The neural basis for novel semantic categorization

Reproducible, data-driven characterization of sleep based on brain dynamics and transitions from whole-night fMRI

Understanding the function of sleep requires studying the dynamics of brain activity across whole-night sleep and their transitions. However, current gold standard polysomnography (PSG) has limited spatial resolution to track brain activity. Additionally, previous fMRI studies were too short to capture full sleep stages and their cycling. To study whole-brain dynamics and transitions across whole-night sleep, we used an unsupervised learning approach, the Hidden Markov model (HMM), on two-night, 16 hr fMRI recordings of 12 non-sleep-deprived participants who reached all PSG-based sleep stages. This method identified 21 recurring brain states and their transition probabilities, beyond PSG-defined sleep stages. The HMM trained on one night accurately predicted the other, demonstrating unprecedented reproducibility. We also found functionally relevant subdivisions within rapid eye movement (REM) and within non-REM 2 stages. This study provides new insights into brain dynamics and transitions during sleep, aiding our understanding of sleep disorders that impact sleep transitions.

Reproducible, data-driven characterization of sleep based on brain dynamics and transitions from whole-night fMRI

Understanding the function of sleep requires studying the dynamics of brain activity across whole-night sleep and their transitions. However, current gold standard polysomnography (PSG) has limited spatial resolution to track brain activity. Additionally, previous fMRI studies were too short to capture full sleep stages and their cycling. To study whole-brain dynamics and transitions across whole-night sleep, we used an unsupervised learning approach, the Hidden Markov model (HMM), on two-night, 16-hour fMRI recordings of 12 non-sleep-deprived participants who reached all PSG-based sleep stages. This method identified 21 recurring brain states and their transition probabilities, beyond PSG-defined sleep stages. The HMM trained on one night accurately predicted the other, demonstrating unprecedented reproducibility. We also found functionally relevant subdivisions within rapid eye movement (REM) and within non-REM 2 stages. This study provides new insights into brain dynamics and transitions during sleep, aiding our understanding of sleep disorders that impact sleep transitions.

The prefrontal cortex: from monkey to man

The prefrontal cortex is so important to human beings that, if deprived of it, our behaviour is reduced to action-reactions and automatisms, with no ability to make deliberate decisions. Why does the prefrontal cortex hold such importance in humans? In answer, this review draws on the proximity between humans and other primates, which enables us, through comparative anatomical-functional analysis, to understand the cognitive functions we have in common and specify those that distinguish humans from their closest cousins. First, a focus on the lateral region of the prefrontal cortex illustrates the existence of a continuum between rhesus monkeys (the most studied primates in neuroscience) and humans for most of the major cognitive functions in which this region of the brain plays a central role. This continuum involves the presence of elementary mental operations in the rhesus monkey (e.g. working memory or response inhibition) that are constitutive of 'macro-functions' such as planning, problem-solving and even language production. Second, the human prefrontal cortex has developed dramatically compared to that of other primates. This increase seems to concern the most anterior part (the frontopolar cortex). In humans, the development of the most anterior prefrontal cortex is associated with three major and interrelated cognitive changes: (i) a greater working memory capacity, allowing for greater integration of past experiences and prospective futures; (ii) a greater capacity to link discontinuous or distant data, whether temporal or semantic; and (iii) a greater capacity for abstraction, allowing humans to classify knowledge in different ways, to engage in analogical reasoning or to acquire abstract values that give rise to our beliefs and morals. Together, these new skills enable us, among other things, to develop highly sophisticated social interactions based on language, enabling us to conceive beliefs and moral judgements and to conceptualize, create and extend our vision of our environment beyond what we can physically grasp. Finally, a model of the transition of prefrontal functions between humans and non-human primates concludes this review.

Semantic representations in inferior frontal and lateral temporal cortex during picture naming, reading, and repetition

Reading, naming, and repetition are classical neuropsychological tasks widely used in the clinic and psycholinguistic research. While reading and repetition can be accomplished by following a direct or an indirect route, pictures can be named only by means of semantic mediation. By means of fMRI multivariate pattern analysis, we evaluated whether this well-established fundamental difference at the cognitive level is associated at the brain level with a difference in the degree to which semantic representations are activated during these tasks. Semantic similarity between words was estimated based on a word association model. Twenty subjects participated in an event-related fMRI study where the three tasks were presented in pseudo-random order. Linear discriminant analysis of fMRI patterns identified a set of regions that allow to discriminate between words at a high level of word-specificity across tasks. Representational similarity analysis was used to determine whether semantic similarity was represented in these regions and whether this depended on the task performed. The similarity between neural patterns of the left Brodmann area 45 (BA45) and of the superior portion of the left supramarginal gyrus correlated with the similarity in meaning between entities during picture naming. In both regions, no significant effects were seen for repetition or reading. The semantic similarity effect during picture naming was significantly larger than the similarity effect during the two other tasks. In contrast, several regions including left anterior superior temporal gyrus and left ventral BA44/frontal operculum, among others, coded for semantic similarity in a task-independent manner. These findings provide new evidence for the dynamic, task-dependent nature of semantic representations in the left BA45 and a more task-independent nature of the representational activation in the lateral temporal cortex and ventral BA44/frontal operculum.

The moderating role of sex in the relationship between executive functions and academic procrastination in undergraduate students

The objective of the study was to determine if sex plays a moderating role in the relationship between executive functions and academic procrastination in 106 university students of both genders (28.3% male and 71.7% female) between the ages of 18 and 30 years (M = 19.7; SD = 2.7). The Academic Procrastination Scale and the Neuropsychological Battery of Executive Functions and Frontal Lobes (BANFE-2) were used to measure the variables. The results of the study showed that the degree of prediction of the tasks linked to the orbitomedial cortex (involves the orbitofrontal cortex [OFC] and the medial prefrontal cortex [mPFC]) on academic procrastination is significantly moderated by the sex of the university students (β₃ = 0.53; p < 0.01). For men, the estimated effect of the tasks linked to the orbitomedial cortex on the degree of academic procrastination is −0.81. For women, the estimated effect of the tasks linked to the orbitomedial cortex on the degree of academic procrastination is −0.28. In addition, it was shown that sex does not play a moderating role in the relationship between the tasks linked to the dorsolateral prefrontal cortex (dlPFC) and academic procrastination (β₃ = 0.12; p > 0.05). It was also determined that sex does not play a moderating role in the relationship between the tasks linked to the anterior prefrontal cortex (aPFC) and academic procrastination (β₃ = 0.05; p > 0.05). It is concluded that only the executive functions associated with the orbitomedial cortex are moderated by the sex of the university students, where the impact of the tasks linked to the orbitomedial cortex on academic procrastination in men is significantly greater than in women.

