Publications

Abstract

The current study investigated which time components of rapid automatized naming (RAN) predict group differences between dyslexic and non-dyslexic readers (matched for age and reading level), and how these components relate to different reading measures. Subjects performed two RAN tasks (letters and objects), and data were analyzed through a response time analysis. Our results demonstrated that impaired RAN performance in dyslexic readers mainly stem from enhanced inter-item pause times and not from difficulties at the level of post-access motor production (expressed as articulation rates). Moreover, inter-item pause times account for a significant proportion of variance in reading ability in addition to the effect of phonological awareness in the dyslexic group. This suggests that non-phonological factors may lie at the root of the association between RAN inter-item pauses and reading ability. In normal readers, RAN performance was associated with reading ability only at early ages (i.e. in the reading-matched controls), and again it was the RAN inter-item pause times that explain the association.

Abstract

In the present study, the authors investigate how some visual factors related to early stages of visual-object naming modulate naming performance in dyslexia. The performance of dyslexic children was compared with 2 control groups—normal readers matched for age and normal readers matched for reading level—while performing a discrete naming task in which color and dimensionality of the visually presented objects were manipulated. The results showed that 2-dimensional naming performance improved for color representations in control readers but not in dyslexics. In contrast to control readers, dyslexics were also insensitive to the stimulus's dimensionality. These findings are unlikely to be explained by a phonological processing problem related to phonological access or retrieval but suggest that dyslexics have a lower capacity for coding and decoding visual surface features of 2-dimensional representations or problems with the integration of visual information stored in long-term memory.

Abstract

This article summarizes some of the important findings from research evaluating the relationship between poor rapid naming and impaired reading performance. Substantial evidence shows that dyslexic readers have problems with rapid naming of visual items. Early research assumed that this was a consequence of phonological processing deficits, but recent findings suggest that non-phonological processes may lie at the root of the association between slow naming speed and poor reading. The hypothesis that rapid naming reflects an independent core deficit in dyslexia is supported by the main findings: (1) some dyslexics are characterized by rapid naming difficulties but intact phonological skills; (2) evidence for an independent association between rapid naming and reading competence in the dyslexic readers, when the effect of phonological skills was controlled; (3) rapid naming and phonological processing measures are not reliably correlated. Recent research also reveals greater predictive power of rapid naming, in particular the inter-item pause time, for high-frequency word reading compared to pseudoword reading in developmental dyslexia. Altogether, the results are more consistent with the view that a phonological component alone cannot account for the rapid naming performance in dyslexia. Rather, rapid naming problems may emerge from the inefficiencies in visual-orthographic processing as well as in phonological processing.

Abstract

In this study, we systematically review the scientific literature on the effect of color on object recognition. Thirty-five independent experiments, comprising 1535 participants, were included in a meta-analysis. We found a moderate effect of color on object recognition (d = 0.28). Specific effects of moderator variables were analyzed and we found that color diagnosticity is the factor with the greatest moderator effect on the influence of color in object recognition; studies using color diagnostic objects showed a significant color effect (d = 0.43), whereas a marginal color effect was found in studies that used non-color diagnostic objects (d = 0.18). The present study did not permit the drawing of specific conclusions about the moderator effect of the object recognition task; while the meta-analytic review showed that color information improves object recognition mainly in studies using naming tasks (d = 0.36), the literature review revealed a large body of evidence showing positive effects of color information on object recognition in studies using a large variety of visual recognition tasks. We also found that color is important for the ability to recognize artifacts and natural objects, to recognize objects presented as types (line-drawings) or as tokens (photographs), and to recognize objects that are presented without surface details, such as texture or shadow. Taken together, the results of the meta-analysis strongly support the contention that color plays a role in object recognition. This suggests that the role of color should be taken into account in models of visual object recognition.

