Representational organization of novel task sets during proactive encoding

Recent multivariate analyses of brain data have boosted our understanding of the organizational principles that shape neural coding. However, most of this progress has focused on perceptual visual regions (Connolly et al., 2012), whereas far less is known about the organization of more abstract, action-oriented representations. In this study, we focused on humans{\textquoteright} remarkable ability to turn novel instructions into actions. While previous research shows that instruction encoding is tightly linked to proactive activations in fronto-parietal brain regions, little is known about the structure that orchestrates such anticipatory representation. We collected fMRI data while participants (both males and females) followed novel complex verbal rules that varied across control-related variables (integrating within/across stimuli dimensions, response complexity, target category) and reward expectations. Using Representational Similarity Analysis (Kriegeskorte et al., 2008) we explored where in the brain these variables explained the organization of novel task encoding, and whether motivation modulated these representational spaces. Instruction representations in the lateral prefrontal cortex were structured by the three control-related variables, while intraparietal sulcus encoded response complexity and the fusiform gyrus and precuneus organized its activity according to the relevant stimulus category. Reward exerted a general effect, increasing the representational similarity among different instructions, which was robustly correlated with behavioral improvements. Overall, our results highlight the flexibility of proactive task encoding, governed by distinct representational organizations in specific brain regions. They also stress the variability of motivation-control interactions, which appear to be highly dependent on task attributes such as complexity or novelty.SIGNIFICANCE STATEMENTIn comparison with other primates, humans display a remarkable success in novel task contexts thanks to our ability to transform instructions into effective actions. This skill is associated with proactive task-set reconfigurations in fronto-parietal cortices. It remains yet unknown, however, how the brain encodes in anticipation the flexible, rich repertoire of novel tasks that we can achieve. Here we explored cognitive control and motivation-related variables that might orchestrate the representational space for novel instructions. Our results showed that different dimensions become relevant for task prospective encoding depending on the brain region, and that the lateral prefrontal cortex simultaneously organized task representations following different control-related variables. Motivation exerted a general modulation upon this process, diminishing rather than increasing distances among instruction representations

Where do bright ideas occur in our brain? Meta-analytic evidence from neuroimaging studies of domain-specific creativity

Many studies have assessed the neural underpinnings of creativity, failing to find a clear anatomical localization. We aimed to provide evidence for a multi-componential neural system for creativity. We applied a general activation likelihood estimation (ALE) meta-analysis to 45 fMRI studies. Three individual ALE analyses were performed to assess creativity in different cognitive domains (Musical, Verbal, and Visuo-spatial). The general ALE revealed that creativity relies on clusters of activations in the bilateral occipital, parietal, frontal, and temporal lobes. The individual ALE revealed different maximal activation in different domains. Musical creativity yields activations in the bilateral medial frontal gyrus, in the left cingulate gyrus, middle frontal gyrus, and inferior parietal lobule and in the right postcentral and fusiform gyri. Verbal creativity yields activations mainly located in the left hemisphere, in the prefrontal cortex, middle and superior temporal gyri, inferior parietal lobule, postcentral and supramarginal gyri, middle occipital gyrus, and insula. The right inferior frontal gyrus and the lingual gyrus were also activated. Visuo-spatial creativity activates the right middle and inferior frontal gyri, the bilateral thalamus and the left precentral gyrus. This evidence suggests that creativity relies on multi-componential neural networks and that different creativity domains depend on different brain regions

The cognitive neuroscience of visual working memory

Visual working memory allows us to temporarily maintain and manipulate visual information in order to solve a task. The study of the brain mechanisms underlying this function began more than half a century ago, with Scoville and Milner’s (1957) seminal discoveries with amnesic patients. This timely collection of papers brings together diverse perspectives on the cognitive neuroscience of visual working memory from multiple fields that have traditionally been fairly disjointed: human neuroimaging, electrophysiological, behavioural and animal lesion studies, investigating both the developing and the adult brain