Structural connectivity in ventral language pathways characterizes non-verbal autism

Language capacities in autism spectrum disorders (ASD) range from normal scores on standardized language tests to absence of functional language in a substantial minority of 30% of individuals with ASD. Due to practical difficulties of scanning at this severe end of the spectrum, insights from MRI are scarce. Here we used manual deterministic tractography to investigate, for the first time, the integrity of the core white matter tracts defining the language connectivity network in non-verbal ASD (nvASD): the three segments of the arcuate (AF), the inferior fronto-occipital (IFOF), the inferior longitudinal (ILF) and the uncinate (UF) fasciculi, and the frontal aslant tract (FAT). A multiple case series of nine individuals with nvASD were compared to matched individuals with verbal ASD (vASD) and typical development (TD). Bonferroni-corrected repeated measure ANOVAs were performed separately for each tract-Hemisphere (2:Left/Right) × Group (3:TD/vASD/nvASD). Main results revealed (i) a main effect of group consisting in a reduction in fractional anisotropy (FA) in the IFOF in nvASD relative to TD; (ii) a main effect of group revealing lower values of radial diffusivity (RD) in the long segment of the AF in nvASD compared to vASD group; and (iii) a reduced volume in the left hemisphere of the UF when compared to the right, in the vASD group only. These results do not replicate volumetric differences of the dorsal language route previously observed in nvASD, and instead point to a disruption of the ventral language pathway, in line with semantic deficits observed behaviourally in this group.

Multisensory Information Facilitates the Categorization of Untrained Stimuli

Although it has been demonstrated that multisensory information can facilitate object recognition and object memory, it remains unclear whether such facilitation effect exists in category learning. To address this issue, comparable car images and sounds were first selected by a discrimination task in Experiment 1. Then, those selected images and sounds were utilized in a prototype category learning task in Experiments 2 and 3, in which participants were trained with auditory, visual, and audiovisual stimuli, and were tested with trained or untrained stimuli within the same categories presented alone or accompanied with a congruent or incongruent stimulus in the other modality. In Experiment 2, when low-distortion stimuli (more similar to the prototypes) were trained, there was higher accuracy for audiovisual trials than visual trials, but no significant difference between audiovisual and auditory trials. During testing, accuracy was significantly higher for congruent trials than unisensory or incongruent trials, and the congruency effect was larger for untrained high-distortion stimuli than trained low-distortion stimuli. In Experiment 3, when high-distortion stimuli (less similar to the prototypes) were trained, there was higher accuracy for audiovisual trials than visual or auditory trials, and the congruency effect was larger for trained high-distortion stimuli than untrained low-distortion stimuli during testing. These findings demonstrated that higher degree of stimuli distortion resulted in more robust multisensory effect, and the categorization of not only trained but also untrained stimuli in one modality could be influenced by an accompanying stimulus in the other modality.

The role of working memory and visual processing in prototype category learning

To investigate whetherworking memory and visual processing havethe same role or differentrolesin A/B and A/not A prototype category learning,the present study adoptedan A/Bor A/not A category learningtask in control and dual conditions. The results of Experiment 1 showed that an additional dual visual working memory taskrather thanadualverbal working memory task reduced accuracy of the A/B task, whereasnodual tasksinfluencedaccuracy of the A/not A task. The results of Experiment 2 revealed that an additionaldual visual processing task impairedaccuracy of the A/B task, whereas the dual visual processing task did not influence accuracy of the A/not Atask. These results indicate that visual working memory and visual processing play different roles in A/B and A/not A prototype category learning, andsupport that thesetwo types of prototype category learning are mediated by differentmemory systems.

The contributions of the left hippocampus and bilateral inferior parietal lobule to form-meaning associative learning

Existing studies have identified crucial roles for the hippocampus and a distributed set of cortical regions (e.g., the inferior parietal cortex) in learning novel words. Nevertheless, researchers have not clearly determined how the hippocampus and cortical regions dynamically interact during novel word learning, especially during form-meaning associative learning. As a method to address this question, we used an online learning paradigm and representational similarity analysis to explore the contributions of the hippocampus and neocortex to form-meaning associative learning. Twenty-nine native Chinese college students were recruited to learn 30 form-meaning pairs, which were repeated 7 times during fMRI scan. Form-meaning associative learning elicited activations in a wide neural network including regions required for word processing (i.e., the bilateral inferior frontal gyrus and the occipitotemporal cortex), regions required for encoding (i.e., the bilateral parahippocampus and hippocampus), and regions required for cognitive control (i.e., the anterior cingulate cortex and dorsolateral prefrontal cortex). More importantly, our study revealed the differential roles of the left hippocampus and bilateral inferior parietal lobule (IPL) in form-meaning associative learning. Specifically, higher pattern similarity in the bilateral IPL in the early learning phase (repetitions 1 to 3) was related to better learning performance, while higher pattern similarity in the left hippocampus in the late learning phase (repetitions 5 to 7) was associated with better learning performance. These findings indicate that the hippocampus and cortical regions (e.g., the IPL) contribute to form-meaning learning in different stages.

Inferior parietal lobule is sensitive to different semantic similarity relations for concrete and abstract words

Similarity measures, the extent to which two concepts have similar meanings, are the key to understand how concepts are represented, with different theoretical perspectives relying on very different sources of data from which similarity can be calculated. While there is some commonality in similarity measures, the extent of their correlation is limited. Previous studies also suggested that the relative performance of different similarity measures may also vary depending on concept concreteness and that the inferior parietal lobule (IPL) may be involved in the integration of conceptual features in a multimodal system for the semantic categorization. Here, we tested for the first time whether theory-based similarity measures predict the pattern of brain activity in the IPL differently for abstract and concrete concepts. English speakers performed a semantic decision task, while we recorded their brain activity in IPL through fNIRS. Using representational similarity analysis, results indicated that the neural representational similarity in IPL conformed to the lexical co-occurrence among concrete concepts (regardless of the hemisphere) and to the affective similarity among abstract concepts in the left hemisphere only, implying that semantic representations of abstract and concrete concepts are characterized along different organizational principles in the IPL. We observed null results for the decoding accuracy. Our study suggests that the use of the representational similarity analysis as a complementary analysis to the decoding accuracy is a promising tool to reveal similarity patterns between theoretical models and brain activity recorded through fNIRS.

Stimulus modality influences the acquisition and use of the rule-based strategy and the similarity-based strategy in category learning

This study aimed to investigate whether stimulus modality influenced the acquisition and use of the rule-based strategy and the similarity-based strategy in category learning and whether the use of the two strategies was supported by shared or separate neural substrates. To address these issues, we combined behavioral and fNIRS methods in a modified prototype distortion task in which each category member has one rule feature and ten similarity features, and each type of feature can be presented in either the visual modality or the auditory modality. The results in Experiment 1 revealed that the learning effect in the "auditory rule-visual similarity" condition was the highest among all four conditions; further analysis revealed that in the "auditory rule-visual similarity" condition, the number of participants who used the rule-based strategy was more than the number of participants who used the similarity-based strategy, and the learning effect was always much higher for the rule-based strategy than for the similarity-based strategy. The behavioral results in Experiment 2 replicated the main findings in Experiment 1, and the fNIRS results showed that the use of the visual rule-based strategy was mediated by the dorsolateral prefrontal cortex, whereas the use of the auditory similarity-based strategy mainly engaged in the superior temporal gyrus, and the use of the visual similarity-based strategy mainly engaged in the inferior temporal gyrus. The results in Experiment 3 revealed that when the stimuli had only one type of feature, the visual rule rather than the auditory rule was learned more easily. The results provide new evidence that the stimulus modality can influence the acquisition and use of the rule-based strategy and the similarity-based strategy in category learning and that the use of the two types of strategies is supported by separate neural substrates both in the auditory modality and the visual modality.

