Trimodal processing of complex stimuli in inferior parietal cortex is modality-independent

In humans, multisensory mechanisms facilitate object processing through integration of sensory signals that match in their temporal and spatial occurrence as well as their meaning. The generalizability of such integration processes across different sensory modalities is, however, to date not well understood. As such, it remains unknown whether there are cerebral areas that process object-related signals independently of the specific senses from which they arise, and whether these areas show different response profiles depending on the number of sensory channels that carry information. To address these questions, we presented participants with dynamic stimuli that simultaneously emitted object-related sensory information via one, two, or three channels (sight, sound, smell) in the MR scanner. By comparing neural activation patterns between various integration processes differing in type and number of stimulated senses, we showed that the left inferior frontal gyrus and areas within the left inferior parietal cortex were engaged independently of the number and type of sensory input streams. Activation in these areas was enhanced during bimodal stimulation, compared to the sum of unimodal activations, and increased even further during trimodal stimulation. Taken together, our findings demonstrate that activation of the inferior parietal cortex during processing and integration of meaningful multisensory stimuli is both modality-independent and modulated by the number of available sensory modalities. This suggests that the processing demand placed on the parietal cortex increases with the number of sensory input streams carrying meaningful information, likely due to the increasing complexity of such stimuli.

Resilience and cortical thickness: a MRI study

Resilience is defined as the psychological resistance which enables the processing of stress and adverse life events and thus constitutes a key factor for the genesis of psychiatric illness. However, little is known about the morphological correlates of resilience in the human brain. Hence, the aim of this study is to examine the neuroanatomical expression of resilience in healthy individuals. 151 healthy subjects were recruited and had to complete a resilience-specific questionnaire (RS-11). All of them underwent a high-resolution T1-weighted MRI in a 3T scanner. Fine-grained cortical thickness was analyzed using FreeSurfer. We found a significant positive correlation between the individual extent of resilience and cortical thickness in a right hemispherical cluster incorporating the lateral occipital cortex, the fusiform gyrus, the inferior parietal cortex as well as the middle and inferior temporal cortex, i.e., a reduced resilience is associated with a decreased cortical thickness in these areas. We lend novel evidence for a direct linkage between psychometric resilience and local cortical thickness. Our findings in a sample of healthy individuals show that a lower resilience is associated with a lower cortical thickness in anatomical areas are known to be involved in the processing of emotional visual input. These regions have been demonstrated to play a role in the pathogenesis of stress and trauma-associated disorders. It can thus be assumed that neuroanatomical variations in these cortical regions might modulate the susceptibility for the development of stress-related disorders.

Distinct representations in occipito-temporal, parietal, and premotor cortex during action perception revealed by fMRI and computational modeling

Visual processing of actions is supported by a network consisting of occipito-temporal, parietal, and premotor regions in the human brain, known as the Action Observation Network (AON). In the present study, we investigate what aspects of visually perceived actions are represented in this network using fMRI and computational modeling. Human subjects performed an action perception task during scanning. We characterized the different aspects of the stimuli starting from purely visual properties such as form and motion to higher-aspects such as intention using computer vision and categorical modeling. We then linked the models of the stimuli to the three nodes of the AON with representational similarity analysis. Our results show that different nodes of the network represent different aspects of actions. While occipito-temporal cortex performs visual analysis of actions by means of integrating form and motion information, parietal cortex builds on these visual representations and transforms them into more abstract and semantic representations coding target of the action, action type and intention. Taken together, these results shed light on the neuro-computational mechanisms that support visual perception of actions and provide support that AON is a hierarchical system in which increasing levels of the cortex code increasingly complex features.

