Talks and Conference Presentations
Society for Neuroscience
36th Annual Meeting
November 14-18, 2006
Controlled Scanpath Variation Modulates Face-Specific Activity in the Fusiform Gyrus
James P. Morris1 and Gregory McCarthy1
Activation evoked by face and object processing in the ventral occipitotemporal cortex (VOTC) is strongly influenced by stimulus and behavioral manipulations. Because these same manipulations can also affect visual scanpath, it is possible that differences in VOTC activity may be due to differences in visual scanpath. We have investigated the influence of experimentally guided saccades and fixations on fMRI activation in brain regions specialized for face and object processing. In our first study, subjects viewed a static image of a face, a flower, or a static gray field in separate experimental runs, while a small fixation cross made a discrete jump within the image every 500 ms. We found that large saccades made over faces and flowers evoke significantly more activity within the VOTC. Of particular interest was the predefined face area, where large saccades made over a face, but not a flower, evoked strong activation changes relative to baseline. In a second study we investigated the influence of qualitative differences in scanpath on face activity in the predefined face area of the VOTC. Each run consisted of alternating blocks in which the subject was guided to make a series of saccades and fixations - i.e., a scanpath. Typical scanpaths were defined as a scanpath in which the fixation cross landed on the eyes or the mouth in 90% of all trials. Atypical scanpaths were defined as scanpaths in which the fixation cross landed on the eyes or mouth on 12% of all trials. The average saccade length was identical in both Typical and Atypical blocks, and both were preceded by a baseline block where the fixation cross made much smaller jumps in the middle of the screen. Within the functionally predefined face area of the VOTC, Typical scanpaths evoked significantly more activity when compared to Atypical scanpaths. Taken together, these results demonstrate that fMRI activation within face and object processing regions of the VOTC is highly sensitive to both the magnitude and pattern of eye movements. These findings illustrate the potential confounding influence of uncontrolled eye movements for neuroimaging studies of face and object perception in normal and clinical populations.
Social perception and reward systems that predict tendency toward altruistic behavior
Dharol Tankersley1,3, C. Jill Stowe4, and Scott A. Huettel1,2
Altruism refers to situations in which an organism acts to benefit another organism while incurring no direct benefit and sometimes even carrying a cost. The neural mechanisms underlying differences in altruism across individuals -- which may include variations in how social rewards are perceived or valued -- remain unknown. To investigate the neural bases of altruism, we measured brain activation using functional magnetic resonance imaging (fMRI) while subjects (n=27) performed a modified version of the monetary-incentive-delay (MID) reaction-time task. Subjects began the experiment by selecting a charity. At the beginning of each trial, an instruction screen indicated who would be playing (the subject or the computer) and who would receive any money earned (the subject or the charity). On playing trials, a reward was earned (for themselves or for charity) if the subject responded to a target stimulus within a threshold time interval. On watching trials, the computer responded with timing drawn from a distribution yoked to that of the subject's responses. After the scanning session, subjects completed a questionnaire assessing the frequency of different altruistic behaviors.
A small set of brain regions exhibited greater activation when subjects watched the computer play the game than when the subjects played the game themselves. These included the posterior cingulate cortex, bilateral posterior superior temporal sulcus (pSTS), bilateral parahippocampal cortex, the right temporal pole, and the right dorsolateral prefrontal cortex. Greater activation was seen in a much more distributed set of regions in fronto-parietal and fronto-striatal areas in the opposite contrast, when subjects played the game vs. when subjects watched the computer play the game. We found that altruism scores predicted fMRI activation in the right pSTS, such that subjects who evinced more right pSTS activation had higher altruism scores and subjects with less right pSTS activation had lower altruism scores. Hierarchical regression analyses revealed that the right pSTS was the only region that independently predicted intersubject differences in altruism scores. Given prior reports of a role of the pSTS in attributions of agency, these results indicate that the capacity to empathize or detect another's mental states and actions is a central component of altruistic behavior.