Building Memory Representations for Exemplar-Based Judgment: A Role for Ventral Precuneus

The brain networks underlying human multiple-cue judgment, the judgment of a continuous criterion based on multiple cues, have been examined in a few recent studies, and the ventral precuneus has been found to be a key region. Specifically, activation differences in ventral precuneus (as measured with functional magnetic resonance imaging, fMRI) has been linked to an exemplar-based judgment process, where judgments are based on memory for previous similar cases. Ventral precuneus is implicated in various episodic memory processes, notably such that increased activity during learning in this region as well as in the ventromedial prefrontal cortex (vmPFC) and the medial temporal lobes (MTL) have been linked to retrieval success. The present study used fMRI during a multiple-cue judgment task to gain novel neurocognitive evidence informative for the link between learning-related activity changes in ventral precuneus and exemplar-based judgment. Participants (N = 27) spontaneously learned to make judgments during fMRI, in a multiple-cue judgment task specifically designed to induce exemplar-based processing. Contrasting brain activity during late learning to early learning revealed higher activity in ventral precuneus, the bilateral MTL, and the vmPFC. Activity in the ventral precuneus and the vmPFC was found to parametrically increase between each judgment event, and activity levels in the ventral precuneus predicted performance after learning. These results are interpreted such that the ventral precuneus supports the aspects of exemplar-based processes that are related to episodic memory, tentatively by building, storing, and being implicated in retrieving memory representations for judgment.

Distinct Functional Network Connectivity for Abstract and Concrete Mental Imagery

In several behavioral psycholinguistic studies, it has been shown that concrete words are processed more efficiently. They can be remembered faster, recognized better, and can be learned easier than abstract words. This fact is called concreteness effect. There are fMRI studies which compared the neural representations of concrete and abstract concepts in terms of activated regions. In the present study, a comparison has been made between the condition-specific connectivity of functional networks (obtained by group ICA) during imagery of abstract and concrete words. The obtained results revealed that the functional network connectivity between three pairs of networks during concrete imagery is significantly different from that of abstract imagery (FDR correction at the significance level of 0.05). These results suggest that abstract and concrete concepts have different representations in terms of functional network connectivity pattern. Remarkably, in all of these network pairs, the connectivity during concrete imagery is significantly higher than that of abstract imagery. These more coherent networks include both linguistic and visual regions with a higher engagement of the right hemisphere, so the results are in line with dual coding theory. Additionally, these three pairs of networks include the contrasting regions which have shown stronger activation either in concrete or abstract word processing in former studies. The findings imply that the brain is more integrated and synchronized at the time of concrete imagery and it may explain the reason of faster concrete words processing. In order to validate the results, we used functional network connectivity distributions (FNCD). Wilcoxon rank-sum test was used to check if the abstract and concrete FNCDs extracted from whole subjects are the same. The result revealed that the corresponding distributions are different which indicates two different patterns of connectivity for abstract and concrete word processing. Also, the mean of FNCD is significantly higher at the time of concrete imagery than that of abstract imagery. Furthermore, FNCDs at the single-subject level are significantly more left-skewed or equally, include more strong connectivity for concrete imagery.

A Similarity-Based Process for Human Judgment in the Parietal Cortex

One important distinction in psychology is between inferences based on associative memory and inferences based on analysis and rules. Much previous empirical work conceive of associative and analytical processes as two exclusive ways of addressing a judgment task, where only one process is selected and engaged at a time, in an either-or fashion. However, related work indicate that the processes are better understood as being in interplay and simultaneously engaged. Based on computational modeling and brain imaging of spontaneously adopted judgment strategies together with analyses of brain activity elicited in tasks where participants were explicitly instructed to perform similarity-based associative judgments or rule-based judgments (n = 74), we identified brain regions related to the two types of processes. We observed considerable overlap in activity patterns. The precuneus was activated for both types of judgments, and its activity predicted how well a similarity-based model fit the judgments. Activity in the superior frontal gyrus predicted the fit of a rule-based judgment model. The results suggest the precuneus as a key node for similarity-based judgments, engaged both when overt responses are guided by similarity-based and rule-based processes. These results are interpreted such that similarity-based processes are engaged in parallel to rule-based-processes, a finding with direct implications for cognitive theories of judgment.

Probing culture in the head: the neural correlates of relational models

Relational Models Theory or RMT proposes that there are four universal ways in which socio-economic relations can be organized. According to the RMT, each of its four relational models (Communal Sharing, Authority Ranking, Equality Matching, and Market Pricing) is associated with a distinct cognitive representation, with a cumulative pattern in which each relational model is a superset of the next lower model. This report for the first time uses a combination of cognitive and the social neuroscience to put this model to the test. RMT proposes that members of every culture use all four relational models, just in different proportions. It should therefore be possible to study their neural correlates in a mono-cultural sample. In this study, thirty-nine European-American students were imaged in a 3T Siemens Trio with a 24-channel head coil while rating the extent to which each relational model organized relationships with each of thirty-two acquaintances/friend/relatives in a boxcar design. FreeSurfer Functional Analysis Stream (FS-FAST) analyses revealed distinct patterns of activation for each of the relational models. The activations did not follow a cumulative hierarchical pattern, suggestive that this aspect of the RMT model should be revised.

Anterior Temporal Lobe Morphometry Predicts Categorization Ability

Categorization is the mental operation by which the brain classifies objects and events. It is classically assessed using semantic and non-semantic matching or sorting tasks. These tasks show a high variability in performance across healthy controls and the cerebral bases supporting this variability remain unknown. In this study we performed a voxel-based morphometry study to explore the relationships between semantic and shape categorization tasks and brain morphometric differences in 50 controls. We found significant correlation between categorization performance and the volume of the gray matter in the right anterior middle and inferior temporal gyri. Semantic categorization tasks were associated with more rostral temporal regions than shape categorization tasks. A significant relationship was also shown between white matter volume in the right temporal lobe and performance in the semantic tasks. Tractography revealed that this white matter region involved several projection and association fibers, including the arcuate fasciculus, inferior fronto-occipital fasciculus, uncinate fasciculus, and inferior longitudinal fasciculus. These results suggest that categorization abilities are supported by the anterior portion of the right temporal lobe and its interaction with other areas.