Abstract

In the present study, the authors explore in detail the level of visual object recognition at which perceptual color information improves the recognition of color diagnostic and noncolor diagnostic objects. To address this issue, 3 object recognition tasks, with different cognitive demands, were designed: (a) an object verification task; (b) a category verification task; and (c) a name verification task. They found that perceptual color information improved color diagnostic object recognition mainly in tasks for which access to the semantic knowledge about the object was necessary to perform the task; that is, in category and name verification. In contrast, the authors found that perceptual color information facilitates noncolor diagnostic object recognition when access to the object’s structural description from long-term memory was necessary—that is, object verification. In summary, the present study shows that the role of perceptual color information in object recognition is dependent on color diagnosticity

Abstract

The first objective of this study was to compare the brain network engaged by preference classification and the standard grammaticality classification after implicit artificial syntax acquisition by re-analyzing previously reported event-related fMRI data. The results show that preference and grammaticality classification engage virtually identical brain networks, including Broca’s region, consistent with previous behavioral findings. Moreover, the results showed that the effects related to artificial syntax in Broca’s region were essentially the same when masked with variability related to natural syntax processing in the same participants. The second objective was to explore CNTNAP2-related effects in implicit artificial syntax learning by analyzing behavioral and event-related fMRI data from a subsample. The CNTNAP2 gene has been linked to specific language impairment and is controlled by the FOXP2 transcription factor. CNTNAP2 is expressed in language related brain networks in the developing human brain and the FOXP2–CNTNAP2 pathway provides a mechanistic link between clinically distinct syndromes involving disrupted language. Finally, we discuss the implication of taking natural language to be a neurobiological system in terms of bounded recursion and suggest that the left inferior frontal region is a generic on-line sequence processor that unifies information from various sources in an incremental and recursive manner.

Abstract

Neste artigo fazemos uma revisão breve de investigações actuais com técnicas comportamentais e de neuroimagem funcional sobre a aprendizagem de uma linguagem artificial em crianças e adultos. Na secção final, discutimos uma possível associação entre dislexia e aprendizagem implícita. Resultados recentes sugerem que a presença de um défice ao nível da aprendizagem implícita pode contribuir para as dificuldades de leitura e escrita observadas em indivíduos disléxicos.

Abstract

A aquisição de competências de leitura e de escrita pode ser vista como um processo formal de transmissão cultural, onde interagem factores neurobiológicos e culturais. O treino sistemático exigido pela aprendizagem da leitura e da escrita poderá produzir mudanças quantitativas e qualitativas tanto a nível cognitivo como ao nível da organização do cérebro. Estudar sujeitos iletrados e letrados representa, assim, uma oportunidade para investigar efeitos de uma aprendizagem específica no desenvolvimento cognitivo e suas bases cerebrais. Neste trabalho, revemos um conjunto de investigações comportamentais e com métodos de imagem cerebral que indicam que a literacia tem um impacto nas nossas funções cognitivas e na organização cerebral. Mais especificamente, discutiremos diferenças entre letrados e iletrados para domínios cognitivos verbais e não-verbais, sugestivas de que a arquitectura cognitiva é formatada, em parte, pela aprendizagem da leitura e da escrita. Os dados de neuroimagem funcionais e estruturais são também indicadores que a aquisição de uma ortografia alfabética interfere nos processos de organização e lateralização das funções cognitivas.

Abstract

Work on animals indicates that BOLD is preferentially sensitive to local field potentials, and that it correlates most strongly with gamma band neuronal synchronization. Here we investigate how the BOLD signal in humans performing a cognitive task is related to neuronal synchronization across different frequency bands. We simultaneously recorded EEG and BOLD while subjects engaged in a visual attention task known to induce sustained changes in neuronal synchronization across a wide range of frequencies. Trial-by-trial BOLD luctuations correlated positively with trial-by-trial fluctuations in high-EEG gamma power (60–80 Hz) and negatively with alpha and beta power. Gamma power on the one hand, and alpha and beta power on the other hand, independently contributed to explaining BOLD variance. These results indicate that the BOLD-gamma coupling observed in animals can be extrapolated to humans performing a task and that neuronal dynamics underlying high- and low-frequency synchronization contribute independently to the BOLD signal.

Abstract

In individuals with ASD, difficulties with language comprehension are most evident when higher-level semantic-pragmatic language processing is required, for instance when context has to be used to interpret the meaning of an utterance. Until now, it is unclear at what level of processing and for what type of context these difficulties in language comprehension occur. Therefore, in the current fMRI study, we investigated the neural correlates of the integration of contextual information during auditory language comprehension in 24 adults with ASD and 24 matched control participants. Different levels of context processing were manipulated by using spoken sentences that were correct or contained either a semantic or world knowledge anomaly. Our findings demonstrated significant differences between the groups in inferior frontal cortex that were only present for sentences with a world knowledge anomaly. Relative to the ASD group, the control group showed significantly increased activation in left inferior frontal gyrus (LIFG) for sentences with a world knowledge anomaly compared to correct sentences. This effect possibly indicates reduced integrative capacities of the ASD group. Furthermore, world knowledge anomalies elicited significantly stronger activation in right inferior frontal gyrus (RIFG) in the control group compared to the ASD group. This additional RIFG activation probably reflects revision of the situation model after new, conflicting information. The lack of recruitment of RIFG is possibly related to difficulties with exception handling in the ASD group.