Neurophysiology of the macaque fronto-parietal magnitude system

In primates, the magnitude system resides in a fronto-parietal network. Single neurons in the monkey prefrontal cortex (PFC) and ventral intraparietal area (VIP) exhibit higher responses to a certain number of stimulus items regardless of their appearance or even sensory modality. Neuroimaging studies in humans show corresponding activation in human fronto-parietal areas during enumeration tasks. However, these areas are also involved in many other executive functions and, thus, the responses of single neurons within the network could be shaped by many factors. Understanding how information about magnitude develops within single neurons in this network was the objective of this thesis. This thesis includes five studies addressing various aspects of the primate frontoparietal magnitude system. First, we determined the role of behavioural relevance in shaping neuronal responses to number. Using enumerable coloured stimuli that naïve macaque monkeys discriminated based on their colour rather than number, we examined the selectivity of neuronal responses towards the number of stimuli. We simultaneously recorded single neurons in VIP and PFC. We compared these neurons to those recorded after a period of training for both monkeys, while they discriminated the stimuli based on number. In all the recording sessions, we also mapped the visual receptive fields (RF) of neurons using a passive fixation task. We created RF maps for a large number of spatially-selective neurons in each area and compared the RFs of pairs of neurons recorded at the same electrode tip. We then differentiated the extent of interaction between the RF and number selectivity in both areas. Neurons in both PFC and VIP were selective for number despite the monkeys being numerically-naïve and number being the behaviourally irrelevant stimulus feature. Post training, neurons in PFC were modulated by behavioural relevance and their selectivity for number became stronger as a result. VIP neurons did not show such an effect. We found that PFC RFs were predominantly contralateral and VIP RFs, foveal. Regardless of RF location and size, we observed heterogeneous and sometimes, inverted RFs in neurons adjacent to each other, more frequently in PFC than in VIP. Lastly, neurons in both PFC and VIP were strongly number-selective even when the number stimuli were shown outside their RFs. Our results provided valuable insight into the organisation of the magnitude system in primates. The presence of number-selective neuronal responses in numerically-naïve monkeys even when the number of stimuli was behaviourally irrelevant confirmed that our magnitude system processes magnitude spontaneously as a natural category. The strict spatiotopic organisation of RFs characteristic of early visual areas is progressively lower in VIP and PFC. Together, these results point to a hierarchy in the fronto-parietal areas we studied, with PFC located at the apex of the magnitude system and VIP upstream to it

Causal Influence of Linguistic Learning on Perceptual and Conceptual Processing: A Brain-Constrained Deep Neural Network Study of Proper Names and Category Terms.

Language influences cognitive and conceptual processing, but the mechanisms through which such causal effects are realized in the human brain remain unknown. Here, we use a brain-constrained deep neural network model of category formation and symbol learning and analyze the emergent model\u27s internal mechanisms at the neural circuit level. In one set of simulations, the network was presented with similar patterns of neural activity indexing instances of objects and actions belonging to the same categories. Biologically realistic Hebbian learning led to the formation of instance-specific neurons distributed across multiple areas of the network, and, in addition, to cell assembly circuits of shared neurons responding to all category instances-the network correlates of conceptual categories. In two separate sets of simulations, the network learned the same patterns together with symbols for individual instances [ proper names (PN)] or symbols related to classes of instances sharing common features [ category terms (CT)]. Learning CT remarkably increased the number of shared neurons in the network, thereby making category representations more robust while reducing the number of neurons of instance-specific ones. In contrast, proper name learning prevented a substantial reduction of instance-specific neurons and blocked the overgrowth of category general cells. Representational similarity analysis further confirmed that the neural activity patterns of category instances became more similar to each other after category-term learning, relative to both learning with PN and without any symbols. These network-based mechanisms for concepts, PN, and CT explain why and how symbol learning changes object perception and memory, as revealed by experimental studies

Hemispheric differences in semantic cognition and their contribution to behaviour