Ignore Similarity If You Can: A Computational Exploration of Exemplar Similarity Effects on Rule Application

It is generally assumed that when making categorization judgments the cognitive system learns to focus on stimuli features that are relevant for making an accurate judgment. This is a key feature of hybrid categorization systems, which selectively weight the use of exemplar- and rule-based processes. In contrast, Hahn et al. (2010) have shown that people cannot help but pay attention to exemplar similarity, even when doing so leads to classification errors. This paper tests, through a series of computer simulations, whether a hybrid categorization model developed in the ACT-R cognitive architecture (by Anderson and Betz, 2001) can account for the Hahn et al. dataset. This model implements Nosofsky and Palmeri's (1997) exemplar-based random walk model as its exemplar route, and combines it with an implementation of Nosofsky et al. (1994) rule-based model RULEX. A thorough search of the model's parameter space showed that while the presence of an exemplar-similarity effect on response times was associated with classification errors it was possible to fit both measures to the observed data for an unsupervised version of the task (i.e., in which no feedback on accuracy was given). Difficulties arose when the model was applied to a supervised version of the task in which explicit feedback on accuracy was given. Modeling results show that the exemplar-similarity effect is diminished by feedback as the model learns to avoid the error-prone exemplar-route, taking instead the accurate rule-route. In contrast to the model, Hahn et al. found that people continue to exhibit robust exemplar-similarity effects even when given feedback. This work highlights a challenge for understanding how and why people combine rules and exemplars when making categorization decisions.

The Neural Consequences of Semantic Richness

Some concepts have richer semantic representations than others. That is, when considering the meaning of concepts, subjects generate more information (more features, more associates) for some concepts than for others. This variability in semantic richness influences responses in speeded tasks that involve semantic processing, such as lexical decision and semantic categorization tasks. It has been suggested that concepts with richer semantic representations build stronger attractors in semantic space, allowing faster settling of activation patterns and thus faster responding. Using event-related functional magnetic resonance imaging, we examined the neural activation associated with semantic richness by contrasting activation for words with high and low numbers of associates in a semantic categorization task. Results were consistent with faster semantic settling for words with richer representations: Words with a low number of semantic associates produced more activation than words with a high number of semantic associates in a number of regions, including left inferior frontal and inferior temporal gyri.

The Neural Correlates of Similarity- and Rule-based Generalization

The idea that there are multiple learning systems has become increasingly influential in recent years, with many studies providing evidence that there is both a quick, similarity-based or feature-based system and a more effortful rule-based system. A smaller number of imaging studies have also examined whether neurally dissociable learning systems are detectable. We further investigate this by employing for the first time in an imaging study a combined positive and negative patterning procedure originally developed by Shanks and Darby [Shanks, D. R., & Darby, R. J. Feature- and rule-based generalization in human associative learning. Journal of Experimental Psychology: Animal Behavior Processes, 24, 405-415, 1998]. Unlike previous related studies employing other procedures, rule generalization in the Shanks-Darby task is beyond any simple non-rule-based (e.g., associative) account. We found that rule- and similarity-based generalization evoked common activation in diverse regions including the pFC and the bilateral parietal and occipital lobes indicating that both strategies likely share a range of common processes. No differences between strategies were identified in whole-brain comparisons, but exploratory analyses indicated that rule-based generalization led to greater activation in the right middle frontal cortex than similarity-based generalization. Conversely, the similarity group activated the anterior medial frontal lobe and right inferior parietal lobes more than the rule group did. The implications of these results are discussed.

Category learning in Alzheimer's disease and normal cognitive aging depends on initial experience of feature variability

Semantic category learning is dependent upon several factors, including the nature of the learning task, as well as individual differences in the quality and heterogeneity of exemplars that an individual encounters during learning. We trained healthy older adults (n=39) and individuals with a diagnosis of Alzheimer's disease or Mild Cognitive Impairment (n=44) to recognize instances of a fictitious animal, a "crutter". Each stimulus item contained 10 visual features (e.g., color, tail shape) which took one of two values for each feature (e.g., yellow/red, curly/straight tails). Participants were presented with a series of items (learning phase) and were either told the items belonged to a semantic category (explicit condition) or were told to think about the appearance of the items (implicit condition). Half of participants saw learning items with higher similarity to an unseen prototype (high typicality learning set), and thus lower between-item variability in their constituent features; the other half learned from items with lower typicality (low typicality learning set) and higher between-item feature variability. After the learning phase, participants were presented with test items one at a time that varied in the number of typical features from 0 (antitype) to 10 (prototype). We examined between-subjects factors of learning set (lower or higher typicality), instruction type (explicit or implicit), and group (patients vs. elderly control). Learning in controls was aided by higher learning set typicality: while controls in both learning set groups demonstrated significant learning, those exposed to a high-typicality learning set appeared to develop a prototype that helped guide their category membership judgments. Overall, patients demonstrated more difficulty with category learning than elderly controls. Patients exposed to the higher-typicality learning set were sensitive to the typical features of the category and discriminated between the most and least typical test items, although less reliably than controls. In contrast, patients exposed to the low-typicality learning set showed no evidence of learning. Analysis of structural imaging data indicated a positive association between left hippocampal grey matter density in elderly controls but a negative association in the patient group, suggesting differential reliance on hippocampal-mediated learning. Contrary to hypotheses, learning did not differ between explicit and implicit conditions for either group. Results demonstrate that category learning is improved when learning materials are highly similar to the prototype.

Temporo-parietal connectivity uniquely predicts reading change from childhood to adolescence

Previous research has shown that left posterior middle temporal gyrus (pMTG) is a core node in the semantic network, and cross-sectional studies have shown that activation in this region changes developmentally and is related to skill measured concurrently. However, it is not known how functional connectivity with this region changes developmentally, and whether functional connectivity is related to future gains in reading. We conducted a longitudinal functional magnetic resonance imaging (fMRI) study in 30 typically developing children (aged 8-15) to examine whether initial brain measures, including activation and connectivity, can predict future behavioral improvement in a semantic judgment task. Participants were scanned on entering the study (time 1, T1) and a follow-up period of 2years (time 2, T2). Character pairs were arranged in a continuous variable according to association strength (i.e. strong versus weak), and participants were asked to determine if these visually presented pairs were related in meaning. Our results demonstrated greater developmental changes from time 1 to time 2 for weaker association pairs in the left pMTG for the children (aged 8-11) as compared to the adolescents (aged 12-15). Moreover, the results showed greater developmental changes from time 1 to time 2 for weaker association pairs in connectivity between the pMTG and inferior parietal lobule (IPL) for the children as compared to the adolescents. Furthermore, a hierarchical stepwise regression model revealed that connectivity between the pMTG and IPL in weak association pairs was uniquely predictive of behavioral improvement from time 1 to time 2 for the children, but not the adolescents. Taken together, the activation results suggest relatively rapid development before adolescence of semantic representations in the pMTG. Moreover, the connectivity results of pMTG with IPL tentatively suggest that early development of semantic representations may be facilitated by enhanced engagement of phonological short-term memory.