Abstract

Language acquisition in both natural and artificial language learning settings crucially depends on extracting information from sequence input. A shared sequence learning mechanism is thus assumed to underlie both natural and artificial language learning. A growing body of empirical evidence is consistent with this hypothesis. By means of artificial language learning experiments, we may therefore gain more insight in this shared mechanism. In this paper, we review empirical evidence from artificial language learning and computational modelling studies, as well as natural language data, and suggest that there are two key factors that help determine processing complexity in sequence learning, and thus in natural language processing. We propose that the specific ordering of non-adjacent dependencies (i.e., nested or crossed), as well as the number of non-adjacent dependencies to be resolved simultaneously (i.e., two or three) are important factors in gaining more insight into the boundaries of human sequence learning; and thus, also in natural language processing. The implications for theories of linguistic competence are discussed.

Abstract

Previous studies have shown a significant association between reading skills and the performance on visuo-motor tasks. In order to clarify whether reading and writing skills modulate non-linguistic domains, we investigated the performance of two literacy groups on a visuo-motor integration task with non-linguistic stimuli. Twenty-one illiterate participants and twenty matched literate controls were included in the experiment. Subjects were instructed to use the right or the left index finger to point to and touch a randomly presented target on the right or left side of a touch screen. The results showed that the literate subjects were significantly faster in detecting and touching targets on the left compared to the right side of the screen. In contrast, the presentation side did not affect the performance of the illiterate group. These results lend support to the idea that having acquired reading and writing skills, and thus a preferred left-to-right reading direction, influences visual scanning. (JINS, 2007, 13, 359–364

Abstract

Irrelevant speech effect (ISE) is defined as a decrement in visually presented digit-list short-term memory performance due to exposure to irrelevant auditory material. Perhaps the most successful theoretical explanation of the effect is the changing state hypothesis. This hypothesis explains the effect in terms of confusion between amodal serial order cues, and represents a view based on the interference caused by the processing of similar order information of the visual and auditory materials. An alternative view suggests that the interference occurs as a consequence of the similarity between the visual and auditory contents of the stimuli. An important argument for the former view is the observation that ISE is almost exclusively observed in tasks that require memory for serial order. However, most short-term memory tasks require that both item and order information be retained in memory. An ideal task to investigate the sensitivity of maintenance of serial order to irrelevant speech would be one that calls upon order information but not item information. One task that is particularly suited to address this issue is serial recognition. In a typical serial recognition task, a list of items is presented and then probed by the same list in which the order of two adjacent items has been transposed. Due to the re-presentation of the encoding string, serial recognition requires primarily the serial order to be maintained while the content of the presented items is deemphasized. In demonstrating a highly significant ISE of changing versus steady-state auditory items in a serial recognition task, the present finding lends support for and extends previous empirical findings suggesting that irrelevant speech has the potential to interfere with the coding of the order of the items to be memorized.

Abstract

Common activations in prefrontal cortex (PFC) during episodic and semantic long-term memory (LTM) tasks have been hypothesized to reflect functional overlap in terms of working memory (WM) and cognitive control. To evaluate a WM account of LTM-general activations, the present study took into consideration that cognitive task performance depends on the dynamic operation of multiple component processes, some of which are stimulus-synchronous and transient in nature; and some that are engaged throughout a task in a sustained fashion. PFC and WM may be implicated in both of these temporally independent components. To elucidate these possibilities we employed mixed blocked/event-related functional magnetic resonance imaging (fMRI) procedures to assess the extent to which sustained or transient activation patterns overlapped across tasks indexing episodic and semantic LTM, attention (ATT), and WM. Within PFC, ventrolateral and medial areas exhibited sustained activity across all tasks, whereas more anterior regions including right frontopolar cortex were commonly engaged in sustained processing during the three memory tasks. These findings do not support a WM account of sustained frontal responses during LTM tasks, but instead suggest that the pattern that was common to all tasks reflects general attentional set/vigilance, and that the shared WM-LTM pattern mediates control processes related to upholding task set. Transient responses during the three memory tasks were assessed relative to ATT to isolate item-specific mnemonic processes and were found to be largely distinct from sustained effects. Task-specific effects were observed for each memory task. In addition, a common item response for all memory tasks involved left dorsolateral PFC (DLPFC). The latter response might be seen as reflecting WM processes during LTM retrieval. Thus, our findings suggest that a WM account of shared PFC recruitment in LTM tasks holds for common transient item-related responses rather than sustained state-related responses that are better seen as reflecting more general attentional/control processes.

