| Recent neuroimaging studies suggest that amygdala involvement in human emotion may be lateralized (Hamann, Ely, Hoffman, & Kilts, 2002). The present study examines the specific role of the left and right amygdalae in emotional processing. In Experiments 1 and 2, we observed that left unilateral temporal lobectomy (LTL) patients fail to show potentiated startle while expecting a shock while control subjects and right unilateral temporal lobectomy (RTL) patients do show potentiated startle. RTL patients, however, fail to show potentiated startle during viewing of affective pictures while control subjects and LTL patients do show potentiated startle. Together, these findings suggest a double dissociation between left and right medial temporal lobe damage in the modulation of fear responses. Anticipating shock was the result of a linguistic/cognitive representation acquired through language, and processing verbally mediated material generally involves the left hemisphere. In contrast, viewing emotional pictures involved direct exposure to visual information, which appears to activate the right hemisphere. Additional evidence from case studies suggests the amygdala is responsible for this modulation. To further test this hypothesis Experiments 3 and 4, which examine startle eyeblink during imagery, were undertaken. Results were consistent with a linguistic/cognitive representation explanation of the double dissociation found in Experiments 1 and 2 but did not reach significance. Directions for future research are suggested. |
