When Do Individual Differences Make a Difference

My assertion that repression is not a universal "mechanism" illustrates the more widespread and broader problem of using a physiological analogy to explain a psychological process. Freud explained repression as the organism's internal flight from danger. He was implicitly comparing repression to a physiological mechanism associated with what was yet to be called homeostasis. (In chapter 5, I will discuss homeo-stasis, emotions, and the protobiological self as midbrain functions.) At the level of the biological self, there may be universal physiological mechanisms. At the more complex level of personhood, individual differences cannot be ignored, and universals analogous to physiological mechanisms become suspect as explanations.

Whether or not individual differences can be bracketed in neuroscience would then depend on whether such global functions as meaning construction are being investigated.5 It would appear from the enormous success of neurobiology at the levels of molecular and cellular biology that individual differences at these levels can be bracketed and treated as "noise." The selective influence of the self does not enter into individual neurons or synaptic junctions. However, when considering the dynamics of global brain functions, the variations of individual selves will assume greater significance. In neuroscience some methods of investigation mask such individual differences, while others do not. For example, brain-imaging techniques such as fMRI use statistical methods that average out the observations obtained from individual subjects (for a description, see Frackowiak, Friston, et al. 1997). When a different technique is used, such as magnetic encephalography, individual differences, between subjects become apparent. In an experiment that employed magnetic encephalography (MEG) significant differences between individuals were observed. Edelman and Tononi (2000) described the neural correlates of consciousness in an experiment using binocular rivalry. The localities of the brain that coincided with consciousness differed in different subjects. When Walter Freeman (1999b) used the EEG to investigate the rabbit brain's response to odors, he discovered that the pattern of amplitude modulation was unique for each individual rabbit, each rabbit having its own distinctive signature. If rabbits can be said to have imaginations, their imaginations are those of unique individuals.

These findings should not surprise us, for experience sculpts the brain, unlike the liver or kidney. It is now widely recognized that genetic instruction cannot account for the brain's complexity. As Oliver Sacks (1990) observed in his review of Edelman's contribution, "Our brains create structures in the light of our experiences." Gerald Edelman's Theory of Neuronal Group Selection explains that although the anatomy of the brain is constrained by genes, connectivity at the level of synapses is established by somatic selection during the individual's development, beginning within the uterus and extending throughout the entire life cycle. The brains of identical twins are appreciably different. Edel-man's theory is a theory of Darwinian selection in somatic time rather than in evolutionary time. As Sacks (1990) further noted, "Darwin provided a picture of the evolution of species; Edelman has provided a picture of the evolution of the individual nervous system, as it reflects life experiences of each individual human being."

That brains organize essential behaviors not in accordance with a genetic code but as a result of an individual's trials and errors has been confirmed by investigators of infant motor development. Thelen and Smith (1994) have conclusively demonstrated that each human infant learns to reach for objects or learns to walk in its own distinct fashion. Their research demonstrates the uniqueness of individual solutions to developmental challenges.

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