Though a powerful and penetrating tool, neuroimaging technologies and the studies that rely upon those technologies, remain a relatively blunt instrument, overly broad in scope. Brain imaging studies reveal information about various brain regions in relation to one another, According to the pioneering neuroscientist, Joseph LeDoux, reliance on such studies to provide precise information about specific brain functioning is analogous to drawing conclusions about New York City based on a study of New York State (Big Think, 2010). Instead, LeDoux makes a compelling and cohesive argument that the development of each unique personality, comprising each person's interconnected cognitive, emotional, and behavioral patterns, is determined at a much more miniscule and precise level: the synaptic level.
Synapses are the space between neurons that function as switching or relay stations. Synapses pass along (transmit) information from one neuron to the next. Though neurons serve as the brain's communication system, the synapses between neurons ultimately serve an equally critical role. They provide a means through which information becomes stored within the brain as the various forms of memory.
Importantly, multiple incoming signals from multiple neurons may arrive at the same synapse at the same time. As these signals arrive, they compete with one another to influence whether or not an outbound signal will occur, and if so, which particular route the signal will take. The outcomes of these competitions change the routing structure of the synapse itself so that in the future, particular routes are favored over others. Therefore, certain outcomes are more likely than others to reoccur. It has been estimated there are more than 100 trillion synapses in the human brain. Thus, there is nearly an infinite number of instances in the brain where converging neurons merge their outputs to enable the storage of memory.
According the LeDoux (2002), nature (genetic make-up) and nurture (life experiences) both influence the encoding of information at the synaptic level. Each person has a unique synaptic pattern, formed first by genetics and then heavily modified by life experiences. The cumulative state of the synapses and the information encoded into these connections is the key to understanding who we are. In other words, personality reflects specific patterns of interconnectivity that manifest over time between the neurons in each individual's brain.
Having built a case for the critical importance of the brain and its synapses as the ultimate determinate of personality, we will be the first to admit that we have not provided much detail as to how this important process really works. For that, we recommend Dr. LeDoux's very readable book, The synaptic self: How our brains become who we are, and specifically therein, the chapter on "synaptic sickness" for insight into how synaptic processes create predispositions towards the emotional difficulties associated with personality disorders.
Despite these exciting developments, research into the neurobiology of personality and personality disorders is still in its infancy. There is no one overarching and cohesive theory covering the neurobiology of personality disorders at this time. As Depue and Lenzenweger (2005) point out, such a model would have to consider a large number of factors that underlie the dimensions of personality traits, and that interact with each other in incredibly complex ways.