Katharina Dressel

The separation of processing stages in a lexical interference fMRI-paradigm

In picture-word interference paradigms, the picture naming process is influenced by an additional presentation of linguistic distractors. Naming response times (RTs) are speeded (facilitation) by associatively-related and phonologically-related words when compared to unrelated words, while they are slowed down by categorically-related words (inhibition), given that distractor onsets occur at appropriate stimulus onset asynchronies (SOAs). In the present study with healthy subjects, we for the first time integrated all four auditorily presented distractor types into a single paradigm at an SOA of -200 ms, in order to directly compare behavioral and neural interference effects between them. The behavioral study corroborated results of previous studies and revealed that associatively-related distractors speeded RTs even more than phonologically-related distractors, thereby becoming equally fast as naming without distractors. Distractors were assumed to specifically enhance activation of brain areas corresponding to processing stages as determined in a cognitive model of word production (Indefrey, P., Levelt, W.J.M., 2004. The spatial and temporal signatures of word production components. Cognition 92, 101-144.). Functional magnetic resonance imaging (fMRI) at 3 T revealed activation of left superior temporal gyrus exclusively for phonologically-related distractors, and activation of left or right lingual gyrus exclusively for associatively-related and categorically-related distractors, respectively. Moreover, phonologically-related distractors elicited phonological-phonetic networks, and both semantic distractors evoked areas associated with mental imagery, semantics, and episodic memory retrieval and associations. While processes involved in distractor inhibition (e.g., conflict/competition monitoring) and high articulatory demands were observed for categorically-related distractors, priming of articulatory planning was revealed for associatively-related distractors. We conclude that activations of neural networks as obtained by the fMRI interference paradigm can be predicted from a cognitive model.

Model-oriented naming therapy in semantic dementia: A single-case fMRI study

Background: Studies on anomia treatment in semantic dementia demonstrate that re-learning is possible, but maintenance and generalisation of improvements are limited. Changes in cortical activation associated with anomia treatment have already been demonstrated in aphasic patients after stroke. Recovery of brain functions under the impact of deficit-specific treatment in semantic dementia has not been explored yet. Nevertheless, recent activation studies using language tasks in patients with neurodegenerative diseases report altered activation patterns, involving diverse brain regions ipsi- or contralateral to the primarily affected left hemisphere. Aims: The purpose of the present study was to investigate if phonological and semantic cueing hierarchies established for naming therapy in aphasia were also effective in a patient with semantic dementia. Moreover, we aimed to examine changes of brain activity associated with anomia treatment. Methods & Procedures: One individual with semantic dementia participated in the present study. Over a period of 4 weeks the participant received an intensive model-oriented treatment with phonological and semantic cueing hierarchies. Two pre-tests and two post-tests (one immediately after training and one 2 months later) were administered. The second pre-test and both follow-ups were registered inside the scanner. Outcomes & Results: Behaviourally, both treatments resulted in specific training effects, which subsequently decreased over time. Concerning functional magnetic resonance imaging data, improved naming following therapy was mirrored by changes in cortical activity, predominantly located in right superior and inferior temporal gyrus. Conclusions: Cueing hierarchies were successful, resulting in specific and immediate treatment effects, corroborating previous treatment studies in semantic dementia. Treatment-induced changes in cortical activity were mainly concentrated in right temporal cortex. Since right-sided modulation of cortical activity was associated with training-induced improvements in task performance, it may reflect right hemispheric compensatory mechanisms in this participant.

To carry or not to carry — Is this the question? Disentangling the carry effect in multi-digit addition

Recent research has suggested addition performance to be determined by both the need for a carry operation and problem size. Nevertheless, it has remained debatable, how these two factors are interrelated. In the current study, this question was pursued by orthogonally manipulating carry and problem size in two-digit addition verification. As the two factors interacted reliably, our results indicate that the carry effect is moderated by number magnitude processing rather than representing a purely procedural, asemantic sequence of processing steps. Moreover, it was found that the carry effect may not be a purely categorical effect but may be driven by continuous characteristics of the sum of the unit digits as well. Since the correct result of a carry problem can only be derived by integrating and updating the magnitudes of tens and units within the place-value structure of the Arabic number system, the present study provides evidence for the idea that decomposed processing of tens and units also transfers to mental arithmetic.

Correct and erroneous picture naming responses in healthy subjects

In this functional magnetic resonance imaging study, brain activations of correct and erroneous picture naming responses were investigated in 34 healthy subjects using an event-related design. We regarded main effects comprising all (ALL), false (FAL), or correct (COR) responses only. Despite the rare error occurrence, activation maxima differed between all three main effects. To investigate the influence of naming accuracy on brain activations, we therefore (1) considered the number of errors as covariates, and (2) compared carefully matched sets of FAL and COR for subjects with higher error rates. As a result, activations in left middle/medial frontal gyrus were significantly correlated with number of errors. The neural substrate of naming errors appears to be separated in several subsystems of activation: first bilateral activations in anterior cingulate cortex (ACC), prefrontal, and premotor regions associated with monitoring processes; second the involvement of right (para)hippocampal gyrus most likely indicating post-error processes of retention; third perisylvian (especially inferior frontal) language areas. These activations were not restricted to false responses, but were with less intensity also recruited for correct responses. In contrast, there was no specific activation for successful name retrieval in correct trials. To conclude, the underlying processing mechanisms of erroneous and correct naming responses are strikingly similar; self-monitoring appears to be a general mechanism of the naming process.