A Comparison of the neural correlates that underlie rule-based and information-integration category learning

The influential competition between verbal and implicit systems (COVIS) model proposes that category learning is driven by two competing neural systems-an explicit, verbal, system, and a procedural-based, implicit, system. In the current fMRI study, participants learned either a conjunctive, rule-based (RB), category structure that is believed to engage the explicit system, or an information-integration category structure that is thought to preferentially recruit the implicit system. The RB and information-integration category structures were matched for participant error rate, the number of relevant stimulus dimensions, and category separation. Under these conditions, considerable overlap in brain activation, including the prefrontal cortex, basal ganglia, and the hippocampus, was found between the RB and information-integration category structures. Contrary to the predictions of COVIS, the medial temporal lobes and in particular the hippocampus, key regions for explicit memory, were found to be more active in the information-integration condition than in the RB condition. No regions were more activated in RB than information-integration category learning. The implications of these results for theories of category learning are discussed. Hum Brain Mapp 37:3557-3574, 2016. © 2016 Wiley Periodicals, Inc.

How the brain learns how few are "many": An fMRI study of the flexibility of quantifier semantics

Previous work has shown that the meaning of a quantifier such as "many" or "few" depends in part on quantity. However, the meaning of a quantifier may vary depending on the context, e.g. in the case of common entities such as "many ants" (perhaps several thousands) compared to endangered species such as "many pandas" (perhaps a dozen). In a recent study (Heim et al., 2015 Front. Psychol.) we demonstrated that the relative meaning of "many" and "few" may be changed experimentally. In a truth value judgment task, displays with 40% of circles in a named color initially had a low probability of being labeled "many". After a training phase, the likelihood of acceptance 40% as "many" increased. Moreover, the semantic learning effect also generalized to the related quantifier "few" which had not been mentioned in the training phase. Thus, fewer 40% arrays were considered "few." In the present study, we tested the hypothesis that this semantic adaptation effect was supported by cytoarchitectonic Brodmann area (BA) 45 in Broca's region which may contribute to semantic evaluation in the context of language and quantification. In an event-related fMRI study, 17 healthy volunteers performed the same paradigm as in the previous behavioral study. We found a relative signal increase when comparing the critical, trained proportion to untrained proportions. This specific effect was found in left BA 45 for the trained quantifier "many", and in left BA 44 for both quantifiers, reflecting the semantic adjustment for the untrained but related quantifier "few." These findings demonstrate the neural basis for processing the flexible meaning of a quantifier, and illustrate the neuroanatomical structures that contribute to variable meanings that can be associated with a word when used in different contexts.

Mapping the emotional landscape: The role of specific emotions in conceptual categorization

Although researchers generally subscribe to the opinion that emotions play a critical role in cognition, very few (see Niedenthal, Halberstadt, & Innes-Ker, 1999) have examined the specific interaction between the emotional state of the perceiver and the emotional meaning of stimuli in conceptual categorization - an important aspect of "higher-level" cognition. Niedenthal et al. (1999) advanced a fine-grained theory of emotional response categorization, arguing that emotional states increase the tendency to categorize concepts into a predictable set of emotional response categories characterized by the common, distinct emotional responses elicited by the concepts. Based on the pioneering work of Niedenthal et al., we further argued that (1) the specific emotion experienced by the individual should selectively facilitate the categorization of concepts associated with the same emotion, (2) both in terms of category inclusion and category exclusion, and (3) this facilitation effect should not be contingent on the awareness of the emotional state. In three experiments, participants were induced to experience different emotional states through movies or a facial-feedback manipulation. They judged whether or not a target concept belonged to the same category as the two comparison concepts. Some of the concept triads shared emotional associations, while others didn't. Results showed that emotive participants had a greater tendency than those in a neutral mood to group concepts according to their emotional associations, and to distinguish concepts with different emotional associations. They were also more efficient in categorizing concepts that had specific emotional meaning corresponding to their own emotional state than to other emotional concepts. Furthermore, participants posing a disgust expression without their knowledge showed higher tendency to categorize concepts according to their relevance to disgust. Implications and potential applications of the findings were discussed.

Frontotemporal neural systems supporting semantic processing in Alzheimer's disease

We hypothesized that semantic memory for object concepts involves both representations of visual feature knowledge in modality-specific association cortex and heteromodal regions that are important for integrating and organizing this semantic knowledge so that it can be used in a flexible, contextually appropriate manner. We examined this hypothesis in an fMRI study of mild Alzheimer's disease (AD). Participants were presented with pairs of printed words and asked whether the words matched on a given visual-perceptual feature (e.g., guitar, violin: SHAPE). The stimuli probed natural kinds and manufactured objects, and the judgments involved shape or color. We found activation of bilateral ventral temporal cortex and left dorsolateral prefrontal cortex during semantic judgments, with AD patients showing less activation of these regions than healthy seniors. Moreover, AD patients showed less ventral temporal activation than did healthy seniors for manufactured objects, but not for natural kinds. We also used diffusion-weighted MRI of white matter to examine fractional anisotropy (FA). Patients with AD showed significantly reduced FA in the superior longitudinal fasciculus and inferior frontal-occipital fasciculus, which carry projections linking temporal and frontal regions of this semantic network. Our results are consistent with the hypothesis that semantic memory is supported in part by a large-scale neural network involving modality-specific association cortex, heteromodal association cortex, and projections between these regions. The semantic deficit in AD thus arises from gray matter disease that affects the representation of feature knowledge and processing its content, as well as white matter disease that interrupts the integrated functioning of this large-scale network.

Two-stage categorization in brand extension evaluation: electrophysiological time course evidence

A brand name can be considered a mental category. Similarity-based categorization theory has been used to explain how consumers judge a new product as a member of a known brand, a process called brand extension evaluation. This study was an event-related potential study conducted in two experiments. The study found a two-stage categorization process reflected by the P2 and N400 components in brand extension evaluation. In experiment 1, a prime–probe paradigm was presented in a pair consisting of a brand name and a product name in three conditions, i.e., in-category extension, similar-category extension, and out-of-category extension. Although the task was unrelated to brand extension evaluation, P2 distinguished out-of-category extensions from similar-category and in-category ones, and N400 distinguished similar-category extensions from in-category ones. In experiment 2, a prime–probe paradigm with a related task was used, in which product names included subcategory and major-category product names. The N400 elicited by subcategory products was more significantly negative than that elicited by major-category products, with no salient difference in P2. We speculated that P2 could reflect the early low-level and similarity-based processing in the first stage, whereas N400 could reflect the late analytic and category-based processing in the second stage.

