Crossmodal integration of auditory and visual information, such as phonemes and graphemes, is a critical skill for fluent reading. Previous work has demonstrated that white matter connectivity along the arcuate fasciculus (AF) is predicted by reading skill and that crossmodal processing particularly activates the posterior STS (pSTS). However, the relationship between this crossmodal activation and white matter integrity has not been previously reported. We investigated the interrelationship of crossmodal integration, both in terms of behavioral performance and pSTS activity, with AF tract coherence using a rhyme judgment task in a group of 47 children with a range of reading abilities. We demonstrate that both response accuracy and pSTS activity for crossmodal (auditory–visual) rhyme judgments was predictive of fractional anisotropy along the left AF. Unimodal (auditory-only or visual-only) pSTS activity was not significantly related to AF connectivity. Furthermore, activity in other reading-related ROIs did not show the same AV-only AF coherence relationship, and AV pSTS activity was not related to connectivity along other language-related tracts. This study is the first to directly show that crossmodal brain activity is specifically related to connectivity in the AF, supporting its role in phoneme–grapheme integration ability. More generally, this study helps to define an interdependent neural network for reading-related integration.
To sustain successful behavior in dynamic environments, active organisms must be able to learn from the consequences of their actions and predict action outcomes. One of the most important discoveries in systems neuroscience over the last 15 years has been about the key role of the neurotransmitter dopamine in mediating such active behavior. Dopamine cell firing was found to encode differences between the expected and obtained outcomes of actions. Although activity of dopamine cells does not specify movements themselves, a recent study in humans has suggested that tonic levels of dopamine in the dorsal striatum may in part enable normal movement by encoding sensitivity to the energy cost of a movement, providing an implicit “motor motivational” signal for movement. We investigated the motivational hypothesis of dopamine by studying motor performance of patients with Parkinson disease who have marked dopamine depletion in the dorsal striatum and compared their performance with that of elderly healthy adults. All participants performed rapid sequential movements to visual targets associated with different risk and different energy costs, countered or assisted by gravity. In conditions of low energy cost, patients performed surprisingly well, similar to prescriptions of an ideal planner and healthy participants. As energy costs increased, however, performance of patients with Parkinson disease dropped markedly below the prescriptions for action by an ideal planner and below performance of healthy elderly participants. The results indicate that the ability for efficient planning depends on the energy cost of action and that the effect of energy cost on action is mediated by dopamine.
A key task for the brain is to determine which pieces of information are worth storing in memory. To build a more complete representation of the environment, memory systems may prioritize new information that has not already been stored. Here, we propose a mechanism that supports this preferential encoding of new information, whereby prior experience attenuates neural activity for old information that is competing for processing. We evaluated this hypothesis with fMRI by presenting a series of novel stimuli concurrently with repeated stimuli at different spatial locations in Experiment 1 and from different visual categories (i.e., faces and scenes) in Experiment 2. Subsequent memory for the novel stimuli could be predicted from the reduction in activity in ventral temporal cortex for the accompanying repeated stimuli. This relationship was eliminated in control conditions where the competition during encoding came from another novel stimulus. These findings reveal how prior experience adaptively guides learning toward new aspects of the environment.
Refreshing is the component cognitive process of directing reflective attention to one of several active mental representations. Previous studies using functional magnetic resonance imaging (fMRI) suggested that refresh tasks involve a component process of initiating refreshing as well as the top-down modulation of representational regions central to refreshing. However, those studies were limited by fMRI’s low temporal resolution. In the present study, we used electroencephalography (EEG) to examine the timecourse of refreshing on the scale of milliseconds rather than seconds. Event-related potential (ERP) analyses showed that a typical refresh task does have a distinct electrophysiological response as compared to a control condition, and includes at least two main temporal components: an earlier (~400ms) positive peak reminiscent of a P3 response, and a later (~800ms–1400ms) sustained positivity over several sites reminiscent of the late directing attention positivity (LDAP). Overall, the evoked potentials for refreshing representations from three different visual categories (faces, scenes, words) were similar, but multivariate pattern analysis (MVPA) showed that some category information was nonetheless present in the EEG signal. When related to previous fMRI studies, these results are consistent with a two-phase model, with the first phase dominated by frontal control signals involved in initiating refreshing and the second by the top-down modulation of posterior perceptual cortical areas that constitutes refreshing a representation. This study also lays the foundation for future studies of the neural correlates of reflective attention at a finer temporal resolution than is possible using fMRI.