Abstract

In an event-related fMRI study, we examined the cortical networks involved in establishing reference during language comprehension. We compared BOLD responses to sentences containing referentially ambiguous pronouns (e.g., “Ronald told Frank that he…”), referentially failing pronouns (e.g., “Rose told Emily that he…”) or coherent pronouns. Referential ambiguity selectively recruited medial prefrontal regions, suggesting that readers engaged in problem-solving to select a unique referent from the discourse model. Referential failure elicited activation increases in brain regions associated with morpho-syntactic processing, and, for those readers who took failing pronouns to refer to unmentioned entities, additional regions associated with elaborative inferencing were observed. The networks activated by these two referential problems did not overlap with the network activated by a standard semantic anomaly. Instead, we observed a double dissociation, in that the systems activated by semantic anomaly are deactivated by referential ambiguity, and vice versa. This inverse coupling may reflect the dynamic recruitment of semantic and episodic processing to resolve semantically or referentially problematic situations. More generally, our findings suggest that neurocognitive accounts of language comprehension need to address not just how we parse a sentence and combine individual word meanings, but also how we determine who's who and what's what during language comprehension.

Abstract

The current understanding of hemispheric interaction is limited. Functional hemispheric specialization is likely to depend on both genetic and environmental factors. In the present study we investigated the importance of one factor, literacy, for the functional lateralization in the inferior parietal cortex in two independent samples of literate and illiterate subjects. The results show that the illiterate group are consistently more right-lateralized than their literate controls. In contrast, the two groups showed a similar degree of left-right differences in early speech-related regions of the superior temporal cortex. These results provide evidence suggesting that a cultural factor, literacy, influences the functional hemispheric balance in reading and verbal working memory-related regions. In a third sample, we investigated grey and white matter with voxel-based morphometry. The results showed differences between literacy groups in white matter intensities related to the mid-body region of the corpus callosum and the inferior parietal and parietotemporal regions (literate > illiterate). There were no corresponding differences in the grey matter. This suggests that the influence of literacy on brain structure related to reading and verbal working memory is affecting large-scale brain connectivity more than grey matter per se.

Abstract

Using event-related functional magnetic resonance imaging, we identified brain regions involved in storing associations of events discontinuous in time into long-term memory. Participants were scanned while memorizing item-triplets including simultaneous and discontinuous associations. Subsequent memory tests showed that participants remembered both types of associations equally well. First, by constructing the contrast between the subsequent memory effects for discontinuous associations and simultaneous associations, we identified the left posterior parahippocampal region, dorsolateral prefrontal cortex, the basal ganglia, posterior midline structures, and the middle temporal gyrus as being specifically involved in transforming discontinuous associations into episodic memory. Second, we replicated that the prefrontal cortex and the medial temporal lobe (MTL) especially the hippocampus are involved in associative memory formation in general. Our findings provide evidence for distinct neural operation(s) that supports the binding and storing discontinuous associations in memory. We suggest that top-down signals from the prefrontal cortex and MTL may trigger reactivation of internal representation in posterior midline structures of the first event, thus allowing it to be associated with the second event. The dorsolateral prefrontal cortex together with basal ganglia may support this encoding operation by executive and binding processes within working memory, and the posterior parahippocampal region may play a role in binding and memory formation.

