The neural basis of phonological working memory (WM) was investigated through an examination of the effects of irrelevant speech distractors and disruptive neural stimulation from transcranial ...magnetic stimulation (TMS). Embedded processes models argue that the same regions involved in speech perception are used to support phonological WM whereas buffer models assume that a region separate from speech perception regions is used to support WM. Thus, according to the embedded processes approach but not the buffer approach, irrelevant speech and TMS to the speech perception region should disrupt the decoding of phonological WM representations. According to the buffer account, decoding of WM items should be possible in the buffer region despite distraction and should be disrupted with TMS to this region. Experiment 1 used fMRI and representational similarity analyses (RSA) with a delayed recognition memory paradigm using nonword stimuli. Results showed that decoding of memory items in the speech perception regions (superior temporal gyrus, STG) was possible in the absence of distractors. However, the decoding evidence in the left STG was susceptible to interference from distractors presented during the delay period whereas decoding in the proposed buffer region (supramarginal gyrus, SMG) persisted. Experiment 2 examined the causal roles of the speech processing region and the buffer region in phonological WM performance using TMS. TMS to the SMG during the early delay period caused a disruption in recognition performance for the memory nonwords, whereas stimulations at the STG and an occipital control region did not affect WM performance. Taken together, results from the two experiments are consistent with predictions of a buffer model of phonological WM, pointing to a critical role of the left SMG in maintaining phonological representations.
In cognitive network neuroscience, the connectivity and community structure of the brain network is related to measures of cognitive performance, like attention and memory. Research in this emerging ...discipline has largely focused on two measures of connectivity-modularity and flexibility-which, for the most part, have been examined in isolation. The current project investigates the relationship between these two measures of connectivity and how they make separable contribution to predicting individual differences in performance on cognitive tasks. Using resting state fMRI data from 52 young adults, we show that flexibility and modularity are highly negatively correlated. We use a Brodmann parcellation of the fMRI data and a sliding window approach for calculation of the flexibility. We also demonstrate that flexibility and modularity make unique contributions to explain task performance, with a clear result showing that modularity, not flexibility, predicts performance for simple tasks and that flexibility plays a greater role in predicting performance on complex tasks that require cognitive control and executive functioning. The theory and results presented here allow for stronger links between measures of brain network connectivity and cognitive processes.
Buffer accounts of verbal short-term memory (STM) assume dedicated buffers for maintaining different types of information (e.g., phonological, visual) whereas embedded processes accounts argue ...against the existence of buffers and claim that STM consists of the activated portion of long-term memory (LTM). We addressed this debate by determining whether STM recruits the same neural substrate as LTM, or whether additional regions are involved in short-term storage. Using fMRI with representational similarity analysis (RSA), we examined the representational correspondence of multi-voxel neural activation patterns with the theoretical predictions for the maintenance of both phonological and semantic codes in STM. We found that during the delay period of a phonological STM task, phonological representations could be decoded in the left supramarginal gyrus (SMG) but not the superior temporal gyrus (STG), a speech processing region, for word stimuli. Whereas the pattern in the SMG was specific to phonology, a different region in the left angular gyrus showed RSA decoding evidence for the retention of either phonological or semantic codes, depending on the task context. Taken together, the results provide clear support for a dedicated buffer account of phonological STM, although evidence for a semantic buffer is equivocal.
Abstract
Buffer versus embedded processes accounts of short-term memory (STM) for phonological information were addressed by testing subjects' perception and memory for speech and non-speech auditory ...stimuli. Univariate and multivariate (MVPA) approaches were used to assess whether brain regions recruited in recognizing speech were involved in maintaining speech representations over a delay. As expected, a left superior temporal region was found to support speech perception. However, contrary to the embedded processes approach, this region failed to show a load effect, or any sustained activation, during a maintenance delay. Moreover, MVPA decoding during the maintenance stage was unsuccessful in this region by a perception classifier or an encoding classifier. In contrast, the left supramarginal gyrus showed both sustained activation and a load effect. Using MVPA, stimulus decoding was successful during the delay period. In addition, a functional connectivity analysis showed that, as memory load increased, the left temporal lobe involved in perception became more strongly connected with the parietal region involved in maintenance. Taken together, the findings provide greater support for a buffer than embedded processes account of phonological STM.
