Dissociated responses in the amygdala and orbitofrontal cortex to bottom–up and top–down components of emotional evaluation

Abstract

Although emotional responses to stimuli may be automatic, explicit evaluation of emotion is a voluntary act. These bottom-up and top-down processes may be supported by distinct neural systems. Previous studies reported bottom-up responses in the amygdala, top-down responses in the orbital and ventromedial prefrontal cortices, and top-down modulation of the amygdalar response. The current study used event-related fMRI on fifteen healthy males to examine these responses in the absence of stimulus anticipation or task repetition. Factorial analysis distinguished bottom-up responses in the amygdala from top-down responses in the orbitofrontal cortex. Activation of ventromedial prefrontal cortex and modulation of amygdalar response were not observed, and future studies may investigate whether these effects are contingent upon anticipation or cognitive set. KeywordsAffect; fMRI; event-related; factorial; anticipation The ability to evaluate our feelings is essential to normal emotional function. Although emotional responses to stimuli may be automatic, explicit evaluation of emotion is a voluntary act. Accordingly, the bottom-up 1 , or stimulus-driven, and top-down, or task-driven, components of emotional evaluation may be mediated by different neural systems. Studies of emotional evaluation using fMRI have associated bottom-up processing with the amygdala and top-down processing with the orbital and ventromedial prefrontal cortices. Furthermore, some studies reported modulation of the amygdala response under different task conditions, representing top-down modulation of bottom-up processing. However, technical issues with many of these studies (use of blocked designs, which confound responses to stimuli with Corresponding author: Paul Wright, Centre for Speech, Language, and the Brain, Department of Experimental Psychology, University of Cambridge, Downing Street, Cambridge CB2 3EB, UK, Tel: +44 1223 766454, Fax: +44 1223 766452, Email: paul@csl.psychol.cam.ac.uk. Publisher's Disclaimer: This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final citable form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. 1 Generation of emotional responses to stimuli may require associative processing determined by the individual's experience and therefore may include "top-down" components, but for brevity, we refer to neural responses that correlate with changes in stimulus content as "bottom-up". anticipation, and varying baseline controls tasks) render interpretation somewhat ambiguous. Therefore, the current study uses an optimized event-related emotional evaluation paradigm to attempt to locate distinct and interacting neural responses to the bottom-up and top-down componen...

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