The establishment of reference is essential to language comprehension. The goal of this study was to examine listeners’ sensitivity to referential ambiguity as a function of individual variation in attention, working memory capacity, and verbal ability. Participants listened to stories in which two entities were introduced that were either very similar (e.g., two oaks) or less similar (e.g., one oak and one elm). The manipulation rendered an anaphor in a subsequent sentence (e.g., oak) ambiguous or unambiguous. EEG was recorded as listeners comprehended the story, after which participants completed tasks to assess working memory, verbal ability, and the ability to use context in task performance. Power in the alpha and theta frequency bands when listeners received critical information about the discourse entities (e.g., oaks) was used to index attention and the involvement of the working memory system in processing the entities. These measures were then used to predict an ERP component that is sensitive to referential ambiguity, the Nref, which was recorded when listeners received the anaphor. Nref amplitude at the anaphor was predicted by alpha power during the earlier critical sentence: Individuals with increased alpha power in ambiguous compared with unambiguous stories were less sensitive to the anaphor's ambiguity. Verbal ability was also predictive of greater sensitivity to referential ambiguity. Finally, increased theta power in the ambiguous compared with unambiguous condition was associated with higher working-memory span. These results highlight the role of attention and working memory in referential processing during listening comprehension.
We used fMRI to investigate the roles played by perilesional and contralesional cortical regions during language production in stroke patients with chronic aphasia. We applied comprehensive psycholinguistic analyses based on well-established models of lexical access to overt picture-naming responses, which were evaluated using a single trial design that permitted distinction between correct and incorrect responses on a trial-by-trial basis. Although both correct and incorrect naming responses were associated with left-sided perilesional activation, incorrect responses were selectively associated with robust right-sided contralesional activity. Most notably, incorrect responses elicited overactivation in the right inferior frontal gyrus that was not observed in the contrasts for patients’ correct responses or for responses of age-matched control subjects. Errors were produced at slightly later onsets than accurate responses and comprised predominantly semantic paraphasias and omissions. Both types of errors were induced by pictures with greater numbers of alternative names, and omissions were also induced by pictures with late acquired names. These two factors, number of alternative names per picture and age of acquisition, were positively correlated with activation in left and right inferior frontal gyri in patients as well as control subjects. These results support the hypothesis that some right frontal activation may normally be associated with increasing naming difficulty, but in patients with aphasia, right frontal overactivation may reflect ineffective effort when left hemisphere perilesional resources are insufficient. They also suggest that contralesional areas continue to play a role—dysfunctional rather than compensatory—in chronic aphasic patients who have experienced a significant degree of recovery.
Prior lesion and functional imaging studies have highlighted the importance of the left ventral occipital-temporal (LvOT) cortex for visual word recognition. Within this area, there is a posterior-anterior hierarchy of sub-regions that are specialised for different stages of orthographic processing. The aim of the present fMRI study was to dissociate the effects of subword orthographic typicality (e.g., cider [high] versus cynic [low]) from the effect of lexicality (e.g., pollen [word] versus pillen [pseudoword]). We therefore orthogonally manipulated the orthographic typicality of written words and pseudowords (nonwords and pseudohomophones) in a visual lexical decision task. Consistent with previous studies, we identified greater activation for pseudowords than words (i.e., an effect of lexicality) in posterior LvOT cortex. In addition, we revealed higher activation for atypical than typical strings, irrespective of lexicality, in a left inferior occipital region that is posterior to LvOT cortex. When lexical decisions were made more difficult in the context of pseudohomophone foils, left anterior temporal activation also increased for atypical relative to typical strings. The latter finding agrees with the behaviour of patients with progressive anterior temporal lobe degeneration, who have particular difficulty recognising words with atypical orthography. The most novel outcome of this study is that, within a distributed network of regions supporting orthographic processing, we have identified a left inferior occipital region that is particularly sensitive to the typicality of subword orthographic patterns.