Abstract

Previous research suggests that learning an alphabetic written language influences aspects of the auditory-verbal language system. In this study, we examined whether literacy influences the notion of words as phonological units independent of lexical semantics in literate and illiterate subjects. Subjects had to decide which item in a word- or pseudoword pair was phonologically longest. By manipulating the relationship between referent size and phonological length in three word conditions (congruent, neutral, and incongruent) we could examine to what extent subjects focused on form rather than meaning of the stimulus material. Moreover, the pseudoword condition allowed us to examine global phonological awareness independent of lexical semantics. The results showed that literate performed significantly better than illiterate subjects in the neutral and incongruent word conditions as well as in the pseudoword condition. The illiterate group performed least well in the incongruent condition and significantly better in the pseudoword condition compared to the neutral and incongruent word conditions and suggest that performance on phonological word length comparisons is dependent on literacy. In addition, the results show that the illiterate participants are able to perceive and process phonological length, albeit less well than the literate subjects, when no semantic interference is present. In conclusion, the present results confirm and extend the finding that illiterate subjects are biased towards semantic-conceptual-pragmatic types of cognitive processing.

Abstract

Spaced learning with time to consolidate leads to more stabile memory traces. However, little is known about the neural correlates of trace stabilization, especially in humans. The present fMRI study contrasted retrieval activity of two well-learned sets of face-location associations, one learned in a massed style and tested on the day of learning (i.e., labile condition) and another learned in a spaced scheme over the course of one week (i.e., stabilized condition). Both sets of associations were retrieved equally well, but the retrieval of stabilized association was faster and accompanied by large-scale changes in the network supporting retrieval. Cued recall of stabilized as compared with labile associations was accompanied by increased activity in the precuneus, the ventromedial prefrontal cortex, the bilateral temporal pole, and left temporo–parietal junction. Conversely, memory representational areas such as the fusiform gyrus for faces and the posterior parietal cortex for locations did not change their activity with stabilization. The changes in activation in the precuneus, which also showed increased connectivity with the fusiform area, are likely to be related to the spatial nature of our task. The activation increase in the ventromedial prefrontal cortex, on the other hand, might reflect a general function in stabilized memory retrieval. This area might succeed the hippocampus in linking distributed neocortical representations.

Abstract

The medial temporal lobe (MTL) is crucial for declarative memory formation, but the function of its subcomponents in associative memory formation remains controversial. Most functional imaging studies on this topic are based on a stepwise approach comparing a condition with and one without associative encoding. Extending this approach we applied additionally a parametric analysis by varying the amount of associative memory formation. We found a hippocampal subsequent memory effect of almost similar magnitude regardless of the amount of associations formed. By contrast, subsequent memory effects in rhinal and parahippocampal cortices were parametrically and positively modulated by the amount of associations formed. Our results indicate that the parahippocampal region supports associative memory formation as tested here and the hippocampus adds a general mnemonic operation. This pattern of results might suggest a new interpretation. Instead of having either a fixed division of labor between the hippocampus (associative memory formation) and the rhinal cortex (non-associative memory formation) or a functionally unitary MTL system, in which all substructures are contributing to memory formation in a similar way, we propose that the location where associations are formed within the MTL depends on the kind of associations bound: If visual single-dimension associations, as used here, can already be integrated within the parahippocampal region, the hippocampus might add a general purpose mnemonic operation only. In contrast, if associations have to be formed across widely distributed neocortical representations, the hippocampus may provide a binding operation in order to establish a coherent memory.

Abstract

Progesterone, or rather its neuroactive metabolite allopregnanolone, modulates amygdala activity and thereby influences anxiety. Cognition and, in particular, memory are also altered by allopregnanolone. In the present study, we investigated whether allopregnanolone modulates memory for biologically salient stimuli by influencing amygdala activity, which in turn may affect neural processes in other brain regions. A single progesterone dose was administered orally to healthy young women in a double-blind, placebo-controlled, crossover design, and participants were asked to memorize and recognize faces while undergoing functional magnetic resonance imaging. Progesterone decreased recognition accuracy without affecting reaction times. The imaging results show that the amygdala, hippocampus, and fusiform gyrus supported memory formation. Importantly, progesterone decreased responses to faces in the amygdala and fusiform gyrus duringmemoryencoding, whereas it increased hippocampal responses. The progesterone-induced decrease in neural activity in the amygdala and fusiform gyrus predicted the decrease in memory performance across subjects. However, progesterone did not modulate the differential activation between subsequently remembered and subsequently forgotten faces in these areas. A similar pattern of results was observed in the fusiform gyrus and prefrontal cortex during memory retrieval. These results suggest that allopregnanolone impairs memory by reducing the recruitment of those brain regions that support memory formation and retrieval. Given the important role of the amygdala in the modulation of memory, these results suggest that allopregnanolone alters memory by influencing amygdala activity, which in turn may affect memory processes in other brain regions