Neural substrates of similarity and rule-based strategies in judgment

Making accurate judgments is a core human competence and a prerequisite for success in many areas of life. Plenty of evidence exists that people can employ different judgment strategies to solve identical judgment problems. In categorization, it has been demonstrated that similarity-based and rule-based strategies are associated with activity in different brain regions. Building on this research, the present work tests whether solving two identical judgment problems recruits different neural substrates depending on people's judgment strategies. Combining cognitive modeling of judgment strategies at the behavioral level with functional magnetic resonance imaging (fMRI), we compare brain activity when using two archetypal judgment strategies: a similarity-based exemplar strategy and a rule-based heuristic strategy. Using an exemplar-based strategy should recruit areas involved in long-term memory processes to a larger extent than a heuristic strategy. In contrast, using a heuristic strategy should recruit areas involved in the application of rules to a larger extent than an exemplar-based strategy. Largely consistent with our hypotheses, we found that using an exemplar-based strategy led to relatively higher BOLD activity in the anterior prefrontal and inferior parietal cortex, presumably related to retrieval and selective attention processes. In contrast, using a heuristic strategy led to relatively higher activity in areas in the dorsolateral prefrontal and the temporal-parietal cortex associated with cognitive control and information integration. Thus, even when people solve identical judgment problems, different neural substrates can be recruited depending on the judgment strategy involved.

Perceptual Category Judgment Deficits are Related to Prefrontal Decision Making Abnormalities in Schizophrenia

Previous studies of perceptual category learning in patients with schizophrenia generally demonstrate impaired perceptual category learning; however, traditional cognitive studies have often failed to address the relationship of different cortical regions to perceptually based category learning and judgments in healthy participants and patients with schizophrenia. In the present study, perceptual category learning was examined in 26 patients with schizophrenia and 25 healthy participants using a dot-pattern category learning task. In the training phase, distortions of a prototypical dot pattern were presented. In the test phase, participants were shown the prototype, low and high distortions of the prototype, and random dot patterns. Participants were required to indicate whether the presented dot pattern was a member of the category of dot-patterns previously presented during the study phase. Patients with schizophrenia displayed an impaired ability to make judgments regarding marginal members of novel, perceptually based categories relative to healthy participants. Category judgment also showed opposite patterns of strong, significant correlations with behavioral measures of prefrontal cortex function in patients relative to healthy participants. These results suggest that impaired judgments regarding novel, perceptually based category membership may be due to abnormal prefrontal cortex function in patients with schizophrenia.

The representation of category typicality in the frontal cortex and its cross-linguistic variations

When asked to judge the membership of typical (e.g., car) vs. atypical (e.g., train) pictures of a category (e.g., vehicle), native English (N=18) and native Chinese speakers (N=18) showed distinctive patterns of brain activity despite showing similar behavioral responses. Moreover, these differences were mainly due to the amount and pervasiveness of category information linguistically embedded in the everyday names of the items in the respective languages, with important differences across languages in how pervasive category labels are embedded in item-level terms. Nonetheless, the left inferior frontal gyrus and the bilateral medial frontal gyrus are the most consistent neural correlates of category typicality that persist across languages and linguistic cues. These data together suggest that both cross- and within-language differences in the explicitness of category information have strong effects on the nature of categorization processes performed by the brain.

Age-related vulnerability in the neural systems supporting semantic processing

Our ability to form abstract representations of objects in semantic memory is crucial to language and thought. The utility of this information relies both on the representations of sensory-motor feature knowledge stored in long-term memory and the executive processes required to retrieve, manipulate, and evaluate this semantic knowledge in a task-relevant manner. These complementary components of semantic memory can be differentially impacted by aging. We investigated semantic processing in normal aging using functional magnetic resonance imaging (fMRI). Young and older adults were asked to judge whether two printed object names match on a particular feature (for example, whether a tomato and strawberry have the same color). The task thus required both retrieval of relevant visual feature knowledge of object concepts and evaluating this information. Objects were drawn from either natural kinds or manufactured objects, and were queried on either color or shape in a factorial design. Behaviorally, all subjects performed well, but older adults could be divided into those whose performance matched that of young adults (better performers) and those whose performance was worse (poorer performers). All subjects activated several cortical regions while performing this task, including bilateral inferior and lateral temporal cortex and left frontal and prefrontal cortex. Better performing older adults showed increased overall activity in bilateral premotor cortex and left lateral occipital cortex compared to young adults, and increased activity in these brain regions relative to poorer performing older adults who also showed gray matter atrophy in premotor cortex. These findings highlight the contribution of domain-general executive processing brain regions to semantic memory, and illustrate differences in how these regions are recruited in healthy older adults.

Category-specific semantic memory: converging evidence from bold fMRI and Alzheimer's disease

Patients with Alzheimer's disease have category-specific semantic memory difficulty for natural relative to manufactured objects. We assessed the basis for this deficit by asking healthy adults and patients to judge whether pairs of words share a feature (e.g. "banana:lemon-COLOR"). In an fMRI study, healthy adults showed gray matter (GM) activation of temporal-occipital cortex (TOC) where visual-perceptual features may be represented, and prefrontal cortex (PFC) which may contribute to feature selection. Tractography revealed dorsal and ventral stream white matter (WM) projections between PFC and TOC. Patients had greater difficulty with natural than manufactured objects. This was associated with greater overlap between diseased GM areas correlated with natural kinds in patients and fMRI activation in healthy adults for natural kinds. The dorsal WM projection between PFC and TOC in patients correlated only with judgments of natural kinds. Patients thus remained dependent on the same neural network as controls during judgments of natural kinds, despite disease in these areas. For manufactured objects, patients' judgments showed limited correlations with PFC and TOC GM areas activated by controls, and did not correlate with the PFC-TOC dorsal WM tract. Regions outside of the PFC-TOC network thus may help support patients' judgments of manufactured objects. We conclude that a large-scale neural network for semantic memory implicates both feature knowledge representations in modality-specific association cortex and heteromodal regions important for accessing this knowledge, and that patients' relative deficit for natural kinds is due in part to their dependence on this network despite disease in these areas.

Regional differences in the developmental trajectory of lateralization of the language network

The timing and developmental factors underlying the establishment of language dominance are poorly understood. We investigated the degree of lateralization of traditional frontotemporal and modulatory prefrontal-cerebellar regions of the distributed language network in children (n = 57) ages 4 to 12--a critical period for language consolidation. We examined the relationship between the strength of language lateralization and neuropsychological measures and task performance. The fundamental language network is established by four with ongoing maturation of language functions as evidenced by strengthening of lateralization in the traditional frontotemporal language regions; temporal regions were strongly and consistently lateralized by age seven, while frontal regions had greater variability and were less strongly lateralized through age 10. In contrast, the modulatory prefrontal-cerebellar regions were the least strongly lateralized and degree of lateralization was not associated with age. Stronger core language skills were significantly correlated with greater right lateralization in the cerebellum.