Orthographic Typicality; Lexicality; Left Ventral Occipital-Temporal Cortex; Left Inferior Occipital Cortex; Left Anterior Temporal Cortex
Dual tasking (e.g., walking or standing while performing a cognitive task) disrupts performance in one or both tasks, and such dual-task costs increase with aging into senescence. Dual tasking activates a network of brain regions including pFC. We therefore hypothesized that facilitation of prefrontal cortical activity via transcranial direct current stimulation (tDCS) would reduce dual-task costs in older adults. Thirty-seven healthy older adults completed two visits during which dual tasking was assessed before and after 20 min of real or sham tDCS targeting the left pFC. Trials of single-task standing, walking, and verbalized serial subtractions were completed, along with dual-task trials of standing or walking while performing serial subtractions. Dual-task costs were calculated as the percent change in markers of gait and postural control and serial subtraction performance, from single to dual tasking. Significant dual-task costs to standing, walking, and serial subtraction performance were observed before tDCS (p < .01). These dual-task costs were less after real tDCS as compared with sham tDCS as well as compared with either pre-tDCS condition (p < .03). Further analyses indicated that tDCS did not alter single task performance but instead improved performance solely within dual-task conditions (p < .02). These results demonstrate that dual tasking can be improved by modulating prefrontal activity, thus indicating that dual-task decrements are modifiable and may not necessarily reflect an obligatory consequence of aging. Moreover, tDCS may ultimately serve as a novel approach to preserving dual-task capacity into senescence.
A central feature of voluntary movement is the sense of volition, but when this sense arises in the course of movement formulation and execution is not clear. Many studies have explored how the brain might be actively preparing movement prior to the sense of volition, however, because the timing of the sense of volition has depended on subjective and retrospective judgements these findings are still regarded with a degree of scepticism. Electroencephalographic (EEG) events such as beta event-related desynchronization (βERD) and movement-related cortical potentials (MRCPs) are associated with the brain’s programming of movement. Using an optimized EEG signal derived from multiple variables we were able to make real-time predictions of movements in advance of their occurrence with a low false positive rate. We asked subjects what they were thinking at the time of prediction: sometimes they were thinking about movement, and other times they were not. Our results indicate that the brain can be preparing to make voluntary movements while subjects are thinking about something else.
Volition; Free will; Electroencephalography; Event-related Desynchronization; Brain Computer Interface; Electrophysiology
One of the multiple interacting systems involved in the selection and execution of voluntary actions is the primary motor cortex (PMC). We aimed to investigate whether the transcranial direct current stimulation (tDCS) of this area can modulate hand choice. A perceptual decision-making task was administered. Participants were asked to classify rectangles with different height-to-width ratios into horizontal and vertical rectangles using their right and left index fingers while their PMC was stimulated either bilaterally or unilaterally. Two experiments were conducted with different stimulation conditions: the first experiment (n = 12) had only one stimulation condition (bilateral stimulation), and the second experiment (n = 45) had three stimulation conditions (bilateral, anodal unilateral, and cathodal unilateral stimulations). The second experiment was designed to confirm the results of the first experiment and to further investigate the effects of anodal and cathodal stimulations alone in the observed effects. Each participant took part in two sessions. The laterality of stimulation was reversed over the two sessions. Our results showed that anodal stimulation of the PMC biases participants’ responses toward using the contralateral hand whereas cathodal stimulation biases responses toward the ipsilateral hand. Brain stimulation also modulated the RT of the left hand in all stimulation conditions: Responses were faster when the response bias was in favor of the left hand and slower when the response bias was against it. We propose two possible explanations for these findings: the perceptual bias account (bottom–up effects of stimulation on perception) and the motor-choice bias account (top–down modulation of the decision-making system by facilitation of response in one hand over the other). We conclude that motor responses and the choice of hand can be modulated using tDCS.
