Our initial studies concentrated on the role of the amygdala in emotional forms of learning and memory. The amygdala is a structure in the medial temporal lobe that is known to participate in emotional and motivational functions in non-human animals, but its involvement in human emotion has been difficult to specify. We found that neurologic patients with damage to this brain region were impaired at consolidating long-term memories for arousing words. They also failed to acquire autonomic fear responses to warning cues that predicted the delivery of aversive sensory stimulation. These patients, however, performed normally on other learning and memory tasks involving emotional stimuli that were low in arousal. We confirmed that the amygdala is critically involved in conditioned fear learning and arousing stimulus encoding using fMRI in healthy adults. These findings indicate that the human amygdala makes a selective contribution to memory performance for stimuli that are highly-arousing.
Currently, this line of work is being extended to understand how the amygdala interacts with other brain regions during learning and memory tasks. We have recently shown that amnesic patients with damage to the hippocampus, another medial temporal lobe structure, show a different pattern of performance on fear conditioning paradigms. Unlike patients with amygdala damage, hippocampal amnesiacs can acquire autonomic fear reactions on simple tasks despite having no conscious recollection of what they learned. However, they fail to subsequently reinstate their fear reactions given appropriate spatial cues in the environment. To determine how the amygdala and hippocampus interact with neocortical brain regions during memory encoding and retrieval tasks, we are using whole-brain fMRI in combination with ERP recordings and concurrent psychophysiological measures in healthy subjects.
Although we have determined that memories for emotional events are generally superior to those for neutral events, it is not clear what mechanisms are responsible for this retention advantage. As mentioned above, memory consolidation is one potential contributing factor. Another possibility is that emotional stimuli receive preferential attention upon their initial encounter, which promotes long-term memory storage. Using eye tracking methods, we have shown that emotionally-arousing pictures (paired with neutral ones) modulate visuospatial attention in two ways -- first by orienting the initial direction of attention to the emotional scene in the pair, and second by sustaining attention on the emotional scene over time. Interestingly, these attentional effects were similar in young and aging adults and early-stage Alzheimer's disease patients.
The attention paid to emotional events, however, comes at a cost. By detracting available processing resources away from other stimuli or task-relevant computations, emotional thoughts or experiences can disrupt mental operations. We are currently examining the neural correlates of emotional distraction during attention-demanding tasks. We hypothesize that maintaining attentional focus in the face of task-irrelevant emotional distraction requires an interaction between dorsal and ventral processing streams in the brain. An imbalance in the distribution of activity along these networks may underlie emotional dysregulation in a variety of affective disorders.
