Ana Raposo

Functional Significance of Striatal Responses during Episodic Decisions: Recovery or Goal Attainment?

Memory retrieval is typically a goal-directed behavior, and as such, potentially influenced by reinforcement and motivation processes. Although striatal activation is often evident during memory retrieval, its functional significance remains unclear because typical memory paradigms do not control the motivational significance of memory decisions. We used event-related functional magnetic resonance imaging (fMRI) to investigate striatal activation during recognition with and without performance-linked monetary incentives. During initial performance in the absence of incentives, dorsal striatal activation for “Old” memory conclusions nonetheless exceeded that for “New” conclusions regardless of the accuracy of these conclusions. In contrast, subsequent scans paired incentives with either “Old” or “New” conclusions and demonstrated greater activation for whichever judgment was potentially rewarded, both with and without performance feedback. The data demonstrate that striatal activation during recognition judgments does not signal monetary reward receipt, cognitive feedback, or successful episodic retrieval. Instead, it is heavily dependent upon satisfaction of the subjective goals of the observer.

Contributions of frontopolar cortex to judgments about self, others and relations

Activation in frontopolar cortex (FPC; BA 10) has been associated both with attending to mental states and with integrating multiple mental relations. However, few previous studies have manipulated both of these cognitive processes, precluding a clear functional distinction among regions within FPC. To address this issue, we developed an fMRI task that combined mentalizing and relational integration processes. Participants saw blocks of single words and performed one of three judgments: how pleasant or unpleasant they found each word (Self condition), how a specific friend would evaluate the pleasantness of the word (Other condition), or the difference between their own pleasantness judgment and that of their friend (Relational condition). We found that medial FPC was modulated by Other relative to Self judgments, consistent with a role in mentalizing. Lateral FPC was significantly activated during Relational compared to Self judgements, suggesting that this region is particularly involved in relational integration. The results point to a strong functional dissociation between medial and lateral FPC. In addition, the data demonstrate a role for lateral FPC in the social domain, provided that the task requires the integration of ones preferences with those of others.

The hierarchical organization of semantic memory: Executive function in the processing of superordinate concepts

Research on the processing of objects at different hierarchical levels has suggested that understanding superordinate concepts (e.g. fruit), relative to basic level concepts (e.g. apple), requires greater semantic control demands. Yet, it is unclear which factors underlie this difference in executive processing. We built on previous research showing that superordinate concepts have less shared features among their members and therefore may involve higher semantic control requirements. To test this hypothesis, we developed an fMRI study in which we orthogonally manipulated feature sharedness (more shared vs. less shared) and concept level (superordinate vs. basic) in a sentence verification task. Sentences involving less shared features, relative to more shared features, significantly engaged the L lateral PFC. Importantly, sentences that included superordinate concepts, relative to those with basic level concepts, also revealed a stronger response in L lateral PFC, along with posterior temporal gyrus activation. There was also a significant interaction between feature sharedness and concept level in several PFC regions and L posterior temporal areas. The results suggest that relative to basic level concepts, processing superordinate concepts requires extra semantic control in L lateral PFC to coordinate information that is less shared by other members of the category level. These findings demonstrate that feature sharedness impacts the neural basis of semantic knowledge, and is a critical dimension in the processing of superordinate concepts.

Ventrolateral prefrontal cortex and self-initiated semantic elaboration during memory retrieval.

Left ventrolateral prefrontal cortex (LVPFC) is often implicated in neuroimaging studies of context memory retrieval. This activation has been argued to reflect proactive semantic processing that facilitates recollection of past events, or instead to reflect a reactive response to experienced episodic interference. We investigated these characterizations in an fMRI study that manipulated the relative distinctiveness of encoding across subsequent targets and lures by varying encoding task manipulations. Critically, during later testing, retrieval queries and prior target processing where held constant across the distinctive and non-distinctive testing conditions, and therefore any differences in cortical activity would be linked to subject-initiated retrieval strategies. We found that LVPFC activity was specific to context retrieval under distinctive conditions even though this condition demonstrated the least interference. The results suggest that this region is critical for self-initiated semantic elaboration during retrieval, and this conclusion was bolstered by finding that LVPFC activity predicted individual differences in context memory discrimination. In line with Tulvings Encoding Specificity Principle, we suggest that subjects actively construct semantic retrieval cues, reflected in increased VLPFC activation, in an attempt to isolate the distinctive semantic features of hypothetical experiences when possible. If successful, this improves the match between retrieval cue and engram and facilitates performance.

Structural dimensions of object pictures: Organization and relation to object decision and naming

The present paper evaluated the nature of the organization of 22 structural measures of object pictures from the Snodgrass and Vanderwart (1980) picture set (Study 1), and their contribution to object decision and to object naming latencies (Studies 2 and 3). Study 1 employed a principal components analysis and provided evidence of four underlying components: “Object parts”, “internal details”, “object contours”, and “variability of the representation”. Study 2 examined the contribution of these components to object decision and object naming and highlighted variability of the representation and internal details as the most relevant indexes of structural similarity. Study 3 investigated the interactions between these structural components and lexical frequency. Main results showed an interaction effect between variability of the representation and lexical frequency and other effects associated to internal details. Implications for the concept of structural similarity and for object recognition are discussed from a continuous and cascade processing perspective.

Sensitivity and salience of form-function correlations of objects: evidence from feature tasks.