Previous work has shown that neurons in the prefrontal cortex (PFC) show selectivity for learned categorical groupings. In contrast, brain regions lower in the visual hierarchy, such as inferior temporal cortex, do not seem to favor category information over information about physical appearance. However, the role of premotor cortex (PMC) in categorization has not been studied, despite evidence that PMC is strongly engaged by well learned tasks and reflects learned rules. Here, we directly compare PFC neurons to those in the PMC during visual categorization. Unlike PFC, relatively few PMC neurons distinguished between categories of visual images during a delayed match-to-category task. However, despite the lack of category information in the PMC, more than half of the neurons in both PFC and PMC reflected whether the category of a test image did or did not match the category of a sample image (i.e., had match information). Thus, PFC neurons represented all variables required to solve the cognitive problem while PMC neurons instead represented only the final decision variable that drove the appropriate motor action required to obtain a reward. This dichotomy fits well with the PFC's hypothesized role in learning arbitrary information and directing behavior as well as the PMC's role in motor planning.
Adolescence is a period characterized by increased sensitivity to social cues, as well as increased risk-taking in the presence of peers. For example, automobile crashes are the leading cause of death for adolescents, and driving with peers increases the risk of a fatal crash. Growing evidence points to an interaction between neural systems implicated in cognitive control and social and emotional context in predicting adolescent risk. We tested such a relationship in recently licensed teen drivers. Participants completed an fMRI session in which neural activity was measured during a response inhibition task, followed by a separate driving simulator session 1 week later. Participants drove alone and with a peer who was randomly assigned to express risk-promoting or risk-averse social norms. The experimentally manipulated social context during the simulated drive moderated the relationship between individual differences in neural activity in the hypothesized cognitive control network (right inferior frontal gyrus, BG) and risk-taking in the driving context a week later. Increased activity in the response inhibition network was not associated with risk-taking in the presence of a risky peer but was significantly predictive of safer driving in the presence of a cautious peer, above and beyond self-reported susceptibility to peer pressure. Individual differences in recruitment of the response inhibition network may allow those with stronger inhibitory control to override risky tendencies when in the presence of cautious peers. This relationship between social context and individual differences in brain function expands our understanding of neural systems involved in top–down cognitive control during adolescent development.
The lateral intraparietal area (LIP) of the dorsal visual stream is thought to play an important role in visually directed orienting, or the guidance of where to look and pay attention. LIP can also respond selectively to differently shaped objects. We sought to understand how and to what extent short-term and long-term experience with visual orienting can determine the nature of responses of LIP neurons to objects of different shapes. We taught monkeys to arbitrarily associate centrally presented objects of various shapes with orienting either toward or away from a preferred peripheral spatial location of a neuron. For some objects the training lasted for less than a single day, while for other objects the training lasted for several months. We found that neural responses to visual objects are affected both by such short-term and long-term experience, but that the length of the learning period determines exactly how this neural plasticity manifests itself. Short-term learning over the course of a single training session affects neural responses to objects, but these effects are only seen relatively late after visual onset; at this time, the neural responses to newly learned objects start to resemble those of familiar over-learned objects that share their meaning or arbitrary association. Long-term learning, on the other hand, affects the earliest and apparently bottom-up responses to visual objects. These responses tend to be greater for objects that have repeatedly been associated with looking toward, rather than away from, LIP neurons’ preferred spatial locations. Responses to objects can nonetheless be distinct even though the objects have both been similarly acted on in the past and will lead to the same orienting behavior in the future. Our results therefore also indicate that a complete experience-driven override of LIP object responses is difficult or impossible.
Here we provide novel convergent evidence across three independent cohorts of healthy adults (n=531) demonstrating that a common polymorphism in the gene encoding the α2 subunit of neuronal voltage-gated type II sodium channels (SCN2A) predicts human general cognitive ability or “g.” Using meta-analysis, we demonstrate that the minor T allele of a common polymorphism (rs10174400) in SCN2A is associated with significantly higher “g” independent of gender and age. We further demonstrate using resting-state fMRI data from our discovery cohort (n=236) that this genetic advantage may be mediated by increased capacity for information processing between the dorsolateral prefrontal cortex and dorsal anterior cingulate cortex, which support higher cognitive functions. Collectively, these findings fill a gap in our understanding of the genetics of general cognitive ability and highlight a specific neural mechanism through which a common polymorphism shapes inter-individual variation in “g.”