Voxel-based lesion analysis of brain regions underlying reading and writing

The neural basis of reading and writing has been a source of inquiry as well as controversy in the neuroscience literature. Reading has been associated with both left posterior ventral temporal zones (termed the "visual word form area") as well as more dorsal zones, primarily in left parietal cortex. Writing has also been associated with left parietal cortex, as well as left sensorimotor cortex and prefrontal regions. Typically, the neural basis of reading and writing are examined in separate studies and/or rely on single case studies exhibiting specific deficits. Functional neuroimaging studies of reading and writing typically identify a large number of activated regions but do not necessarily identify the core, critical hubs. Last, due to constraints on the functional imaging environment, many previous studies have been limited to measuring the brain activity associated with single-word reading and writing, rather than sentence-level processing. In the current study, the brain correlates of reading and writing at both the single- and sentence-level were studied in a large sample of 111 individuals with a history of chronic stroke using voxel-based lesion symptom mapping (VLSM). VLSM provides a whole-brain, voxel-by-voxel statistical analysis of the role of distinct regions in a particular behavior by comparing performance of individuals with and without a lesion at every voxel. Rather than comparing individual cases or small groups with particular behavioral dissociations in reading and writing, VLSM allowed us to analyze data from a large, well-characterized sample of stroke patients exhibiting a wide range of reading and writing impairments. The VLSM analyses revealed that reading was associated with a critical left inferior temporo-occipital focus, while writing was primarily associated with the left supramarginal gyrus. Separate VLSM analyses of single-word versus sentence-level reading showed that sentence-level reading was uniquely associated with anterior to mid-portions of the middle and superior temporal gyri. Both single-word and sentence-level writing overlapped to a great extent in the left supramarginal gyrus, but sentence-level writing was associated with additional underlying white matter pathways such as the internal capsule. These findings suggest that critical aspects of reading and writing processes diverge, with reading relying critically on the ventral visual recognition stream and writing relying on a dorsal visuo-spatial-motor stream.

To create or to recall original ideas: Brain processes associated with the imagination of novel object uses

This fMRI study investigated what brain processes contribute to the generation of new ideas. Brain activation was measured while participants generated new original object uses, recalled original object uses, or recalled common object uses. Post-scan evaluations were used to confirm what ideas were newly generated on the spot or actually retrieved from memory. When compared to the recall of common ideas, the generation of new and old original ideas showed a similar activation pattern including activation of bilateral parahippocampal and mPFC regions, suggesting that the construction of new ideas builds on similar processes like the reconstruction of original ideas from episodic memory. As a difference, the generation of new object uses involved higher activation of a focused cluster in the left supramarginal gyrus compared to the recall of original ideas. This finding adds to the converging evidence that the left supramarginal gyrus is crucially involved in the construction of novel representations, potentially by integrating memory content in new ways and supporting executively demanding mental simulations. This study deepens our understanding of how creative thought builds on and goes beyond memory.

Parietal abnormalities are related to avoidance in social anxiety disorder: a study using voxel-based morphometry and manual volumetry

Evidence is accumulating that various mental disorders are related to neural abnormalities in the parietal cortices that are associated with the default mode network (DMN). Participants comprised 67 persons with social anxiety disorder (SAD) and 64 matched healthy controls who underwent structural magnetic resonance imaging (MRI) and a comprehensive clinical assessment. Voxel-based morphometry (VBM) across the entire brain and manual volumetry of the parietal cortices were performed. The results indicate abnormal manually segmented volumes or gray matter (GM) volumes within the precuneus, postcentral gyrus and inferior parietal cortex, as well as in the premotor cortices including the supplementary motor cortex. Significant negative correlations were obtained between parietal, especially precuneus, abnormalities and social avoidance severity, indicating stronger avoidance in SAD participants with smaller volumes or less GM. We conclude that pathological avoidance behaviors in SAD are associated with structural deficits of parietal regions that are associated with the DMN, which has been shown to mediate introspection and reflection upon one's own mental state in healthy humans.

Early MEG markers for reading Chinese phonograms: evidence from radical combinability and consistency effects

Studies using functional magnetic resonance imaging have indicated that activities in the left inferior frontal cortex and left temporoparietal regions are associated with orthographic neighborhood size. To elucidate the temporal dynamics of reading-related cortical activities, we manipulated two types of neighborhood properties for Chinese phonograms, phonetic combinability and consistency. By using source analysis techniques in combination with magnetoencephalography, the results demonstrated a combinability effect in the right fusiform gyrus at ∼ 170 ms, which may reflect perceptual expertise in processing Chinese orthography. During 200 ms to 250 ms, the left anterior insula showed larger activity in reading small combinability characters than in reading large combinability characters, and the left inferior parietal cortex showed greater activity in reading low consistency characters than in reading high consistency characters. These results indicate that the left anterior insula cortex and left inferior parietal cortex may play important roles in the early stages of reading Chinese phonograms.