Abstract

Knowing what is going to happen next, that is, the capacity to predict upcoming events, modulates the extent to which aversive stimuli induce stress and anxiety. We explored this issue by manipulating the temporal predictability of aversive events by means of a visual cue, which was either correlated or uncorrelated with pain stimuli (electric shocks). Subjects reported lower levels of anxiety, negative valence and pain intensity when shocks were predictable. In addition to attenuate focus on danger, predictability allows for correct temporal estimation of, and selective attention to, the sensory input. With functional magnetic resonance imaging, we found that predictability was related to enhanced activity in relevant sensory-discriminative processing areas, such as the primary and secondary sensory cortex and posterior insula. In contrast, the unpredictable more aversive context was correlated to brain activity in the anterior insula and the orbitofrontal cortex, areas associated with affective pain processing. This context also prompted increased activity in the posterior parietal cortex and lateral prefrontal cortex that we attribute to enhanced alertness and sustained attention during unpredictability.

Abstract

The human brain supports acquisition mechanisms that extract structural regularities implicitly from experience without the induction of an explicit model. It has been argued that the capacity to generalize to new input is based on the acquisition of abstract representations, which reflect underlying structural regularities in the input ensemble. In this study, we explored the outcome of this acquisition mechanism, and to this end, we investigated the neural correlates of artificial syntactic classification using event-related functional magnetic resonance imaging. The participants engaged once a day during an 8-day period in a short-term memory acquisition task in which consonant-strings generated from an artificial grammar were presented in a sequential fashion without performance feedback. They performed reliably above chance on the grammaticality classification tasks on days 1 and 8 which correlated with a corticostriatal processing network, including frontal, cingulate, inferior parietal, and middle occipital/occipitotemporal regions as well as the caudate nucleus. Part of the left inferior frontal region (BA 45) was specifically related to syntactic violations and showed no sensitivity to local substring familiarity. In addition, the head of the caudate nucleus correlated positively with syntactic correctness on day 8 but not day 1, suggesting that this region contributes to an increase in cognitive processing fluency.

Abstract

There is evidence for cognitive as well as neural plasticity across the adult life span, although aging is associated with certain constraints on plasticity. In the current paper, we argue that the age-related reduction in cognitive plasticity may be due to (a) deficits in general processing resources, and (b) failure to engage in task-relevant cognitive operations. Memory-training research suggests that age-related processing deficits (e.g., executive functions, speed) hinder older adults from utilizing mnemonic techniques as efficiently as the young, and that this age difference is reflected by diminished frontal activity during mnemonic use. Additional constraints on memory plasticity in old age are related to difficulties that are specific to the task, such as creating visual images, as well as in binding together the information to be remembered. These deficiencies are paralleled by reduced activity in occipito-parietal and medial–temporal regions, respectively. Future attempts to optimize intervention-related gains in old age should consider targeting both general processing and task-specific origins of age-associated reductions in cognitive plasticity.

Abstract

The apolipoprotein E {varepsilon}4 (APOE {varepsilon}4) is the main known genetic risk factor for Alzheimer's disease. Genetic assessments in combination with other diagnostic tools, such as neuroimaging, have the potential to facilitate early diagnosis. In this large-scale functional MRI (fMRI) study, we have contrasted 30 APOE {varepsilon}4 carriers (age range: 49–74 years; 19 females), of which 10 were homozygous for the {varepsilon}4 allele, and 30 non-carriers with regard to brain activity during a semantic categorization task. Test groups were closely matched for sex, age and education. Critically, both groups were cognitively intact and thus symptom-free of Alzheimer's disease. APOE {varepsilon}4 carriers showed reduced task-related responses in the left inferior parietal cortex, and bilaterally in the anterior cingulate region. A dose-related response was observed in the parietal area such that diminution was most pronounced in homozygous compared with heterozygous carriers. In addition, contrasts of processing novel versus familiar items revealed an abnormal response in the right hippocampus in the APOE {varepsilon}4 group, mainly expressed as diminished sensitivity to the relative novelty of stimuli. Collectively, these findings indicate that genetic risk translates into reduced functional brain activity, in regions pertinent to Alzheimer's disease, well before alterations can be detected at the behavioural level.