SCN2A; general cognitive ability; “g” prefrontal cortex; functional magnetic resonance imaging (fMRI)
The ability to control online motor corrections is key to dealing with unexpected changes arising in the environment with which we interact. How the CNS controls online motor corrections is poorly understood, but evidence has accumulated in favor of a submovement-based model in which apparently continuous movement is segmented into distinct submovements. Although most studies have focused on submovements’ kinematic features, direct links with the underlying neural dynamics have not been extensively explored. This study sought to identify an electroencephalographic signature of submovements. We elicited kinematic submovements using a double-step displacement paradigm. Participants moved their wrist toward a target whose direction could shift mid-movement with a 50% probability. Movement kinematics and cortical activity were concurrently recorded with a low-friction robotic device and high-density electroencephalography. Analysis of spatiotemporal dynamics of brain activation and its correlation with movement kinematics showed that the production of each kinematic submovement was accompanied by (1) stereotyped topographic scalp maps and (2) frontoparietal ERPs time-locked to submovements. Positive ERP peaks from frontocentral areas contralateral to the moving wrist preceded kinematic submovement peaks by 220–250 msec and were followed by positive ERP peaks from contralateral parietal areas (140–250 msec latency, 0–80 msec before submovement peaks). Moreover, individual subject variability in the latency of frontoparietal ERP components following the target shift significantly predicted variability in the latency of the corrective submovement. Our results are in concordance with evidence for the intermittent nature of continuous movement and elucidate the timing and role of frontoparietal activations in the generation and control of corrective submovements.
Working memory (WM) is strongly influenced by attention. In visual working-memory tasks, recall performance can be improved by an attention-guiding cue presented before encoding (precue) or during maintenance (retrocue). Although precues and retrocues recruit a similar fronto-parietal control network, the two are likely to exhibit some processing differences, since precues invite anticipation of upcoming information, while retrocues may guide prioritisation, protection, and selection of information already in mind. Here we explored the behavioral and electrophysiological differences between precueing and retrocueing in a new visual working-memory task designed to permit a direct comparison between cueing conditions. We found marked differences in event-related potential (ERP) profiles between the precue and retrocue conditions. In line with precues primarily generating an anticipatory shift of attention toward the location of an upcoming item, we found a robust lateralization in late cue-evoked potentials associated with target anticipation. Retrocues elicited a different pattern of ERPs that was compatible with an early selection mechanism, but not with stimulus anticipation. In contrast to the distinct ERP patterns, alpha band (8-14 Hz) lateralization was indistinguishable between cue types (reflecting, in both conditions, the location of the cued item). We speculate that whereas alpha-band lateralization after a precue is likely to enable anticipatory attention, lateralization after a retrocue may instead enable the controlled spatiotopic access to recently encoded visual information.
Attention: Visual; Memory: working memory; Alpha Oscillations; EEG; Event-related potential
Changes in language functions during normal aging are greater for phonological compared to semantic processes. To investigate the behavioral and neural basis for these age-related differences, we used functional magnetic resonance imaging (fMRI) to examine younger and older adults who made semantic and phonological decisions about pictures. The behavioral performance of older adults was less accurate and less efficient than younger adults’ in the phonological task, but did not differ in the semantic task. In the fMRI analyses, the semantic task activated left-hemisphere language regions, while the phonological task activated bilateral cingulate and ventral precuneus. Age-related effects were widespread throughout the brain, and most often expressed as greater activation for older adults. Activation was greater for younger compared to older adults in ventral brain regions involved in visual and object processing. Although there was not a significant Age x Condition interaction in the whole-brain fMRI results, correlations examining the relationship between behavior and fMRI activation were stronger for younger compared to older adults. Our results suggest that the relationship between behavior and neural activation declines with age and this may underlie some of the observed declines in performance.