Using action understanding to understand the left inferior parietal cortex in the human brain

Humans have a sophisticated knowledge of the actions that can be performed with objects. In an fMRI study we tried to establish whether this depends on areas that are homologous with the inferior parietal cortex (area PFG) in macaque monkeys. Cells have been described in area PFG that discharge differentially depending upon whether the observer sees an object being brought to the mouth or put in a container. In our study the observers saw videos in which the use of different objects was demonstrated in pantomime; and after viewing the videos, the subject had to pick the object that was appropriate to the pantomime. We found a cluster of activated voxels in parietal areas PFop and PFt and this cluster was greater in the left hemisphere than in the right. We suggest a mechanism that could account for this asymmetry, relate our results to handedness and suggest that they shed light on the human syndrome of apraxia. Finally, we suggest that during the evolution of the hominids, this same pantomime mechanism could have been used to 'name' or request objects.

Functional connectivity in task-negative network of the Deaf: effects of sign language experience

Prior studies investigating cortical processing in Deaf signers suggest that life-long experience with sign language and/or auditory deprivation may alter the brain’s anatomical structure and the function of brain regions typically recruited for auditory processing (Emmorey et al., 2010; Pénicaud et al., 2013 inter alia). We report the first investigation of the task-negative network in Deaf signers and its functional connectivity—the temporal correlations among spatially remote neurophysiological events. We show that Deaf signers manifest increased functional connectivity between posterior cingulate/precuneus and left medial temporal gyrus (MTG), but also inferior parietal lobe and medial temporal gyrus in the right hemisphere- areas that have been found to show functional recruitment specifically during sign language processing. These findings suggest that the organization of the brain at the level of inter-network connectivity is likely affected by experience with processing visual language, although sensory deprivation could be another source of the difference. We hypothesize that connectivity alterations in the task negative network reflect predictive/automatized processing of the visual signal.

Re-evaluating the role of TPJ in attentional control: contextual updating?

The right temporo-parietal junction (TPJ) is widely considered as part of a network that reorients attention to task-relevant, but currently unattended stimuli (Corbetta and Shulman, 2002). Despite the prevalence of this theory in cognitive neuroscience, there is little direct evidence for the principal hypothesis that TPJ sends an early reorientation signal that "circuit breaks" attentional processing in regions of the dorsal attentional network (e.g., the frontal eye fields) or is completely right lateralized during attentional processing. In this review, we examine both functional neuroimaging work on TPJ in the attentional literature as well as anatomical findings. We first critically evaluate the idea that TPJ reorients attention and is right lateralized; we then suggest that TPJ signals might rather reflect post-perceptual processes involved in contextual updating and adjustments of top-down expectations; and then finally discuss how these ideas relate to the electrophysiological (P300) literature, and to TPJ findings in other cognitive and social domains. We conclude that while much work is needed to define the computational functions of regions encapsulated as TPJ, there is now substantial evidence that it is not specialized for stimulus-driven attentional reorienting.

To create or to recall? Neural mechanisms underlying the generation of creative new ideas

This fMRI study investigated brain activation during creative idea generation using a novel approach allowing spontaneous self-paced generation and expression of ideas. Specifically, we addressed the fundamental question of what brain processes are relevant for the generation of genuinely new creative ideas, in contrast to the mere recollection of old ideas from memory. In general, creative idea generation (i.e., divergent thinking) was associated with extended activations in the left prefrontal cortex and the right medial temporal lobe, and with deactivation of the right temporoparietal junction. The generation of new ideas, as opposed to the retrieval of old ideas, was associated with stronger activation in the left inferior parietal cortex which is known to be involved in mental simulation, imagining, and future thought. Moreover, brain activation in the orbital part of the inferior frontal gyrus was found to increase as a function of the creativity (i.e., originality and appropriateness) of ideas pointing to the role of executive processes for overcoming dominant but uncreative responses. We conclude that the process of idea generation can be generally understood as a state of focused internally-directed attention involving controlled semantic retrieval. Moreover, left inferior parietal cortex and left prefrontal regions may subserve the flexible integration of previous knowledge for the construction of new and creative ideas.

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Functional imaging was performed during spontaneous self-paced idea generation.

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Overt responses were recorded and evaluated for novelty and creativity.

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Brain activation of newly created and recalled ideas was compared.

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The generation of new ideas involved stronger activation of the left IPC.

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Creativity of ideas was related to activation of the left IFG.