eastern philosophies such as Buddhism, Hinduism, Taoism, and Confucianism, view the self as an illusion or a transient construct. The research outlined in the recent New Scientist article provides scientific evidence to back up this claim. It seems that modern science is finally beginning to cotton on to what eastern philosophers have already known for thousands of years.