Motor affordance and its role for visual working memory: evidence from fMRI studies

We examined the role of motor affordances of objects for working memory retention processes. Three experiments are reported in which participants passively viewed pictures of real world objects or had to retain the objects in working memory for a comparison with an S2 stimulus. Brain activation was recorded by means of functional magnetic resonance imaging (fMRI). Retaining information about objects for which hand actions could easily be retrieved (manipulable objects) in working memory activated the hand region of the ventral premotor cortex (PMC) contralateral to the dominant hand. Conversely, nonmanipulable objects activated the left inferior frontal gyrus. This suggests that working memory for objects with motor affordance is based on motor programs associated with their use. An additional study revealed that motor program activation can be modulated by task demands: Holding manipulable objects in working memory for an upcoming motor comparison task was associated with left ventral PMC activation. However, retaining the same objects for a subsequent size comparison task led to activation in posterior brain regions. This suggests that the activation of hand motor programs are under top down control. By this they can flexibly be adapted to various task demands. It is argued that hand motor programs may serve a similar working memory function as speech motor programs for verbalizable working memory contents, and that the premotor system mediates the temporal integration of motor representations with other task-relevant representations in support of goal oriented behavior

Dissociable brain mechanisms for inhibitory control: Effects of interference content and working memory capacity

In this study, event-related fMRI was used to examine whether the resolution of interference arising from two different information contents activates the same or different neuronal circuitries. In addition, we examined the extent to which these inhibitory control mechanisms are modulated by individual differences in working memory capacity. Two groups of participants with high and low working memory capacity [high span (HS) and low span (LS) participants, respectively] performed two versions of an item recognition task with familiar letters and abstract objects as stimulus materials. Interference costs were examined by means of the recent negative probe technique with otherwise identical testing conditions across both tasks. While the behavioral interference costs were of similar magnitude in both tasks, the underlying brain activation pattern differed between tasks: The object task interference-effects (higher activation in interference trials than in control trials) were restricted to the anterior intraparietal sulcus (IPS). Interference effects for familiar letters were obtained in the anterior IPS, the left postero-ventral and the right dorsolateral prefrontal cortex (PFC) as well as the precuneus. As the letters were more discernible than the objects, the results suggest that the critical feature for PFC and precuneus involvement in interference resolution is the saliency of stimulus-response mappings. The interference effects in the letter task were modulated by working memory capacity: LS participants showed enhanced activation for interference trials only, whereas for HS participants, who showed better performance and also lower interference costs in the letter task, the above-mentioned neuronal circuitry was activated for interference and control trials, thereby attenuating the interference effects. The latter results support the view that HS individuals allocate more attentional resources for the maintenance of task goals in the face of interfering information from preceding trials with familiar stimulus materials

Language processing within the human medial temporal lobe

Although the hippocampal formation is essential for verbal memory, it is not fully understood how it contributes to language comprehension. We recorded event-related potentials (ERPs) directly from two substructures of the medial temporal lobe (MTL), the rhinal cortex and the hippocampus proper, while epilepsy patients listened to sentences that either were correct or contained semantic or syntactic violations. Semantic violations elicited a large negative ERP response peaking at approximately 400 ms in the rhinal cortex. In contrast, syntactically incorrect sentences elicited a negative deflection of 500-800 ms in the hippocampus proper. The results suggest that functionally distinct aspects of integration in language comprehension are supported by different MTL structures: the rhinal cortex is involved in semantic integration, whereas the hippocampus proper subserves processes of syntactic integration. An analysis of phase synchronization within the gamma band between rhinal and hippocampal recording sites showed that both of the above-mentioned ERP components were preceded by an increase of phase synchronization. In contrast to these short phasic increases of phase synchronization in both violation conditions, correct sentences were associated with a long-lasting synchronization in a late time window, possibly reflecting the integration of semantic and syntactic information as required for normal comprehension

Cortical activity reduction with stimulus repetition: A whole-head MEG analysis

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The impact of auditory working memory training on the fronto-parietal working memory network

