In neuropsychology

Neuropsychology

Neuropsychology studies the structure and function of the brain related to specific psychological processes and behaviors. The term neuropsychology has been applied to lesion studies in humans and animals. It has also been applied to efforts to record electrical activity from individual cells in...

 the left brain interpreter refers to the construction of explanations by the left brain

Left Brain

Left Brain, born Vyron Dalyan Turner, is an American record producer, rapper, and photographer from Los Angeles. He serves as one of the main producers in OFWGKTA, having produced portions on nearly all Odd Future releases...

 in order to make sense of the world by reconciling new information with what was known before. The left brain interpreter attempts to rationalize, reason and generalize new information it receives in order to relate the past and the present.

Left brain interpretation is a case of the lateralization of brain function

Lateralization of brain function

A longitudinal fissure separates the human brain into two distinct cerebral hemispheres, connected by the corpus callosum. The sides resemble each other and each hemisphere's structure is generally mirrored by the other side. Yet despite the strong anatomical similarities, the functions of each...

 that applies to "explanation generation" rather than other lateralized activities. Although the concept of the left brain interpreter was initially based on experiments on patients with split brains, it has since been shown to apply to the everyday behavior of people at large.

The discovery

The concept was first introduced by Michael Gazzaniga

Michael Gazzaniga

Michael S. Gazzaniga is a professor of psychology at the University of California, Santa Barbara, where he heads the new SAGE Center for the Study of the Mind. He is one of the leading researchers in cognitive neuroscience, the study of the neural basis of mind...

 while he performed research on split-brain

Split-brain

Split-brain is a lay term to describe the result when the corpus callosum connecting the two hemispheres of the brain is severed to some degree. The surgical operation to produce this condition is called corpus callosotomy and is usually used as a last resort to treat otherwise intractable epilepsy...

 patients during the early 1970s with Roger Sperry at the California Institute of Technology

California Institute of Technology

The California Institute of Technology is a private research university located in Pasadena, California, United States. Caltech has six academic divisions with strong emphases on science and engineering...

. Sperry eventually received the 1981 Nobel Prize

Nobel Prize

The Nobel Prizes are annual international awards bestowed by Scandinavian committees in recognition of cultural and scientific advances. The will of the Swedish chemist Alfred Nobel, the inventor of dynamite, established the prizes in 1895...

 in Medicine for his contributions to split-brain research.

In performing the initial experiments, Gazzaniga and his colleagues observed what happened when the left and right hemispheres in the split brains of patients were unable to communicate with each other. In these experiments when patients were shown an image within the right visual field (which maps to the left brain hemisphere), an explanation of what was seen could be provided. However, when the image was only presented to the left visual field (which maps to the right brain hemisphere) the patients stated that they didn’t see anything.

However, when asked to point to objects similar to the image, the patients succeeded. Gazzaniga interpreted this by postulating that although the right brain could see the image it could not generate a verbal response to describe it.

Decades of experiments

Since the initial discovery, a number of more detailed experiments have been performed to further clarify how the left brain "interprets" new information to assimilate and justify it. These experiments have included the projection of specific images, ranging from facial expressions to carefully constructed word combinations, and functional magnetic resonance

Functional magnetic resonance imaging

Functional magnetic resonance imaging or functional MRI is a type of specialized MRI scan used to measure the hemodynamic response related to neural activity in the brain or spinal cord of humans or other animals. It is one of the most recently developed forms of neuroimaging...

 (fMRI) tests.

Many of the studies and experiments build on the initial approach of Gazzaniga in which the right hemisphere is instructed to do things that the left hemisphere is unaware of, e.g. by providing the instructions within the visual field that is only accessible to the right brain. The left brain interpreter will nonetheless construct a contrived explanation for the action, unaware of the instruction the right brain had received.

The typical fMRI experiments have a "block mode", in which specific behavioral tasks are arranged into blocks and are performed over a period of time. The fMRI responses from the blocks are then compared. In fMRI studies by Koutstaal the level of sensitivity of the right visual cortex with respect to the single exposure of an object (e.g. a table) on two occasions was measured against the display of two distinct tables at once. This contrasted with the left hemisphere's lower level of sensitivity to variations.

Although the concept of the left brain interpreter was initially based on experiments on patients with split brains, it has since been shown to apply to the everyday behavior of people at large.

Reconciling the past with the present

The drive to seek explanations and provide interpretations is a general human trait, and the left brain interpreter can be seen as the glue that attempts to hold the story together, in order to provide a sense of coherence to the mind. In reconciling the past and the present, the left brain interpreter may confer a sense of comfort to a person, by providing a feeling of consistency and continuity in the world. This may in turn produce feelings of security that the person knows how "things will turn out" in the future.

However, the facile explanations provided by the left brain interpreter may also enhance the opinion of a person about themselves and produce strong biases which prevent the person from seeing themselves in the light of reality and repeating patterns of behavior which led to past failures. The explanations generated by the left brain interpreter may be balanced by right brain systems which follow the constraints of reality to a closer degree.

The checks and balances provided by the right brain hemisphere may thus avoid scenarios that eventually lead to delusion via the continued construction of biased explanations. In 2002 Gazzaniga stated that the three decades of research in the field had taught him that the left hemisphere is far more inventive in interpreting facts than the right hemisphere's more truthful, literal approach to information management.

See also

• Bicameralism
  Bicameralism (psychology)
  Bicameralism is a hypothesis in psychology that argues that the human brain once assumed a state in which cognitive functions were divided between one part of the brain which appears to be "speaking", and a second part which listens and obeys—a bicameral mind...
  
  
• Brain asymmetry
  Brain asymmetry
  Brain asymmetry can refer to at least two quite distinct findings:* Neuroanatomical differences between the left and right sides of the brain* Lateralized functional differences: Lateralization of brain function...