aging; functional MRI; Linguistics: semantics
To make sense of our dynamic and complex auditory environment, we must be able to parse the sensory input into usable parts and pick out relevant sounds from all the potentially distracting auditory information. While it is unclear exactly how we accomplish this difficult task, Gamble and Woldorff (2014) recently reported an ERP study of an auditory target-search task in a temporally and spatially distributed, rapidly presented, auditory scene. They reported an early, differential, bilateral activation (beginning ~60 ms) between feature-deviating Target stimuli and physically equivalent feature-deviating Nontargets, reflecting a rapid Target-detection process. This was followed shortly later (~130 ms) by the lateralized N2ac ERP activation, reflecting the focusing of auditory spatial attention toward the Target sound and paralleling attentional-shifting processes widely studied in vision.
Here we directly examined the early, bilateral, Target-selective effect to better understand its nature and functional role. Participants listened to midline-presented sounds that included Target and Nontarget stimuli that were randomly either embedded in a brief rapid stream or presented alone. The results indicate that this early bilateral effect results from a template for the Target that utilizes its feature deviancy within a stream to enable rapid identification. Moreover, individual-differences analysis showed that the size of this effect was larger for subjects with faster response times. The findings support the hypothesis that our auditory attentional systems can implement and utilize a context-based relational template for a Target sound, making use of additional auditory information in the environment when needing to rapidly detect a relevant sound.
Older adults exhibit a reduced ability to ignore task-irrelevant stimuli; however, it remains to be determined where along the information processing stream the most salient age-associated changes occur. In the current study, event related potentials (ERPs) provided an opportunity to determine whether age-related differences in processing task-irrelevant stimuli were uniform across information processing stages or disproportionately affect either early or late selection. ERPs were measured in young and old adults during a color-selective attention task in which subjects responded to target letters in a specified color (attend condition) while ignoring letters in a different color (ignore condition). Old subjects were matched to two groups of young subjects on the basis of neuropsychological test performance: one using age-appropriate norms and the other using test scores not adjusted for age. There were no age-associated differences in the magnitude of early selection (attend – ignore), as indexed by the size of the anterior selection positivity (SP) and posterior selection negativity (SN). During late selection, as indexed by P3b amplitude, both groups of young subjects generated neural responses to target letters under the attend versus ignore conditions that were highly differentiated. In striking contrast, old subjects generated a P3b to target letters with no reliable differences between conditions. Individuals who were slow to initiate early selection appeared to be less successful at executing late selection. Despite relative preservation of the operations of early selection, processing delays may lead older subjects to allocate excessive resources to task-irrelevant stimuli during late selection.
People must constantly select among potential thoughts and actions in the face of competition from (a) multiple task-relevant options (underdetermined competition) and (b) strongly dominant options that are not appropriate in the current context (prepotent competition). These types of competition are ubiquitous during language production. In this work, we investigate the neural mechanisms that allow individuals to effectively manage these cognitive control demands and to quickly choose words with few errors. Using fMRI, we directly contrast underdetermined and prepotent competition within the same task (verb generation) for the first time, allowing localization of the neural substrates supporting the resolution of these two types of competition. Using a neural network model, we investigate the possible mechanisms by which these brain regions support selection. Together, our findings demonstrate that all competition is not alike: resolving prepotent competition and resolving underdetermined competition rely on partly dissociable neural substrates and mechanisms. Specifically, activation of left ventrolateral prefrontal cortex is specific to resolving underdetermined competition between multiple appropriate responses, most likely via competitive lateral inhibition. In contrast, activation of left dorsolateral prefrontal cortex is sensitive to both underdetermined competition and prepotent competition from response options that are inappropriate in the current context. This region likely provides top-down support for task-relevant responses, which enables them to out-compete prepotent responses in the selection process that occurs in left ventrolateral prefrontal cortex.