Working memory training has been widely used to investigate working memory processes. We have shown previously that visual working memory benefits only from intra-modal visual but not from across-modal auditory working memory training. In the present functional magnetic resonance imaging study we examined whether auditory working memory processes can also be trained specifically and which training-induced activation changes accompany theses effects. It was investigated whether working memory training with strongly distinct auditory materials transfers exclusively to an auditory (intra-modal) working memory task or whether it generalizes to a (across-modal) visual working memory task. We used adaptive n-back training with tonal sequences and a passive control condition. The memory training led to a reliable training gain. Transfer effects were found for the (intra-modal) auditory but not for the (across-modal) visual transfer task. Training-induced activation decreases in the auditory transfer task were found in two regions in the right inferior frontal gyrus. These effects confirm our previous findings in the visual modality and extents intra-modal effects in the prefrontal cortex to the auditory modality. As the right inferior frontal gyrus is frequently found in maintaining modality-specific auditory information, these results might reflect increased neural efficiency in auditory working memory processes. Furthermore, task-unspecific (amodal) activation decreases in the visual and auditory transfer task were found in the right inferior parietal lobule and the superior portion of the right middle frontal gyrus reflecting less demand on general attentional control processes. These data are in good agreement with amodal activation decreases within the same brain regions on a visual transfer task reported previously

Orienting asymmetries and lateralized processing of sounds in humans

<p>Abstract</p> <p>Background</p> <p>Lateralized processing of speech is a well studied phenomenon in humans. Both anatomical and neurophysiological studies support the view that nonhuman primates and other animal species also reveal hemispheric differences in areas involved in sound processing. In recent years, an increasing number of studies on a range of taxa have employed an orienting paradigm to investigate lateralized acoustic processing. In this paradigm, sounds are played directly from behind and the direction of turn is recorded. This assay rests on the assumption that a hemispheric asymmetry in processing is coupled to an orienting bias towards the contralateral side. To examine this largely untested assumption, speech stimuli as well as artificial sounds were presented to 224 right-handed human subjects shopping in supermarkets in Germany and in the UK. To verify the lateralized processing of the speech stimuli, we additionally assessed the brain activation in response to presentation of the different stimuli using functional magnetic resonance imaging (fMRI).</p> <p>Results</p> <p>In the naturalistic behavioural experiments, there was no difference in orienting behaviour in relation to the stimulus material (speech, artificial sounds). Contrary to our predictions, subjects revealed a significant left bias, irrespective of the sound category. This left bias was slightly but not significantly stronger in German subjects. The fMRI experiments confirmed that the speech stimuli evoked a significant left lateralized activation in BA44 compared to the artificial sounds.</p> <p>Conclusion</p> <p>These findings suggest that in adult humans, orienting biases are not necessarily coupled with lateralized processing of acoustic stimuli. Our results – as well as the inconsistent orienting biases found in different animal species – suggest that the orienting assay should be used with caution. Apparently, attention biases, experience, and experimental conditions may all affect head turning responses. Because of the complexity of the interaction of factors, the use of the orienting assay to determine lateralized processing of sound stimuli is discouraged.</p

Mirroring Intentional Forgetting in a Shared-Goal Learning Situation

Background: Intentional forgetting refers to the surprising phenomenon that we can forget previously successfully encoded memories if we are instructed to do so. Here, we show that participants cannot only intentionally forget episodic memories but they can also mirror the ‘‘forgetting performance’ ’ of an observed model. Methodology/Principal Findings: In four experiments a participant observed a model who took part in a memory experiment. In Experiment 1 and 2 observers saw a movie about the experiment, whereas in Experiment 3 and 4 the observers and the models took part together in a real laboratory experiment. The observed memory experiment was a directed forgetting experiment where the models learned two lists of items and were instructed either to forget or to remember the first list. In Experiment 1 and 3 observers were instructed to simply observe the experiment (‘‘simple observation’ ’ instruction). In Experiment 2 and 4, observers received instructions aimed to induce the same learning goal for the observers and the models (‘‘observation with goal-sharing’ ’ instruction). A directed forgetting effect (the reliably lower recall of to-be-forgotten items) emerged only when models received the ‘‘observation with goal-sharing’ ’ instruction (P,.001 in Experiment 2, and P,.05 in Experiment 4), and it was absent when observers received the ‘‘simple observation’’ instruction (P..1 in Experiment 1 and 3). Conclusion: If people observe another person with the same intention to learn, and see that this person is instructed t