This thesis investigated hemispheric differences in semantic cognition and their contribution to behaviour, using resting-state and task-based fMRI in conjunction with automated meta-analyses and cognitive decoding. The controlled semantic cognition framework proposes that distinct brain regions support the long-term representation of heteromodal conceptual knowledge and semantic control processes that retrieve currently-relevant aspects of knowledge. However, previous studies have not investigated whether these components have distinct patterns of lateralisation. Chapter 2 assessed intrinsic connectivity of four regions implicated in semantic cognition: anterior temporal lobe, angular gyrus, inferior frontal gyrus, and posterior middle temporal gyrus. Semantic sites in the left hemisphere showed connectivity with both control regions and default mode network, whilst their right hemisphere homotopes showed connectivity with control regions and visual and attentional systems. Semantic control regions showed the strongest lateralisation. Chapter 3 examined hemispheric specialisation of the anterior temporal lobes, strongly implicated in semantic representation. It assessed the relationship between differential intrinsic connectivity and behaviour outside the scanner on a semantic categorisation task previously shown to be sensitive to lateralisation. Graded differences in connectivity between left and right anterior temporal lobes, and from right anterior temporal cortex to the visual system related to semantic efficiency. Finally, Chapter 4 tested the specificity of the semantic control system and its relationship to domain-general control. Using a task known to engage domain-general inhibition, but introducing semantic content, this chapter yields evidence that regions implicated in semantic control are not sensitive to challenging tasks that require exercising controlled processing, and instead are specific to semantic processing. Together, these results constitute evidence for a component-process architecture in the semantic cognition system, with different patterns of lateralisation for the semantic representation and control systems. Within these systems, the results confirm the specific nature of semantic control, and fit with the graded-hub architecture of semantic representation

Causal Influence of Linguistic Learning on Perceptual and Conceptual Processing: A Brain-Constrained Deep Neural Network Study of Proper Names and Category Terms

Language influences cognitive and conceptual processing, but the mechanisms through which such causal effects are realized in the human brain remain unknown. Here, we use a brain-constrained deep neural network model of category formation and symbol learning and analyze the emergent model’s internal mechanisms at the neural circuit level. In one set of simulations, the network was presented with similar patterns of neural activity indexing instances of objects and actions belonging to the same categories. Biologically realistic Hebbian learning led to the formation of instance-specific neurons distributed across multiple areas of the network, and, in addition, to cell assembly circuits of “shared” neurons responding to all category instances—the network correlates of conceptual categories. In two separate sets of simulations, the network learned the same patterns together with symbols for individual instances [“proper names” (PN)] or symbols related to classes of instances sharing common features [“category terms” (CT)]. Learning CT remarkably increased the number of shared neurons in the network, thereby making category representations more robust while reducing the number of neurons of instance-specific ones. In contrast, proper name learning prevented a substantial reduction of instance-specific neurons and blocked the overgrowth of category general cells. Representational similarity analysis further confirmed that the neural activity patterns of category instances became more similar to each other after category-term learning, relative to both learning with PN and without any symbols. These network-based mechanisms for concepts, PN, and CT explain why and how symbol learning changes object perception and memory, as revealed by experimental studies

The semantic representation of social groups and its neural substrate

Neuropsychological studies described brain damaged patients with a deficit at recognizing exemplars from some semantic categories while being still able to recognize exemplars from other categories, and vice versa. This evidence suggested that categories such as animals, plants, artifacts and conspecifics might be independently organized in the brain. Several theories tried to explain the category specificity, and proposed that concepts are represented in the brain according to the modality of their features, on the relevance of a domain for survival or on the degree of inter-correlation between features. Perhaps one limitation on investigation on how categories are represented in the brain has to do with the poor characterization of the concept about conspecifics often limited to famous and familiar persons as unique entities, and as such not very comparable with the other categories of stimuli. Recent findings suggested that even the knowledge about categories of conspecifics defined as social groups might well be represented independently of other categories.In the current thesis I investigated whether social group knowledge is indeed represented independently of other categories, consistently with previous findings, and the eventual neural substrates of such knowledge. In two different studies, I tested the knowledge of patients with brain tumors and neurodegenerative diseases about social groups, animate and inanimate entities. Correlating patients\u2019 behavioural performance with structural MRI data, I found that the lesion of a left-lateralized set of areas was selectively associated with the impairment in naming social group pictures. Specifically, inferior frontal gyrus, insula and anterior temporal cortex were associated with social group processing in both the studies. Since these areas were reported to be involved in emotional processing, In a third study with healthy individuals, I tested whether one of the above brain regions, within the opercular part of inferior frontal gyrus, might be involved in processing social groups per se or in processing the valence of stimuli. Results revealed that this area was involved in the processing of negative stimuli and suggested that the semantic impairment in processing social groups might be related to the intrinsic emotional value of this category of stimuli. This pattern of findings suggests that human conceptual knowledge is associated with modality-specific processing areas, and that social group representation might interacts with emotional features