Different people have different temperaments, moods, and behavior profiles that tend to remain constant over a lifetime. Are these temperamental distinctions also reflected in basic brain differences? Schwartz et al. studied the well-established temperamental differences of inhibited versus uninhibited behavior to novelty. They found that people classified in terms of these temperamental categories at the age of 2 showed differential fMRI responses to unfamiliar faces in the brain structure of the amygdala when tested as adults. How stable is a synapse that has just undergone long-term potentiation (LTP) or long-term depression (LTD) in real life? Zhuo et al. (see the Perspective by Chiu and Weliky) induced synaptic plasticity in the retinotectal system of the frog Xenopus. However, in a time window of about 20 minutes, subsequent spontaneous or uncorrelated activity could diminish or even reverse previously induced LTP or LTD. Stable and long-lasting changes in synaptic strength could only be induced if the induction protocol was repeated several times in a spaced fashion, with intervals of several minutes between the plasticity induction events.
C. E. Schwartz, C. I. Wright, L. M. Shin, J. Kagan, S. L. Rauch, Inhibited and uninhibited infants "grown up": Adult amygdalar response to novelty. Science 300, 1952-1953 (2003). [Abstract] [Full Text]