Semantic context and visual feature effects in object naming: an fMRI study using arterial spin labeling

Previous behavioral studies reported a robust effect of increased naming latencies when objects to be named were blocked within semantic category, compared to items blocked between category. This semantic context effect has been attributed to various mechanisms including inhibition or excitation of lexico-semantic representations and incremental learning of associations between semantic features and names, and is hypothesized to increase demands on verbal self-monitoring during speech production. Objects within categories also share many visual structural features, introducing a potential confound when interpreting the level at which the context effect might occur. Consistent with previous findings, we report a significant increase in response latencies when naming categorically related objects within blocks, an effect associated with increased perfusion fMRI signal bilaterally in the hippocampus and in the left middle to posterior superior temporal cortex. No perfusion changes were observed in the middle section of the left middle temporal cortex, a region associated with retrieval of lexical–semantic information in previous object naming studies. Although a manipulation of visual feature similarity did not influence naming latencies, we observed perfusion increases in the perirhinal cortex for naming objects with similar visual features that interacted with the semantic context in which objects were named. These results provide support for the view that the semantic context effect in object naming occurs due to an incremental learning mechanism, and involves increased demands on verbal self-monitoring

Enhancement and suppression in a lexical interference fMRI-paradigm

Previous picture-word interference (PWI) fMRI-paradigms revealed ambiguous mechanisms underlying facilitation and inhibition in healthy subjects. Lexical distractors revealed increased (enhancement) or decreased (suppression) activation in language and monitoring/control areas. Performing a secondary examination and data analysis, we aimed to illuminate the relation between behavioral and neural interference effects comparing target-related distractors (REL) with unrelated distractors (UNREL). We hypothesized that interference involves both (A) suppression due to priming and (B) enhancement due to simultaneous distractor and target processing. Comparisons to UNREL should remain distractor unspecific even at a low threshold. (C) Distractor types with common characteristics should reveal overlapping brain areas. In a 3T MRI scanner, participants were asked to name pictures while auditory words were presented (stimulus onset asynchrony [SOA] = –200 msec). Associatively and phonologically related distractors speeded responses (facilitation), while categorically related distractors slowed them down (inhibition) compared to UNREL. As a result, (A) reduced brain activations indeed resembled previously reported patterns of neural priming. Each target-related distractor yielded suppressions at least in areas associated with vision and conflict/competition monitoring (anterior cingulate cortex [ACC]), revealing least priming for inhibitors. (B) Enhancements concerned language-related but distractor-unspecific regions. (C) Some wider brain regions were commonly suppressed for combinations of distractor types. Overlapping areas associated with conceptual priming were found for facilitatory distractors (inferior frontal gyri), and areas related to phonetic/articulatory processing (precentral gyri and left parietal operculum/insula) for distractors sharing feature overlap. Each distractor with semantic relatedness revealed nonoverlapping suppressions in lexical-phonological areas (superior temporal regions). To conclude, interference combines suppression of areas well known from neural priming and enhancement of language-related areas caused by dual activation from target and distractor. Differences between interference and priming need to be taken into account. The present interference paradigm has the potential to reveal the functioning of word-processing stages, cognitive control, and responsiveness to priming at the same time

Gender specific neural correlates of emotion and cognition

Evidence suggests that regions within the anterior cingulate cortex (ACC) are sensitive both to emotional and cognitive task demands. This experiment asked whether emotional and cognitive demands are processed separately by ventral and dorsal regions within the ACC, respectively. Results revealed significant individual variability between changes in anxiety and response times with practice during performance of a verb generation task. Correlational analyses of the functional magnetic resonance imaging (fMRI) data were inconclusive. However, exploratory analyses suggest that while the ventral and dorsal subdivisions of the medial prefrontal cortex, which encompasses the ACC, make specialized contributions to the processing of emotion and cognition, respectively, the two subdivisions also appear to interact. These analyses also suggest that there could be a difference in how women and men balance the competing demands of emotion and cognition that might be related to differences in self-concept and neural activity in the default mode network

Analyzing Reading Specialization Using fMRI, rs-fcMRI, and Development

Reading is an important, phylogenetically new skill. While neuroimaging studies have identified brain regions used in reading, it is unclear to what extent these regions become specialized for use predominantly in reading versus other tasks. The goal of this dissertation is to investigate the extent to which reading specialization exists at the region and network level, with a focus on orthography, the visual processing of words and letters. I used task-based and resting state functional connectivity: rs-fcMRI) studies to investigate the specialization of orthographic processing, purportedly localized to a left occipito-temporal fusiform cortex region. In Chapter 2, we find no visual region specialized for words or letter strings as compared to line drawn pictures and Amharic character strings: which compose the Ethiopian writing system). Rather, the region appears to be generally involved in visual processing with properties useful for reading, including the ability to process complex stimuli in groups. In Chapter 3, we use rs-fcMRI to demonstrate functional relationships between the left occipito-temporal fusiform cortex and spatial attention regions rather than regions consistently activated in reading tasks. In Chapter 4, we extend these findings by looking at the pattern of functional connectivity in a large network of reading-related regions found in a meta-analysis of reading studies. Using graph theoretic measures on resting state data, we did not find preferential functional connections between regions predominantly used in reading. Rather, we showed the network was basically composed of previously described, more general communities. Comparing the network structure of children and adults also shows few reading specific changes, but rather a change from local to distributed network structure, also seen previously. In Chapter 5, we describe a comparison of activity during matching and naming tasks, and show task-dependent processing differences in reading-related regions. Such differences also indicate a lack of specificity for reading, and suggest the need for careful task design. Together these results indicate a lack of neural specialization for reading at either the regional or network level, suggesting that fluent reading is instead performed by co-opting existing neural systems

The Attentional Control of Reading: Insights from Behavior, Imaging and Development

The process by which the initially attention-requiring task of transforming scribbles into meaningful concepts eventually becomes facile remains a central riddle of cognitive neuroscience. This body of work represents an effort to provide forward movement in answering the question of how attentional control mediates the process of reading, both by considering different stages of reading competence (development) and by seeking convergence between types of evidence (behavior and imaging). Inspired by a study published by Balota and colleagues in 2000, the paradigm used throughout this work involves comparing a simple speeded reading task vs. a regularize ( sound out ) task (Balota et al. 2000). In the first data chapter, I replicate the essential findings of the Balota et al. study in 2 young adult cohorts, confirming that stimulus characteristics, including lexicality and frequency, influence reading task performance in a manner that is modulated by top-down attentional control. I furthermore argue that the reaction time (RT) patterns are consistent with 2 distinct mechanisms by which top-down attentional control interacts with reading processes, pathway control and response checking. I then present evidence, motivated by the 2-mechanism hypothesis, that 2 sets of brain regions, including members of previously defined attentional control networks, show separable activity patterns that map nicely onto roles reflecting pathway control and response checking. In the second data chapter, I show that 8-10 year old children, like young adults, can perform the regularize task. Unexpectedly, the early readers are faster than the experienced readers to regularize, and this speed advantage for children holds for both words and pseudowords. Because children are slower than adults across a range of cognitive tasks (e.g., Kail 1991) - with children showing particular immaturity with regard to inhibiting prepotent responses (e.g., Davidson et al. 2006) - the developmental observation is remarkable in and of itself. Complemented by a cadre of post hoc analyses, the age groups differences can also be interpreted as additional support for the 2-mechanism interaction of attention and reading. Together, these results suggest that dissociable subcomponents of attentional control interact with subcomponents of reading processing, and that these interactions are dynamic across skill development and across task demands