Talks and Conference Presentations
Society for Neuroscience
35th Annual Meeting
November 12-16, 2005
Face and Object Processing In the Fusiform Gyrus: A Comparison of Intracranial ERP Recordings and Functional MRI
M.T. Diaz1, J.P. Morris1, K. Vives3, D.D. Spencer3, G. McCarthy1,2
The degree to which visual processing within ventral extrastriate brain regions, including the fusiform gyrus, is domain specific is a contentious issue. Part of the controversy may stem from the differing nature of the measures used to investigate this issue. Functional MRI measures hemodynamic changes that evolve over seconds and involve venous elements that may overestimate the spatial extent of neural activation. Direct electrical recording through subdural electrode strips and grids provide an alternative measure of neural activity with high spatial and temporal resolution. Here we will discuss two experiments that used identical presentations of visual stimuli comprising many object categories including faces. Direct electrical recordings in a sample of patients undergoing intracranial investigation for epilepsy were compared to fMRI responses evoked by the same stimuli in controls. In the present studies, we presented a series of objects from several categories and faces. Interspersed within this series were abstract patterns with the same spatial frequency and luminance as the faces and objects. Results from the intracranial study indicated large focal potentials in the fusiform gyrus for faces, but not for non-face objects. In the fMRI study, large ventral activations were found in which a medial to lateral distribution of response was noted, where medial regions, which extended to the parahippocampal gyrus, responded more strongly to objects and lateral regions responded more strongly to faces.
Occipitotemporal Activation Evoked by the Perception of Human Bodies is Inhibited by the Presence of the Face
J.P. Morris1, K.A. Pelphrey1, G. McCarthy1
Prior studies have identified discrete brain regions in occipitotemporal cortex that are preferentially activated by faces and bodies. Here we investigated the degree to which activation in these regions is influenced by the presence, or implied presence, of the face and other body parts of a partially occluded actor in a familiar setting. Subjects continuously viewed a static image of a lecture hall while actors appeared briefly in various poses. There were three conditions: No Occlusion, in which the actor appeared with limbs, torso, and face clearly visible; Face Occlusion, in which the actor appeared with his or her face occluded by a textbook; and Body Occlusion, in which the actor appeared behind a podium with only face and shoulders visible. Using event-related functional MRI at 4 Tesla, we obtained strong activation in those regions previously identified as important for face and body perception. These regions included ventral occipitotemporal cortex (VOTC) and two portions of lateral occipitotemporal cortex (LOTC), one centered upon the middle occipital gyrus and the other in the posterior superior temporal sulcus. Activity within medial VOTC was strongest for the Face Occlusion condition. The presence of a face increased activation within the lateral fusiform gyrus and medial inferior temporal gyrus. Activation of the LOTC near the middle occipital gyrus was strongest when the torso and limbs were visible, but the face was occluded. Adding a visible face resulted in a marked reduction in activation. The results are discussed with concern to current theories of face processing and social perception.
Evidence of Resource Limitation for Involuntary Visual Attention: An fMRI Study
G. Yucel1, G. McCarthy1,3, A. Belger1,2
Previous studies suggest that involuntary auditory attention evoked by unattended auditory stimuli is not influenced by the current focus of attention. However, prior studies from our laboratory have found that processing of unattended auditory tones in the auditory and frontal regions is modulated by top-down attentional demands and resource availability. Whether detection of unattended visual stimuli is altered by the availability of attentional resources has not been established. The goal of the current study was to examine the automaticity of these activations, their modulation by attentional shifts, and the neuroanatomical distribution of any attentional effects upon visual deviance detection. We designed an event-related functional magnetic resonance imaging (fMRI) study during which subjects performed a continuous perceptual-motor visual tracking task whose difficulty was modulated by changing the control dynamics of a joystick. Changes in the anatomical localization, spatial distribution, and intensity of the blood oxygenation level dependent (BOLD) response associated with unattended visual changes were examined during a low- and high-tracking difficulty conditions of the primary visual task. Visual stimuli consisted of frequently presented “standard” visual stimuli and infrequent, “deviant” visual stimuli of 150ms duration. Results indicated that the unattended deviant stimuli elicited BOLD activation in visual, frontal, fusiform, and parietal regions. The intensity and extent of the activation to the deviant stimuli were decreased as a function of the demands of the primary visual task in these regions. Furthermore, modulating the difficulty of the primary task also yielded differential activations in prefrontal regions. These findings suggest that processing of unattended visual stimuli is restricted by the attentional demands of a primary task, as previously demonstrated for unattended auditory deviant tones.
Neural Correlates of the Detrimental Effect of Emotional Distracters on Working Memory Performance: Event-Related fMRI Evidence
F. Dolcos1, G. McCarthy1,2
Although the neural mechanisms underlying the beneficial effect of emotion on cognitive functions (e.g., episodic memory) have been extensively investigated, the neural correlates of the detrimental effect of emotion are largely unknown. We investigated the effect of emotional and non-emotional distracters on the neural mechanisms associated with working memory (WM) maintenance operations. Event-related fMRI were recorded while young healthy participants performed a delayed-response WM task for faces, with novel stimuli presented as distracters during the delay interval. Novel stimuli consisted of high-distracting meaningful pictures (both emotional and neutral), and low-distracting meaningless pictures, (i.e., scrambled version of the meaningful pictures). As expected, WM performance was lower for the high-distracting conditions than for the low-distracting condition, with emotional distracters having the most detrimental effect on performance. Paralleling this behavioral effect, delay activity in the dorsolateral prefrontal cortex (dlPFC), a region typically associated with WM maintenance operations, was decreased in the presence of high-distracting conditions, with emotional distracters producing the highest decrease. Similar patterns of activity were observed in other dorsal brain regions, including superior parietal cortex. Moreover, an opposite pattern was observed in ventral brain regions, including the ventrolateral PFC and the amygdala, which showed the highest increase in delay activity to the presence of emotional distracters. These results provide direct functional neuroimaging evidence that the detrimental effect of emotional distracters on ongoing cognitive processes are associated with cognitive-affective interactions mediated by interplays between a dorsal neural system associated with executive processing and a ventral system associated with affective processing.
Probability Transitions In a Decision Making Under Risk Paradigm
E.M. Dagenbach1, S.A. Huettel2,3
We investigated how transitions in probability influenced brain activation in a task involving decision making under uncertainty. Our subjects chose between two types of gambles: singles that had a known probability (e.g., 90%) of winning a monetary reward, and doubles that could take either of two possible probabilities (e.g., 80% or 100%) with equal odds of each. If a double was chosen, then the probability to be played was revealed following the subject's choice (e.g., the subject actually played a 80% gamble). During the experiment, we measured changes in the amount of deoxygenated hemoglobin, an index of local neuronal activity, using functional Magnetic Resonance Imaging (fMRI). We hypothesized that we would observe activation associated with transitions in reward probability, even when those transitions were not contingent upon decisions made by subjects or the delivery of a reward.
Decision Ambiguity Modulates Activation of the Posterior Inferior Frontal Sulcus
S.A. Huettel1,2, B.T. Warner1, E.M. Gordon1, C.J. Stowe4, M.L. Platt3
Many decisions are made under limited information about potential outcomes. When two or more outcomes are possible, with knowable probabilities, decisions are made under risk. Conversely, decisions made with limited knowledge of outcome probabilities are made under ambiguity. The distinction between risk and ambiguity has been long debated within the economics literature (see Knight, 1921). In the current study, we investigated using functional magnetic resonance imaging (fMRI) whether risk and ambiguity evoke distinct patterns of neural activity during decision making.