Semantic categorisation of novel objects in frontotemporal dementia

Impaired semantic memory is ubiquitous in frontotemporal dementia (FTD), including patients with semantic dementia (SD), progressive nonfluent aphasia (PNFA) and nonaphasic FTD patients with a deficit in executive and social functioning (EXEC/SOC). One hypothesis attributes this to the degradation of specific categories of knowledge in semantic memory. This study explores the alternate hypothesis that impaired semantic memory in FTD can also reflect limitations in the categorisation processes that determine object meaning. Patients were taught a novel semantic category under two conditions: rule-based categorisation, where executive resources support the evaluation of specific features to determine category membership; and similarity-based categorisation, where category membership is determined by the overall resemblance of an item to a prototype or recalled exemplars. In the first experiment, patients learned a novel category composed of highly salient features. For SD patients, we found category membership judgment profiles following rule-based and similarity-based training that resembled the performance of control subjects. Categorisation was impaired following rule-based training in PNFA and EXEC/SOC patients. In the second experiment, we modified the category so that membership was determined by less salient features, thus increasing the burden on executive resources. Under these circumstances, SD patients' categorisation profiles continued to resemble those of control subjects, PNFA patients' category judgments were governed by feature salience, and EXEC/SOC patients' judgments were limited by impaired executive resources. These observations suggest that the semantic memory deficit in SD largely reflects degraded feature knowledge for familiar objects, while impaired semantic memory in PNFA and in EXEC/SOC patients largely reflects a deficit in the processes associated with semantic categorisation.

Category learning increases discriminability of relevant object dimensions in visual cortex

Learning to categorize objects can transform how they are perceived, causing relevant perceptual dimensions predictive of object category to become enhanced. For example, an expert mycologist might become attuned to species-specific patterns of spacing between mushroom gills but learn to ignore cap textures attributable to varying environmental conditions. These selective changes in perception can persist beyond the act of categorizing objects and influence our ability to discriminate between them. Using functional magnetic resonance imaging adaptation, we demonstrate that such category-specific perceptual enhancements are associated with changes in the neural discriminability of object representations in visual cortex. Regions within the anterior fusiform gyrus became more sensitive to small variations in shape that were relevant during prior category learning. In addition, extrastriate occipital areas showed heightened sensitivity to small variations in shape that spanned the category boundary. Visual representations in cortex, just like our perception, are sensitive to an object's history of categorization.

Normal aging and the dissociable prototype learning systems

Dissociable prototype learning systems have been demonstrated behaviorally and with neuroimaging in younger adults as well as with patient populations. In A/not-A (AN) prototype learning, participants are shown members of category A during training, and during test are asked to decide whether novel items are in category A or are not in category A. Research suggests that AN learning is mediated by a perceptual learning system. In A/B (AB) prototype learning, participants are shown members of category A and B during training, and during test are asked to decide whether novel items are in category A or category B. In contrast to AN, research suggests that AB learning is mediated by a declarative memory system. The current study examined the effects of normal aging on AN and AB prototype learning. We observed an age-related deficit in AB learning, but an age-related advantage in AN learning. Computational modeling supports one possible interpretation based on narrower selective attentional focus in older adults in the AB task and broader selective attention in the AN task. Neuropsychological testing in older participants suggested that executive functioning and attentional control were associated with better performance in both tasks. However, nonverbal memory was associated with better AN performance, while visual attention was associated with worse AB performance. The results support an interactive memory systems approach and suggest that age-related declines in one memory system can lead to deficits in some tasks, but to enhanced performance in others.

Decoding abstract and concrete concept representations based on single-trial fMRI data

Previously, multi-voxel pattern analysis has been used to decode words referring to concrete object categories. In this study we investigated if single-trial-based brain activity was sufficient to distinguish abstract (e.g., mercy) versus concrete (e.g., barn) concept representations. Multiple neuroimaging studies have identified differences in the processing of abstract versus concrete concepts based on the averaged activity across time by using univariate methods. In this study we used multi-voxel pattern analysis to decode functional magnetic resonance imaging (fMRI) data when participants perform a semantic similarity judgment task on triplets of either abstract or concrete words with similar meanings. Classifiers were trained to identify individual trials as concrete or abstract. Cross-validated accuracies for classifying trials as abstract or concrete were significantly above chance (P < 0.05) for all participants. Discriminating information was distributed in multiple brain regions. Moreover, accuracy of identifying single trial data for any one participant as abstract or concrete was also reliably above chance (P < 0.05) when the classifier was trained solely on data from other participants. These results suggest abstract and concrete concepts differ in representations in terms of neural activity patterns during a short period of time across the whole brain.

Learning shapes spatiotemporal brain patterns for flexible categorical decisions

Learning is thought to facilitate our ability to perform complex perceptual tasks and optimize brain circuits involved in decision making. However, little is known about the experience-dependent mechanisms in the human brain that support our ability to make fine categorical judgments. Previous work has focused on identifying spatial brain patterns (i.e., areas) that change with learning. Here, we take advantage of the complementary high spatial and temporal resolution of simultaneous electroencephalography-functional magnetic resonance imaging (EEG-fMRI) to identify the spatiotemporal dynamics between cortical networks involved in flexible category learning. Observers were trained to use different decision criteria (i.e., category boundaries) when making fine categorical judgments on morphed stimuli (i.e., radial vs. concentric patterns). Our findings demonstrate that learning acts on a feedback-based circuit that supports fine categorical judgments. Experience-dependent changes in the behavioral decision criterion were associated with changes in later perceptual processes engaging higher occipitotemporal and frontoparietal circuits. In contrast, category learning did not modulate early processes in a medial frontotemporal network that are thought to support the coarse interpretation of visual scenes. These findings provide evidence that learning flexible criteria for fine categorical judgments acts on distinct spatiotemporal brain circuits and shapes the readout of sensory signals that provide evidence for categorical decisions.

Category structure and the two learning systems of COVIS

An influential multi-process model of category learning, COmpetition between Verbal and Implicit Systems (COVIS), suggests that a verbal or a procedural category learning process is adopted, depending on the nature of the learning problem. While the architectural assumptions of COVIS have been widely supported, there is still uncertainty regarding the types of category structures that are likely to engage each of the COVIS systems. We examined COVIS in an fMRI study with two novel (in terms of COVIS research) categorizations. One of the categorizations could be described by a simple, unidimensional, rule that was expected to favor the verbal system. The other categorization possessed characteristics typically associated with the procedural system, but could also potentially be verbalized using a rule more complex than the ones previously associated with the verbal system. We found that both categorizations engaged regions associated with the verbal system. Additionally, for both categorizations, frontal lobe regions (including left ventrolateral frontal cortex) were more engaged in the first compared to the second session, possibly reflecting the greater use of hypothesis-testing processes in the initial stages of category acquisition. In sum, our results extend our knowledge of the conditions under which the verbal system will operate. These findings indicate that much remains to be understood concerning the precise interplay of the verbal and procedural categorization systems.

