How do we become what we are? How do we change?
Imagine an open hillside with no path. One day, some hikers come along and trudge up to the top of the hill, leaving a faint track of beaten grass where they have walked. The next day other hikers arrive and follow the faint outline left by the first hikers. Day after day hikers naturally follow this ever more pronounced track until it becomes a well-worn trail, attracting future hikers to its inviting curve. Then one day, some curious and adventurous trekkers decide to go off the beaten path and forge a new trail. Thereafter, the same process that occurred on the first trail repeats on the second.
Our brains and nervous systems develop in much the same experience-dependant ways. Every experience leaves a neural trace, encoding as memory. These experiences then become more likely to reoccur in the future.
Human experience comes about from two processes that interact with each other. The first comes from our evolutionary past. This is expressed through the organisation and development of the nervous system. This leads to billions of neurons organising into neural networks that seek the opportunity to grow.
Our ‘neural architecture’ is also shaped and grows in response to relationships. The human brain is a social organ. It grows through positive and negative interactions with others. These interactions become encoded within our brains. These experiences become neurobiological structures as nature and nurture interact to shape who we are and who we become. When neural networks do not develop fully or are not integrated with the rest of the brain, we experience problems in our lives and in our relationships.
Neurons are small units that process information and make up all parts of the nervous system. A part of the brain like the amygdala or the hippocampus is made up of a large number of neurons that work together to perform certain jobs. These neurons need to be able to organise and re-organise so that we can learn, act and adapt to different situations.
A neuron can fire or it can ‘not fire’. That is all it can do. The different capabilities we have come from the complex interactions and messages sent between neurons. The brain might be thought of as being like the lights in a city. When all the lights are on a certain pattern is formed. When they are all off a different pattern is formed. And when some are on and some are off lots of alternative patterns can be formed.
Neurons organise into neural networks. These networks can be made up of just a few neurons in some animals, but in human brains there are millions of connections happening in these neural nets. These neural networks encode and organise all our behaviours from walking, to understanding stories, to developing scientific theories. These neural networks can connect with lots of other networks which integrates their different functions.
Neurons fire in response to a stimulus. The firing of these neurons then causes other neurons to fire. This results in a particular experience or a behaviour happening. Connections between neurons either have an excitatory (cause other to fire) or an inhibitory (stop others from firing) effect on other neurons.
Firing patterns are called the network’s instantiation. These develop through experience. Experience encodes all our abilities, emotions etc. into different types of memory. When these firing patterns repeat often, they form patterns of behaviour and experience. These patterns are called ‘learning’ and it takes new learning to create new patterns that changes the relationships between neurons within these networks. New learning may also happen when one network stops the activity of another. This is how we build and re-build the brain. Neurons are the building blocks and the networks are the structures.
When a baby tries to walk, her successes and failures become stored in networks that are involved in balance and movement. After a number of successes, these neural networks allow walking to happen naturally. All of our behaviours are the result of patterns that are already established through past learning, which is activated automatically without thinking.
Learning happens through changes in the connections between neurons, the expansion of neurons and the growth of new neurons. Plasticity is the ability of the nervous system to change in response to experience. Neurons grow through the branching out of dendrites to other neurons as a result of new experiences. While neurons connect to form neural networks, these networks must connect with other networks to perform complex functions. For example, when telling a story we must be able to integrate the networks involved in language, emotion and memory.