Recent work in cognitive neuroscience has focused on analyzing the brain as a network, rather than as a collection of independent regions. Prior studies taking this approach have found that ...individual differences in the degree of modularity of the brain network relate to performance on cognitive tasks. However, inconsistent results concerning the direction of this relationship have been obtained, with some tasks showing better performance as modularity increases and other tasks showing worse performance. A recent theoretical model Chen, M., & Deem, M. W. 2015. Development of modularity in the neural activity of children's brains.
016009 suggests that these inconsistencies may be explained on the grounds that high-modularity networks favor performance on simple tasks whereas low-modularity networks favor performance on more complex tasks. The current study tests these predictions by relating modularity from resting-state fMRI to performance on a set of simple and complex behavioral tasks. Complex and simple tasks were defined on the basis of whether they did or did not draw on executive attention. Consistent with predictions, we found a negative correlation between individuals' modularity and their performance on a composite measure combining scores from the complex tasks but a positive correlation with performance on a composite measure combining scores from the simple tasks. These results and theory presented here provide a framework for linking measures of whole-brain organization from network neuroscience to cognitive processing.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
Attention is often extolled for its selective neural properties. Yet, when powerfully captured by a salient unexpected event, attention can give rise to a broad cascade of systemic effects for ...evaluating and adaptively responding to the event. Using graph theory analysis combined with fMRI, we show here that the extensive psychophysiological and cognitive changes associated with such attention capture are related to large-scale distributed changes in the brain's functional connectivity. Novel task-irrelevant "oddball" stimuli presented to subjects during the performance of a target-search task triggered an increase in internetwork functional connectivity that degraded the brain's network modularity, thereby facilitating the integration of information. Furthermore, this phenomenon habituated with repeated oddball presentations, mirroring the behavior. These functional network connectivity changes are remarkably consistent with those previously obtained with conscious target perception, thus raising the possibility that large-scale internetwork connectivity changes triggered by attentional capture and awareness rely on common neural network dynamics.
The selective properties of attention have been extensively studied. There are some circumstances in which attention can have widespread and systemic effects, however, such as when it is captured by an unexpected, salient stimulus or event. How are such effects propagated in the human brain? Using graph theory analysis of fMRI data, we show here that salient task-irrelevant events produced a global increase in the functional integration of the brain's neural networks.
•Greater fMRI activity was observed in the left than the right STG during a sublexical speech perception task.•TMS disrupted performance during a speech perception task when applied to the left ...anterior STG relative to a control region.•TMS on the left posterior STG and the right STG during a speech perception task did not significantly disrupt performance.•A causal role of the left anterior STG on speech perception was established but not of the right STG.
Debate continues regarding the necessary role of right superior temporal gyrus (STG) regions in sublexical speech perception given the bilateral STG activation often observed in fMRI studies. To evaluate the causal roles, TMS pulses were delivered to inhibit and disrupt neuronal activity at the left and right STG regions during a nonword discrimination task based on peak activations from a blocked fMRI paradigm assessing speech vs. nonspeech perception (N = 20). Relative to a control region located in the posterior occipital lobe, TMS to the left anterior STG (laSTG) led to significantly worse accuracy, whereas TMS to the left posterior STG (lpSTG) and right anterior STG (raSTG) did not. Although the disruption from TMS was significantly greater for the laSTG than for raSTG, the difference in accuracy between the laSTG and lpSTG did not reach significance. The results argue for a causal role of the laSTG but not raSTG in speech perception. Further research is needed to establish the source of the differences between the laSTG and lpSTG.
PDF