Abstract

Literacy and education represent essential aspects of contemporary society and subserve important aspects of socialization and cultural transmission. The study of illiterate subjects represents one approach to investigate the interactions between neurobiological and cultural factors in cognitive development, individual learning, and their influence on the functional organization of the brain. In this chapter we review some recent cognitive, neuroanatomic, and functional neuroimaging results indicating that formal education influences important aspects of the human brain. Taken together this provides strong support for the idea that the brain is modulated by literacy and formal education, which in turn change the brains capacity to interact with its environment, including the individual's contemporary culture. In other words, the individual is able to participate in, interact with, and actively contribute to the process of cultural transmission in new ways through acquired cognitive skills.

Abstract

The irrelevant speech effect illustrates that sounds that are irrelevant to a visually presented short-term memory task still interfere with neuronal function. In the present study we explore the functional and effective connectivity of such interference. The functional connectivity analysis suggested an interaction between the level of irrelevant speech and the correlation between in particular the left superior temporal region, associated with verbal working memory, and the left medial temporal lobe. Based on this psycho-physiological interaction, and to broaden the understanding of this result, we performed a network analysis, using a simple network model for verbal working memory, to analyze its interaction with the medial temporal lobe memory system. The results showed dissociations in terms of network interactions between frontal as well as parietal and temporal areas in relation to the medial temporal lobe. The results of the present study suggest that a transition from phonological loop processing towards an engagement of episodic processing might take place during the processing of interfering irrelevant sounds. We speculate that, in response to the irrelevant sounds, this reflects a dynamic shift in processing as suggested by a closer interaction between a verbal working memory system and the medial temporal lobe memory system.

Abstract

Doubts have been cast on the strict dissociation between short- and long-term memory systems. Specifically, several neuroimaging studies have shown that the medial temporal lobe, a region almost invariably associated with long-term memory, is involved in active short-term memory maintenance. Furthermore, a recent study in hippocampally lesioned patients has shown that the hippocampus is critically involved in associating objects and their locations, even when the delay period lasts only 8 s. However, the critical feature that causes the medial temporal lobe, and in particular the hippocampus, to participate in active maintenance is still unknown. This study was designed in order to explore hippocampal involvement in active maintenance of spatial and non-spatial associations. Eighteen participants performed a delayed-match-to-sample task in which they had to maintain either object–location associations, color–number association, single colors, or single locations. Whole-brain activity was measured using event-related functional magnetic resonance imaging and analyzed using a random effects model. Right lateralized hippocampal activity was evident when participants had to maintain object–location associations, but not when they had to maintain object–color associations or single items. The present results suggest a hippocampal involvement in active maintenance when feature combinations that include spatial information have to be maintained online.

Abstract

Previous work has shown that illiterate subjects are better at naming two-dimensional representations of real objects when presented as colored photos as compared to black and white drawings. This raises the question if color or textural details selectively improve object recognition and naming in illiterate compared to literate subjects. In this study, we investigated whether the surface texture and/or color of objects is used to access stored object knowledge in illiterate subjects. A group of illiterate subjects and a matched literate control group were compared on an immediate object naming task with four conditions: color and black and white (i.e., grey-scaled) photos, as well as color and black and white (i.e., grey-scaled) drawings of common everyday objects. The results show that illiterate subjects perform significantly better when the stimuli are colored and this effect is independent of the photographic detail. In addition, there were significant differences between the literacy groups in the black and white condition for both drawings and photos. These results suggest that color object information contributes to object recognition. This effect was particularly prominent in the illiterate group

Abstract

Retrieval of recently acquired declarative memories depends on
the hippocampus, but with time, retrieval is increasingly sustainable
by neocortical representations alone. This process has been
conceptualized as system-level consolidation. Using functional
magnetic resonance imaging, we assessed over the course of three
months how consolidation affects the neural correlates of memory
retrieval. The duration of slow-wave sleep during a nap/rest
period after the initial study session and before the first scan
session on day 1 correlated positively with recognition memory
performance for items studied before the nap and negatively with
hippocampal activity associated with correct confident recognition.
Over the course of the entire study, hippocampal activity for
correct confident recognition continued to decrease, whereas activity
in a ventral medial prefrontal region increased. These findings,
together with data obtained in rodents, may prompt a
revision of classical consolidation theory, incorporating a transfer
of putative linking nodes from hippocampal to prelimbic prefrontal
areas.