Introduction to Neuroscience and Personality

I'm an amateur in neuroscience, and it will probably show in this and subsequent posts. Nevertheless, it is useful to write down what one is learning about in any case. If you see that I am wrong on a matter of fact, please tell me about it. 

History

Human personality has been an object of study for thousands of years. Starting in the middle of the 20th century, advances in neurobiology made it possible to begin to study neurophysiological processes that might be linked to personality. Before that, personality researchers were only able to observe and classify general behavioral traits. While this approach allows for a holistic approach to personality (seeing the "forest," not just the trees), definitions and classifications are inherently inexact, subject to misinterpretation, and lacking in scientific rigor. Socionics and other personality typologies fall into this category. 

The development of technology for studying brain functioning has opened up new avenues for exploration. A nuts-and-bolts understanding of how the brain works and how behavior is generated can ultimately show us the "trees" of which the "forest" of personality is made. Most likely, the coming years will see many new ideas about personality that increasingly integrate data from neuroscience. Indeed, both the academic world and the educated public have grown accustomed to neuroscientific explanations for psychological phenomena and have come to expect them. This is part of the century-long advance of biology into the behavioral and social sciences, with darwinian natural selection as the overarching explanatory paradigm. 

Definitions

There are a number of partially overlapping terms in this area, so here I will give some definitions:

• Neuroscience - the scientific study of the nervous system. Considered a branch of the biological sciences. An umbrella term than encompasses most of the other fields listed.
• Neuropsychology - the applied scientific discipline that studies the structure and function of the brain related to specific psychological processes and overt behaviors. Considered a branch of psychology.
• Neurobiology - the study of the cells of the nervous system and their organization. Considered a subdivision of neuroscience and biology.
• Neurophysiology - the study of nervous system function.
• Neurology - a medical field dealing with disorders of the nervous system.

Usefulness of neuroscience for the study of personality 

The defining feature of personality is that it differs from person to person. Therefore, for neuroscience to be integrated with personality psychology, neurobiological parameters must be discovered that vary significantly between people. It seems natural that researchers' attention will first be focused on general properties of the nervous system, and then on variations of those properties as they come to understand them better. 

Though neuroscience is still in its infancy, some such brain characteristics have already been discovered that seem to have a bearing on personality (list is probably partial):

• levels of neurotransmitters (there are many)
• size of different parts of the brain
• localization of brain activity

In addition, though not specifically relating to the brain, varying levels of hormones produced by the endocrine system have also been found to influence personality, such as testosterone, estrogen, and cortisol. The effects of these hormones are felt throughout the body, not just in the brain. 

Neuroscience methods and tools

Neuroscience studies phenomena that can be observed directly through the use of special equipment. Assessment of individual neuropsychological characteristics can take place through direct (brain scanning and other neurophysiological measurements) or indirect (observing performance during tasks known to be associated with kinds of neural activity) means. 

Brain scans are used to investigate the structure and functioning of the brain directly and include the following tools. The first two capture brain structure, while the last two depict its current functioning:

• MRI (Magnetic Resonance Imagine) - shows tissue composition of body/brain through the use of magnetic fields
  
• CAT/CT (Computed Axial Tomography) - shows structural makeup of body/brain through the use of x-rays which are computer processed to produce a 3-D model.
• fMRI (functional Magnetic Resonance Imaging) - uses magnetic field to show blood flow activity in the body/brain, which correlates highly, but not absolutely, to neural activity.
• PET (Positron Emission Tomography) - shows how and where body/brain responds to a particular molecule that was injected in the bloodstream and contains a radioactive tracer isotope. 

In addition to brain scans, electroencephalography (EEG) and magnetoencephalography (MEG) may be performed to record the levels and characteristics of electrical activity and magnetic fields, respectively, associated with neural activity.

Indirect methods are also used to study brain functioning. These include standardized neuropsychological tests of performance on tasks linked to specific neurocognitive processes, such as memory and verbal proficiency tests, and experimental tests measuring reaction time and accuracy on a particular task thought to be related to a specific neurocognitive process.

Prospects and difficulties 

Some of the tools listed above have been used on a limited scale to study people with different personal characteristics (skills, destructive behavior patterns, etc.), sometimes revealing observable differences in brain structure or functioning. Neurotransmitter levels probably play a significant role in shaping personality, but they are hard to measure directly because the brain doesn't leak them out to the rest of the body, and invasive procedures involve considerable risk of harm. Some commercial sources claim that neurotransmitter levels can be determined through urine tests, but this is debatable. Personality and behavior questionnaires such as those developed by Helen Fisher at chemistry.com may or may not accurately predict the level of neurotransmitters and hormones they are supposed to reflect. To their credit, the object of study is known and measurable in principle, even if there are difficulties at the present.

People of the same socionic type (or MBTI type, or whatever) could be run through brain scans to find commonalities, but this would require determining their types beforehand through inherently nonobjective means or by using a test of questionable validity. I doubt such a project could receive academic funding. I will continue to look into this topic. 

UPDATE APRIL 1, 2009: I just received a new book in the mail called Neurodynamics of Personality that talks in depth about the connections between physiology and psychology, and how new knowledge of the brain's workings sheds light on personality. I plan to read this book soon and incorporate it into new blog posts.