Rehabilitation of arithmetic fact retrieval via extensive practice: A combined fMRI and behavioural case-study

The present study investigates the effects of a training of arithmetic fact retrieval in a patient suffering from particular difficulties with multiplication facts. Over a period of four weeks simple multiplication facts were trained extensively. The outcome of the training was assessed behaviourally and changes in cerebral activation patterns were investigated using fMRI. The training led to a change in calculation strategies: Prior to training, the patient used predominantly time-consuming back-up strategies, after training he relied increasingly on the direct retrieval of arithmetic facts from long-term memory. Regarding the fMRI results, prefrontal activations were observed for untrained problems, which can be attributed to the application of back-up strategies strongly relying on fronto-executive functions. Interestingly, significant foci of activation for both trained and untrained items were found in the angular gyrus of the right hemisphere, which, however, differed in their exact localisation. For the trained condition, activations were observed in anterior parts of the angular gyrus which may be related to the training-based automatisation in fact retrieval. Activations in the untrained condition were found in a more posterior portion of the angular gyrus, that might be attributable to one of the patients back-up strategies, namely to recite a whole multiplication row to get to the correct answer.

Categorical and continuous - disentangling the neural correlates of the carry effect in multi-digit addition

BackgroundRecently it was suggested that the carry effect observed in addition involves both categorical and continuous processing characteristics.MethodsIn the present study, we aimed at identifying the specific neural correlates associated with processing either categorical or continuous aspects of the carry effect in an fMRI study on multi-digit addition.ResultsIn line with our expectations, we observed two distinct parts of the fronto-parietal network subserving numerical cognition to be associated with either one of these two characteristics. On the one hand, the categorical aspect of the carry effect was associated with left-hemispheric language areas and the basal ganglia probably reflecting increased demands on procedural and problem solving processes. Complementarily, the continuous aspect of the carry effect was associated with increased intraparietal activation indicating increasing demands on magnitude processing as well as place-value integration with increasing unit sum.ConclusionsIn summary, the findings suggest representations and processes underlying the carry effect in multi-digit addition to be more complex and interactive than assumed previously.

Reduced precuneus deactivation during object naming in patients with mild cognitive impairment, Alzheimer's disease, and frontotemporal lobar degeneration.

The precuneus is part of the default network of the human brain, which exhibits a high level of activity during the resting state and lower activity during task-related behavior. Typically, the posterior midline areas show this characteristic response in functional magnetic resonance imaging (fMRI) studies. In Alzheimer’s disease (AD) and mild cognitive impairment (MCI), subjects exhibit a lack of this typical deactivation. The interpretation of these findings, however, is obfuscated by the presence of local pathology and atrophy in AD. In contrast to AD, in patients with early frontotemporal lobar degeneration (FTLD), the precuneus is virtually free of local neuropathology. In this study, we demonstrate reduced fMRI signal in the precuneus in a group of patients with FTLD during a confrontation naming task. We show that this effect in FTLD patients was (1) similar to that observed in AD and MCI and (2) not related to the degree of gray matter atrophy in the precuneus. We hypothesize that reduced deactivation of the default network is not related to local pathology but to a lack of connectivity, which decreases in both FTLD and AD, the major cortical dementias.

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

Longitudinal cerebral diffusion changes reflect progressive decline of language and cognition.

Language deficits are regularly found in cortical neurodegenerative diseases. The progression of language deficits shows a considerable inter-individual variability even within one diagnostic group. We aimed at detecting patterns of altered diffusion as well as atrophy of cerebral gray and white matter which underlie ongoing language-related deterioration in patients with cortical neurodegenerative diseases. Diffusion tensor imaging and T1-weighted MRI data of 26 patients with clinically diagnosed neurodegenerative disorders were acquired at baseline and 14 months later in this prospective study. Language functions were assessed with a confrontation naming test and the Token Test. Diffusion and voxel-based morphometric measures were calculated and correlates of language performance were evaluated. Across all patients, the naming impairment was related to diffusion (false discovery rate-corrected P<0.05 at baseline) and atrophy abnormalities (family-wise error (FWE)-corrected P<0.05 at follow-up) primarily in the left temporal lobe. Deficits in the Token Test were correlated with predominantly left frontal MRI abnormalities (FWE-corrected P<0.05). The Token Test performance decline over 14 months was accompanied by further increasing abnormalities in the frontal cortex, left caudate, parietal cortex (all FWE-corrected P<0.05), and posterior callosal body (FWE-corrected P=0.055). Both diffusion and structural MRI were apt to elucidate the underpinnings of inter-individual differences in language-related deficits and to detect longitudinal changes that accompanied ongoing cognition and language decline, with mean diffusivity appearing most sensitive. This might indicate the usefulness of diffusion measures as markers for successful intervention in therapy studies.

Patterns of linguistic and numerical performance in aphasia

BackgroundEmpirical research on the relationship between linguistic and numerical processing revealed inconsistent results for different levels of cognitive processing (e.g., lexical, semantic) as well as different stimulus materials (e.g., Arabic digits, number words, letters, non-number words). Information of dissociation patterns in aphasic patients was used in order to investigate the dissociability of linguistic and numerical processes. The aim of the present prospective study was a comprehensive, specific, and systematic investigation of relationships between linguistic and numerical processing, considering the impact of asemantic vs. semantic processing and the type of material employed (numbers compared to letters vs. words).MethodsA sample of aphasic patients (n = 60) was assessed with a battery of linguistic and numerical tasks directly comparable for their cognitive processing levels (e.g., perceptual, morpho-lexical, semantic).Results and conclusionsMean performance differences and frequencies of (complementary) dissociations in individual patients revealed the most prominent numerical advantage for asemantic tasks when comparing the processing of numbers vs. letters, whereas the least numerical advantage was found for semantic tasks when comparing the processing of numbers vs. words. Different patient subgroups showing differential dissociation patterns were further analysed and discussed. A comprehensive model of linguistic and numerical processing should take these findings into account.