Bruce Hood - The Domesticated Brain - A Pelican Introduction (Pelican Books)

Many drives can become self-defeating. Some of us eat too much despite the warnings that we are ruining our health, whereas others starve themselves to death. Fighting often gets us into trouble and fleeing is not always the best thing to do when one should stand one’s ground. Making unwelcome advances or engaging in sexual acts in public is not acceptable in decent society. Addicts knowingly abuse legal and illegal substances that will put them in an early grave. Chronic gamblers can squander away their families’ futures and still believe that they can turn their luck around. There are those who feel the need to scream obscenities in public when it is the last thing anyone wants to hear. When we cannot stop these urges, we are no longer in control of our actions.

We all have the potential to be slaves to our urges and impulses and every so often we fail to keep them under control. How many of us have lost our tempers behind the wheel of a car, said things that should have remained as inner thoughts or acted in ways that we never thought we could? In the cold light of day, we often know what we should think, say or do, but sometimes our urges and impulses get the better of us in the heat of the moment.

Scorpions may be rigid and inflexible, but humans possess a much greater capability to control our urges because we have evolved brain circuitry that plays a critical role in regulating our thoughts and actions. These mechanisms of self-control, shaped and strengthened by domestication, are essential for regulating behaviours in social settings. Without this self-control, we are in danger of being ostracized from the group.

The executive suite in our brain

The capacity for self-control is supported by neural mechanisms that traverse through the frontal lobes. Throughout human evolution, the frontal lobes expanded as our brains grew bigger and account for one-third of the human cortical hemispheres. 1Although the human frontal lobes are bigger than those of the great apes, they are not proportionally larger than would be expected for an ape brain of human size. 2However, as we noted in the preface, it is not so much the overall size but rather the way the microcircuitry of our frontal lobes is organized that is crucial to processing power. If you put a brain through a meat slicer, the cross-section reveals that there is more surface area where the cortical neurons are, tucked in the deep grooves and folds of the human brain in comparison to other apes. If you unfold the brain, humans would have more grey-matter surface area and therefore more potential for connectivity in the frontal lobes. 3However, it is the change in this connectivity of the grey matter with experience that makes us so different from our closest primate cousins. 4

In the adult brain, the frontal lobes are massively interconnected to most other regions of the brain and their size is largely due to the communicating neural fibres that make up the white matter beneath the grey-matter layer. However, this connectivity increases as the frontal lobes wire up to the rest of the brain. In comparison to other structures, the frontal lobes have the longest period of development, and during childhood they expand nearly twice as much as some other regions. 5In comparison to apes and monkeys, who peak earlier in the synaptic explosion of growth that we described in Chapter 2, genes that control synaptic formation delay peak connectivity until as late as five years in humans, which explains why this brain region is the last to start wiring up. 6

This delayed peak of activity in the wiring programme may have significant relevance to changes in behaviour. There is a noticeable shift in frontal brain activity between three and four years of age, when there is also a vast improvement in toddlers’ abilities to plan and control thoughts and behaviours. 7They become less impulsive, which may be a consequence of this changing brain connectivity which helps to regulate behaviours. 8

Another fascinating role for the frontal lobes is that they enabled humans uniquely to imagine different possible futures – to mentally time travel and make plans for the future. 9In fact, humans may be the only species that are able to contemplate the future. 10Many animals, including rodents like hamsters and squirrels, can store and hoard food for the future, but these could simply be automatic reflexive behaviours that are triggered without much thought. Bonobos will carry around the correct tool for retrieving food for as long as fourteen hours, showing that they can anticipate the future for at least half a day. 11But that’s hardly the same as planning for next year’s harvest. In one observation, cebus monkeys that were regularly fed once a day gobbled down as much food as possible until they were no longer hungry. They were always given more than they could eat in one sitting, but once they had eaten their fill, instead of saving it for another day they behaved like frat boys in a food fight and threw it out of the cage. 12

Humans on the other hand plan for all sorts of future events. Much of our daily lives are taken up in preparation for anticipated outcomes. Our routines of schooling and employment are activities that pay dividends many years down the road. We even plan for our retirement decades in advance. Unlike most other animals, we can save for a rainy day. That level of foresight requires the integrity of the frontal lobes, which explains why only about a third of three-year-olds can tell you about what they are going to do tomorrow whereas twice as many four-year-olds can. 13Immaturity and damage to these regions condemn us to living in the here and now, with little concern for how things might turn out.

The silent manager

The frontal lobes occupy an exalted position in the history of neuroscience. 14The eighteenth-century Swedish scientist Emanuel Swedenborg first proposed that they were the seat of human intellect, a proposition that was later supported by the phrenologist Franz Gall in the nineteenth century. However, the activity of the frontal lobes remained surprisingly elusive to investigation. When Canadian neurosurgeon Wilder Penfield, who pioneered brain surgery on fully conscious patients in the 1940s, applied electrical stimulation to the surface of the brain, he noted how different areas triggered specific sensations or body twitches. In contrast, stimulation of the frontal lobes remained ‘silent’. So what do the frontal lobes do?

What don’t the frontal lobes do is probably the more useful question. Rather than being the focus of function, the frontal lobes are like New York’s Grand Central Station, London’s Heathrow airport or any large communication hub, receiving and sending information, linking up all the regions from the sensory systems, motor systems, emotional and memory regions spread throughout the brain. The massive amount of interconnectivity with the other brain areas indicates that the frontal lobes play a role in just about every aspect of human thought and behaviour. Rather than being localized in the frontal lobes, complex activities are integrated throughout this region like a neural junction box. 15

Behaviour that requires planning, coordination and control enlists the activity of the frontal lobes. Even those activities that are automatic, such as the urges and impulses controlled deep inside the midbrain, need to be integrated into the rest of our behavioural repertoire so that they don’t get us into trouble. One way to think about the frontal lobes is to imagine their role as like a senior executive management team overseeing a large company. To be successful, a company must operate economically without wasting too much time and resources. The company needs to be able to take stock of the market, estimate demands, monitor current resources and set into action a planned strategy. The company will need to anticipate economic changes and plan for the future. Although there may be subdivisions in the company that compete for more resources than others, they have to be regulated so that the company as a whole can be more successful. This is why we need executives to manage the various operations that make the business run more efficiently as well as competitively. These executive functions monitor, coordinate, regulate and plan our thoughts and actions. Planning, memory, inhibition and attention are four executive functions (EFs) that operate from within a region that sits back from the front part of the brain, known as the prefrontal cortex (PFC).