Listening to emotion: Auditory processing and the amygdala

The amygdala is a major neural structure engaged in coding the emotional content of multi-modal signals. Processing emotional cues and using this information to mediate behavioural responses are two essential aspects of human-environment interaction. The focus of this chapter is on the role of the amygdala in processing the emotional meaning of auditory stimuli. Two major classes of sounds are discussed: external sounds in the environment (urban soundscapes) and internalised 'phantom' sounds (tinnitus). Auditory perception has been studied using single sound source clips, or acoustically richer, more naturalistic soundscape recordings. Typically, brain imaging studies of emotionally evocative sounds have focused on examining unpleasant or aversive single-source sounds relative to neutral sounds. Reports of an amygdalar response to pleasant sounds are less consistent. One recent study sought to report the neural basis of a cognitive response to a wide range of natural urban soundscapes using functional magnetic resonance imaging (fMRI). Results indicate that soundscapes evoking a positive or negative emotional response resulted in a pattern of neural activity, including the amygdala. This work is discussed in relation to the importance of the amygdala in processing the external acoustic environment. The amygdala also plays a role in processing subjective =phantom' sounds and has been proposed in models of tinnitus to account for the emotional distress that can occur for some sufferers. Recent evidence points to the involvement of limbic regions, particularly the amygdala, in tinnitus pathogenesis. Preliminary results from an ongoing fMRI study on the involvement of the amygdala in tinnitus are presented and discussed in relation to theories about the emotional aspects of the condition. The final section of this chapter discusses the technical constraints inherent in utilising fMRI to measure brain activity in both the amygdala and auditory cortex, with the aim of aiding future research in this area.