Connections Through Time, Issue 12: July
- September 2001
The prefrontal cortex is vital
How do we recall and store
information long enough to work with it. Here's a defining quote from a Scientific
researchers are beginning to fathom the neural processes underlying "working memory"--the limited, short-term store of currently relevant information that we draw on when we comprehend a sentence, follow a previously decided plan of action or remember a telephone number. When we bring to mind the name of Russia's president, for instance, that information is temporarily copied from long-term memory into working memory.
The prefrontal cortex of the brain appears to be a key part of the nervous
system controlling working memory.
Advanced imaging techniques were first used in 1997 to show the moment-by-moment
brain activity involved in seeing a face or a series of letters, holding it
briefly in working memory, and then recalling it. Two research teams supported
by the National Institute of Mental Health (NIMH) reported on the studies using
functional magnetic resonance imaging (fMRI). These
studies were the first in humans to demonstrate sustained activity in the
prefrontal cortex while information is held in mind.
Working memory disorders, such as schizophrenia, illustrate the importance of the "executive functions" of the prefrontal cortex which include decision making, attention, and planning. Researchers believe that the high concentrations of nerve fibers containing the neurotransmitter dopamine are central to working memory and executive functions. Neurotransmitters are chemicals which transmit messages from neuron to neuron via synapses. They act by binding to molecules called receptors. Monkeys have been used extensively to study the effects of various chemicals on the brain. The figure at the right shows the brain of a monkey and the prefrontal cortex. The inset shows a dopamine synapse.
2001 report from the NIMH discusses a
genetic link between dopamine activity in the prefrontal cortex to working
memory tasks and to a slightly increased risk for schizophrenia:
The finding, which must still be confirmed by independent teams of investigators, emerged from an ongoing study of people with schizophrenia and their siblings. The study is among the first to suggest a mechanism by which a gene might confer susceptibility to a mental illness, say the researchers. Daniel Weinberger, M.D., Michael Egan, M.D., NIMH Clinical Brain Disorders Branch, and colleagues, report on their results in the May 29, 2001 Proceedings of the National Academy of Sciences.
The most disabling form of mental illness, schizophrenia affects one percent of the adult population, typically in young adulthood, with hallucinations, delusions, social withdrawal, flattened emotions and loss of social and personal care skills. Although its cause remains a mystery, evidence suggests that it is at least 80% heritable, stemming from complex interactions among several genes and non-genetic influences. Several chromosomal regions have been implicated, but none have been definitely confirmed and no genes have yet been linked to the disorder.
Given the syndrome's daunting complexity, Weinberger and colleagues have been studying many traits to identify those that patients share with their well siblings, hoping to turn up clues to susceptibility genes. Their brain imaging studies had revealed that both well siblings and patients falter on tasks of working memory and show abnormal activation of the prefrontal cortex, which is required for such "executive" functions. Studies have shown that the chemical messenger dopamine plays a pivotal role in tuning the activity of the prefrontal cortex during such tasks.
Executive functions associated
prefrontal cortex and working memory include:
- initiation and overall control of deliberate actions
- initiation and overall control of goal directed behavior
- decision making
However, it is crucial to recognize that most of these functions are phenomena of distributed neural processing and without a unique location of their own, either in frontal cortex or elsewhere. (Ref.)
The prefrontal cortex is central to organizing the distributed information contained in the nervous system.
We wonder how this growing body of knowledge concerning our nervous systems
relate to how the subconscious mind accesses and communicates intuitive
information to the conscious mind. The prefrontal cortex is probably involved with
this communication process. Intuitive information and the mind are
discussed in the next
Machinery of Thought, Scientific American Article, Aug 1997
Dynamics of Working Memory, National Institute of Mental Health Press
Release, April, 1997
Prefrontal Cortex and Schizophrenia, Brain Briefings, Summer 1995
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Intuition: "It's All in Your Mind" Applications: An Online Protocol for Exploring Your Intuition
The Machinery of Thought, Scientific American Article, Aug 1997
fMRI Reveals Dynamics of Working Memory, National Institute of Mental Health Press Release, April, 1997
The Prefrontal Cortex and Schizophrenia, Brain Briefings, Summer 1995
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