Talks and Conference Presentations

Society for Neuroscience
31st Annual Meeting
November 10-15, 2001
San Diego, California

• Prefrontal Cortex Activation is Evoked by the Violation of Local Stimulus Expectancies
  Scott A. Huettel, Peter B. Mack, Gregory McCarthy
  Brain Imaging and Analysis Center, Duke University, Durham, NC

  The results of many cognitive neuroscience studies have converged on prefrontal cortex (PFC) as a primary locus for working memory and executive processing in the brain. Given the diversity of cognitive functions attributed to PFC, it is important to investigate whether task components like response selection are sufficient to elicit its activation. We analyzed changes in response strategy in a two-stimulus, two-response classification task, using event-related fMRI at 1.5T. Circles (C) and squares (S) were presented one at a time (2s interval) at fixation, with each shape requiring a different button press. Our analysis examined how activation to a stimulus depended upon its preceding sequence. If PFC activity results from changes in response strategy, then stimuli that violate the expected pattern of previous responses should evoke more activity than stimuli that continue a pattern (e.g., CCCS > CCCC). Furthermore, activation increases should be seen for violations both of repeating (e.g., SSSSC) and of alternating (e.g., SCSCC) sequences. Our results confirmed these predictions. Primary activation foci were found in the inferior frontal, middle frontal, and anterior cingulate gyri. Activation amplitude increased with increasing pattern length before violation, for both repeating and alternating sequences. These results imply that changes in response strategy may elicit PFC activation even when response and memory requirements of the task do not change across stimuli.

  View Presentation (HTML)

• Influence of Distraction upon Delay-interval Activity in a Working Memory Task: A Functional MRI Study
  Amishi P. Jha, Brian T. Miller, Gregory McCarthy
  Brain Imaging and Analysis Center, Duke University, Durham, NC

  In a previous study (Jha & McCarthy, 2000), a face working memory delayed-recognition task was used to examine prefrontal (PFC) and fusiform (FFG) activity as memory load varied. Within both PFC and FFG, increases in memory load resulted in greater transient activity to memory cues. Within PFC, these transient responses were followed by load insensitive sustained delay activity. Activity within FFG returned to baseline during the delay-interval. Here we examined the effect of distraction on sustained delay activity. A 3-face memory cue was followed by an 18-sec delay-interval that ended with the presentation of a 1-face memory probe. The subjects’ task was to determine if the memory probe matched any of the memory cue faces. During the delay interval, a random number of previously unseen faces, phase-scrambled faces (unrecognizable as faces), or no distracting stimuli were presented. Transient responses to the memory cues were comparable across all trial types within PFC and FFG. Within PFC, delay activity was greatest during face-distraction followed by lower amplitude activity for the scrambled-face and no distraction trials. Within FFG, delay activity was greatest during face-distraction followed by scrambled-face distraction. No delay activity was observed during the no-distraction trials. Thus, delay activity within PFC may reflect operations needed to prevent task-specific distraction whereas FFG activity likely reflects sensory processing of distractors.

  View Poster (PDF)