The present research evaluates the sensitivity and salience of form–function correlations in contrast with other types of feature correlations (function–function, form–form) in adults and using real object features (from tools and utensils). In Experiment 1, the participants judged the relation between the form and function features of tools. In Experiment 2, participants were asked to generate a second feature related to a given form or function feature. In Experiment 3, participants were asked to make a lexical decision in which form and function features were used as primes and targets. The results showed that even though participants were sensitive to form–function correlations, these were not particularly salient when compared with other feature-type correlations, notably function–function correlations. Our data underline the overall importance of function information to object representations and the impact of the statistical co-occurrence of features when processing object features.

Cognitive functioning in chronic post-stroke aphasia

ABSTRACT There is a minimal amount of knowledge regarding the cognitive abilities of people with aphasia. We evaluated the performance of individuals with chronic aphasia (AP) and control participants without aphasia (CP) with left hemisphere stroke in a battery of nonverbal cognitive tests and its relationship with aphasia severity, comprehension abilities, and speech fluency in a prospective cross-sectional study. Cognitive evaluation comprised 10 nonverbal tests. Scores were converted to age and education adjusted standard scores. Forty-eight AP and 32 CP were included. AP average scores were below normal range in three tests: Camel and Cactus Test, immediate recall of 5 Objects Test and Spatial Span. The mean test scores were significantly lower in AP than in CP, except in four tests. Aphasia severity and verbal comprehension ability correlated significantly with semantic memory, constructive abilities and attention/processing speed tests. Subjects with nonfluent aphasia had lower scores than CP in memory, executive functions and attention tests, while subjects with fluent aphasia showed lower scores in memory tests only. On average half of the individuals with aphasia exhibit results within the normal range. Nonetheless, their performance was worse than that of controls, despite the fact that many tests do not correlate with the severity of language disorder.

Concept typicality responses in the semantic memory network.

For decades concept typicality has been recognized as critical to structuring conceptual knowledge, but only recently has typicality been applied in better understanding the processes engaged by the neurological network underlying semantic memory. This previous work has focused on one region within the network - the Anterior Temporal Lobe (ATL). The ATL responds negatively to concept typicality (i.e., the more atypical the item, the greater the activation in the ATL). To better understand the role of typicality in the entire network, we ran an fMRI study using a category verification task in which concept typicality was manipulated parametrically. We argue that typicality is relevant to both amodal feature integration centers as well as category-specific regions. Both the Inferior Frontal Gyrus (IFG) and ATL demonstrated a negative correlation with typicality, whereas inferior parietal regions showed positive effects. We interpret this in light of functional theories of these regions. Interactions between category and typicality were not observed in regions classically recognized as category-specific, thus, providing an argument against category specific regions, at least with fMRI.

Cognitive performance and aphasia recovery

Abstract Objectives This study assessed cognitive performance of subjects with aphasia during the acute stage of stroke and evaluated how such performance relates to recovery at 3 months. Materials & methods Patients with aphasia following a left hemisphere stroke were evaluated during the first (baseline) and the fourth-month post onset. Assessment comprised non-verbal tests of attention/processing speed (Symbol Search, Cancelation Task), executive functioning (Matrix Reasoning, Tower of Hanoi, Clock Drawing, Motor Initiative), semantic (Camel and Cactus Test), episodic and immediate memory (Memory for Faces Test, 5 Objects Memory Test, and Spatial Span. Recovery was measured by the Token Test score at 3 months. The impact of baseline performance on recovery was evaluated by logistic regression adjusting for age, education, severity of aphasia and the Alberta Stroke Program Early CT (ASPECT) score. Results Thirty-nine subjects (with a mean of 66.5 ± 10.6 years of age, 17 men) were included. Average baseline cognitive performance was within normal range in all tests except in memory tests (semantic, episodic and immediate memory) for which scores were ≤−1.5sd. Subjects with poor aphasia recovery (N = 27) were older and had fewer years of formal education but had identical ASPECT score compared to those with favorable recovery. Considering each test individually, the score obtained on the Matrix Reasoning test was the only one to predict aphasia recovery (Exp(B)=24.085 p = 0.038). Conclusions The Matrix Reasoning Test may contribute to predict aphasia recovery. Cognitive performance is a measure of network disruption but may also indicate the availability of recovery strategies.

The neural bases of price estimation: Effects of size and precision of the estimate

HIGHLIGHTSfMRI study of market price estimation.Webers law predicted performance.Medial PFC showed positive correlation with price estimation.IPS showed negative correlation with Weber fraction.Distinguishable neural effects for size and precision of price estimates. ABSTRACT People are often confronted with the need of estimating the market price of goods. An important question is how people estimate prices, given the variability of products and prices available. Using event‐related fMRI, we investigated how numerical processing modulates the neural bases of retail price estimation by focusing on two numerical dimensions: the size and precision of the estimates. Participants were presented with several product labels and made market price estimates for those products. Measures of product buying frequency and market price variability were also collected. The estimation of higher prices required longer response times, was associated with greater variation in responses across participants, and correlated with increasing medial and lateral prefrontal cortex (PFC) activity. Moreover, price estimates followed Webers law, a hallmark feature of numerical processing. Increasing accuracy in price estimation, indexed by decreasing Weber fraction, engaged the intraparietal sulcus (IPS), a critical region in numerical processing. Our findings provide evidence for distinguishable neural mechanisms associated with the size and the precision of price estimates.