Time courses of left and right amygdalar responses to fearful facial expressions

Despite the many studies highlighting the role of the amygdala in fear perc eption, few have examined differences between right and left amygdalar resp onses. Using functional magnetic resonance imaging (fMRI), we examined neur al responses in three groups of healthy volunteers (n = 18) to alternating blocks of fearful and neutral faces. Initial observation of extracted time series of both amygdalae to these stimuli indicated more rapid decreases of right than left amygdalar responses to fearful faces, and increasing magni tudes of right amygdalar responses to neutral faces with time. We compared right and left responses statistically by modeling each time series with (1 ) a stationary fit model (assuming a constant magnitude of amygdalar respon se to consecutive blocks of fearful faces) and (2) an adaptive model (no as sumptions). Areas of significant sustained nonstationarity (time series poi nts with significantly greater adaptive than stationary model fits) were de monstrated for both amygdalae. There was more significant nonstationarity o f right than left amygdalar responses to neutral, and left than right amygd alar responses to fearful faces. These findings indicate significant variab ility over time of both right and left amygdalar responses to fearful and n eutral facial expressions and are the first demonstration of specific diffe rences in time courses of right and left amygdalar responses to these stimu li. Hum. Brain Mapping 12:193-202, 2001. (C) 2001 Wiley-Liss, Inc.