Lateralization of brain functions: tolerance of ambiguity, uncertainty, and complexity

Lateralization refers to the observation of differences between the two cerebral hemisphreres; these include structural differences, differences in activiation to stimuli, involvement in information processing within the brain, and consequences of neurological damage or dysfunction.

The two halves of the cortex are very similar but not identical. Differences can be seen at both a gross anatomical level (the left planum temproal are often larger than the corresponding area in the right hemisphere; the right hemisphere is heavier and contains more white matter than the left); and at a cellular level. How these differences relate to brain function (and dysfunction) has been and continues to be an exciting area of investigation.

One very consistent finding is that the left hemisphere often is found to show a disportionate load when lanaguage is involve. This leads to statements ("hypotheses") such as: "the left hemisphere is specialized for langauge function", "langauage is usually lateralized in the left hemisphere", and similar sentiments that you have heard in both the popular press and in many text books, and probably in some lectures. And it is certainly true that, if we had most of you under a PET or fMRI scanner and were giving you "langauge tasks", your left hemisphere would be lighting up our screen (consuming more glucose or oxygen or whatever we were using as a measure of neuron activity).

In almost any multiple choice test you might be taking, if you were asked about left hemispheric specialization and one of the response options concerned language--that would be the smart choice. But is that really what is going on here? The truth is that we do not completely know and some caution is advised in how far we generalize from the data available to what we conclude this means regarding hemispheric functioning.

Goldbert (2001; Goldberg & Costa, 1981) suggests that the right hemisphere is specialized for processing novel, complex, and disparate information (stuff you are just beginning to try and make sense of); and the left hemisphere is specialized for processing well known, routinized, and automatic responses (for instance: langague after it is well established or well rehearsed motor routines). In a similar vein, Luria suggested the left hemishpere was more prepared to process sequential information (linear processes) and the right hemisphere more simultaneous information (parallel processing).

On a more speculative level--From this perspective the hemispheric differences would be less likely seen as evolving to support the emerging language and analytical thinking abilities of early hominds, and more as pre-existing differences that were opportunistically recruited as language functions began to emerge. And this could have implications for ideas such as Chomsky's LAD (langauge acquisition device) hypothesis.