Expertise modulates the neural basis of context dependent recognition of objects and their relations

Recognition of objects and their relations is necessary for orienting in real life. We examined cognitive processes related to recognition of objects, their relations, and the patterns they form by using the game of chess. Chess enables us to compare experts with novices and thus gain insight in the nature of development of recognition skills. Eye movement recordings showed that experts were generally faster than novices on a task that required enumeration of relations between chess objects because their extensive knowledge enabled them to immediately focus on the objects of interest. The advantage was less pronounced on random positions where the location of chess objects, and thus typical relations between them, was randomized. Neuroimaging data related experts' superior performance to the areas along the dorsal stream-bilateral posterior temporal areas and left inferior parietal lobe were related to recognition of object and their functions. The bilateral collateral sulci, together with bilateral retrosplenial cortex, were also more sensitive to normal than random positions among experts indicating their involvement in pattern recognition. The pattern of activations suggests experts engage the same regions as novices, but also that they employ novel additional regions. Expert processing, as the final stage of development, is qualitatively different than novice processing, which can be viewed as the starting stage. Since we are all experts in real life and dealing with meaningful stimuli in typical contexts, our results underline the importance of expert-like cognitive processing on generalization of laboratory results to everyday life.

Developmental changes in the inferior frontal cortex for selecting semantic representations

Functional magnetic resonance imaging (fMRI) was used to examine the neural correlates of semantic judgments to Chinese words in a group of 10-15 year old Chinese children. Two semantic tasks were used: visual-visual versus visual-auditory presentation. The first word was visually presented (i.e. character) and the second word was either visually or auditorily presented, and the participant had to determine if these two words were related in meaning. Different from English, Chinese has many homophones in which each spoken word corresponds to many characters. The visual-auditory task, therefore, required greater engagement of cognitive control for the participants to select a semantically appropriate answer for the second homophonic word. Weaker association pairs produced greater activation in the mid-ventral region of left inferior frontal gyrus (BA 45) for both tasks. However, this effect was stronger for the visual-auditory task than for the visual-visual task and this difference was stronger for older compared to younger children. The findings suggest greater involvement of semantic selection mechanisms in the cross-modal task requiring the access of the appropriate meaning of homophonic spoken words, especially for older children.

After the P3: late executive processes in stimulus categorization

Two experiments examined the hypothesis that dual systems of stimulus evaluation for categorization can be observed in event-related potentials: one whose duration is indexed by the latency of the P3 component, and a second evident in a later frontal potential. Subjects categorized artificial animals by a "two out of three" rule. Stimuli with two visual features of their own category and one feature of a different category (i.e., near the boundary between categories) elicited very prolonged reaction times as compared to stimuli with three features from a single category. This response time (RT) delay was not accompanied by a delayed P3, suggesting that the P3 indexed only a first pass of stimulus evaluation. The near-boundary stimuli elicited more positive potentials than far-boundary stimuli at prefrontal and frontotemporal sites, suggesting that a secondary stage of stimulus evaluation was triggered when detection of single features or simple conjunctions was insufficient to support a correct decision. The frontal potential that was sensitive to categorization difficulty was of opposite polarity to frontal potentials previously observed in manipulations of working memory. The roles of frontal executive processes in categorization and memory tasks are discussed.

Can we measure memes?

Memes are the fundamental unit of cultural evolution and have been left upon the periphery of cognitive neuroscience due to their inexact definition and the consequent presumption that they are impossible to measure. Here it is argued that although a precise definition of memes is rather difficult it does not preclude highly controlled experiments studying the neural substrates of their initiation and replication. In this paper, memes are termed as either internally or externally represented (i-memes/e-memes) in relation to whether they are represented as a neural substrate within the central nervous system or in some other form within our environment. It is argued that neuroimaging technology is now sufficiently advanced to image the connectivity profiles of i-memes and critically, to measure changes to i-memes over time, i.e., as they evolve. It is argued that it is wrong to simply pass off memes as an alternative term for "stimulus" and "learnt associations" as it does not accurately account for the way in which natural stimuli may dynamically "evolve" as clearly observed in our cultural lives.

Two systems of reasoning: architecture and relation to emotion

Distinguishing cognitive systems that support intuition and deliberation has proven necessary to explain how people reason,1, 2 decide,3 categorize,4 form attitudes,5 make confidence6 and moral7 judgments, and prioritize goals.8 Both behavioral and neuroimaging evidence show that the evidence supports similar distinctions in each field. Deliberative processing enlists working memory, and intuitive processing depends more directly on long-term memory retrieval. One of the key unanswered questions concerns how the systems interact. The data suggest that one of the key functions of deliberation is to suppress intuition. It does not invariably succeed, however, and leakage is common. Another question concerns the relations between affect and reasoning systems. The evidence suggests that emotions are not exclusively related to the intuitive system. Instead, emotional reactions that are directly tied to the perception of objects and events (e.g., fear) are associated with intuition, emotions that arise when alternative possibilities are considered (e.g., regret) are tied to deliberation, and moods (e.g., happy, sad) influence how much each system is relied on. Copyright © 2010 John Wiley & Sons, Ltd. For further resources related to this article, please visit the WIREs website.

Specialization of the rostral prefrontal cortex for distinct analogy processes

Analogical reasoning is central to learning and abstract thinking. It involves using a more familiar situation (source) to make inferences about a less familiar situation (target). According to the predominant cognitive models, analogical reasoning includes 1) generation of structured mental representations and 2) mapping based on structural similarities between them. This study used functional magnetic resonance imaging to specify the role of rostral prefrontal cortex (PFC) in these distinct processes. An experimental paradigm was designed that enabled differentiation between these processes, by temporal separation of the presentation of the source and the target. Within rostral PFC, a lateral subregion was activated by analogy task both during study of the source (before the source could be compared with a target) and when the target appeared. This may suggest that this subregion supports fundamental analogy processes such as generating structured representations of stimuli but is not specific to one particular processing stage. By contrast, a dorsomedial subregion of rostral PFC showed an interaction between task (analogy vs. control) and period (more activated when the target appeared). We propose that this region is involved in comparison or mapping processes. These results add to the growing evidence for functional differentiation between rostral PFC subregions.

Symbolic gestures and spoken language are processed by a common neural system

Symbolic gestures, such as pantomimes that signify actions (e.g., threading a needle) or emblems that facilitate social transactions (e.g., finger to lips indicating "be quiet"), play an important role in human communication. They are autonomous, can fully take the place of words, and function as complete utterances in their own right. The relationship between these gestures and spoken language remains unclear. We used functional MRI to investigate whether these two forms of communication are processed by the same system in the human brain. Responses to symbolic gestures, to their spoken glosses (expressing the gestures' meaning in English), and to visually and acoustically matched control stimuli were compared in a randomized block design. General Linear Models (GLM) contrasts identified shared and unique activations and functional connectivity analyses delineated regional interactions associated with each condition. Results support a model in which bilateral modality-specific areas in superior and inferior temporal cortices extract salient features from vocal-auditory and gestural-visual stimuli respectively. However, both classes of stimuli activate a common, left-lateralized network of inferior frontal and posterior temporal regions in which symbolic gestures and spoken words may be mapped onto common, corresponding conceptual representations. We suggest that these anterior and posterior perisylvian areas, identified since the mid-19th century as the core of the brain's language system, are not in fact committed to language processing, but may function as a modality-independent semiotic system that plays a broader role in human communication, linking meaning with symbols whether these are words, gestures, images, sounds, or objects.