Talks and Conference Presentations
Society for Neuroscience
33rd Annual Meeting
November 8-12, 2003
New Orleans, Louisiana
Brain systems associated with violations of expectation: Contextual uncertainty modulates activity in a prefrontal-parietal network
Scott A. Huettel1-4, Peter B. Mack1, Gregory McCarthy1,3-6
Common neural substrates of behavioral selection and working memory: evidence from functional MRI
Gregory McCarthy1,3-6, Ronald J. Viola1, Allen W. Song1,5, Scott A. Huettel1-4
Different Neural Representations for Content and Function Words
Michele T. Diaz1,2 and Gregory McCarthy1,2,3
Content and function words differ in their purpose and semantic content. Different neural bases for these types of words have been supported by previous research (e.g. Friederici et al., 2000). We investigated semantic processing of content and function words using functional Magnetic Resonance Imaging (fMRI). Previous fMRI studies investigating semantic processing involved passive reading, an explicit semantic task, or comparisons across tasks (e.g. Petersen et al., 1990, Binder et al., 1997, Mummery et al., 1999). While these manipulations involve semantic processing, it is likely that other processes are also involved (e.g. strategic processes, intrusive thoughts,differential attentional demands). In the present experiment, a stream of random letter strings (2/sec) was displayed, to which participants performed a matching task. Incidental to the overt task, content and function words were interspersed randomly among nonwords every 12 to 15 seconds. The purpose of the task was to limit the amount of overt, strategic processing of the content and function words, while ensuring that the stimuli were viewed. The two types of words were contrasted in order to investigate areas of activation associated with 1) the processing words versus a baseline of nonwords and 2) differential levels of semantic processing. An inverse spiral acquisition sequence was utilized to better capture anterior temporal areas, areas that have been linked to semantic processing through lesion studies, but have been traditionally difficult toimage with fMRI.
The BOLD fMRI Refractory Effect is Specific to Stimulus Attributes: Evidence from a Visual Motion Paradigm
Olufolajimi O. Obembe1,2,4, Marty G. Woldorff4,6,7, Allen W. Song1,5,8 & Scott A. Huettel1,3,4,7
Functional magnetic resonance imaging (fMRI) studies have demonstrated that the hemodynamic response (HDR) to a stimulus attenuates upon repeated presentation of similar stimuli at short intervals (less than 6s) [1-3]. Known as the HDR refractory effect, this attenuation has been postulated to reflect either a nonspecific effect of large vessels draining functionally related brain regions, or an adaptation of neurons (or neuro-microvascular interactions) that are sensitive to the common attributes of successive stimuli [4-6]. In the latter case, one might expect to observe a difference between the refractory effect to identical stimuli and the refractory effect to stimuli which varied along a single attribute.
We investigated this possibility using moving gratings that differed only in their direction of motion. Stimuli were presented using a fast event-related design that included randomly presented static gratings for hemodynamic deconvolution [7,8]. We found that congruent motion elicited a robust refractory effect in motion-processing visual cortex and that incongruent stimuli did not. This observation is consistent with the view that the fMRI refractory effect reflects an adaptation of either the neural circuitry responsive to a stimulus attribute or the coupling between this circuitry and its local microvasculature; large-vessel contributions do not play a dominant role.
Cortical Activation Evoked by Involuntary Auditory Attention is Resource-limited: an fMRI Study
Günes H. Yücel1, Christopher M. Petty1, Gregory McCarthy1, and Aysenil Belger1,2
Task-irrelevant novel and salient stimuli, such as changes in visual position or auditory pitch, can capture attention involuntarily, away from task-relevant information. Recent studies have associated auditory involuntary attention shifts with fronto-temporal networks, which also appear to contribute to the generation of the mismatch negativity (MMN) event-related potential (ERP) component (Alho, 1995; Escera, 2000). While the temporal cortical contribution has been suggested to represent the early detection of unattended auditory deviant events, frontal sources have been suggested to reflect a signal to trigger a shift of attention towards the initially unattended stimuli (Näätänen, 1992). Whether detection of unattended salient events is altered by the availability of attentional resources has not been established. This study investigated the modulation of the fronto-temporal neural mechanisms that mediate involuntary or reflexive auditory attention using a dual-task design that controls carefully available attentional resources while simultaneously probing with task irrelevant stimuli (Wickens, 1976; Wickens et al., 1983). Using functional magnetic resonance imaging (fMRI), we evaluated whether cortical responses to irrelevant auditory stimuli were altered by modulation of the complexity of a primary visual tracking task. In particular, we examined whether the neural correlates of involuntary shifts were automatic and insuppressible, or whether they were modulated by the availability of attentional resources allocated to a primary task.