Adaptive memory retrieval requires mechanisms of cognitive control that facilitate the recovery of goal-relevant information. Frontoparietal systems are known to support control of memory retrieval. However, the mechanisms by which the brain acquires, evaluates, and adapts retrieval strategies remain unknown. Here, we provide evidence that ventral striatal activation tracks the success of a retrieval strategy and correlates with subsequent reliance on that strategy. Human participants were scanned with fMRI while performing a lexical decision task. A rule was provided that indicated the likely semantic category of a target word given the category of a preceding prime. Reliance on the rule improved decision-making, as estimated within a drift diffusion framework. Ventral striatal activation tracked the benefit that relying on the rule had on decision-making. Moreover, activation in ventral striatum correlated with a participant’s subsequent reliance on the rule. Taken together, these results support a role for ventral striatum in learning and evaluating declarative retrieval strategies.
Voluntary episodic memories require an intentional memory search, whereas involuntary episodic memories come to mind spontaneously without conscious effort. Cognitive neuroscience has largely focused on voluntary memory, leaving the neural mechanisms of involuntary memory largely unknown. We hypothesized that because the main difference between voluntary and involuntary memory is the controlled retrieval processes required by the former, there would be greater frontal activity for voluntary than involuntary memories. Conversely, we predicted that other components of the episodic retrieval network would be similarly engaged in the two types of memory. During encoding, all participants heard sounds, half paired with pictures of complex scenes and half presented alone. During retrieval, paired and unpaired sounds were presented panned to the left or to the right. Participants in the involuntary group were instructed to indicate the spatial location of the sound, whereas participants in the voluntary group were asked to additionally recall the pictures that had been paired with the sounds. All participants reported the incidence of their memories in a post-scan session. Consistent with our predictions, voluntary memories elicited greater activity in dorsal frontal regions than involuntary memories, whereas other components of the retrieval network, including medial temporal, ventral occipitotemporal, and ventral parietal regions were similarly engaged by both types of memories. These results clarify the distinct role of dorsal frontal and ventral occipitotemporal regions in predicting strategic retrieval and recalled information, respectively, and suggest that while there are neural differences in retrieval, involuntary memories share neural components with established voluntary memory systems.
Millions of adults worldwide are faced with the task of learning a second language (L2). Understanding the neural mechanisms that support this learning process is an important area of scientific inquiry. However, most previous studies on the neural mechanisms underlying L2 acquisition have focused on characterizing the results of learning, relying upon end-state outcome measures in which learning is assessed after it has occurred, rather than on the learning process itself. In the present study, we adopted a novel and more direct approach to investigate neural mechanisms engaged during L2 learning, in which we recorded ERPs from beginning adult learners as they were exposed to an unfamiliar L2 for the first time. Learners’ proficiency in the L2 was then assessed behaviorally using a grammaticality judgment task, and ERP data acquired during initial L2 exposure were sorted as a function of performance on this task. High proficiency learners showed a larger N100 effect to open-class content words compared to closed-class function words, while low proficiency learners did not show a significant N100 difference between open- and closed-class words. In contrast, amplitude of the N400 word category effect correlated with learners’ L2 comprehension, rather than predicting syntactic learning. Taken together, these results indicate that learners who spontaneously direct greater attention to open- rather than closed-class words when processing L2 input show better syntactic learning, suggesting a link between selective attention to open-class content words and acquisition of basic morphosyntactic rules. These findings highlight the importance of selective attention mechanisms for L2 acquisition.
Both the passage of time and external distraction make it difficult to keep attention on the task at hand. We tested the hypothesis that time-on-task and external distraction pose independent challenges to attention, and that the brain’s cholinergic system selectively modulates our ability to resist distraction. Participants with a polymorphism limiting cholinergic capacity (Ile89Val variant (rs1013940) of the choline transporter gene SLC5A7) and matched controls completed self-report measures of attention and a laboratory task that measured decrements in sustained attention with and without distraction. We found evidence that distraction and time-on-task effects are independent and that the cholinergic system is strongly linked to greater vulnerability to distraction. Ile89Val participants reported more distraction during everyday life than controls, and their task performance was more severely impacted by the presence of an ecologically valid video distractor (similar to a television playing in the background). These results are the first to demonstrate a specific impairment in cognitive control associated with the Ile89Val polymorphism, and add to behavioral and cognitive neuroscience studies indicating the cholinergic system’s critical role in overcoming distraction.